A Solar System Found Crowded With Seven Earth-Sized Exoplanets

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Seven Earth-sized rocked planets have been detected around the red dwarf star TRAPPIST-1. The system is 40 light years away, but is considered to be an easy system to study — as explanet research goes. (NASA)

Seven planets orbiting one star.  All of them roughly the size of Earth.  A record three in what is considered the habitable zone, the distance from the host star where liquid water could exist on the surface.  The system a mere 40 light-years away.

The latest impressive additions to the world of exoplanets orbit the dwarf star known as TRAPPIST-1, named after a European Southern Observatory telescope in Chile.

Previously a team of astronomers based in Belgium discovered three  planets around this dim star, but now that number has increased to include the largest number of Earth-sized planets found to date, as well as the largest number in one solar system in the habitable zone.

This is a very different kind of sun-and-exoplanet system than has generally been studied.  The broad quest for an Earth-sized planet in a habitable zone has focused on stars of the size and power of our sun.  But this one is 8 percent the mass of our sun —  not that much larger than Jupiter — and with a luminosity (or energy) but 0.05 percent of that put out by our sun.

The TRAPPIST-1 findings underscore one of the recurring and intriguing aspects of the exoplanet discoveries of the past two decades — the solar systems out there are a menagerie of very different shapes and sizes, with exoplanets of a wild range of sizes orbiting an equally wide range of types and sizes of stars.

Michaël Gillon of the STAR Institute at the University of Liège in Belgium, and lead author of the discovery reported in the journal Nature, put it this way: “This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth.”

At a NASA press conference, he also said that “small stars like this are much more frequent than stars like ours.  Now we have seven Earth-sized planets to study, three in the habitable or ‘Goldilocks’ zone, and that’s quite promising for search for life beyond Earth.”

He said that the planets are so close to each other than if a person was on the surface of one, the others would provide a wonderful close-up view, rather like our view of the moon.

This diagram compares the orbits of the newly-discovered planets around the faint red star TRAPPIST-1 with the Galilean moons of Jupiter and the inner Solar System. All the planets found around TRAPPIST-1 orbit much closer to their star than Mercury is to the Sun, but as their star is far fainter, they are exposed to similar levels of irradiation as Venus, Earth and Mars in the Solar System.

The orbits of the Trappist-1 planets are not much greater than those of Jupiter’s Galilean moon system, and are considerably smaller than the orbit of Mercury in the solar system. However, TRAPPIST-1’s small size and low temperature mean that the energy reaching its planets is similar to that received by the inner planets in our solar system. TRAPPIST-1c, d and f, for instance, receive similar amounts of energy as Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, the authors said, though their orbital distances make some of them more likely candidates than others.  So far there has been no confirmation of water on the planets, but the search has intensified.

“The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our sun,” co-author Amaury Triaud said.  “Planets would need to be in far closer orbits than we see in our solar system if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1.”

Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbor liquid water — assuming no alternative heating processes are occurring

TRAPPIST-1e, f, and g, however, represent the sweet spot for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water if other conditions were present.

As Sara Seager, an MIT pioneer in the study of exoplanet atmospheres, said in the NASA press conference, “with this discovery we’ve taken a giant, accelerated leap forward.  In one system, we have room so that if one planet in the habitable zones is not quite right (for study and possibly biology) we have many other chances.  This Goldilocks has many sisters.”

Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate, added: “This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life. Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”

The telescope at the center of the discoveries is TRAPPIST-South (TRAnsiting Planets and PlanetesImals Small Telescope–South), s small 60 cm telescope at the La Silla Observatory in Chile devoted to the study of planetary systems.  The robotic telescope is operated from a control room in Liège, Belgium. The project is led by the Department of Astrophysics, Geophysics and Oceanography of the University of Liège, in close collaboration with the Geneva Observatory (Switzerland). TRAPPIST–South is mostly funded by the Belgian Fund for Scientific Research with the participation of the Swiss National Science Foundation. (ESO)

The discovery of the four additional Earth-sized planets was made during a global campaign of observataion, most especially by NASA’s infrared Spitzer Space Telescope.

Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC in Pasadena, California, called it “the most exciting result I have seen in the 14 years of Spitzer operations…Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets.”

Because the Trappist-1 system is so relatively easy to observe, and because it is providing such riches, many ground- based observatories have joined in the search.

Dips in the star’s light output caused by each of the seven planets passing in front of it — events known as transits — allowed the astronomers to infer information about their sizes, compositions and orbits. They found that at least the inner six planets are comparable in both size and temperature to the Earth.

These new discoveries make the TRAPPIST-1 system a very important target for future study. The Hubble Space Telescope is already being used to search for atmospheres around the planets and team leader Gillon said the James Webb Space Telescope, scheduled to launch in 2018, can potentially begin a rigorous examination of the atmospheres of the planets.

“These planets are accesible to observations with JWST.  We will be able to study the atmospheres, the greenhouse gas compositions.  We will search for gases that might be produced by life,” said Gillon.

This artist’s concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses and distances from the host star. The system has been revealed through observations from NASA’s Spitzer Space Telescope and the ground-based TRAPPIST (TRAnsiting Planets and and PlanetesImals Small Telescope) telescope, as well as other ground-based observatories.  (NASA)

But there are also significant barriers to habitability in the TRAPPIST-1 system.

Because the planets are so close to their host star — the first has an orbit of 1.5 days, the second an orbit of 2.4 days and the third an ill-defined orbit of between 4.5 and 73 days — that means they are tidally-locked, as is our moon.  Not long ago, exoplanet scientists doubted that a planet that doesn’t rotate can be truly habitable since the extremes of hot and cold would be too great.  That view has changed with creation of models that suggest tidal locking is not necessarily fatal for habitability, but it most likely does make it more difficult to achieve.

A larger potential barrier is that the dwarf star once was quite different.  Jonathan Fortney, a University of California at Santa Clara specialist in dwarf stars and brown dwarfs (objects which are too large to be called planets and too small to be stars), focused on that stellar history:

“One thing to keep in mind is that this star was much much brighter in the past,” he said in an email a while back. “M stars (like TRAPPIST-1) are hottest when they are young and take a long time to cool off and settle down.  Their energy comes from contraction at first.  A star like this takes 1 billion years to even settle onto the main sequence (where it starts burning hydrogen).”

Gillon said that the age of the star system was not well understood, but that it was at least a half billion years old.

Shawn Domogal-Goldman, a research space scientist at the Goddard Space Flight Center with a focus on exoplanets, said that the big news of the day for him is that the questions raised about conditions on red or M dwarf stars is that “they’re all testable on the TRAPPIST-1 planets in the near term.

“We can do follow-up observations of these worlds with the Hubble and JWST. Yesterday, I would have said ‘you can test these hypotheses with Webb but you kind of need the perfect target.’ Well, today we kind of have the perfect target.”

This diagram shows how the light of the dim red ultra cool dwarf star TRAPPIST-1 fades as each of its seven known planets passes in front of it and blocks some of its light. The larger planets create deeper dips and the more distance ones have longer lasting transits as they are orbiting more slowly. These data were obtained from observations made with the NASA Spitzer Space Telescope. (NASA)

From the total of 2,687 stars known to have exoplanets (as of February 15, 2017), there are a total of 602 known multiplanetary systems, or stars with at least two confirmed planets. About 280 of these have only two confirmed exoplanets, but some have a significantly larger number.

The star with the most confirmed planets is our sun with eight (after the demotion of Pluto), while the stars with the most confirmed exoplanets are Kepler-90, HD 10180 and HR 8832, with 7 confirmed planets each.  In 2012, two more exoplanet candidates were proposed but not yet confirmed for HD 10180, which would bring the total to 9 exoplanets in that system.

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Three Star Ballet, With Exoplanet

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This artist's impression shows a view of the triple-star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Located about 320 light-years from Earth in the constellation of Centaurus (The Centaur), HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one of very few directly imaged planets. With a temperature of around 580 degrees Celsius and an estimated mass of four Jupiter masses, it is also one of the coldest and least massive directly-imaged exoplanets.
An artist’s impression of the triple-star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Located about 320 light-years from Earth in the constellation of Centaurus (The Centaur), HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one of very few directly imaged planets. (ESO/Luis Calcada)

It hardly seems possible, but researchers have detected a planet in apparently stable orbit within a three star system — a configuration now known as a trinary.

The ubiquity of binary stars has been understood for some time, and the presence of exoplanets orbiting around and within them is no longer a surprise.  But this newest planet detected — four times the mass of Jupiter — is most unusual because trinary systems are not known to be particularly conducive to keeping planets in orbit, and especially not a planet in an extremely wide (i.e., 550 year) orbit.

Yet this planet has found the sweet spot between the stars where it balances the gravitational pulls of the three.  The system is a relative toddler at 16 million years old, and so the researchers involved in its detection say it may later be ejected from the system.  But for now, it is the only known planet of its kind.

The discovery, reported in the journal Science, was made using the European Southern Observatory’s Very Large Telescope (VLT) in Chile’s Atacama desert.  The team was from the University of Arizona in Tucson and was led by Daniel Apai, an assistant professor of Astronomy and Planetary Sciences who leads a planet finding and observing group.  That team includes research doctoral student Kevin Wagner, the first author on the paper.

“It is not clear how this planet ended up on its wide orbit in this extreme system — and we can’t say yet what this means for our broader understanding of the types of planetary systems — but it shows that there is more variety out there than many would have deemed possible,” Wagner said.

This new planet is a gas giant and definitely not habitable, but the possible universe of exoplanets that just might meet some of the basic criteria for habitability may well have grown.

“What we do know is that planets in multi-star systems have been studied far less often, but are potentially just as numerous as planets in single-star systems,” Wagner said.

An artist's rendering of the Kepler-16 system, showing the binary star being orbited by Kepler-16b
An artist’s rendering of the Kepler-16 system, showing the binary star being orbited by Kepler-16b.  The planet was the first confirmed to have a circumbinary 0rbit — traveling around both stars in 229 days.  (NASA)

Astronomers estimate that about half of the stars we see in the sky are actually two stars or more.  Stars are created when massive clouds of gas and dust collapse in on themselves, and sometimes that results in a fragmenting into multiple stars.

Two of the stars in the HD 131399 system are close together, twirling around each other like a spinning dumbbell.  The third and far brightest star, which is located about 300 times further away than the distance between Earth and the sun,  is orbited by the new gas giant planet HD 131399Ab. With a temperature of around 580 degrees Celsius and an estimated mass of four Jupiter masses, it is one of the coldest and least massive directly-imaged exoplanets.

The three-star system and the planet were found using direct imagining of thermal emissions, as opposed to the traditional techniques of searching for the effects of an exoplanet on the host sun and other planets.

This planet discovery was a first for SPHERE, the Spectro-Polarimetric High-Contrast Exoplanet Research Instrument, which took a decade to build.  The instrument is sensitive to infrared light and is capable of detecting the heat signatures of young planets picked up by the Very Large Telescope’s mirrors.  SPHERE has a coronograph to block out the otherwise blinding light of the host star, and new capabilities to  correct for disturbances caused by features of our atmosphere.

Apai said that detecting a planet in such a triple system was both surprising and “really cool.”

“We’re now are going back and take a careful look at all the other triple systems that haven’t been observed because we didn’t think planets could be there. I’m very curious to continue to study this system to figure out whether the planet formed in that odd orbit or if it moved there after encountering another planet or one of the double stars.”

Here is a wonderful video animation of the choreography of the stars and planet, the work of the ESO’s Luis Calçada and Martin Kornmesser:

As is so often the case, the discovery involved substantial serendipity;  it was not at all what the group was looking for.

Rather, Apai’s team has been looking to prove, or disprove, a confounding pattern in exoplanet discoveries:  most of the (very few) planets discovered via direct imaging were found around stars with masses about twice of the sun’s mass, while only one planet has been found around a sun-like star.  Most were also short orbital period planets, unlike the one with a 550-year orbit just discovered. If this pattern of detections were found to be a feature of the galaxy as a whole, it would challenge some components of the basic planet formation model.

“Strangely, most of the eight or so planets discovered via direct imaging were found around stars with masses about twice of the Sun’s mass, while – up to now – around Sun-like stars only one Jovian planet was discovered,” he said in an email.

So the group set out to study about 100 stars more massive than the Sun to determine how many of them have giant planets that can be imaged — with the goal of seeing whether they are really more common than around Sun-like stars, or if it was just a coincidence.

While that campaign will continue for another year finding the three star exoplanet may well become their most significant finding.

Wagner, who first saw the presence of the exoplanet in the SPHERE data, confirmed the finding during observations a half year later.

“For much of the planet’s year the stars appear close together, giving it a familiar night-side and day-side with a unique triple-sunset and sunrise each day,” he said. “As the planet orbits and the stars grow further apart each day, they reach a point where the setting of one coincides with the rising of the other – at which point the planet is in near-constant daytime for about one-quarter of its orbit, or roughly 140 Earth-years.”

The precise orbit of the planet has actually not yet been determined, and doing so is one of Wagner’s next tasks.  The team knows that the planet is 80 times further from the A star than the Earth is from our sun, and that the A and BC stars are 300 times further away from each other. Asked if that orbit could change dramatically, even becoming circumtrinary around all three stars, he said it was quite unlikely but that it couldn’t be ruled out.

Wagner used an apt quote to describe his reaction to the discovery, one attributed to many great astrophysicists but originally probably from Arthur Stanley Eddington,  who helped confirm Einstein’s General Theory of Relativity in the early 1900s.

“Not only is the universe stranger than we imagine,” he said, “it is stranger than we can imagine.”

This annotated composite image shows the newly discovered exoplanet HD 131399Ab in the triple-star system HD 131399. The image of the planet was obtained with the SPHERE imager on the ESO Very Large Telescope in Chile. This is the first exoplanet to be discovered by SPHERE and one of very few directly-imaged planets. With a temperature of around 580 degrees Celsius and an estimated mass of four Jupiter masses, it is also one of the coldest and least massive directly-imaged exoplanets. This picture was created from two separate SPHERE observations: one to image the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than in would in reality in comparison to the stars.
This picture was created from two separate SPHERE observations: one to image the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than in would in reality in comparison to the stars. (ESO)
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The Pale Red Dot Campaign

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Alpha and Beta Centauri are the bright stars; Proxima Centauri is the small, faint one circles in red.
Alpha Centauri A and B are the bright stars; Proxima Centauri, a red dwarf star, is the small, faint one circled in red. (NASA, Julia Figliotti)

Astronomers have been trying for decades to find a planet orbiting Proxima Centauri, the star closest to our sun and so a natural and tempting target.  Claims of an exoplanet discovery have been made before, but so far none have held up.

Now, in a novel and very public way, a group of European astronomers have initiated a focused effort to change all that with their Pale Red Dot Campaign.  Based at the La Silla Observatory in Chile, and supported by  networks of smaller telescopes around the world, they will over the next three months observe Proxima and its environs and then will spend many more months analayzing all that they find.  And in an effort to raise both knowledge and excitement, the team will tell the world what they’re doing and finding over Twitter, Facebook, blogs and other social and traditional media of all kind.

“We have reason to be hopeful about finding a planet, but we really don’t know what will happen,” said Guillem Anglada-Escudé  of Queen Mary University, London, one of the campaign organizers.  “People will have an opportunity to learn how astronomers do their work finding exoplanets, and they’ll be able to follow our progress.  If we succeed, that would be wonderful and important.  And if no planet is detected, that’s very important too.”

The Pale Blue Dot, as photographed by Voyager 1 (NASA)
The Pale Blue Dot, as photographed by Voyager 1 (NASA)

The name of the campaign is, of course, a reference to the iconic “Pale Blue Dot” image of Earth taken by the Voyager 1 spacecraft in 1990, when it was well beyond Pluto.  The image came to symbolize our tiny but precious place in the galaxy and universe.

But rather than potentially finding a pale blue dot, any planet orbiting the red dwarf star Proxima Centauri would reflect the reddish light of the the star, which lies some 4.2 light years away from our solar system.  Proxima — as well as 20 of the 30 stars in our closest  neighborhood — is reddish because it is considerably smaller and less luminous than a star like our sun.

Anglada-Escudé said he is cautiously optimistic about finding a planet because of earlier Proxima observations that he and colleagues made at the same observatory.  That data, he said, suggested the presence of a planet 1.2 to 1.5 times the size of Earth, within the habitable zone of the star.

“We did not and are not making claims in terms of having discovered a planet,”  he said.  “We’re saying that we detected signals that could mean there is a planet.  This is why we’ve planned this campaign — to see if the signal is telling us something real.”  He described the campaign as a “partnership between scientists involved in the observations and European Southern Observatory.”

Even without a previous signal, it’s a reasonable bet that Proxima does have at least one planet orbiting it.  Based on the results of the Kepler Space Telescope survey in particular, there is a consensus of sorts in the astronomy community that on average, every star has at least one planet circling it.

Alpha Centauri A and Alpha Centauri B are a binary pair, while Proxima Centauri is far away but is xxx
Alpha Centauri A, Alpha Centauri B and Proxima Centauri make up a three-star system, although Proxima Centauri is a distant .2 lightyears away rom the other two.  (Ian Morrison)

Paul Butler, a pioneer in planet hunting at the Carnegie Institution of Washington who has done extensive observing of Proxima with his team at Las Campanas Observatory in Chile, will be providing data to the Pale Red Dot campaign.  Proxima search results from the ESO’s Very Large Telescope at Paranal, Chile, will also be provided to campaign.

Butler said that in some ways Proxima “is the most exciting star in the sky.  It’s the very nearest star and so the discovery of a planet there would be huge – front page of the paper around the world.”

What’s more, he said, such a discovery could be enormously helpful in motivating Congress and taxpayers to spend the money needed for what is considered the holy grail of planet hunting — building a space-based exoplanet observatory that could directly image exoplanets.  “We have to give people a clear reasons to spend all that money and finding a potentially habitable planet around Proxima, that would be it.”

 Hubble Space Telescope image is our closest stellar neighbour: Proxima Centauri, just over four light-years from Earth. Although it looks bright through the eye of Hubble, Proxima Centauri -- with only about one eight the mass of our sun -- is not visible to the naked eye.Shining brightly in this Hubble image is our closest stellar neighbour: Proxima Centauri. Proxima Centauri lies in the constellation of Centaurus (The Centaur), just over four light-years from Earth. Although it looks bright through the eye of Hubble, as you might expect from the nearest star to the Solar System, Proxima Centauri is not visible to the naked eye. Its average luminosity is very low, and it is quite small compared to other stars, at only about an eighth of the mass of the Sun. However, on occasion, its brightness increases. Proxima is what is known as a “flare star”, meaning that convection processes within the star’s body make it prone to random and dramatic changes in brightness. The convection processes not only trigger brilliant bursts of starlight but, combined with other factors, mean that Proxima Centauri is in for a very long life. Astronomers predict that this star will remain middle-aged — or a “main sequence” star in astronomical terms — for another four trillion years, some 300 times the age of the current Universe. These observations were taken using Hubble’s Wide Field and Planetary Camera 2 (WFPC2). Proxima Centauri is actually part of a triple star system — its two companions, Alpha Centauri A and B, lie out of frame. Although by cosmic standards it is a close neighbour, Proxima Centauri remains a point-like object even using Hubble’s eagle-eyed vision, hinting at the vast scale of the Universe around us.
A Hubble Space Telescope image of Proxima Centauri, just over four light-years from Earth. Proxima Centauri — with only about one eight the mass of our sun — is not visible to the naked eye. Its average luminosity is very low but, on occasion, its brightness increases. Proxima is what is known as a “flare star” — where convection processes within the star’s make it prone to random and dramatic changes in brightness. (NASA)

Proxima and the other Alpha Centauri stars are also an especially appealing target because they have loomed so large in science fiction.  From Robert Heinlein’s “Ophans of the Sky” stories of crews traveling to Proxima to Isaac Asimov’s “Foundation and Earth ” set around Alpha Centauri and more recently to the James Cameron’s movie “Avatar,” also set in the Centauri neighborhood, these closer-by have been a frequent and logical destination.

While Alpha Centauri B has gotten much scientific attention in recent years with a reported but still unconfirmed and now often dismissed planet candidate, Proxima Centauri has been the object of much observation, too, and that has begun to define what kinds of planets might and might not be present.

So far, the work of Butler’s team has not found any particularly promising signs of a planetary-caused Proxima wobble.  But he said nothing established so far about Proxima rules out the presence of a small planet relatively close to the sun — the very time-consuming observations needed to potentially detect that size planet just haven’t been done.

Similarly, the Very Large Telescope results ruled out the presence of Saturn-size planets with many-year orbits and Neptune-size planets with orbits less than about 40 day, and no planets more than 6 to 10 Earths in the habitable zone.  This is actually promising news, since the absence of larger planets in the habitable zone leaves the field open for smaller ones.

Two other teams are now focused on Proxima as well.  One is led by David Kipping of Columbia University  using the Canadian Microvariability & Oscillations of STars space telescope (MOST) to search for transits.  The other is led by Kailash Sahu of the Space Science Telescope Institute in Baltimore, using the Hubble Space Telescope for microlensing of the star. The stars are aligned for the microlensing event this month.

A ring of telescopes at ESO's La Silla observatory. La Silla, in  the  southern part of the Atacama desert, 600 km north of  Santiago de  Chile,  was ESO's first observation site. The telescopes are 2400 metres  above  sea level, providing excellent observing conditions. ESO  operates the 3.6-m telescope, the  New Technology Telescope (NTT), and   the 2.2-m Max-Planck-ESO telescope  at La Silla. La Silla also hosts  national telescopes, such as the 1.2-m  Swiss  Telescope and the 1.5-m  Danish Telescope.
A ring of telescopes at ESO’s La Silla observatory. La Silla, in the southern part of the Atacama desert, 600 km north of Santiago de Chile, was ESO’s first observation site. The telescopes are 2400 metres above sea level, providing excellent observing conditions. ESO operates the 3.6-m telescope, the New Technology Telescope (NTT), and the 2.2-m Max-Planck-ESO telescope at La Silla. La Silla also hosts national telescopes, such as the 1.2-m Swiss Telescope and the 1.5-m Danish Telescope. (ESO)

The Pale Red Dot observing began last week and will run for two and a half month using the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory (ESO) telescope at La Silla, Chile. The observations — like those made at the Magellan and at Paranal — look for tiny wobbles in the star’s motion created by the gravitational pull of an orbiting planet. (More on how the radial velocity method works, as well as other connections to and details about the campaign can be found at:  https://palereddot.org/introduction/)

The campaign is the beneficiary of a substantial amount of HARPS observing time — 25 minutes of observing for 60 nights in a row — which is essential to confidently detect the presence of a small, Earth-sized planet.

Other robotic telescopes — including the Burst Optical Observer and Transient Exploring System,  the Las Cumbres Observatory Global Telescope Network and the Astrograph for the Southern Hemisphere II — will participate.  The role of these automated telescopes is to measure the brightness of Proxima each night, a backup that will help astronomers determine whether the wobbles of the star detected via radial velocity are the tug of an orbiting planet or activity on the surface of the star. Anglada-Escudé said that after a full analysis, the findings will offered to a peer-reviewed journal and published.

While the goal of the campaign is definitely to detect a planet orbiting our closest stellar neighbor, it is also very consciously a public outreach effort for astronomy and exoplanets.  Everything about the campaign will be made public, and often immediately via Twitter and other social media.  It will provide a window, said Anglada-Escudé, into how planet-hunting astronomy works.

Guillem Anglada-Escude
Guillem Anglada-Escudé is leading the Pale Red Dot campaign.

“We think this to be a good way to explain things that are not obvious to the public, to show them that looking for planets is not always excitement and ‘eurekas.’   We’ll show life at the observatory, how our observations are made, what happens as we analyze the data.  And if in the end we don’t find evidence of a planet, we will have shown how we search for such tiny objects so far away, and do it with a pretty amazing precision.”

Involving the public so early and often definitely brings risks, since the campaign could certainly come up empty-handed.  But in terms of real-life planet hunting, that result is hardly unusual.  An awful lot of planet-hunting campaigns end without a detection.

When red dwarf stars, also called M dwarfs, are found with orbiting planets, they tend to be much closer in than with more massive stars, and their habitable zones are also much more narrow.  Initially, red dwarfs were not considered good candidates for habitable planets because they are so relatively small — between 50 to 5 percent the mass of our sun.  Any planets orbiting close to a red dwarf would likely be tidally locked as well, with only one side ever facing the sun.  The pull of the host star causes the locking.

These issues and more earlier led scientists to dismiss red dwarf exoplanets as unlikely to be habitable. That unpromising view has changed with the creation of models for tidally locked planets that could be habitable, and with the discovery of many exoplanets orbiting around the red dwarfs.  These small suns actually  constitute more than 70 percent of the stars in the sky, although very few of the ones you can see without a telescope.

So the time seems ripe for a substantial exoplanet campaign at Proxima — one that just might find a planet and that certainly has a lot to teach the public.

Sites where you can follow the campaign:
Twitter: @Pale_red_dot #palereddot
Facebook page:  ‘Pale Red Dot’

 Artist rendering of a cold desert on a planet orbiting Proxima Centauri. (Vladimir Romanyuk, Space Engine)
Artist rendering of a cold desert on a planet orbiting Proxima Centauri. (Vladimir Romanyuk, Space Engine)
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