Astronomy

Do most planetary systems have fewer planets than the solar system?

Do most planetary systems have fewer planets than the solar system?


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It is my impression that most planetary systems have, at most, three to four planets. Is that real? Or is it just that we lack the ability to detect most planets?


Perhaps the way to answer this is ask - could we detect the planets in our solar system if we were looking at the Sun, using current technology, from distances of many light years?

The short answer is that we could detect Jupiter using the Doppler radial velocity technique, if we observed for more than 10 years (at least one orbit is required). If we were lucky, and the orientation is right, we might then also be able to detect a transit of Venus or the Earth, using a satellite observatory like Kepler. Kepler could detect Earthlike planets by the transit technique, but the solar system is not "flat" enough that you would observe multiple transiting planets.

So the answer is that we would currently have seen Jupiter and maybe one other planet. Therefore we cannot at the moment conclude that 8 planets is an unusually high number; it may be quite typical. Although we do know that solar systems can be much more densely populated with planets (in their "terrestrial planet zones") than our own.


There are two things to consider when thinking about this.

The first is that by virtue of living within our solar system, we are much closer to our planets, have a much easier time seeing and documenting them. We can point ground based telescopes at them and get reasonably detailed pictures of them. The point is, since we're so close, we're less likely to miss planets; But it should be noted there may still be planets in our Solar System we have not documented

Secondly is that we're really not all that great at identifying extra solar planets. Most techniques for doing this require the exo-planet to be rather large, on the scale or our gas giants.

Because of these two points, it's hard to definitively answer this question. We have identified multiple solar systems containing more than one planet, but that doesn't mean we have identified ALL planets in these systems.


The Weirdest Solar System We've Found So Far? You May Be In It

Before we found the first exoplanets &mdash planets orbiting other stars &mdash it seemed reasonable to suppose that other planetary systems looked like ours: small, rocky planets close to a Sun-like star, a big Jupiter and a few other gas giants farther out.

But after a quarter century of discovery revealing thousands of exoplanets in our galaxy, things look very different. In a word, we are &ldquoweird&rdquo &mdash at least among the planetary systems found so far.

Just how weird is still a matter of debate. And weirdness is relative. We&rsquove detected &ldquohot Jupiters&rdquo in scorching, star-hugging orbits around their stars, where a &ldquoyear&rdquo &mdash one trip around the star &mdash takes only a few days. We&rsquove found a string of small, rocky worlds, all in Earth&rsquos size-range, in lock-step orbits around a tiny red-dwarf star called TRAPPIST-1. We&rsquove seen systems with one or more planets that are larger than Earth and smaller than Neptune. The properties of these worlds are a mystery because they&rsquore unlike anything in our solar system &mdash and yet, they&rsquore among the most common types of exoplanets discovered so far.

In all this variety, we&rsquove seen nothing yet that quite resembles our own setup: a Sun-like star with a retinue of rocky planets close in and more distant gas giants (including a domineering Jupiter).


Record Nine-Planet Star System Discovered?

Alien star likely has more planets than the sun, astronomers say.

A star about 127 light-years from Earth may have even more planets than the sun, which would make the planetary system the most populated yet found.

According to a new study, HD 10180—a sunlike star in the southern constellation Hydrus—may have as many as nine orbiting planets, besting the eight official planets in our solar system.

The star first made headlines in 2010 with the announcement of five confirmed planets and two more planetary candidates.

Now, reanalysis of nearly a decade's worth of data has not only confirmed the existence of the two possible planets but also uncovered the telltale signals of two additional planets possibly circling the star, bringing the total to nine.

"There certainly is, according to my results, strong evidence that this is the most populous planetary system detected—possibly even richer than the solar system," said study leader Mikko Tuomi, an astronomer at the University of Hertfordshire in the U.K.

"But the two new planetary signals I report exceed the detection threshold only just."

Early indications are that both newly detected worlds are super-Earths—planets slightly larger than Earth with rocky surfaces—but more measurements will be needed to confirm their existence.

The planetary system around HD 10180 is too far from Earth for us to see directly. (Related: "First Pictures of Alien Planet System Revealed.")

Instead, astronomers detected the planets by measuring their gravitational tugs on the host star using the High Accuracy Planet Searcher (HARPS) instrument on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile.

The five established planets are between 12 and 25 times the mass of Earth and are all around the sizes of Uranus or Neptune, meaning the worlds are most likely icy gas giants.

Of the two newly confirmed planets, one is about 65 times the mass of Earth, and it orbits farther beyond the main group. The other planet is a super-Earth 1.3 times the mass of our home world that circles very close to the host star.

The two new, unconfirmed planets also have tight orbits: A planet thought to be 1.9 times the mass of Earth completes its orbit in 10 days, while the other world is likely 5.1 Earth masses with an orbit lasting 68 days.

That means, if the planets do exist, they'd be unlikely candidates to host life.

"They are likely hot planets without dense, gaseous atmospheres, because they are just so close to their star," Tuomi said.

The astronomer now hopes to take more measurements and verify the planets are really there.

Tuomi also hopes to scan the skies for other crowded planetary systems like HD 10180. (Also see "'Solar Systems' Common Across the Galaxy, NASA Probe Hints.")

"We have only just started to detect planets, and the known exoplanet systems are but a tip of the iceberg," he said.

"So [our] solar system is only one example among a spectrum of different planetary systems we will find in the near future and [is] definitely not unique."


Compared to Other Planetary Systems, Our Solar System Is Apparently a Mess

Our Solar System may be home, but researchers are now discovering that it's not really much like the other kids. According to a survey of 909 planets orbiting 355 stars, our home planetary system is a little on the dishevelled side - and others are a lot more orderly.

A study led by astrophysicist Lauren Weiss of the Université de Montréal has found that, in other solar systems with multiple planets, the planets are much more similar in size to one another, and their orbits are more evenly spaced.

If you look at a diagram of the Solar System, you can see that we're sort of all over the shop. We have planets of all shapes and sizes, and the distances between the orbits around the Sun vary wildly.

Scientists used to think this was probably pretty normal, but as we have learned more about exoplanets - thanks in large part to the planet hunting space observatory Kepler - several old assumptions have been challenged.

Using data from some of the thousands of exoplanets located using Kepler, Weiss and her team used the W. M. Keck Observatory in Mauna Kea, Hawaii to obtain high-resolution spectral data of 1,305 stars hosting 2,025 planets.

Using these data, the team was able to measure the sizes of the planets transiting, or passing in front of, their host stars. As they do so, the light from the star dims slightly, and it is the properties of this dimming that allows the team to calculate the planet-to-star radius ratios for every orbiting body.

For the study, the team focussed on 909 planets divided between 355 multi-planet systems, located mostly between 1,000 and 4,000 light-years from Earth.

And they tended to fall into two patterns, which the researchers were not expecting. Firstly, the planets tended to be around the same size as their neighbours, meaning planet sizes in exoplanet systems are often roughly uniform.

Secondly, the distances between planetary orbits were fairly even.

Graph showing sizes and distances of multi-planet systems with more than four planets. (Weiss et al.)

"The planets in a system tend to be the same size and regularly spaced, like peas in a pod. These patterns would not occur if the planet sizes or spacings were drawn at random," Weiss said.

In other words, if the size of one planet or orbital distance in a system is known, astronomers could make a more accurate prediction about the size or orbital distance of another planet than drawing a random planet out of a hat to construct an artificial planet system.

They also found only a very weak correlation between star mass and planet radius, which means it's probably not stellar mass that enforces planet size.

And, they found, when there is some size variation in a planetary system, the planet closest to the star will be smaller, especially if the planet has a short orbital period - possibly because of photoevaporation.

This finding has implications about how planetary systems form - and gives us some clues as to how our budding Solar System was different.

The most accepted hypothesis currently is that the protoplanetary disc of dust and debris that surrounds a newborn star gradually coalesces and accretes into planetary bodies. If the disc is relatively even, it's reasonable to conclude that even planetary systems, such as those observed by the researchers, can evolve from this disc.

So what happened with the Solar System? The researchers believe Jupiter and Saturn had something to do with it. The two gas giants formed early in the Solar System's history, and there's evidence to suggest that they disrupted its early structure in some way.

So a more uniform planetary system is one that probably has had relatively few disruptions. In order to test this, the team's next project will be to look for Jupiter-sized exoplanets in multi-planet systems, and see if theses systems are consistent with the hypothesis.

The team's research has been published in The Astronomical Journal.


Astronomers Find 6-Pack of Planets in Alien Solar System

Astronomers have discovered an alien solar system in which six planets are orbiting a sunlike star, with five of the newfound worlds in close-knit configuration.

Few stars have been observed with planetary arrangements like our solar system, making this a compelling find. The newfound exoplanet system was sighted by astronomers using NASA's planet-hunting Kepler space observatory.

The smallest of the new alien planets is about 2.3 times the mass of Earth. None of the extrasolar planets are inside the so-called "habitable zone"—– orbits where liquid water could exist on their surfaces, scientists said.

Astronomers made the serendipitous find after poring over Kepler's observations of the changing brightness of the system's parent star — called Kepler-11 — as the orbiting planets passed in front of the star.

The discovery of five small planets with close orbits around the single star, with another planet farther out with a longer orbit, was unexpected, to say the least, the researchers said. The star Kepler-11 is about 2,000 light-years from Earth.

"We think this is the biggest thing in exoplanets since the discovery of 51 Pegasi b, the first exoplanet, back in 1995," said one of the study's lead authors, Jack Lissauer, of NASA's Ames Research Center in Moffett Field, Calif., in a news briefing Monday (Jan. 31).

Lissauer and his colleagues used the Kepler data to analyze the orbital dynamics of the Kepler-11 system and determine the sizes, masses and likely compositions of the planets. The system is compelling because of the number of planets around the host star, their relatively small sizes, and their tightly packed orbits. [Gallery: The Strangest Alien Planets]

"Not only is this an amazing planetary system, it also validates a powerful new method to measure the masses of planets," said Daniel Fabrycky, a postdoctoral fellow at the University of California, Santa Cruz, and one of the co-authors of the new study.

The results of the Kepler-11 study are detailed in the Feb. 3 issue of the journal Nature. They are among the latest discoveries from the Kepler mission, which unveiled a massive amount of data early today that includes hundreds more candidates for potential alien planets. NASA will discuss the latest Kepler discoveries during a 1 p.m. EST (1800 GMT) press conference today.

Meet the Kepler-11 solar system

The five inner planets in the Kepler-11 system range in size from 2.3 to 13.5 times the mass of Earth.

Their orbital periods are all less than 50 days (between 10 and 47 days), which means all five planets and their orbits would fit inside the orbit of Mercury in our solar system.

The sixth planet has an undetermined mass, but it is larger than the other five and follows an orbit that takes it farther from the parent star. It completes one orbit every 118 Earth days.

"Of the six planets, the most massive are potentially like Neptune and Uranus, but the three lowest mass planets are unlike anything we have in our solar system," said Jonathan Fortney, an assistant professor of astronomy and astrophysics at UCSC, who led the work on understanding the structure and composition of the Kepler-11 planets.

More than 100 transiting planets have been observed by Kepler and other telescopes, but the vast majority of them are Jupiter-like gas giants, and almost all of them are single-planet systems. To date, astronomers have confirmed the existence of more than 500 alien planets using ground-based and space-based telescopes.

Before the detection of the Kepler-11 system, astronomers had size and mass calculations for only three exoplanets smaller than Neptune.

Now, measurements from a single planetary system have added five more, and they are among the smallest, Lissauer said.

What are they made of?

Like most of the planets in our solar system, all of the Kepler-11 planets orbit their parent star in roughly the same plane.

These observations reinforce the idea that planets form in flattened disks of gas and dust spinning around a star, and the disk pattern is preserved even after planetary formation, Fabrycky said.

"The coplanar orbits in our solar system inspired this theory in the first place, and now we have another good example," Fabrycky said. "But that and the sunlike star are the only parts of Kepler-11 that are like the solar system."

The densities of the planets, which were calculated from their mass and size, shed some light on their compositions. All six planets were found to have densities lower than Earth's.

"The Kepler-11 system of low mass planets that have low densities implies most of their volumes are made of light elements," Fortney said. "It looks like the inner two could be mostly water, with possibly a thin skin of hydrogen-helium gas on top, like mini-Neptunes. The ones farther out have densities less than water, which seems to indicate significant hydrogen-helium atmospheres."

With scorching hot atmospheres of hydrogen and helium, these planets are not considered habitable, but these results were surprising, since small, hot planets typically have a difficult time holding onto a lightweight atmosphere.

"These planets are pretty hot because of their close orbits, and the hotter it is the more gravity you need to keep the atmosphere," Fortney said. "My students and I are still working on this, but our thoughts are that all these planets probably started with more massive hydrogen-helium atmospheres, and we see the remnants of those atmospheres on the ones farther out. The ones closer in have probably lost most of it."

Part of the equation

The researchers are excited about finding six planets around Kepler-11 because the ability to make valuable comparisons among planets within the same system will help them understand the system's formation and evolution as a whole.

"Kepler-11 is actually telling us a great deal about planets as individual bodies and planetary systems," Fortney said. "Comparative planetary science is how we've come to understand our solar system, so this is much better than just finding more solitary hot Jupiters around other stars."

For instance, the close proximity of the inner planets is an indication that they probably did not form where they are now, Fortney added.

&ldquoAt least some must have formed farther out and migrated inward. If a planet is embedded in a disk of gas, the drag on it leads to the planet spiraling inward over time," he said. "So formation and migration had to happen early on.&rdquo

In search of alien planets

The planet-hunting Kepler space telescope detects planets that transit in front of their host star, causing periodic wobbles in the brightness of the star. The dips in brightness help scientists determine how big a potential planet is in terms of its radius. The time in between transits tells them the orbital period of the planetary candidate.

To determine the mass of the Kepler-11 planets, Fabrycky and his colleagues analyzed slight variations in the orbital periods caused by the gravitational interactions among the planets themselves.

"The timing of the transits is not perfectly periodic, and that is the signature of the planets gravitationally interacting," Fabrycky said. "By developing a model of the orbital dynamics, we worked out the masses of the planets and verified that the system can be stable on longtime scales of millions of years."

The sixth planet in the Kepler-11 system is too far apart from the others that this orbital perturbation method cannot be used to determine its mass, Fabrycky said.

Previously, detections of transiting planets have been corroborated with observations from powerful ground-based telescopes that can confirm the planet and determine its mass using Doppler spectroscopy, which measures the change in the star's motion caused by the gravitational tug of the planet.

In the case of Kepler-11, however, the planets are too small and the star, at 2,000 light-years away, is too faint to use Doppler spectroscopy.

And since the Kepler mission is aimed at finding small, potentially habitable Earth-size planets in our galaxy, the new method of using orbital dynamics could find much broader applications.

"We will need to use orbital dynamics a lot with the Kepler mission to measure the masses of planets we expect to be doing a lot of these analyses," Fabrycky said.

The spacecraft is scheduled to continue collecting data on the Kepler-11 system for the remainder of its mission, and with the additional data, the researchers hope to make more accurate measurements of the planets and their interactions.

"Not only have we learned a lot to date, but we're going to learn even more as the Kepler spacecraft continues to observe this gem of a system for the remainder of its mission," Lissauer said.


So is it all about telescopes?

Large telescopes are the most visible tools in astronomy, but smaller instruments and research programs are essential to optimize the advance of knowledge. For example, research programs focused on the continued study of the planets in the solar system will provide information about how exoplanets form around other stars.

An illustration of NASA’s Wide Field Infrared Survey Telescope (WFIRST). When it launches in the mid-2020s, this telescope’s sophisticated technology will block out the glare from distant stars, revealing the planets in orbit around them. Credit


Artificial intelligence predicts which planetary systems will survive

While three planets have been detected in the Kepler-431 system, little is known about the shapes of their orbits. On the left are a large number of superimposed orbits for each planet that are consistent with observations. An international team of astrophysicists led by Princeton's Daniel Tamayo removed all the unstable configurations that would have already collided and couldn't be observed today. Doing this with previous methods would take over a year of computer time. With their new model SPOCK, it takes 14 minutes. Credit: Daniel Tamayo

Why don't planets collide more often? How do planetary systems—like our solar system or multi-planet systems around other stars—organize themselves? Of all of the possible ways planets could orbit, how many configurations will remain stable over the billions of years of a star's life cycle?

Rejecting the large range of unstable possibilities—all the configurations that would lead to collisions—would leave behind a sharper view of planetary systems around other stars, but it's not as easy as it sounds.

"Separating the stable from the unstable configurations turns out to be a fascinating and brutally hard problem," said Daniel Tamayo, a NASA Hubble Fellowship Program Sagan Fellow in astrophysical sciences at Princeton. To make sure a planetary system is stable, astronomers need to calculate the motions of multiple interacting planets over billions of years and check each possible configuration for stability—a computationally prohibitive undertaking.

Astronomers since Isaac Newton have wrestled with the problem of orbital stability, but while the struggle contributed to many mathematical revolutions, including calculus and chaos theory, no one has found a way to predict stable configurations theoretically. Modern astronomers still have to "brute-force" the calculations, albeit with supercomputers instead of abaci or slide rules.

Tamayo realized that he could accelerate the process by combining simplified models of planets' dynamical interactions with machine learning methods. This allows the elimination of huge swaths of unstable orbital configurations quickly—calculations that would have taken tens of thousands of hours can now be done in minutes. He is the lead author on a paper detailing the approach in the Proceedings of the National Academy of Sciences. Co-authors include graduate student Miles Cranmer and David Spergel, Princeton's Charles A. Young Professor of Astronomy on the Class of 1897 Foundation, Emeritus.

For most multi-planet systems, there are many orbital configurations that are possible given current observational data, of which not all will be stable. Many configurations that are theoretically possible would "quickly"—that is, in not too many millions of years—destabilize into a tangle of crossing orbits. The goal was to rule out those so-called "fast instabilities."

"We can't categorically say 'This system will be OK, but that one will blow up soon,'" Tamayo said. "The goal instead is, for a given system, to rule out all the unstable possibilities that would have already collided and couldn't exist at the present day."

Instead of simulating a given configuration for a billion orbits—the traditional brute-force approach, which would take about 10 hours—Tamayo's model instead simulates for 10,000 orbits, which only takes a fraction of a second. From this short snippet, they calculate 10 summary metrics that capture the system's resonant dynamics. Finally, they train a machine learning algorithm to predict from these 10 features whether the configuration would remain stable if they let it keep going out to one billion orbits.

"We called the model SPOCK—Stability of Planetary Orbital Configurations Klassifier —partly because the model determines whether systems will 'live long and prosper,'" Tamayo said.

SPOCK determines the long-term stability of planetary configurations about 100,000 times faster than the previous approach, breaking the computational bottleneck. Tamayo cautioned that while he and his colleagues haven't "solved" the general problem of planetary stability, SPOCK does reliably identify fast instabilities in compact systems, which they argue are the most important in trying to do stability constrained characterization.

"This new method will provide a clearer window into the orbital architectures of planetary systems beyond our own," Tamayo said.

But how many planetary systems are there? Isn't our solar system the only one?

In the past 25 years, astronomers have found more than 4,000 planets orbiting other stars, of which almost half are in multi-planet systems. But since small exoplanets are extremely challenging to detect, we still have an incomplete picture of their orbital configurations.

"More than 700 stars are now known to have two or more planets orbiting around them," said Professor Michael Strauss, chair of Princeton's Department of Astrophysical Sciences. "Dan and his colleagues have found a fundamentally new way to explore the dynamics of these multi-planet systems, speeding up the computer time needed to make models by factors of 100,000. With this, we can hope to understand in detail the full range of solar system architectures that nature allows."

SPOCK is especially helpful for making sense of some of the faint, far-distant planetary systems recently spotted by the Kepler telescope, said Jessie Christiansen, an astrophysicist with the NASA Exoplanet Archive who was not involved in this research. "It's hard to constrain their properties with our current instruments," she said. "Are they rocky planets, ice giants, or gas giants? Or something new? This new tool will allow us to rule out potential planet compositions and configurations that would be dynamically unstable—and it lets us do it more precisely and on a substantially larger scale than was previously available."


Close and Tranquil Solar System Has Astronomers Excited

From the perspective of planet hunters and planet characterizers, a desirable solar system to explore is one that is close to ours, that has a planet (or planets) in the star’s habitable zone, and has a host star that is relatively quiet. This is especially important with the very common red dwarf stars, which are far less luminous than stars such as our sun but tend to send out many more powerful — and potentially planet sterilizing — solar flares.

The prolific members of the mostly European and Chilean Red Dots astronomy team believe they have found such a system about 11 light years away from us. The system — GJ 887 — has an unusually quiet red dwarf host, has two planets for sure and another likely that orbits at a life-friendly 50-day orbit. It is the 12th closest planetary system to our sun.

It is that potential third planet, which has shown up in some observations but not others, that would be of great interest. Because it is so (relatively) close to Earth, it would be a planet where the chemical and thermal make-up of its atmosphere would likely be possible to measure.

The Red Dots team — which was responsible for the first detection of a planet orbiting Proxima Centauri and also Barnard’s star — describes the system in an article in the journal Science. Team leader Sandra Jeffers of Goettingen University in Germany said in an email that GJ 887 “will be an ideal target because it is such a quiet star — no starspots or energetic outbursts or flares.”

In an accompanying Perspective article in Science, Melvyn Davies of Lund University in Sweden wrote that “If further observations confirm the presence of the third planet in the habitable zone, then GJ 887 could become one of the most studied planetary systems in the solar neighborhood.”

GJ 877 is roughly half as massive as our sun — large for its type of star — and is the brightest red dwarf in the sky. It was observed each night for three months using the European Southern Observatory’s HARPS spectrograph in La Silla, Chile.

That data, combined with archival data from colleagues going back 20 years, confirmed the presence of two orbiting super-Earths sized planets, i.e., planets which have a mass greater than the Earth’s but substantially below those of our local ice giants Uranus and Neptune.

These two confirmed planets, however, orbit quite close to the star and so would be expected to be far too hot to support life.

But that suspected third planet orbiting in about 50 days is far enough out to be in the star’s habitable zone — at a distance from its host star where water on its surface would be liquid (as opposed to frozen water or water vapor) for some of the time. This is one of the key indicators of planetary habitability, though is certainly not the only one.

This is how the detections occurred, as explained by Jeffers in an email:

“With exoplanet hunting it’s very easy to detect a signal but not so easy to actually determine where the signal is coming from. We’ve been looking at GJ 887 for nearly 20 years with the aim to detect its planets. When we analyzed the data again in 2017 we saw indications that there were planetary signals in GJ 887, however we weren’t 100% certain they came from the planets.”

“So we went back and observed GJ 887 again every night for 80 to 90 nights. In this data set we saw that the 9.8 day signal repeated 8 times (a very clear detection) and the 21 day signal repeated 4 times (another very clear detection).”

“With the 50 day signal we only saw this once during the 80-90 nights so we need to go back and look again at GJ887 over at least 60 nights to confirm or refute this signal.”

The Red Dots group finds exoplanets via the radial velocity method — which detects host star “wobbles” caused by the gravitational pull of orbiting planets.

One of the most attractive features of GJ 887 is that it’s a red dwarf has very few starspots and flares. If GJ 887 was as active as our sun, it is likely that a strong, outflowing stellar wind would simply sweep away the planets’ atmospheres. With those starspots and flares absent, the newly discovered planets around GJ 887 have a better chance of keeping their atmospheres and potentially hosting life.

The other interesting feature the team discovered is that the brightness of GJ887 is almost constant. This makes it relatively easy to detect the atmospheres of planets in system, making it a prime target for the long awaited James Webb Space Telescope, scheduled to launch next year. Unlike almost all current space and ground telescopes, JWST will be able to directly image exoplanets rather than identifying and studying them indirectly through the effect of exoplanets on a host star. Scientists using direct imaging technology can far more effectively characterize exoplanet atmospheres.

If a third planet in a habitable zone is confirmed, then GJ 887 will likely join the ranks of TRAPPIST -1 as a planetary system of great interest to astronomers and those looking for life beyond Earth. Three Earth-sized rocky planets were identified orbiting TRAPPIST -1 in 2015 and four more terrestrial planets have since been found — making it a prime target for scientists.

Like GJ 887, TRAPPIST -1 is a red dwarf star. But unlike GJ 887, TRAPPIST -1 has been found to have powerful solar flares that could strip away any atmospheres.

The Red Dot team began with Guillem Anglada-Escudé of the Queen Mary University of London, Sandra Jeffers and others. Originally called the “Pale Red Dot” team, their initial focus was on Proxima Centauri, the star closest to our solar system. The name is a nod to the “Pale Blue Dot,” a photograph of planet Earth taken on in 1990, by the Voyager 1 space probe from a record distance of 3.7 billion miles.

In 2016 the team was the first to identify a planet orbiting Proxima (also a red dwarf) and two years later they played a central role in the discovery a planet orbiting Barnard’s Star, another of those closest stars to Earth. Today’s Red Dot campaigns are supported by the European Southern Observatory and universities in Chile, the United Kingdom, Spain and Germany.

Jeffers said that a large group of astronomers join to write proposals for Red Dot telescope time, and that from this group there is a core team of ten to fifteen people who do most of the observing and data analysis. Another ten scientists join in writing the papers when they can contribute.

Jeffers said that the group has observed in a third Red Dots campaign and that “we would have been taking data for Red Dots #4 if it wasn’t for the Covid-19 fallout. “

The Many Worlds Blog chronicles the search for evidence of life beyond Earth written by author/journalist Marc Kaufman. The “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, a research coordination network supported by the NASA Astrobiology Program. Any opinions expressed are the author’s alone.

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Sun-Like Star May Have More Planets Than Our Solar System

A star already known to host five alien planets may actually be home to a whopping nine full-fledged worlds - a planetary arrangement that, if confirmed, would outnumber our own solar system and set a new record for the most populated system of extrasolar planets yet found.

The sun-like star, called HD 10180, is located approximately 127 light-years away from Earth. In a previous study that was published in August 2010, astronomers identified five confirmed alien worlds and two planetary candidates.

Now a new study confirms both previous candidates in the HD 10180 system, and also suggests that two more planets could be orbiting the star. This could bring the tally up to nine planets, said lead author Mikko Tuomi, an astronomer at the University of Hertfordshire in the U.K. Our solar system, by comparison, has eight official planets (with Mercury closest to the sun and Neptune at the farthest end). Pluto and several other smaller objects are considered dwarf planets, not full-blown worlds.

"The data indicates that there are not only seven but likely as many as nine planets in the system," Tuomi told SPACE.com in an email interview. "The two new planets appear to have orbital periods of roughly 10 and 68 days and masses of 1.9 and 5.1 times that of Earth, which enables the classification of them as hot super-Earths, i.e. planets with likely scorchingly hot rocky surfaces."

Tuomi re-analyzed observations collected between November 2003 and June 2010 by the planet-hunting HARPS spectrograph instrument, which is mounted on a 3.6-meter telescope at the European Southern Observatory in La Silla, Chile. [Infographic: Planets Large and Small Populate Our Galaxy]

Since the newly detected candidates are still unconfirmed, more research is needed to determine if they are bona fide planets, and not erroneous signals.

"While the existence of the larger of these two is well supported by the data, the signal corresponding to the smaller one exceeds the detection threshold only barely, which gives it a very small but non-eligible probability of being a false positive," Tuomi said.

Since the planets in the HD 10180 system are too distant to be directly observed, astronomers use HARPS to monitor the gravitational pulls that the planets exert on their host star.

The five previously confirmed planets are relatively large and orbit the parent star at intervals that range from just six days to 600 days. The two newly confirmed planets are also super-Earths, with one that orbits tightly around HD 10180, while the other has an orbit that swings beyond the others.

Observations of the masses of the new planetary candidates and their distances from the star indicate that they likely have orbital periods of approximately 10 and 68 days. They are likely both rocky planets with surfaces hotter than that of Mercury, Tuomi added.

But even if they are confirmed as actual planets, neither are located in a circumstellar region known as the habitable zone, where conditions could be suitable for liquid water to exist on a planet's surface.

"They are certainly not in the habitable zone and likely have no prospects for hosting life," Tuomi said. "However, one of the Neptune-sized planets in the system with an orbital period of 600 days is actually in the middle of the habitable zone, which makes it an interesting target when the better detection methods enable us to observe moons orbiting exoplanets in the future."

As instruments and observatories become more sophisticated, and as astronomers hone planet-hunting techniques, densely populated systems similar to HD 10180 and our own solar system could be discovered in greater numbers.

"This certainly tells our methods are sufficient for detecting richly populated planetary systems," Tuomi said. "Just how common they are, we do not know based on only two examples. My guess would be that they are very common, though, because they are very hard to detect and we already have one when the precision of our instruments enables the detection of these systems only barely."

The finding also suggests that similar planetary systems could be more common throughout the universe than was previously thought.

"Scientifically this would not be of much significance because it has been suspected for a long time that such populous planetary systems exist in the universe," Tuomi said. "Philosophically, though, it shows that our very own solar system is not special in this respect either &mdash systems with great numbers of planets are very likely common throughout the universe and it is only a matter of time when we find even richer systems."

The study has been accepted for publication in the journal Astronomy and Astrophysics.


Nasa scientists discover planetary system

Astronomers have discovered a planetary system made up of six planets orbiting a Sun-like star that is more than 2,000 light years from Earth. It is the largest number of planets found so far around a single star.

More than 100 planets have been seen outside our solar system, but most are Jupiter-like gas giants, and almost all are in single-planet systems.

Jack Lissauer, a scientist at Nasa's Ames research centre in California and a lead author on a paper published tomorrow in the journal Nature, said that the Kepler-11 finding was "the biggest thing in exoplanets since the discovery of 51 Pegasi B, the first exoplanet, back in 1995".

The five inner planets of the Kepler-11 system are between 2.3 and 13.5 times the mass of the Earth, and make their orbits in less than 50 days. All of them are so close to their star that their orbits would fit within that of Mercury in our solar system. The sixth planet has an orbital period of 118 days and sits at a distance from its star that is half the Sun-Earth distance.

Lissauer said it was unexpected to find a system where planets could be so close to one another and there could be so many of them on such a flat plane. "The Kepler-11 system is flatter than a CD," he said. "If placed within our solar system, Kepler-11's six planets would lie between those of the sun's innermost planets, Mercury and Venus."

Astronomers found the planets by analysing data from the Kepler space telescope. Every time a planet passes between its star and an observer, it is said to be transiting by measuring how often and how much the star dimmed in brightness as planets crossed in front of it, they were able to measure the size and density of the planets.

To calculate masses, astronomers measured the slight variations in the orbital periods of the planets caused by gravitational interactions among them.

Most of the volume of the Kepler-11 planets is made of light elements, according to Jonathan Fortey of the University of California, Santa Cruz. "It looks like the inner two could be mostly water, with possibly a thin skin of hydrogen-helium gas on top, like mini-Neptunes. The ones farther out have densities less than water, which seems to indicate significant hydrogen-helium atmospheres."

Though none of the six planets found resemble Earth, Lissauer did not discount the idea that there could be more planets orbiting the star, one of which could be more Earth-like. The sixth planet, for example, is at a temperature of around 120C-170C, so any planets further out could be cooler. "It's possible there could be an Earth-sized planet in the habitable zone, because we're not seeing any of these big planets out there," he said.