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I'm trying to think of a good word for an asteroid/planetoid that has no stable orbit but has been ejected from a system and is passing close to a sun. Any help?
See nnnnnn's comment below.
The NASA website, describing 'oumuamuam, uses the term "interstellar object." Extrasolar asteroid would seem to be another option. I haven't seen a unique word different from asteroid that originated outside of the solar system.
It seems a simple prefix is sufficient to describe objects beyond the solar system, i.e. exoplanet.
Scienfitic American has an article which uses the term "interstellar object."
Also, see answers to:
The Solar System [b] is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly. [c] Of the objects that orbit the Sun directly, the largest are the eight planets, [d] with the remainder being smaller objects, the dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the natural satellites—two are larger than the smallest planet, Mercury. [e]
The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest planets, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
The Solar System also contains smaller objects. [f] The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations, some objects are large enough to have rounded under their own gravity, though there is considerable debate as to how many there will prove to be.   Such objects are categorized as dwarf planets. The only certain dwarf planet is Pluto, with another trans-Neptunian object, Eris, expected to be, and the asteroid Ceres at least close to being a dwarf planet. [f] In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.
The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy.
Space debris began to accumulate in Earth orbit immediately with the first launch of an artificial satellite Sputnik 1 into orbit in October 1957. But even before that, beside natural ejecta from Earth, humans might have produced ejecta that became space debris, as in the August 1957 Pascal B test.   After the launch of Sputnik, the North American Aerospace Defense Command (NORAD) began compiling a database (the Space Object Catalog) of all known rocket launches and objects reaching orbit: satellites, protective shields and upper-stages of launch vehicles. NASA later published [ when? ] modified versions of the database in two-line element set,  and beginning in the early 1980s the CelesTrak bulletin board system re-published them. 
The trackers [ clarification needed ] who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions.  Some were deliberately caused during the 1960s anti-satellite weapon (ASAT) testing, and others were the result of rocket stages blowing up in orbit as leftover propellant expanded and ruptured their tanks. To improve tracking, NORAD employee John Gabbard [ clarification needed ] kept a separate database. Studying the explosions, Gabbard developed [ when? ] a technique for predicting the orbital paths of their products, and Gabbard diagrams (or plots) are now widely used. These studies were used to improve the modeling of orbital evolution and decay. 
When the NORAD database became publicly available during the 1970s, [ clarification needed ] techniques developed for the asteroid-belt were applied to the study [ by whom? ] to the database of known artificial satellite Earth objects. [ citation needed ]
In addition to approaches to debris reduction where time and natural gravitational/atmospheric effects help to clear space debris, or a variety of technological approaches that have been proposed (with most not implemented) to reduce space debris, a number of scholars have observed that institutional factors—political, legal, economic and cultural "rules of the game"—are the greatest impediment to the cleanup of near-Earth space. By 2014, there was little commercial incentive to reduce space debris, since the cost of dealing with it is not assigned to the entity producing it, but rather falls on all users of the space environment, and rely on human society as a whole that benefits from space technologies and knowledge. A number of suggestions for improving institutions so as to increase the incentives to reduce space debris have been made. These include government mandates to create incentives, as well as companies coming to see economic benefit to reducing debris more aggressively than existing government standard practices.  In 1979 NASA founded the Orbital Debris Program to research mitigation measures for space debris in Earth orbit.  [ failed verification ]
Debris growth Edit
During the 1980s, NASA and other U.S. groups attempted to limit the growth of debris. One trial solution was implemented by McDonnell Douglas for the Delta launch vehicle, [ when? ] by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris.  Other countries were slower to adopt this measure and, due especially to a number of launches by the Soviet Union, the problem grew throughout the decade. 
A new battery of studies followed [ when? ] as NASA, NORAD and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 (when Schefter's article was published) the number of objects was estimated at 5,000,  new detectors in the Ground-based Electro-Optical Deep Space Surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit.  By 2005 this was adjusted upward to 13,000 objects,  and a 2006 study increased the number to 19,000 as a result of an ASAT test and a satellite collision.  In 2011, NASA said that 22,000 objects were being tracked. 
A 2006 NASA model suggested that if no new launches took place the environment would retain the then-known population until about 2055, when it would increase on its own.   Richard Crowther of Britain's Defence Evaluation and Research Agency said in 2002 that he believed the cascade would begin about 2015.  The National Academy of Sciences, summarizing the professional view, noted widespread agreement that two bands of LEO space—900 to 1,000 km (620 mi) and 1,500 km (930 mi)—were already past critical density. 
In the 2009 European Air and Space Conference, University of Southampton researcher Hugh Lewis predicted that the threat from space debris would rise 50 percent in the next decade and quadruple in the next 50 years. As of 2009 [update] , more than 13,000 close calls were tracked weekly. 
A 2011 report by the U.S. National Research Council warned NASA that the amount of orbiting space debris was at a critical level. According to some computer models, the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures". The report called for international regulations limiting debris and research of disposal methods. 
Debris history in particular years Edit
- As of 2009 [update] , 19,000 debris over 5 cm (2 in) were tracked. [by whom?] 
- As of July 2013 [update] , estimates of more than 170 million debris smaller than 1 cm (0.4 in), about 670,000 debris 1–10 cm, and approximately 29,000 larger pieces of debris are in orbit. 
- As of July 2016 [update] , nearly 18,000 artificial objects are orbiting above Earth,  including 1,419 operational satellites. 
- As of October 2019 [update] , nearly 20,000 artificial objects in orbit above the Earth,  including 2,218 operational satellites. 
There are estimated to be over 128 million pieces of debris smaller than 1 cm (0.39 in) as of January 2019. There are approximately 900,000 pieces from one to ten cm. The current count of large debris (defined as 10 cm across or larger  ) is 34,000.  The technical measurement cutoff [ clarification needed ] is c. 3 mm (0.12 in).  Over 98 percent of the 1,900 tons of debris in low Earth orbit as of 2002 was accounted for by about 1,500 objects, each over 100 kg (220 lb).  Total mass is mostly constant [ citation needed ] despite addition of many smaller objects, since they reenter the atmosphere sooner. There were "9,000 pieces of orbiting junk" identified in 2008, with an estimated mass of 5,500 t (12,100,000 lb). 
Low Earth orbit Edit
In the orbits nearest to Earth—less than 2,000 km (1,200 mi) orbital altitude, referred to as low-Earth orbit (LEO)— there have traditionally been few "universal orbits" that keep a number of spacecraft in particular rings (in contrast to GEO, a single orbit that is widely used by over 500 satellites). This is beginning to change in 2019, and several companies have begun to deploy the early phases of satellite internet constellations, which will have many universal orbits in LEO with 30 to 50 satellites per orbital plane and altitude. Traditionally, the most populated LEO orbits have been a number of sun-synchronous satellites that keep a constant angle between the Sun and the orbital plane, making Earth observation easier with consistent sun angle and lighting. Sun-synchronous orbits are polar, meaning they cross over the polar regions. LEO satellites orbit in many planes, typically up to 15 times a day, causing frequent approaches between objects. The density of satellites—both active and derelict—is much higher in LEO. 
Orbits are affected by gravitational perturbations (which in LEO include unevenness of the Earth's gravitational field due to variations in the density of the planet), and collisions can occur from any direction. Impacts between orbiting satellites can occur at up to 16 km/s for a theoretical head-on impact the closing speed could be twice the orbital speed. The 2009 satellite collision occurred at a closing speed of 11.7 km/s (26,000 mph),  creating over 2000 large debris fragments.  These debris cross many other orbits and increase debris collision risk.
It is theorized that a sufficiently large collision of spacecraft could potentially lead to a cascade effect, or even make some particular low Earth orbits effectively unusable for long term use by orbiting satellites, a phenomenon known as the Kessler syndrome.  The theoretical effect is projected to be a theoretical runaway chain reaction of collisions that could occur, exponentially increasing the number and density of space debris in low-Earth orbit, and has been hypothesized to ensue beyond some critical density. 
Crewed space missions are mostly at 400 km (250 mi) altitude and below, where air drag helps clear zones of fragments. The upper atmosphere is not a fixed density at any particular orbital altitude it varies as a result of atmospheric tides and expands or contracts over longer time periods as a result of space weather.  These longer-term effects can increase drag at lower altitudes the 1990s expansion was a factor in reduced debris density.  Another factor was fewer launches by Russia the Soviet Union made most of their launches in the 1970s and 1980s.  : 7
Higher altitudes Edit
At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth's gravity perturbations, solar wind and solar radiation pressure can gradually bring debris down to lower altitudes (where it decays), but at very high altitudes this may take millennia.  Although high-altitude orbits are less commonly used than LEO and the onset of the problem is slower, the numbers progress toward the critical threshold more quickly. [ contradictory ] [ page needed ] 
Many communications satellites are in geostationary orbits (GEO), clustering over specific targets and sharing the same orbital path. Although velocities are low between GEO objects, when a satellite becomes derelict (such as Telstar 401) it assumes a geosynchronous orbit its orbital inclination increases about .8° and its speed increases about 160 km/h (99 mph) per year. Impact velocity peaks at about 1.5 km/s (0.93 mi/s). Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches (within 50 meters) are estimated at one per year.  The collision debris pose less short-term risk than from an LEO collision, but the satellite would likely become inoperable. Large objects, such as solar-power satellites, are especially vulnerable to collisions. 
Although the ITU now requires proof a satellite can be moved out of its orbital slot at the end of its lifespan, studies suggest this is insufficient.  Since GEO orbit is too distant to accurately measure objects under 1 m (3 ft 3 in), the nature of the problem is not well known.  Satellites could be moved to empty spots in GEO, requiring less maneuvering and making it easier to predict future motion.  Satellites or boosters in other orbits, especially stranded in geostationary transfer orbit, are an additional concern due to their typically high crossing velocity.
Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1 was struck by a meteoroid on 11 August 1993 and eventually moved to a graveyard orbit.  On 29 March 2006, the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable  its engineers had enough contact time with the satellite to send it into a graveyard orbit.
Dead spacecraft Edit
In 1958, the United States launched Vanguard I into a medium Earth orbit (MEO). As of October 2009 [update] , it, and the upper stage of its launch rocket, were the oldest surviving artificial space objects still in orbit.   In a catalog of known launches until July 2009, the Union of Concerned Scientists listed 902 operational satellites  from a known population of 19,000 large objects and about 30,000 objects launched. [ citation needed ]
An example of additional derelict satellite debris is the remains of the 1970s/80s Soviet RORSAT naval surveillance satellite program. The satellites' BES-5 nuclear reactors were cooled with a coolant loop of sodium-potassium alloy, creating a potential problem when the satellite reached end of life. While many satellites were nominally boosted into medium-altitude graveyard orbits, not all were. Even satellites that had been properly moved to a higher orbit had an eight-percent probability of puncture and coolant release over a 50-year period. The coolant freezes into droplets of solid sodium-potassium alloy,  forming additional debris. 
In February 2015, the USAF Defense Meteorological Satellite Program Flight 13 (DMSP-F13) exploded on orbit, creating at least 149 debris objects, which were expected to remain in orbit for decades. 
Orbiting satellites have been deliberately destroyed. United States and USSR/Russia have conducted over 30 and 27 ASAT tests, [ clarification needed ] respectively, followed by 10 from China and one from India. [ citation needed ] The most recent ASATs were Chinese interception of FY-1C, trials of Russian PL-19 Nudol, American interception of USA-193 and Indian interception of unstated live satellite. [ citation needed ]
Lost equipment Edit
Space debris includes a glove lost by astronaut Ed White on the first American space-walk (EVA), a camera lost by Michael Collins near Gemini 10, a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir's 15-year life,  a wrench, and a toothbrush.  Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag. 
In characterizing the problem of space debris, it was learned that much debris was due to rocket upper stages (e.g. the Inertial Upper Stage) which end up in orbit, and break up due to decomposition of unvented unburned fuel.  However, a major known impact event involved an (intact) Ariane booster.  : 2 Although NASA and the United States Air Force now require upper-stage passivation, other launchers [ vague ] do not. Lower stages, like the Space Shuttle's solid rocket boosters or Apollo program's Saturn IB launch vehicles, do not reach orbit. 
On 11 March 2000 a Chinese Long March 4 CBERS-1 upper stage exploded in orbit, creating a debris cloud.   A Russian Briz-M booster stage exploded in orbit over South Australia on 19 February 2007. Launched on 28 February 2006 carrying an Arabsat-4A communications satellite, it malfunctioned before it could use up its propellant. Although the explosion was captured on film by astronomers, due to the orbit path the debris cloud has been difficult to measure with radar. By 21 February 2007, over 1,000 fragments were identified.   A 14 February 2007 breakup was recorded by Celestrak.  Eight breakups occurred in 2006, the most since 1993.  Another Briz-M broke up on 16 October 2012 after a failed 6 August Proton-M launch. The amount and size of the debris was unknown.  A Long March 7 rocket booster created a fireball visible from portions of Utah, Nevada, Colorado, Idaho and California on the evening of 27 July 2016 its disintegration was widely reported on social media.  In 2018–2019, three different Atlas V Centaur second stages have broken up.   
In December 2020, scientists confirmed that a previously detected near-Earth object, 2020 SO, was rocket booster space junk launched in 1966 orbiting Earth and the Sun. 
A past debris source was the testing of anti-satellite weapons (ASATs) by the U.S. and Soviet Union during the 1960s and 1970s. North American Aerospace Defense Command (NORAD) files only contained data for Soviet tests, and debris from U.S. tests were only identified later.  By the time the debris problem was understood, widespread ASAT testing had ended the U.S. Program 437 was shut down in 1975. 
The U.S. restarted their ASAT programs in the 1980s with the Vought ASM-135 ASAT. A 1985 test destroyed a 1-tonne (2,200 lb) satellite orbiting at 525 km (326 mi), creating thousands of debris larger than 1 cm (0.39 in). Due to the altitude, atmospheric drag decayed the orbit of most debris within a decade. A de facto moratorium followed the test. 
China's government was condemned for the military implications and the amount of debris from the 2007 anti-satellite missile test,  the largest single space debris incident in history (creating over 2,300 pieces golf-ball size or larger, over 35,000 1 cm (0.4 in) or larger, and one million pieces 1 mm (0.04 in) or larger). The target satellite orbited between 850 km (530 mi) and 882 km (548 mi), the portion of near-Earth space most densely populated with satellites.  Since atmospheric drag is low at that altitude the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft maneuvered to avoid impact from the debris.  Dr. Brian Weeden, U.S. Air Force officer and Secure World Foundation staff member, noted that the 2007 Chinese satellite explosion created an orbital debris of more than 3,000 separate objects that then required tracking.  On 20 February 2008, the U.S. launched an SM-3 missile from the USS Lake Erie to destroy a defective U.S. spy satellite thought to be carrying 450 kg (1,000 lb) of toxic hydrazine propellant. The event occurred at about 250 km (155 mi), and the resulting debris has a perigee of 250 km (155 mi) or lower.  The missile was aimed to minimize the amount of debris, which (according to Pentagon Strategic Command chief Kevin Chilton) had decayed by early 2009.  On 27 March 2019, Indian Prime Minister Narendra Modi announced that India shot down one of its own LEO satellites with a ground-based missile. He stated that the operation, part of Mission Shakti, would defend the country's interests in space. Afterwards, US Air Force Space Command announced they were tracking 270 new pieces of debris but expected the number to grow as data collection continues. 
The vulnerability of satellites to debris and the possibility of attacking LEO satellites to create debris clouds has triggered speculation that it is possible for countries unable to make a precision attack. [ clarification needed ] An attack on a satellite of 10 t (22,000 lb) or more would heavily damage the LEO environment. 
To spacecraft Edit
Space junk can be a hazard to active satellites and spacecraft. It has been theorized that Earth orbit could even become impassable if the risk of collision grows too high.  [ failed verification ]
However, since the risk to spacecraft increases with the time of exposure to high debris densities, it is more accurate to say that LEO would be rendered unusable by orbiting craft. The threat to craft passing through LEO to reach higher orbit would be much lower owing to the very short time span of the crossing.
Uncrewed spacecraft Edit
Although spacecraft are typically protected by Whipple shields, solar panels, which are exposed to the Sun, wear from low-mass impacts. Even small impacts can produce a cloud of plasma which is an electrical risk to the panels. 
Satellites are believed to have been destroyed by micrometeorites and (small) orbital debris (MMOD). The earliest suspected loss was of Kosmos 1275, which disappeared on 24 July 1981 (a month after launch). Kosmos contained no volatile propellant, therefore, there appeared to be nothing internal to the satellite which could have caused the destructive explosion which took place. However, the case has not been proven and another hypothesis forwarded is that the battery exploded. Tracking showed it broke up, into 300 new objects. 
Many impacts have been confirmed since. For example, on 24 July 1996, the French microsatellite Cerise was hit by fragments of an Ariane-1 H-10 upper-stage booster which exploded in November 1986.  : 2 On 29 March 2006, the Russian Ekspress AM11 communications satellite was struck by an unknown object and rendered inoperable.  On 13 October 2009, Terra suffered a single battery cell failure anomaly and a battery heater control anomaly which were subsequently considered likely the result of an MMOD strike.  On 12 March 2010, Aura lost power from one-half of one of its 11 solar panels and this was also attributed to an MMOD strike.  On 22 May 2013, GOES-13 was hit by an MMOD which caused it to lose track of the stars that it used to maintain an operational attitude. It took nearly a month for the spacecraft to return to operation. 
The first major satellite collision occurred on 10 February 2009. The 950 kg (2,090 lb) derelict satellite Kosmos 2251 and the operational 560 kg (1,230 lb) Iridium 33 collided, 500 mi (800 km)  over northern Siberia. The relative speed of impact was about 11.7 km/s (7.3 mi/s), or about 42,120 km/h (26,170 mph).  Both satellites were destroyed, creating thousands of pieces of new smaller debris, with legal and political liability issues unresolved even years later.    On 22 January 2013, BLITS (a Russian laser-ranging satellite) was struck by debris suspected to be from the 2007 Chinese anti-satellite missile test, changing both its orbit and rotation rate. 
Satellites sometimes [ clarification needed ] perform Collision Avoidance Maneuvers and satellite operators may monitor space debris as part of maneuver planning. For example, in January 2017, the European Space Agency made the decision to alter orbit of one of its three  Swarm mission spacecraft, based on data from the US Joint Space Operations Center, to lower the risk of collision from Cosmos-375, a derelict Russian satellite. 
Crewed spacecraft Edit
Crewed flights are naturally particularly sensitive to the hazards that could be presented by space debris conjunctions in the orbital path of the spacecraft. Examples of occasional avoidance maneuvers, or longer-term space debris wear, have occurred in Space Shuttle missions, the MIR space station, and the International Space Station.
Space Shuttle missions Edit
From the early Space Shuttle missions, NASA used NORAD space monitoring capabilities to assess the Shuttle's orbital path for debris. In the 1980s, this used a large proportion of NORAD capacity.  The first collision-avoidance maneuver occurred during STS-48 in September 1991,  a seven-second thruster burn to avoid debris from the derelict satellite Kosmos 955.  Similar maneuvers were initiated on missions 53, 72 and 82. 
One of the earliest events to publicize the debris problem occurred on Space Shuttle Challenger's second flight, STS-7. A fleck of paint struck its front window, creating a pit over 1 mm (0.04 in) wide. On STS-59 in 1994, Endeavour's front window was pitted about half its depth. Minor debris impacts increased from 1998. 
Window chipping and minor damage to thermal protection system tiles (TPS) were already common by the 1990s. The Shuttle was later flown tail-first to take a greater proportion of the debris load on the engines and rear cargo bay, which are not used in orbit or during descent, and thus are less critical for post-launch operation. When flying attached to the ISS, the two connected spacecraft were flipped around so the better-armored station shielded the orbiter. 
A NASA 2005 study concluded that debris accounted for approximately half of the overall risk to the Shuttle.   Executive-level decision to proceed was required if catastrophic impact was likelier than 1 in 200. On a normal (low-orbit) mission to the ISS the risk was approximately 1 in 300, but the Hubble telescope repair mission was flown at the higher orbital altitude of 560 km (350 mi) where the risk was initially calculated at a 1-in-185 (due in part to the 2009 satellite collision). A re-analysis with better debris numbers reduced the estimated risk to 1 in 221, and the mission went ahead. 
Debris incidents continued on later Shuttle missions. During STS-115 in 2006 a fragment of circuit board bored a small hole through the radiator panels in Atlantis ' s cargo bay.  On STS-118 in 2007 debris blew a bullet-like hole through Endeavour ' s radiator panel. 
Impact wear was notable on Mir, the Soviet space station, since it remained in space for long periods with its original solar module panels.  
International Space Station Edit
The ISS also uses Whipple shielding to protect its interior from minor debris.  However, exterior portions (notably its solar panels) cannot be protected easily. In 1989, the ISS panels were predicted to degrade approximately 0.23% in four years due to the "sandblasting" effect of impacts with small orbital debris.  An avoidance maneuver is typically performed for the ISS if "there is a greater than one-in-10,000 chance of a debris strike".  As of January 2014 [update] , there have been sixteen maneuvers in the fifteen years the ISS had been in orbit. 
As another method to reduce the risk to humans on board, ISS operational management asked the crew to shelter in the Soyuz on three occasions due to late debris-proximity warnings. In addition to the sixteen thruster firings and three Soyuz-capsule shelter orders, one attempted maneuver was not completed due to not having the several days' warning necessary to upload the maneuver timeline to the station's computer.    A March 2009 event involved debris believed to be a 10 cm (3.9 in) piece of the Kosmos 1275 satellite.  In 2013, the ISS operations management did not make a maneuver to avoid any debris, after making a record four debris maneuvers the previous year. 
Kessler syndrome Edit
The Kessler syndrome,   proposed by NASA scientist Donald J. Kessler in 1978, is a theoretical scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade effect where each collision generates space debris that increases the likelihood of further collisions.  He further theorized that one implication if this were to occur is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges economically impractical for many generations. 
The growth in the number of objects as a result of the late-1990s studies sparked debate in the space community on the nature of the problem and the earlier dire warnings. According to Kessler's 1991 derivation and 2001 updates,  the LEO environment in the 1,000 km (620 mi) altitude range should be cascading. However, only one major satellite collision incident has occurred: the 2009 satellite collision between Iridium 33 and Cosmos 2251. The lack of obvious short-term cascading has led to speculation that the original estimates overstated the problem.  [ full citation needed ] According to Kessler in 2010 however, a cascade may not be obvious until it is well advanced, which might take years. 
On Earth Edit
Although most debris burns up in the atmosphere, larger debris objects can reach the ground intact. According to NASA, an average of one cataloged piece of debris has fallen back to Earth each day for the past 50 years. Despite their size, there has been no significant property damage from the debris.  Burning up in the atmosphere may also contribute to atmospheric pollution. 
Notable examples of space junk falling to Earth and impacting human life include:
- 1969: five sailors on a Japanese ship were injured when space debris from what was believed to be a Soviet spacecraft struck the deck of their boat. 
- 1978 The Soviet reconnaissance satellite Kosmos 954 reentered the atmosphere over northwest Canada and scattered radioactive debris over northern Canada, some of the debris landing in the Great Slave Lake. 
- 1979 portions of Skylab came down over Australia, and several pieces landed in the area around the Shire of Esperance, which fined NASA $400 for littering. 
- 1987 a 7-foot strip of metal from the Soviet Kosmos 1890 rocket landed between two homes in Lakeport, California, causing no damage
- 1997: an Oklahoma woman, Lottie Williams, was hit, without injury in the shoulder by a 10 cm × 13 cm (3.9 in × 5.1 in) piece of blackened, woven metallic material confirmed as part of the propellant tank of a Delta II rocket which launched a U.S. Air Force satellite the year before. 
- 2001: a Star 48Payload Assist Module (PAM-D) rocket upper stage re-entered the atmosphere after a "catastrophic orbital decay",  crashing in the Saudi Arabian desert. It was identified as the upper-stage rocket for NAVSTAR 32, a GPS satellite launched in 1993. 
- 2002: 6 year old boy Wu Jie became the first person to be injured by direct impact from space debris. He suffered a fractured toe and a swelling on his forehead after a block of aluminum, 80 centimeters by 50 centimeters and weighing 10 kilograms from the outermost shell of the Resource Second Satellite struck him as he sat beneath a persimmon tree in the Shaanxi Province of China. 
- 2003: Columbia disaster, large parts of the spacecraft reached the ground and entire equipment systems remained intact.  More than 83,000 pieces, along with the remains of the six astronauts, were recovered in an area from three to 10 miles around Hemphill in Sabine County, Texas.  More pieces were found in a line from west Texas to east Louisiana, with the westernmost piece found in Littlefield, TX and the easternmost found southwest of Mora, Louisiana.  Debris was found in Texas, Arkansas and Louisiana. In a rare case of property damage, a foot-long metal bracket smashed through the roof of a dentist office.  NASA warned the public to avoid contact with the debris because of the possible presence of hazardous chemicals.  15 years after the failure, people were still sending in pieces with the most recent, as of February 2018, found in the spring of 2017. 
- 2007: airborne debris from a Russian spy satellite was seen by the pilot of a LAN AirlinesAirbus A340 carrying 270 passengers whilst flying over the Pacific Ocean between Santiago and Auckland. The debris was reported within 9.3 kilometres (5 nmi) of the aircraft. 
- 2020: The empty core stage of a Long March-5B rocket made an uncontrolled re-entry - the largest object to do so since the Soviet Union’s 39 ton Salyut-7 space station in 1991 - over Africa and the Atlantic ocean and a 12-meter-long pipe originating from the rocket crashed into the village of Mahounou in Cote d'Ivoire. 
- 2021: a Falcon 9 second stage made an uncontrolled re-entry over Washington state on March 25, producing a widely seen "light show".  A composite-overwrapped pressure vessel survived the re-entry and landed on a farm field. 
Tracking from the ground Edit
Radar and optical detectors such as lidar are the main tools for tracking space debris. Although objects under 10 cm (4 in) have reduced orbital stability, debris as small as 1 cm can be tracked,   however determining orbits to allow re-acquisition is difficult. Most debris remain unobserved. The NASA Orbital Debris Observatory tracked space debris with a 3 m (10 ft) liquid mirror transit telescope.  FM Radio waves can detect debris, after reflecting off them onto a receiver.  Optical tracking may be a useful early-warning system on spacecraft. 
The U.S. Strategic Command keeps a catalog of known orbital objects, using ground-based radar and telescopes, and a space-based telescope (originally to distinguish from hostile missiles). The 2009 edition listed about 19,000 objects.  Other data come from the ESA Space Debris Telescope, TIRA,  the Goldstone, Haystack,  and EISCAT radars and the Cobra Dane phased array radar,  to be used in debris-environment models like the ESA Meteoroid and Space Debris Terrestrial Environment Reference (MASTER).
Measurement in space Edit
Returned space hardware is a valuable source of information on the directional distribution and composition of the (sub-millimetre) debris flux. The LDEF satellite deployed by mission STS-41-C Challenger and retrieved by STS-32 Columbia spent 68 months in orbit to gather debris data. The EURECA satellite, deployed by STS-46 Atlantis in 1992 and retrieved by STS-57 Endeavour in 1993, was also used for debris study. 
The solar arrays of Hubble were returned by missions STS-61 Endeavour and STS-109 Columbia, and the impact craters studied by the ESA to validate its models. Materials returned from Mir were also studied, notably the Mir Environmental Effects Payload (which also tested materials intended for the ISS  ).  
Gabbard diagrams Edit
A debris cloud resulting from a single event is studied with scatter plots known as Gabbard diagrams, where the perigee and apogee of fragments are plotted with respect to their orbital period. Gabbard diagrams of the early debris cloud prior to the effects of perturbations, if the data were available, are reconstructed. They often include data on newly observed, as yet uncatalogued fragments. Gabbard diagrams can provide important insights into the features of the fragmentation, the direction and point of impact.  
An average of about one tracked object per day has been dropping out of orbit for the past 50 years,  averaging almost three objects per day at solar maximum (due to the heating and expansion of the Earth's atmosphere), but one about every three days at solar minimum, usually five and a half years later.  In addition to natural atmospheric effects, corporations, academics and government agencies have proposed plans and technology to deal with space debris, but as of November 2014 [update] , most of these are theoretical, and there is no extant business plan for debris reduction. 
A number of scholars have also observed that institutional factors—political, legal, economic, and cultural "rules of the game"—are the greatest impediment to the cleanup of near-Earth space. There is no commercial incentive, since costs aren't assigned to polluters, but a number of suggestions have been made.  However, effects to date are limited. In the US, governmental bodies have been accused of backsliding on previous commitments to limit debris growth, "let alone tackling the more complex issues of removing orbital debris."  The different methods for removal of space debris has been evaluated by the Space Generation Advisory Council, including French astrophysicist Fatoumata Kébé. 
Growth mitigation Edit
As of the 2010s, several technical approaches to the mitigation of the growth of space debris are typically undertaken, yet no comprehensive legal regime or cost assignment structure is in place to reduce space debris in the way that terrestrial pollution has reduced since the mid-20th century.
To avoid excessive creation of artificial space debris, many—but not all—satellites launched to above-low-Earth-orbit are launched initially into elliptical orbits with perigees inside Earth's atmosphere so the orbit will quickly decay and the satellites then will destroy themselves upon reentry into the atmosphere. Other methods are used for spacecraft in higher orbits. These include passivation of the spacecraft at the end of its useful life as well as the use of upper stages that can reignite to decelerate the stage to intentionally deorbit it, often on the first or second orbit following payload release satellites that can, if they remain healthy for years, deorbit themselves from the lower orbits around Earth. Other satellites (such as many CubeSats) in low orbits below approximately 400 km (250 mi) orbital altitude depend on the energy-absorbing effects of the upper atmosphere to reliably deorbit a spacecraft within weeks or months.
Increasingly, spent upper stages in higher orbits—orbits for which low-delta-v deorbit is not possible, or not planned for—and architectures that support satellite passivation, at end of life are passivated at end of life. This removes any internal energy contained in the vehicle at the end of its mission or useful life. While this does not remove the debris of the now derelict rocket stage or satellite itself, it does substantially reduce the likelihood of the spacecraft destructing and creating many smaller pieces of space debris, a phenomenon that was common in many of the early generations of US and Soviet  spacecraft.
Upper stage passivation (e.g. of Delta boosters  ) by releasing residual propellants reduces debris from orbital explosions however even as late as 2011, not all upper stages implement this practice.  SpaceX used the term "propulsive passivation" for the final maneuver of their six-hour demonstration mission (STP-2) of the Falcon 9 second stage for the US Air Force in 2019, but did not define what all that term encompassed. 
With a "one-up, one-down" launch-license policy for Earth orbits, launchers would rendezvous with, capture and de-orbit a derelict satellite from approximately the same orbital plane.  Another possibility is the robotic refueling of satellites. Experiments have been flown by NASA,  and SpaceX is developing large-scale on-orbit propellant transfer technology. 
Another approach to debris mitigation is to explicitly design the mission architecture to always leave the rocket second-stage in an elliptical geocentric orbit with a low-perigee, thus ensuring rapid orbital decay and avoiding long-term orbital debris from spent rocket bodies. Such missions will often complete the payload placement in a final orbit by the use of low-thrust electric propulsion or with the use of a small kick stage to circularize the orbit. The kick stage itself may be designed with the excess-propellant capability to be able to self-deorbit. 
Although the ITU requires geostationary satellites to move to a graveyard orbit at the end of their lives, the selected orbital areas do not sufficiently protect GEO lanes from debris.  Rocket stages (or satellites) with enough propellant may make a direct, controlled de-orbit, or if this would require too much propellant, a satellite may be brought to an orbit where atmospheric drag would cause it to eventually de-orbit. This was done with the French Spot-1 satellite, reducing its atmospheric re-entry time from a projected 200 years to about 15 by lowering its altitude from 830 km (516 mi) to about 550 km (342 mi).  
The Iridium constellation—95 communication satellites launched during the five-year period between 1997 and 2002—provides a set of data points on the limits of self-removal. The satellite operator—Iridium Communications—remained operational (albeit with a company name change through a corporate bankruptcy during the period) over the two-decade life of the satellites, and by December 2019, had "completed disposal of the last of its 65 working legacy satellites."  However, this process left nearly one-third of the mass of this constellation (30 satellites, 20,400 kg (45,000 lb) of materiel) in LEO orbits at approximately 700 km (430 mi) altitude, where self-decay is quite slow. 29 of these satellites simply failed during their time in orbit and were thus unable to self-deorbit, while one—Iridium 33—was involved in the 2009 satellite collision with the derelict Russian military Kosmos-2251 satellite.  No "Plan B" provision was designed in for removal of the satellites that were unable to remove themselves. However, in 2019, Iridium CEO Matt Desch said that Iridium would be willing to pay an active-debris-removal company to deorbit its remaining first-generation satellites if it were possible for a sufficiently low cost, say " US$10,000 per deorbit, but [he] acknowledged that price would likely be far below what a debris-removal company could realistically offer. 'You know at what point [it’s] a no-brainer, but [I] expect the cost is really in the millions or tens of millions, at which price I know it doesn’t make sense ' " 
Passive methods of increasing the orbital decay rate of spacecraft debris have been proposed. Instead of rockets, an electrodynamic tether could be attached to a spacecraft at launch at the end of its lifetime, the tether would be rolled out to slow the spacecraft.  Other proposals include a booster stage with a sail-like attachment  and a large, thin, inflatable balloon envelope. 
External removal Edit
A variety of approaches have been proposed, studied, or had ground subsystems built to use other spacecraft to remove existing space debris. A consensus of speakers at a meeting in Brussels in October 2012, organized by the Secure World Foundation (a U.S. think tank) and the French International Relations Institute,  reported that removal of the largest debris would be required to prevent the risk to spacecraft becoming unacceptable in the foreseeable future (without any addition to the inventory of dead spacecraft in LEO). To date in 2019, removal costs and legal questions about ownership and the authority to remove defunct satellites have stymied national or international action. Current space law retains ownership of all satellites with their original operators, even debris or spacecraft which are defunct or threaten active missions.
Moreover, as of 2006 [update] , the cost of any of the proposed approaches for external removal is about the same as launching a spacecraft [ failed verification ] and, according to NASA's Nicholas Johnson, [ when? ] not cost-effective.  [ needs update ]
This is beginning to change in the late 2010s, as some companies have made plans to begin to do external removal on their satellites in mid-LEO orbits. For example, OneWeb will utilize onboard self-removal as "plan A" for satellite deorbiting at the end of life, but if a satellite is unable to remove itself within one year of end of life, OneWeb will implement "plan B" and dispatch a reusable (multi-transport mission) space tug to attach to the satellite at an already built-in capture target via a grappling fixture, to be towed to a lower orbit and released for re-entry.  
Remotely controlled vehicles Edit
A well-studied solution uses a remotely controlled vehicle to rendezvous with, capture, and return debris to a central station.  One such system is Space Infrastructure Servicing, a commercially developed refueling depot and service spacecraft for communications satellites in geosynchronous orbit originally scheduled for a 2015 launch.  The SIS would be able to "push dead satellites into graveyard orbits."  The Advanced Common Evolved Stage family of upper stages is being designed with a high leftover-propellant margin (for derelict capture and de-orbit) and in-space refueling capability for the high delta-v required to de-orbit heavy objects from geosynchronous orbit.  A tug-like satellite to drag debris to a safe altitude for it to burn up in the atmosphere has been researched.  When debris is identified the satellite creates a difference in potential between the debris and itself, then using its thrusters to move itself and the debris to a safer orbit.
A variation of this approach is for the remotely controlled vehicle to rendezvous with debris, capture it temporarily to attach a smaller de-orbit satellite and drag the debris with a tether to the desired location. The "mothership" would then tow the debris-smallsat combination for atmospheric entry or move it to a graveyard orbit. One such system is the proposed Busek ORbital DEbris Remover (ORDER), which would carry over 40 SUL (satellite on umbilical line) de-orbit satellites and propellant sufficient for their removal. 
On 7 January 2010 Star, Inc. reported that it received a contract from the Space and Naval Warfare Systems Command for a feasibility study of the ElectroDynamic Debris Eliminator (EDDE) propellantless spacecraft for space-debris removal.  In February 2012 the Swiss Space Center at École Polytechnique Fédérale de Lausanne announced the Clean Space One project, a nanosatellite demonstration project for matching orbit with a defunct Swiss nanosatellite, capturing it and de-orbiting together.  The mission has seen several evolutions to reach a pac-man inspired capture model.  In 2013, Space Sweeper with Sling-Sat (4S), a grappling satellite which captures and ejects debris was studied.  [ needs update ]
In December 2019, the European Space Agency awarded the first contract to clean up space debris. The €120 million mission dubbed ClearSpace-1 (a spinoff from the EPFL project) is slated to launch in 2025. It aims to remove a 100 kg VEga Secondary Payload Adapter (Vespa)  left by Vega flight VV02 in an 800 km (500 mi) orbit in 2013. A "chaser" will grab the junk with four robotic arms and drag it down to Earth's atmosphere where both will burn up. 
Laser methods Edit
The laser broom uses a ground-based laser to ablate the front of the debris, producing a rocket-like thrust that slows the object. With continued application, the debris would fall enough to be influenced by atmospheric drag.   During the late 1990s, the U.S. Air Force's Project Orion was a laser-broom design.  Although a test-bed device was scheduled to launch on a Space Shuttle in 2003, international agreements banning powerful laser testing in orbit limited its use to measurements.  The 2003 Space Shuttle Columbia disaster postponed the project and according to Nicholas Johnson, chief scientist and program manager for NASA's Orbital Debris Program Office, "There are lots of little gotchas in the Orion final report. There's a reason why it's been sitting on the shelf for more than a decade." 
The momentum of the laser-beam photons could directly impart a thrust on the debris sufficient to move small debris into new orbits out of the way of working satellites. NASA research in 2011 indicates that firing a laser beam at a piece of space junk could impart an impulse of 1 mm (0.039 in) per second, and keeping the laser on the debris for a few hours per day could alter its course by 200 m (660 ft) per day.  One drawback is the potential for material degradation the energy may break up the debris, adding to the problem. [ citation needed ] A similar proposal places the laser on a satellite in Sun-synchronous orbit, using a pulsed beam to push satellites into lower orbits to accelerate their reentry.  A proposal to replace the laser with an Ion Beam Shepherd has been made,  and other proposals use a foamy ball of aerogel or a spray of water,  inflatable balloons,  electrodynamic tethers,  electroadhesion,  and dedicated anti-satellite weapons. 
On 28 February 2014, Japan's Japan Aerospace Exploration Agency (JAXA) launched a test "space net" satellite. The launch was an operational test only.  In December 2016 the country sent a space junk collector via Kounotori 6 to the ISS by which JAXA scientists experiment to pull junk out of orbit using a tether.   The system failed to extend a 700-meter tether from a space station resupply vehicle that was returning to Earth.   On 6 February the mission was declared a failure and leading researcher Koichi Inoue told reporters that they "believe the tether did not get released". 
Since 2012, the European Space Agency has been working on the design of a mission to remove large space debris from orbit. The mission, e.Deorbit, is scheduled for launch during 2023 with an objective to remove debris heavier than 4,000 kilograms (8,800 lb) from LEO.  Several capture techniques are being studied, including a net, a harpoon and a combination robot arm and clamping mechanism. 
The RemoveDEBRIS mission plan is to test the efficacy of several ADR technologies on mock targets in low Earth orbit. In order to complete its planned experiments the platform is equipped with a net, a harpoon, a laser ranging instrument, a dragsail, and two CubeSats (miniature research satellites).  The mission was launched on 2 April 2018.
National and international regulation Edit
There is no international treaty minimizing space debris. However, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) published voluntary guidelines in 2007,  using a variety of earlier national regulatory attempts at developing standards for debris mitigation. As of 2008, the committee was discussing international "rules of the road" to prevent collisions between satellites.  By 2013, a number of national legal regimes existed,    typically instantiated in the launch licenses that are required for a launch in all spacefaring nations. 
The U.S. issued a set of standard practices for civilian (NASA) and military (DoD and USAF) orbital-debris mitigation in 2001.    The standard envisioned disposal for final mission orbits in one of three ways: 1) atmospheric reentry where even with "conservative projections for solar activity, atmospheric drag will limit the lifetime to no longer than 25 years after completion of mission" 2) maneuver to a "storage orbit:" move the spacecraft to one of four very broad parking orbit ranges (2,000–19,700 km (1,200–12,200 mi), 20,700–35,300 km (12,900–21,900 mi), above 36,100 km (22,400 mi), or out of Earth orbit completely and into any heliocentric orbit 3) "Direct retrieval: Retrieve the structure and remove it from orbit as soon as practicable after completion of mission."  The standard articulated in option 1, which is the standard applicable to most satellites and derelict upper stages launched, has come to be known as the "25-year rule."  The US updated the ODMSP in December 2019, but made no change to the 25-year rule even though "[m]any in the space community believe that the timeframe should be less than 25 years."  There is no consensus however on what any new timeframe might be. 
In 2002, the European Space Agency (ESA) worked with an international group to promulgate a similar set of standards, also with a "25-year rule" applying to most Earth-orbit satellites and upper stages. Space agencies in Europe began to develop technical guidelines in the mid-1990s, and ASI, UKSA, CNES, DLR and ESA signed a "European Code of Conduct" in 2006,  which was a predecessor standard to the ISO international standard work that would begin the following year. In 2008, ESA further developed "its own "Requirements on Space Debris Mitigation for Agency Projects" which "came into force on 1 April 2008." 
Germany and France have posted bonds to safeguard the property from debris damage. [ clarification needed ]  The "direct retrieval" option (option no. 3 in the US "standard practices" above) has rarely been done by any spacefaring nation (exception, USAF X-37) or commercial actor since the earliest days of spaceflight due to the cost and complexity of achieving direct retrieval, but the ESA has scheduled a 2025 demonstration mission (Clearspace-1) to do this with a single small 100 kg (220 lb) derelict upper stage at a projected cost of €120 million not including the launch costs. 
By 2006, the Indian Space Research Organization (ISRO) had developed a number of technical means of debris mitigation (upper stage passivation, propellant reserves for movement to graveyard orbits, etc.) for ISRO launch vehicles and satellites, and was actively contributing to inter-agency debris coordination and the efforts of the UN COPUOS committee. 
In 2007, the ISO began preparing an international standard for space-debris mitigation.  By 2010, ISO had published "a comprehensive set of space system engineering standards aimed at mitigating space debris. [with primary requirements] defined in the top-level standard, ISO 24113." By 2017, the standards were nearly complete. However, these standards are not binding on any party by ISO or any international jurisdiction. They are simply available for use in any of a variety of voluntary ways. They "can be adopted voluntarily by a spacecraft manufacturer or operator, or brought into effect through a commercial contract between a customer and supplier, or used as the basis for establishing a set of national regulations on space debris mitigation." 
The voluntary ISO standard also adopted the "25-year rule" for the "LEO protected region" below 2,000 km (1,200 mi) altitude that has been previously (and still is, as of 2019 [update] ) used by the US, ESA, and UN mitigation standards, and identifies it as "an upper limit for the amount of time that a space system shall remain in orbit after its mission is completed. Ideally, the time to deorbit should be as short as possible (i.e., much shorter than 25 years)". 
Holger Krag of the European Space Agency states that as of 2017 there is no binding international regulatory framework with no progress occurring at the respective UN body in Vienna. 
Until the End of the World (1991) is a French sci-fi drama set under the backdrop of an out-of-control Indian nuclear satellite, predicted to re-enter the atmosphere, threatening vast populated areas of the Earth. 
In the Planetes, a Japanese hard science fiction manga (1999-2004) and anime (2003-2004), the story revolves around the crew of a space debris collection craft in the year 2075.
Gravity, a 2013 survival film directed by Alfonso Cuaron, is about a disaster on a space mission caused by Kessler syndrome. 
In season 1 of Love, Death & Robots (2019), episode 11, "Helping Hand", revolves around an astronaut being struck by a screw from space debris which knocks her off a satellite in orbit. 
Answer your questions:
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You probably know that a year is 365 days here on Earth. But did you know that on Mercury you’d have a birthday every 88 days? Read this article to find out how long it takes all the planets in our solar system to make a trip around the Sun.
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The biggest planet in our solar system
Each of the planets in our solar system experiences its own unique weather.
Yes, there is ice beyond Earth! In fact, ice can be found on several planets and moons in our solar system.
We can use a planet’s gravitational pull like a scale!
Learn more about what happens when the moon passes between Earth and the sun!
It all has to do with the distance between Earth and the sun and Earth and the moon.
Learn more about asteroids, meteors, meteoroids, meteorites, and comets!
And what can we learn from these space rocks in our solar system?
Make a mask and pretend to be your favorite planet in our solar system!
This future mission will try to find out if life ever existed on the Red Planet!
Mars had water long ago. But did it also have other conditions needed for life?
What did these twin rovers teach us about the history of water on Mars?
Learn more about the first rover to land on Mars!
How do rovers help us learn more about the Red Planet?
The coldest planet in our solar system
The planet that spins on its side
The planet with beautiful rings
The biggest planet in our solar system
The planet with living things
The hottest planet in our solar system
Learn more about the planets in our solar system
Learn to make a graph with the answer!
We have one, but some planets have dozens.
It's not because the Moon gets hit by meteors more often.
Dwarf planet Pluto is still fun to study.
The icy bits past Neptune’s orbit
The smallest planet in our solar system
Interstellar space begins where the sun’s magnetic field stops affecting its surroundings.
How far would we have to travel to get there?
Jupiter's core is very hot and is under tons of pressure!
The answer isn't so simple.
The story starts about 4.6 billion years ago, with a cloud of stellar dust.
Write your own zany adventure story!
For the New Moon, you must eat all the creme filling!
These are yummy and need no baking!
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Turn an old CD into Saturn's rings.
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Explore the many volcanoes in our solar system using the Space Volcano Explorer.
Could they have brought the water to our planet?
Glorious planets and moons to view or print.
These spacecraft traveled to the outer planets!
What do you get when you cross an earthquake with a tidal wave?
Put clues together to find the planets and moons.
What is out there that you cannot see with your bare eyes?
Paint pumpkins with space and Earth science designs
Share these with your friends and family!
And how does it help us find new planets?
Marshmallow? Chewy caramel? Nuts?
Help the big antennas gather data from the spacecraft.
Help Juno reveal Jupiter's true nature.
Paper models of your favorite solar system explorers. This link takes you away from NASA Space Place.
Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that currently has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight and warmth in, which is also essential for life to survive.
Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our Moon, the only one we have, is comprised of a mixture of various rocks and minerals.
Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mountain in the Solar System – Olympus Mons – which rises some 21,229 m (69,649 ft) above the surface, and a giant canyon called Valles Marineris. Valles Marineris is 4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi)!
For comparison, the Grand Canyon in Arizona is about 800 km (500 mi) long and 1.6 km (1 mi) deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent (1/5) of the entire distance around Mars. Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well.
At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one.
Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, but has since evaporated into space. The planet has two small moons called Phobos and Deimos.
Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.
We have written many interesting articles about the inner planets here at Universe Today. Here’s The Solar System Guide as well as The Inner and Outer Planets in Our Solar System.
For more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.
Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.
- Three small bodies have been found in orbit around the pulsar PSR 1257+12. They have been designated “PSR1257+12 A, ..B, and ..C”. One is about the size of the Moon, the other two are about 2 to 3 times the mass of Earth.They were discovered by measuring variations in the pulsation speed of the pulsar which can be interpreted as gravitational effects of three small planets. The original observation has been confirmed but, of course, no direct images have been made — that is way beyond the capabilities of our best telescopes.These planets are believed to have formed after the supernova that produced the pulsar. The present planets would have originally been within the envelope of the progenitor star and therefore wouldn’t have stood much chance of surviving the supernova explosion, and wouldn’t have remained in circular orbits after the explosion.Several decades of timing data on the pulsar PSR 0329+54 (PKS B0329+54) by Tatiana Shabanova (Lebedev Physics Institute) shows evidence of a planet with a 16.9 year period and mass greater than 2 Earth masses.But, while the evidence for these is pretty good, they aren’t really what we’re looking for when we talk about ‘solar systems’.
- It has been known since 1983 that the star Beta Pictoris is surrounded by a disk of gas and dust. Spectra of Beta Pictoris show absorption features which are currently believed to be due to cometary like clouds of gas occultating the star from the debris left over from planetary formation. Though it’s far from certain it is believed by some that planets may already have formed around Beta Pictoris.
HST has observed Beta Pictoris (right) and found the disk to be significantly thinner than previously thought. Estimates based on the Hubble image place the disk’s thickness as no more than one billion miles (1600 million kilometers), or about 1/4 previous estimates from ground-based observations. The disk is tilted nearly edge-on to Earth. Because the dust has had enough time to settle into a flat plane, the disk may be older than some previous estimates. A thin disk also increases the probability that comet-sized or larger bodies have formed through accretion in the disk. Both conditions are believed to be characteristic of a hypothesized circumstellar disk around our own Sun, which was a necessary precursor to the planet-building phase of our Solar Systems, according to current theory.More recent HST observations have shown the disk to be slightly warped as might be expected from the gravitational influence of a planet. This has been confirmed by observations at ESO.
- Recent observations at radio wavelengths of a gas cloud known as Bok Globule B335 have produced images of material collapsing onto a newly born star (only about 150,000 years old). These observations are helping to understand how stars and planets form. The phenomena observed matches the theory of the formation of the solar system — that is, a large gas cloud collapsed to form a star with an attendant circumstellar disk in which, over time, planets accreted from the matter in the disk and orbited the Sun.
- The IRAS satellite found that Vega had too much infrared emission, and that has been attributed to a dust shell (with a mass of maybe Earth’s moon).
- Observations of the very nearby Barnard’s Star were once thought to be evidence of gravitational effects of planets but they now seem to have been in error.
- The star Gl229 seems to contain a 20 Jupiter mass object orbiting at a distance of 44 AU. An object this large is probably a brown-dwarf rather than an ordinary planet.
- What may be the first discovery of a planet orbiting a normal, Sun-like star other than our own has been announced by astronomers studying 51 Pegasi, a spectral type G2-3 V main-sequence star 42 light-years from Earth. At a recent conference in Florence, Italy, Michel Mayor and Didier Queloz of Geneva Observatory explained that they observed 51 Pegasi with a high-resolution spectrograph and found that the star’s line-of-sight velocity changes by some 70 meters per second every 4.2 days. If this is due to orbital motion, these numbers suggest that a planet lies only 7 million kilometers from 51 Pegasi — much closer than Mercury is to the Sun — and that the planet has a mass at least half that of Jupiter. These physical characteristics hinge on the assumption that our line of sight is near the planet’s orbital plane. However, other evidence suggests that this is a good bet. A world merely 7 million km from a star like 51 Pegasi should have a temperature of about 1,000 degrees Celsius, just short of red hot. It was initially thought that it might be a solid body like a very big Mercury but the concensus now seems to be that it is a “hot Jupiter”, a gas planet formed much farther from its star that migrated inward.
These observations have now been confirmed by several independent observers. And there is some evidence for a second planet much farther out that is not yet confirmed.
[ The 5.5-magnitude 51 Pegasi is easily visible in binoculars between Alpha and Beta Pegasi, the western pair of stars in the Great Square of Pegasus. The star’s equinox-2000 coordinates are R.A. 22 hours 57 minutes, Dec. +20 degrees 46 minutes. ]
- On 1/17/96 Geoffrey Marcy andPaul Butler announced the discovery of planets orbiting the stars 70 Virginis and 47 Ursae Majoris. 70 Vir is a G5V (main sequence) star about 78 light-years from Earth 47 UMa is a G0V star about 44 light-years away. These were discovered using the same doppler shift technique that found the planet orbiting 51 Pegasi.
The planet around 70 Vir orbits the star in an eccentric, elongated orbit every 116 days and has a mass about nine times that of Jupiter. Using standard formulas that balance the sunlight absorbed and the heat radiated, Marcy and Butler calculated the temperature of the planet at about 85 degrees Celsius (185 degrees Fahrenheit), cool enough to permit water and complex organic molecules to exist. The star 70 Vir is nearly identical to the Sun, though several hundred degrees cooler and perhaps three billion years older.
The planet around 47 UMa was discovered after analysis of eight years of observations at Lick Observatory. Its period is a little over three years (1100 days), its mass about three times that of Jupiter, and its orbital radius about twice the Earth’s distance from the Sun. This planet too probably has a region in its atmosphere where the temperature would allow liquid water.
- As of April 1996, Drs. Marcy and Butler have discovered yet another planet this time around the star HR3522 (aka Rho 1 Cancri, 55 Cancri) about 45 light years from the Earth. The planet is estimated to be about 0.8 Jupiter masses. It is likely that several more planets will show up in the initial set of 120 stars that they have monitored.
- Several more extra-solar planets have now been discovered by the Butler/Marcy method. It seems likely that there are a very large number of such planets out there.
- Another extra-solar planet has been discovered orbiting 16 Cygni B. But unlike all other previously known planets this one has a very large orbital eccentricity (0.6) its orbit carries it from a closest distance of 0.6 AU from its star to 2.7 AU. This calls into question many theories of planetary formation.
- Detecting extra-solar planets directly is very difficult. Even the Hubble Space Telescope wouldn’t be able to image planets at the expected sizes and distances from their suns.
What HST did find were disks of matter around stars seen in silhouette against the Orion Nebula (called ‘proplyds’, for ‘proto-planetary disks‘ (right). This is great evidence for how common these objects are, but the scale is way too small to say anything directly about planets there. More detailed HST images are now available, too.
The idea of space habitats either in fact or fiction goes back to the second half of the 19th century. "The Brick Moon", a fictional story written in 1869 by Edward Everett Hale, is perhaps the first treatment of this idea in writing. In 1903, space pioneer Konstantin Tsiolkovsky speculated about rotating cylindrical space habitats, with plants fed by the sun, in Beyond Planet Earth.   In the 1920s John Desmond Bernal and others speculated about giant space habitats. Dandridge M. Cole in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating them to use as settlements in various magazine articles and books, notably Islands In Space: The Challenge Of The Planetoids. 
There are a range of reasons for space habitats. Beside human spaceflight supported space exploration, space colonies is an often mentioned particular reason, which can in it be based on reasons like:
- Survival of human civilization and the biosphere, in case of a disaster on the Earth (natural or man-made) 
- Huge resources in space for expansion of human society
- Expansion without any ecosystems to destroy or indigenous peoples to displace
- It could help the Earth by relieving population pressure and taking industry off-Earth.
A number of arguments are made for space habitats having a number of advantages:
Access to solar energy Edit
Space has an abundance of light produced from the Sun. In Earth orbit, this amounts to 1400 watts of power per square meter.  This energy can be used to produce electricity from solar cells or heat engine based power stations, process ores, provide light for plants to grow and to warm space habitats.
Outside gravity well Edit
Earth-to-space habitat trade would be easier than Earth-to-planetary habitat trade, as habitats orbiting Earth will not have a gravity well to overcome to export to Earth, and a smaller gravity well to overcome to import from Earth.
In-situ resource utilization Edit
Space habitats may be supplied with resources from extraterrestrial places like Mars, asteroids, or the Moon (in-situ resource utilization [ISRU]  see Asteroid mining). One could produce breathing oxygen, drinking water, and rocket fuel with the help of ISRU.  It may become possible to manufacture solar panels from lunar materials. 
Asteroids and other small bodies Edit
Most asteroids have a mixture of materials, that could be mined, and because these bodies do not have substantial gravity wells, it would require low delta-V to draw materials from them and haul them to a construction site.  [ full citation needed ]
There is estimated to be enough material in the main asteroid belt alone to build enough space habitats to equal the habitable surface area of 3,000 Earths. 
A 1974 estimate assumed that collection of all the material in the main asteroid belt would allow habitats to be constructed to give an immense total population capacity. Using the free-floating resources of the Solar System, this estimate extended into the trillions. 
Zero g recreation Edit
If a large area at the rotation axis is enclosed, various zero-g sports are possible, including swimming,   hang gliding  and the use of human-powered aircraft.
Passenger compartment Edit
A space habitat can be the passenger compartment of a large spacecraft for colonizing asteroids, moons, and planets. It can also function as one for a generation ship for travel to other planets or distant stars (L. R. Shepherd described a generation starship in 1952 comparing it to a small planet with many people living in it.)  
The requirements for a space habitat are many. They would have to provide all the material needs for hundreds or thousands of humans, in an environment out in space that is very hostile to human life.
Air pressure, with normal partial pressures of oxygen (21%), carbon dioxide and nitrogen (78%), is a basic requirement of any space habitat. Basically, most space habitat designs concepts envision large, thin-walled pressure vessels. The required oxygen could be obtained from lunar rock. Nitrogen is most easily available from the Earth, but is also recycled nearly perfectly. Also, nitrogen in the form of ammonia ( NH
3 ) may be obtainable from comets and the moons of outer planets. Nitrogen may also be available in unknown quantities on certain other bodies in the outer solar system. The air of a habitat could be recycled in a number of ways. One concept is to use photosynthetic gardens, possibly via hydroponics, or forest gardening. [ citation needed ] However, these do not remove certain industrial pollutants, such as volatile oils, and excess simple molecular gases. The standard method used on nuclear submarines, a similar form of closed environment, is to use a catalytic burner, which effectively decomposes most organics. Further protection might be provided by a small cryogenic distillation system which would gradually remove impurities such as mercury vapor, and noble gases that cannot be catalytically burned. [ citation needed ]
Food production Edit
Organic materials for food production would also need to be provided. At first, most of these would have to be imported from Earth. [ citation needed ] After that, feces recycling should reduce the need for imports. [ citation needed ] One proposed recycling method would start by burning the cryogenic distillate, plants, garbage and sewage with air in an electric arc, and distilling the result. [ citation needed ] The resulting carbon dioxide and water would be immediately usable in agriculture. The nitrates and salts in the ash could be dissolved in water and separated into pure minerals. Most of the nitrates, potassium and sodium salts would recycle as fertilizers. Other minerals containing iron, nickel, and silicon could be chemically purified in batches and reused industrially. The small fraction of remaining materials, well below 0.01% by weight, could be processed into pure elements with zero-gravity mass spectrometry, and added in appropriate amounts to the fertilizers and industrial stocks. It is likely that methods would be greatly refined as people began to actually live in space habitats.
Artificial gravity Edit
Long-term on-orbit studies have proven that zero gravity weakens bones and muscles, and upsets calcium metabolism and immune systems. Most people have a continual stuffy nose or sinus problems, and a few people have dramatic, incurable motion sickness. Most habitat designs would rotate in order to use inertial forces to simulate gravity. NASA studies with chickens and plants have proven that this is an effective physiological substitute for gravity. [ citation needed ] Turning one's head rapidly in such an environment causes a "tilt" to be sensed as one's inner ears move at different rotational rates. Centrifuge studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine "spinward" and "antispinward" directions in the centrifuges. [ citation needed ]
Protection from radiation Edit
Some very large space habitat designs could be effectively shielded from cosmic rays by their structure and air. [ citation needed ] Smaller habitats could be shielded by stationary (nonrotating) bags of rock. Sunlight could be admitted indirectly via mirrors in radiation-proof louvres, which would function in the same manner as a periscope.
For instance, 4 metric tons per square meter of surface area could reduce radiation dosage to several mSv or less annually, below the rate of some populated high natural background areas on Earth.  Alternative concepts based on active shielding are untested yet and more complex than such passive mass shielding, but usage of magnetic and/or electric fields to deflect particles could potentially greatly reduce mass requirements.  If a space habitat is located at L4 or L5, then its orbit will take it outside of the protection of the Earth's magnetosphere for approximately two-thirds of the time (as happens with the Moon), putting residents at risk of proton exposure from the solar wind. See Health threat from cosmic rays
Heat rejection Edit
The habitat is in a vacuum, and therefore resembles a giant thermos bottle. Habitats also need a radiator to eliminate heat from absorbed sunlight. Very small habitats might have a central vane that rotates with the habitat. In this design, convection would raise hot air "up" (toward the center), and cool air would fall down into the outer habitat. Some other designs would distribute coolants, such as chilled water from a central radiator.
Meteoroids and dust Edit
The habitat would need to withstand potential impacts from space debris, meteoroids, dust, etc. Most meteoroids that strike the earth vaporize in the atmosphere. Without a thick protective atmosphere meteoroid strikes would pose a much greater risk to a space habitat. Radar will sweep the space around each habitat mapping the trajectory of debris and other man-made objects and allowing corrective actions to be taken to protect the habitat. [ citation needed ]
In some designs (O'Neill/NASA Ames "Stanford Torus" and "Crystal palace in a Hatbox" habitat designs have a non-rotating cosmic ray shield of packed sand (
1.9 m thick) or even artificial aggregate rock (1.7 m ersatz concrete). Other proposals use the rock as structure and integral shielding (O'Neill, "the High Frontier". Sheppard, "Concrete Space Colonies" Spaceflight, journal of the B.I.S.) In any of these cases, strong meteoroid protection is implied by the external radiation shell
4.5 tonnes of rock material, per square meter. 
Note that Solar Power Satellites are proposed in the multi-GW ranges, and such energies and technologies would allow constant radar mapping of nearby 3D space out-to arbitrarily far away, limited only by effort expended to do so.
Proposals are available to move even kilometer-sized NEOs to high Earth orbits, and reaction engines for such purposes would move a space habitat and any arbitrarily large shield, but not in any timely or rapid manner, the thrust being very low compared to the huge mass.
Attitude control Edit
Most mirror geometries require something on the habitat to be aimed at the sun and so attitude control is necessary. The original O'Neill design used the two cylinders as momentum wheels to roll the colony, and pushed the sunward pivots together or apart to use precession to change their angle.
Initial capital outlay Edit
Even the smallest of the habitat designs mentioned below are more massive than the total mass of all items that humans have ever launched into Earth orbit combined. [ citation needed ] Prerequisites to building habitats are either cheaper launch costs or a mining and manufacturing base on the Moon or other body having low delta-v from the desired habitat location.  [ full citation needed ]
The optimal habitat orbits are still debated, and so orbital stationkeeping is probably a commercial issue. The lunar L4 and L5 orbits are now thought to be too far away from the moon and Earth. A more modern proposal is to use a two-to-one resonance orbit that alternately has a close, low-energy (cheap) approach to the Moon, and then to the Earth. [ citation needed ] This provides quick, inexpensive access to both raw materials and the major market. Most habitat designs plan to use electromagnetic tether propulsion, or mass drivers used instead of rocket motors. The advantage of these is that they either use no reaction mass at all, or use cheap reaction mass. [ citation needed ]
O'Neill - The High Frontier Edit
Around 1970, near the end of Project Apollo (1961–1972), Gerard K. O'Neill, an experimental physicist at Princeton University, was looking for a topic to tempt his physics students, most of them freshmen in engineering. He hit upon the idea of assigning them feasibility calculations for large space-habitats. To his surprise, the habitats seemed feasible even in very large sizes: cylinders 8 km (5 mi) in diameter and 32 km (20 mi) long, even if made from ordinary materials such as steel and glass. Also, the students solved problems such as radiation protection from cosmic rays (almost free in the larger sizes), getting naturalistic Sun angles, provision of power, realistic pest-free farming and orbital attitude control without reaction motors. O'Neill published an article about these colony concepts in Physics Today in 1974.  (See the above illustration of such a colony, a classic "O'Neill Colony"). He expanded the article in his 1976 book The High Frontier: Human Colonies in Space.
NASA Ames/Stanford 1975 Summer Study Edit
The result motivated NASA to sponsor a couple of summer workshops led by O'Neill.   Several concepts were studied, with sizes ranging from 1,000 to 10,000,000 people,    [ full citation needed ] including versions of the Stanford torus. Three concepts were presented to NASA: the Bernal Sphere, the Toroidal Colony and the Cylindrical Colony. 
O'Neill's concepts had an example of a payback scheme: construction of solar power satellites from lunar materials. O'Neill did not emphasize the building of solar power satellites as such, but rather offered proof that orbital manufacturing from lunar materials could generate profits. He and other participants presumed that once such manufacturing facilities had started production, many profitable uses for them would be found, and the colony would become self-supporting and begin to build other colonies as well.
The concept studies generated a notable groundswell of public interest. One effect of this expansion was the founding of the L5 Society in the U.S., a group of enthusiasts that desired to build and live in such colonies. The group was named after the space-colony orbit which was then believed to be the most profitable, a kidney-shaped orbit around either of Earth's lunar Lagrange points 5 or 4.
Space Studies Institute Edit
In 1977 O'Neill founded the Space Studies Institute, which initially funded and constructed some prototypes of the new hardware needed for a space colonization effort, as well as producing a number of feasibility studies. One of the early projects, for instance, involved a series of functional prototypes of a mass driver, the essential technology for moving ores efficiently from the Moon to space colony orbits.
Space Baby Names for Girls
Adhara is derived from Arabic roots and means “virgins.”
One of the most brilliant stars in the sky is called Adhara. It’s a bright name too, great for baby girls — you could even choose a spelling variation, such as Adara.
Pronounced Al·cy·o·ne, Alcyone is a name from Greek mythology.
Alcyone was the daughter of Aeolus and married to Ceyx. The pair was happy but enraged the ancient gods by calling each other Hera and Zeus. One day when Ceyx was at sea, his ship sunk, and out of grief, Alcyone threw herself into the ocean.
Alcyone is now notable for being the brightest star in the Pleiades.
Alpha stems from Greek and is the first letter of their alphabet.
In astronomy, Alpha is the name used for the most radiant star in every constellation. It would make a bold pick for a first daughter, giving her some girl boss vibes by letting everyone know she’s number one.
Alula is of Arabic descent and translates to “the first leap.”
It’s the palindromic name of a rare binary star system (two stars that appear as one because of their proximity). If you’re expecting twins, it would be fantastic for the firstborn.
Alya comes from Russia, Turkey, and Arabic-speaking countries, where it relates to “heavens,” “exalted,” and “highborn.”
We know the name from the star system, Theta Serpentis. It’s a common first name given to girls in Islam.
Amalthea is a Greek mythology name meaning “tender goddess.”
Amalthea is believed to be the name of either a goat or a goat-keeping nymph. In Greek legend, she nursed Zeus while he was an infant and kept him safe from his dangerous father, Cronus.
In astronomy, the constellation, Capra (translation: she-goat), is thought to represent Amalthea. It’s also the name of one of Jupiter’s moons.
Andromeda stems from Greek and translates to “advising like a man.”
In Greek legends, Andromeda was the daughter of Cassiopeia, who Athena made into a constellation. The star cluster is called The Bohemian Andromeda.
Aquarius is another Greek name, known as the constellation between Pisces and Capricorn.
The cluster resembles a person pouring water. Aquarius is also the 11th sign of the zodiac and isn’t exactly a common name for babies.
Ariel comes from Hebrew roots and translates to “lion of god.”
This biblical name is seen as the messenger of Ezra and is symbolic of Jerusalem city. In the western world, however, Ariel is more familiar in popular culture as the protagonist in the 1989 Disney movie, The Little Mermaid.
Ariel is also one of Uranus’ moons. It’s the fourth-largest to orbit this distant planet.
Astra means “of the stars.” and has Greek origins.
With intergalactic vibes, Astra is a fantastic space baby name. Some may recognize it from the character, Princess Astra in Doctor Who.
Aurora comes from Latin and means “the dawn.”
The name stems from the Roman goddess of sunrise, who created dew with her tears. According to legends, she traveled from East to West, thus renewing herself each dawn.
It also relates to the scientific phenomenon that causes the Aurora Borealis (Northern Lights) and the Aurora Australis (Southern lights) near the magnetic northern and southern poles.
Belinda comes from German and Spanish roots and translates to “pretty one” or “serpent.”
According to Babylonian mythology, Belinda was a goddess, ruling over heaven and Earth. Alexander Pope used the name for the heroine in his poem, The Rape of the Lock.
Belinda is also the name of one of the moons orbiting Uranus.
Bellatrix is a Latin name, used to define the term “female warrior.”
In astronomy, Bellatrix is the name of a star in the Orion constellation. However, the name has drawn more attention from the evil character in the J.K. Rowling series, Harry Potter. If you can ignore that association, Bellatrix is a beautiful name with an even stronger meaning.
Bianca stems from Italian roots and means “white.”
Bianca has been a contender on the top charts since the beginning of the 1900s and enjoyed immense popularity in the 1990s. The name was given to one of Uranus’ moons when it was discovered by Voyager 2. It’s an Italian and Shakespearean variant of Blanche and would make an excellent pick for winter babies.
Calypso is derived from Greek and is a name for “she who hides.”
According to Greek mythology, Calypso was an island nymph who imprisoned Odysseus for seven years. It’s a colorful name that’s also quite favored for boys.
Calypso is the name of a moon, discovered in 1980, orbiting Saturn.
Capella comes from Latin for “little she-goat.” Capella is the name of the 11th brightest star and carries both astrological and mythological importance.
In astrology, the name symbolizes wealth and military honor. In Roman mythology, it was the goat that nursed Jupiter. Capella is mentioned in several legends, including Persian and Aboriginal.
Cassiopeia was a queen of great vanity in Greek mythology.
Cassiopeia, pronounced kass-ee-oh-pie-ah, was the name of the legendary mother of Andromeda. She was transformed by Zeus into a constellation alongside her daughter for offending Poseidon.
It’s a mouthful of a name, yet attractive and exotic. You could always use the nickname Cassie or Casey.
Celeste comes from Latin and means “of the heavens.” Parents with children already may know it from Queen Celeste of the Babar elephant stories.
A beautiful name that has been in the top 1,000 for over 130 years, Celeste is a good pick for the daughter that means heaven and Earth to you.
In Hindu, Chandra is the moon goddess.
The name peaked in the western world around the 1960s when incense and meditation were the hot new thing. However, because of its resemblance to Sandra, it could easily become favored again.
Charon is from mythology, and the name means “of keen gaze.”
Charon’s pronunciation has everyone scratching their heads. According to Greek mythology, Charon, pronounced kare-on, was the ferrymen of dead souls, dwelling in the underworld. In astronomy, however, Charon, pronounced share-on, is Pluto’s moon.
Cordelia has both Latin and Celtic origins, and it represents “heart” or “daughter of the sea.”
Cordelia was one of King Lear’s daughters, known for her sympathetic nature. Astrologers gave her name to the innermost moon of Uranus. Cordelia has both charm and style — there are loads of possibilities for nicknames, including Cora, Lia, Delia, or Del.
Corona is a Spanish word for “crown.”
Corona is the name for an aura of plasma floating around the sun. Although it’s a beautiful name, many are likely to associate it with the beer or the recent outbreak of a respiratory illness.
Cressida comes from Greek origin and translates to “gold.”
It is the name of one of the smaller moons orbiting Uranus. Cressida has starred in both Greek mythology and Shakespearean literature. Today, it’s familiar as a character from “The Hunger Games,” and the name of author Cressida Cowell.
The bearer of the name Cybele, pronounced Cyb·e·le, has a mighty name to live up to as it means “mother of all gods.”
In Greek mythology, Cybele was the goddess of health, nature, and fertility. Because of the strong association, it’s only fitting that astronomers gave the name to the largest asteroid in our solar system.
The meaning of Danica from Slavic origin, “morning star,” is believed to be a representation of the sun. It resembles Danielle, Dana, and Daniela, but it’s not a variant of those names.
Danica isn’t as common as it was a few years back, but we’re confident it can make a comeback. Racecar driver Danica Patrick has brought the name into the mainstream.
Despina comes from Greek and is a word for “lady.”
Despina is probably best known from Mozart’s opera Cosi fan Tutte, but it’s derived from the Greek mythological name, Despiona. She was the daughter of Demeter and Poseidon. Today, the name also belongs to one of Neptune’s moons.
Dione is derived from Greek sources and translates to “divine queen.”
In Greek legends, Dione, pronounced dy-OH-ne, was the mother of Aphrodite. The name is given to a moon near Saturn. However, it might be confused with Dionne or Dion.
Elara springs from Greek roots.
Elara was a mythological lover of Zeus, who had to give birth to a giant baby (ouch). In astronomy, it’s the lovely name given to one of Jupiter’s moons.
Another Greek name, Electra, means “bright” or “shining.”
Electra is a brilliant choice for a strong girl — it gives off sparky vibes that won’t go unnoticed. Astronomers gave the name to a giant star found in the Taurus constellation.
Eris is a mythological name for the goddess of discord and strife.
The name has also made strides in pop culture. Eris joined forces with Maleficent, the Horned King, and others to form “The Dark Council” to defeat Chernabog’s rise in the universe.
In 2005, Eris became the name of a dwarf planet, sometimes referred to as the tenth planet.
Faye is of English origin and signifies “fairy.”
Faye isn’t the name of a galaxy far away (not that we know of anyway). It is, however, the name of a famous astronomer, Hervé Faye. Faye was the name given to 410 baby girls during 2018 in the U.S.
Flora is a Scottish and Latin name for “flower.”
Flora is the name of an asteroid orbiting the sun. The name is believed to be from the Roman goddess of spring and flowers, who was blessed with eternal youth. Flora is a nature name, excellent for summer and spring baby girls.
Galatea is of Greek lineage and pertains to “she who is milk-white.”
The name stems from the legendary sculptor, Pygmalion, who created his ideal woman from carved ivory, giving her an incredibly pale appearance. When he fell in love with his creation, Aphrodite brought her to life, naming her Galatea due to her skin. Galatea is also the name of a moon circling Neptune, sometimes called Neptune VI.
Gemini is of Latin roots and means “twins.”
Gemini is most famous as the name of the astrological sign. Geminis are into self-love, believing you can only love others after learning to love yourself.
Helene is a French name meaning “bright” or “shining one.”
Helene is the name of a moon belonging to Saturn, discovered in 1980. Helene can be spelled or pronounced in various ways, from Heleen to Helaine. It was a favored name back in 1916 but was off of the popularity charts by 1970.
Hilda springs from Germany, where it means “battle woman.”
Hilda is a short variant of Brunhilda, who was a Valkyrie of Teutonic legend. It is also the name of a group of asteroids, often referred to as “The Hildas.”
Hoshi is a Japanese name, which translates to “star.”
With a short, quick pronunciation, Hoshi is catchy and stylish. Thanks to its astrological meaning, it’s a fantastic pick for parents who dare to be bold.
Ida is of German origin and signifies “industrious one.”
Ida was the name given to an asteroid in the Kronis family by Austrian astronomer Johann Palisa. Ida has great potential — it’s in the group of short, vowel names that are making a comeback, alongside Ava and Ada.
Indu originates from Hindi for “moon.”
Indu is an unusual name, but it’s not on the absurdly, weird, never-gonna-happen list. It’s a stunning moon name, which resembles Luna and Serena.
Juliet comes from English and French origins and signifies “youthful.”
As the essence of romantic names, Juliet is both stylish and delicate. The name has somewhat outgrown its link to Romeo and is ready for use in the U.S. In astronomy, Juliet is the name of a moon near Uranus.
Kamaria is a Swahili word, which means “moonlight.”
Kamaria sounds and looks like an extension of Maria. It has a beautiful lilt when spoken and would make a rare name in the U.S.
Larissa comes from Greek and Russian origins and translates to “citadel.”
In mythology, Larissa was a nymph. Today, it is the name of a moon of Neptune. This name would be a fresh change from the more common Melissa, Clarissa, and even Alyssa.
Luna is an Italian name and was the Roman goddess of the moon.
The word is derived from Latin and has gained popularity in the last couple of years, probably thanks to Luna Lovegood from the Harry Potter series.
Nova stems from Latin roots and means “new.”
In astronomical terms, nova is a star, which suddenly grows in brightness before fading. Nova sounds similar to Noah — it’s crisp and fresh, excellent for a 21st-century baby.
Rhea is Greek and has a lovely translation, “a flowing stream.”
Rhea is an original name with a Greek mythological meaning — she was the earth mother of all gods. Rhea is also the second-largest moon orbiting Saturn. The actress Rhea Perlman is probably the most famous owner of the name.
Selena is of Latin origin and means “moon goddess.”
Selena is a favored name within the Latino community and has several famous bearers, such as Selena Gomez. It’s a stylish name, resembling other contenders such as Celia and Seraphina.
Stella is derived from Latin roots and translates to “star.”
A poet called Sir Philip Sidney first coined the name in his work “Astrophel and Stella.” This name caught on and has been on the U.S. charts for years.
Thalassa is of Greek roots and means “the sea.”
Thalassa is one of the moons of Neptune, discovered and named as recently as 1989. Otherwise, Thalassa is a rarely used name. In ancient times, Thalassa was a personification of the ocean.
Venus was the Roman goddess of love and beauty, an equivalent of Aphrodite. Venus is also the famed second planet from the sun as well as the moniker of tennis champ Venus Williams.
Zaniah is an Arabic name meaning “corner.”
Zaniah is a triple star system in the constellation of Virgo. While it’s not even on the popular name spectrum, Zaniah gives us some edgy vibes.
Comet 67P, robot lab Philae's alien host, nears Sun
An artist's impression of Rosettas lander Philae (back view) on the surface of comet 67P/Churyumov-Gerasimenko
A comet streaking through space with a European robot lab riding piggyback will skirt the Sun this week, setting another landmark in an extraordinary quest to unravel the origins of life on Earth.
Scientists hope the heat of perihelion—when the comet comes closest to the Sun in its orbit—will cause the enigmatic traveller to shed more of its icy crust.
If so, it could spew out pristine particles left from the Solar System's birth 4.6 billion years ago, they believe.
And if Comet 67P/Churyumov-Gerasimenko undergoes this dramatic change, Europe's Rosetta spacecraft will be orbiting nearby, ready to pounce on any clues of how our star system came into being.
"This is the time most of the action happens," said European Space Agency (ESA) expert Mark McCaughrean of the weeks-long peak of comet activity.
The ancient celestial voyager will reach its closest point to our star—some 186 million kilometres (116 million miles)—at about 0200 GMT on Thursday, before embarking on another 6.5-year egg-shaped orbit.
Things have been heating up for weeks, with gas and dust blasting off the comet's surface as solar heat transforms its frozen crust into a space tempest.
This is "the greatest opportunity to catch material and analyse it if you're looking for rare species of molecules," especially organic ones, McCaughrean told AFP.
"We want to look at the more pristine material that might come out" from beneath the layer of icy dust stripped from the surface.
Most exciting would be if the duck-shaped comet's "neck"—which hosts a 500-metre (1,640-foot) crack—were to break in two to reveal the raw insides.
"That's really the Holy Grail. to see the interior of the comet," said McCaughrean, though most scientists believe a breakup is unlikely this time around.
Compromise: Safety vs scienceThe progress of the 'Chury' comet and the Philae as they approach they closes point to the Sun
In any scenario, ground teams working on the 20-year-old Rosetta mission will likely have to wait weeks, if not months, to analyse new data.
For one thing, there has been no word from Philae, their eyes on the ground, since July 9, and its status is unknown.
Right now, 67P with its precious cargo is hurtling through space at 34.17 km per second.
Rosetta has had to move farther away to avoid the confounding effects of the dust storm on its star-tracking navigation system.
The spacecraft now orbits at some 200-300 km from the comet, compared to less than 10 km at its closest in October last year.
"If we were right next to it, bathing in the material, they (scientists) would be super happy," said McCaughrean—but with a high risk of losing Rosetta.
"You have to do a compromise between spacecraft safety and getting as close as possible," added Philae project manager Stephan Ulamec of German space agency DLR.
Rosetta's instruments can still catch particles, but these are less sensitive than Philae's.
Once the most violent outgassing is over, Rosetta will move closer again and seek to re-establish contact with Philae, hoping that somehow the little lab has been going about its scientific business all along.A close-up image of the most active pit, known as Seth 01, observed on the surface of the comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft
But even if Philae has gone permanently silent, scientists can learn a lot from before-and-after images, gas samples and other measurements taken by Rosetta itself.
Some experts believe comets smashed into our infant planet, providing it with precious water and the chemical building blocks for life.
The Rosetta mission has already shown that at least as far as water is concerned, this is not the complete picture.
Water on 67P is of a slightly different chemical composition—a different "flavour" than Earth's.The Philae lander, as seen through Rosetta's OSIRIS narrow-angle camera in November 2014
Rosetta deposited washing machine-sized Philae on the comet on November 12 last year after a 10-year, seven-billion-kilometre trek.
The landing was rough, and the robot tumbled into a ditch shadowed from the Sun's battery-recharging rays. After three days of comet sniffing and prodding, its onboard power ran out, and Philae went into hibernation on November 15.
But as 67P drew closer to the Sun, it recharged and woke up on June 13, only to fall silent again less than a month later.
Just in case it is awake, ground controllers have sent "blind commands" for the lab to activate a few basic experiments during the perihelion period.
Europe's comet-chasing Rosetta mission: timeline
Following is a timeline of Europe's Rosetta mission, which will reach a milestone Thursday when its target, Comet 67P/Churyumov-Gerasimenko,reaches perihelion—the closest point to the Sun in a 6.5-year orbit.
Rosetta, carrying a robot lab called Philae, is launched by Ariane 5 rocket from the European Space Agency's base in Kourou, French Guiana.
Rosetta flies past Earth, using the planet's gravity as a slingshot to boost speed. It zips by Mars in 2007 and twice more by Earth, in 2007 and 2009, to accelerate further.
- June 2011 to January 20, 2014:
At its maximum distance—about 800 million kilometers or 500 million miles—from the Sun and a billion km from home, Rosetta hibernates to conserve energy.
Rosetta arrives at comet 67P, and goes into orbit. It has 11 onboard instruments: cameras, radar, microwave, infrared and other sensors to analyse the comet surface and gases escaping from it.
Rosetta sends down Philae, a 100-kilogramme (220-pound) lab equipped with 10 instruments. After bouncing several times, Philae ends in a ditch, shadowed from the Sun's battery-replenishing rays.
Philae's stored battery power runs out after about 60 hours of work. It sends home reams of data before going into standby mode.
As 67P nears the Sun, Philae's batteries are recharged, it emerges from hibernation and sends home a two-minute message.
Philae goes into "silent mode" after eight intermittent communications with Earth.
- August 13: 67P to come within 186 million km of the Sun, its closest distance to our star.
- September 2016: Projected end of the mission, with Rosetta, now replete of fuel, to be reunited with Philae on the comet surface.
Can Venus help us find exoplanets?…
This post is in response to loyal reader Jarman Day-Bohn’s question, which he left in a comment on the post “Today is transit day….”. Jarman asked:
How much do you think this [transit of Venus] will contribute to the current research experts are performing toward the study of possible earth-like planets out there? I know they were heavily using a technique measuring how much of a star’s light is blocked out by a planet to judge its size and other factors. Will this in any way help that process?
Great question Jarman, thanks for asking! Let’s look into that a little bit more.
But before we get too far into that, let’s think a little more about transits. Whether or not a transit occurs is all based on perspective. From Earth, only Mercury and Venus are interior planets- planets orbiting closer to the Sun- so they’re the only two that can we can see transit the Sun’s disk. If you were on Mars though, you could conceivably see Mercury, Venus, and Earth transits. And if you were on Pluto you could, in theory, see all eight planets transit the Sun. Remember though, as you get further away, even though more planets can be seen transitting the Sun from your perspective, you’re also getting further away, meaning the Sun is going to look smaller and smaller to you, as are the transitting planets. The Sun is only 93 million miles from the Earth (that’s really close astronomically speaking), so the enormous Sun, which is 1 million times larger in volume than the Earth, takes up a relatively large portion of the sky (
0.5 degrees). As you move further away from the Sun, its angular size in the sky will shrink. By the time you got to Pluto, which is 3.67 billion miles from the Sun, but still close astronomically speaking, our local star would look like a bright speck only
0.01 degrees (50 times smaller than in the sky on Earth) probably something similar to the artist’s depiction below.
This artist’s depiction shows what the Sun might look like from an object, like Pluto, that’s in the solar system’s Kuiper Belt. Notice how the relatively close Sun differs from the background stars. Credit: NASA/JPL-Caltech/T. Pyle (SSC)
Now as you travel further from the Sun, let’s say to a planet orbiting another star, and look at our Sun, you could still in theory see all eight planets (and Pluto) transit the Sun, but now you’re trillions of miles from the Sun which is now just point of light in the sky, the same way other stars appear to us in the nighttime sky. The really astounding thing about looking at the other stars in our galaxy (Note: every star you see in the nighttime sky is in the Milky Way, we can’t resolve single stars in other galaxies.) is that they are so incredibly far away that no matter how large a telescope we use, we can never see the disk of the star like we can with the Sun, it just won’t have a large enough angular size. Now matter what, even through the Hubble Space Telescope, stars look like pinpricks of light that astronomers call “point sources“. Which makes actually seeing a planet transit a star, like we can see with Venus, impossible. I’ll remind you that in a previous post entitled “Baseballs, not umbrellas…” I explained the continuing search for exoplanets and covered all three of the main techniques which scientists employ to find these elusive celestial bodies around our galaxy. As Jarman indicated, the most successful and commonly used method of detection is the “transit method”. This is the method that NASA’s Kepler mission has already used to find the first Earth-like rocky exoplanet. However, since I just explained that we can’t actually see the exoplanet transitting the distant star, the only way we can detect the transit is by recording the change in light we see as the exoplanet crosses in front of the star. But again, we don’t actually “see” the transit happen, we just observe the dip in the brightness given off by the star. Similarly, if you were on a ship off the shore and someone walked in front of the lighthouse beacon, you wouldn’t be able to see the person, but you might be able to record the drop in brightness as they walked by.
This artist’s idea of NASA’s Kepler mission looking for exoplanets illustrates the main technique that scientists hope to use to find planets orbiting other stars- called the transit method- but no matter the size of the telescope we can’t actually see the exoplanets transitting the disk of the star. Credit: universetoday.com
But now let’s get back to Jarman’s actual question: can a transit in our solar system, like that of Venus, help scientists to find planets transitting other stars? It might. The transit of Venus is a well-documented and well-understood phenomenon, which scientists have been able to accurately predict and observe at least 6 times in the last 400 years. As I explained in “Looking to launch and preparing for transit…“, the transit of Venus helped us to determine the size of our solar system. And since we’ve actually been able to explore our solar system and have a very good grasp of the size of Venus and the Sun and the distances between the Earth and each of them, we can use the transit of Venus as a calibration tool in our search for extrasolar planets. For instance, scientist can say a planet like Venus, which is so big, transitting in front of a star like the Sun, which is so big, would cause a drop in brightness of this much at this distance. Then we can scale that distance out to other stars and we get some idea of what we need to look for in our search for exoplanets.
So Jarman, there’s your answer: while the spectacular crossing of Venus may not lead to groundbreaking new methods to find exoplanets, it does give us a rare opportunity to view a transit (that involves objects we know a lot about) and use that as a reference point as we continue our search!
Thanks again to Jarman for posing this question and if you, like Jarman, have a question that you’d like to have answered, please leave a comment or use the “Contact astroian” tab at the top of the page to send me an email!