Red Dwarf Stars and the Planets Around Them

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Artist rendering of a red dwarf or M star, with three exoplanets orbiting. About 75 percent of all stars in the sky are the cooler, smaller red dwarfs. (NASA)

It’s tempting to look for habitable planets around red dwarf stars, which put out far less luminosity and so are less blinding.  But is it wise?

That question has been near the top of the list for many exoplanet scientists, especially those involved in the search for habitable worlds.

Red dwarfs are plentiful (about three-quarters of all the stars out there) and the planets orbiting them are easier to observe because the stars are so small compared to our Sun and so an Earth-sized planet blocks a greater fraction of starlight.  Because planets orbiting red dwarfs are much closer in to their host stars, the observing geometry favors detecting more transits.

A potentially rich target, but with some drawbacks that have become better understood in recent years.  Not only are most planets orbiting these red dwarf stars tidally locked, with one side always facing the sun and the other in darkness, but the life history of red dwarfs is problematic.  They start out with powerful flares that many scientists say would sterilize the close-in planets forever.

Also, they are theorized to be prone to losing whatever water remains even if the stellar flares don’t do it. Originally, it was thought that this would happen because of a “runaway greenhouse,” where a warming planet under a brightening star would evaporate enough water from its oceans to create a thick blanket of H2O vapor at high altitudes and block the escape of radiation, leading to further warming and the eventual loss of all the planet’s water.

The parching CO2 greenhouse of a planet like Venus may be the result of that.  Later it was realized that on many planets, another mechanism called the “moist greenhouse” might create a similar thick blanket of water vapor at high altitudes long before a planet ever got to the runaway greenhouse stage.

Finally now has come some better news about red dwarf exoplanets.  Using 3-D models that characterize atmospheres going back, forward and to the sides, researchers found atmospheric conditions quite different from those predicted by 1-D models that capture changes only going from the surface straight up.

One paper found that using some pretty simple observations and calculations, scientists could determine the bottom line likelihood of whether or not the planet would be undone by a moist greenhouse effect.  The other found that these red dwarf exoplanets could have atmospheres that are always heavily clouded, but could still have surface temperatures that are moderate.

The new studies also enlarge the size of the habitable zones in which exoplanets could be orbiting a red dwarf or other “cool” star, making more of them potentially habitable.

The green sections are the habitable zones surround the different star types.  The term refers to the region around a star where water on a planet could remain liquid at least part of the time.  The term does not mean the planets in the zone are necessarily habitable, but that they make it past one particular large hurdle.  (NASA)

 

“This is good news for those of us hoping to find habitable planets,” said Anthony Del Genio, a senior research scientist at NASA’s Goddard Institute for Space Studies (GISS) in New York, and co-author of a new paper in The Astrophysical Journal.

“These studies show that a broader range of planets could have stable climates than we thought.  This is a broadening of the width of the habitable zone by showing that we can get closer to a star and still have a potentially habitable planet.”

Yuka Fujii, author of the Astrophysical Journal article, specializes in exoplanet characterization, planetary atmospheres, planet formation, and origin of life issues. (Nerissa Escanlar)

In a NASA release, the paper’s lead author, Yuka Fujii, said this: “Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study.” Fujii was formerly at NASA GISS and now is a project associate professor  at the Earth-Life Science Institute in Tokyo.

Since telescope time available for exoplanets will be quite limited on observatories such as the James Webb Space Telescope — which has many astronomical tasks to accomplish — the Earth-sized exoplanets around red dwarfs seem to be the more technologically feasible target to observe.

Scientists have to observe Earth-size planets for a long time and for many transits in front of the star to get a good enough signal to interpret. So given that, it will be impossible to observe all, or even many, of the candidate Earth-size planets discovered so far or will be discovered.  Tough choices have to be made.

What the group found using their 3-D models is that unlike the predictions from 1-D models, this moist greenhouse effect does not set in immediately for a particular luminosity of the star. Rather, it occurs more gradually as the star becomes brighter.

That fact, Del Genio said, makes the findings from the new 3-D modeling studies additionally important because they can help observers determine which small, rocky exoplanets might be most promising in terms of habitability.

They do this by identifying — and then eliminating — exoplanets that have undergone what is called a “moist greenhouse” transformation.

Anthony Del Genio, leader of the GISS team using cutting edge Earth climate models to better understand conditions on exoplanets.

A moist greenhouse occurs when a watery exoplanet orbits too close to its host star. Light from the star will then heat the oceans until they begin to evaporate and are lost to space.

This happens when water vapor rises to a layer in the upper atmosphere called the stratosphere and gets broken into its elemental components (hydrogen and oxygen) by ultraviolet light from the star.
The extremely light hydrogen atoms can then escape to space. Planets in the process of losing their oceans this way are said to have entered a “moist greenhouse” state because of their humid stratospheres.

What the group found using their 3-D models is that unlike the runaway greenhouse effect this moist greenhouse effect does not set it immediately at a particular temperature threshold.  Rather, it occurs more gradually, even over eons.

They came to this conclusion because the upper atmosphere heating turned out to be a function of the infrared radiation coming from the stars rather than from turbulent convective activity (as in massive thunderstorms) from the surface, as earlier believed.

The infrared radiation (which is at wavelengths slightly longer than the visible wavelength area of the spectrum) will warm the planet and cause what water is present to eventually. evaporate.

 

This is a plot of what the sea ice distribution could look like on a tidally locked ocean world. The star would be off to the right, blue is where there is open ocean, and white is where there is sea ice.  (NASA/GISS/Anthony Del Genio)

This paper comes on the heels of a related one in the August edition of  The Astrophysical Journal.

Ravi Kopparapu, a research scientist at NASA Goddard and Eric Wolf of the University of Colorado, Boulder came to a similar conclusion about surfaces on exoplanets orbiting red dwarfs. As they wrote in their abstract, the modeling  “implies that some planets around low mass (red dwarf) stars can simultaneously undergo water-loss and remain habitable.”

They also reported general circulation model 3-D modeling that showed moist greenhouse scenarios around red dwarfs were slow moving and took place at relatively low temperatures. As a result, oceans could remain for a long time — even billions of years — as they slowly evaporated.

Both groups use general circulation models (GCM), though different ones.  GCMs are an advanced type of climate model that looks at the general circulation patterns of planetary atmospheres and oceans.  They were initially designed to model Earth’s climate patterns, but now are used for exoplanets as well.

The original theory of the moist greenhouse scenario was put forward in the 1980s by James Kasting of Pennsylvania State University, who also did much original work on the concept of a habitable zone and helped popularize the concept.  Both the runaway greenhouse and the moist greenhouse have become important factors in exoplanet study.

 

 

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Found: Our Nearest Exoplanet Neighbor

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This artist ’ s impression shows a view of the surface of the planet Proxima b orbiting t he red dwarf star Proxima Centauri, the closest star to the Solar System. The double star A lpha Centauri AB also appears in the image to the upper-right of Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, wh ere the temperature is suitable for liquid water to exist on its surface. Credit: ESO/M. Kornmesser
An artist impression of the surface of the candidate planet Proxima b orbiting the red
dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.
(ESO/M. Kornmesser)

No exoplanet can possibly be closer to us than the one just detected around our nearest stellar neighbor, Proxima Centauri.

The long-sought and long-imagined planet is larger than Earth, but small enough to be rocky as opposed to a gas or ice giant.  Making things even more exciting, the planet was detected inside the habitable zone of Proxima, suggesting that the planet could potentially have temperatures that allow for pooling liquid water.

Innumerable questions remain to be answered before we know if it actually is habitable (as opposed to residing in a habitable zone), and far more before we know if it might actually be inhabited.

But the very exciting news is that an exoplanet has almost definitively been found only 4 light-years from our solar system.  There’s every reason to believe it will become the focus of intense and sustained scientific scrutiny.

The detection is the culmination of a “Pale Red Dot” observing campaign that began in earnest early this year to search the regions close to Proxima for exoplanets.  Guillem Anglada-Escudé  of Queen Mary University, London, was a leader that campaign, as well as earlier efforts to dig deeper into decade-old Proxima Centauri data from other teams that hinted at a planet but were far from definitive.

“The signal that a planet orbits Proxima every 11 days is strong, so we have little doubt that it’s there,” AngladaEscude´ said.  “And because this is the closest possible planet outside our solar system, there’s a sense of finding something special, even inspirational.”

His hope is that the detection will become a global “driver,”  a discovery that is significant enough to change how people think about our world, as well as about the possibility that some day humans will explore up close a planet outside our system.

Said Anglada-Escude´:  “The search for life on Proxima b comes next….”

Caption: This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lowe r-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope. Credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani
This picture combines a view of the southern skies over the European Southern Observatory’s 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima b was discovered using the HARPS instrument on the ESO 3.6-metre telescope, as well as by aggressively refining previous measurements taken around Proima Centauri. (Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani)

Indeed, it already has started.  Excitement in the exoplanet world is palpable, and papers based on the finding are already on their way to the public.  Anglada-Escude´ gave early copies of the Proxima paper to a number of groups around the world so they could begin digging deeper.

One such group was the Virtual Planetary Laboratory at the University of Washington, and director Victoria Meadows and research assistant professor Rory Barnes have been looking at and modeling the possible evolutions of Proxima b and how its potential for habitability can be assessed in the years and decades ahead.

“This is a huge discovery,” said Barnes.  “Before Proxima b, we didn’t really know what planet would be of greatest interest, so we had to prepare for whatever we might find.

“Now it’s no longer a question of what is the prime target, where do we want to first focus and dig deep. Now we know exactly what we want to look at.”

Barnes’ paper will focus on models of  the possible evolutions of Proxima b, while Meadows will focus on what researchers should look for in terms of habitability on the planet and what current and future instruments would be best suited for the search.

“The planet is in the habitable zone, but that doesn’t mean it’s habitable,” Meadows said.  “What we’re focused on is what are the surface conditions now, the atmospheric make-up, whether or not there might be an ocean present.  These are very difficult questions to address, and it will definitely take time to develop the instruments we need and for the community to find answers.”

his infographic compares the orbit of the planet around P roxima Centauri (Proxima b) with the same region of the Solar System. Proxima Centauri is smaller and cooler than t he Sun and the planet orbits much closer to its star than Mercury. As a result it lies wel l within the habitable zone, where liquid water can exist on the planet ’ s surface. Credit: ESO/M. Kornmesser/G. Coleman
This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Proxima Centauri is smaller and cooler than the sun and the planet orbits much closer to its star than Mercury does to our sun.  But because Proxima b’s host star put out so much less heat and radiation,  it lies well within the habitable zone,where liquid water can exist on the planet’s surface. (ESO/M. Kornmesser/G. Coleman)

Proxima Centauri is a red dwarf (or M dwarf) star,  a very long-lived but small and cool star compared to our sun.  Red dwarfs are the most common type of star in the galaxy, by far.  To date, however, only a few Earth-mass planets have been discovered in the temperate zones of such stars. But because there are countless billions red dwarf stars, only a small percentage need to have temperate-zone planets to make our galaxy potentially teeming with life.

When it comes to the odds of finding an exoplanet orbiting the star nearest us, I turned to Natalie Bathalia, project scientist for NASA’s Kepler Space Telescope.  Based on statistical analysis of Kepler survey data, she said, we should expect at least one potentially habitable, Earth-size planet orbiting an M dwarf  (or red dwarf)  star within 10 light-years of the solar system.

“Well, it turns out that there are only 7 M dwarfs within 10 light-years of the solar system,”  she said.  “That means we’re ‘roll-of-the-dice’ lucky, not ‘winning-the-lottery’  lucky.  Had it been the latter, I might have been more skeptical.  Instead, I’m relishing the moment.  Numbers aside, I’m certainly feeling like we’ve all just won the cosmic lottery.”

As described in a cover article in the journal Nature, Proxima b was identified by the “Doppler wobble” of its host star — the effect caused by the planet’s gravitational pull. This method was used to discover the first exoplanet around a sun-like star, 51 Pegasi, in 1995.

Guillem Anglada-Escude, leader of the Pale Red Dot campaign and a lecturer at St. Mary's College,London.
Guillem Anglada-Escude´, leader of the Pale Red Dot campaign and a lecturer at St. Mary’s College,London.

Astronomer Paul Butler of the Carnegie Institution for Science was one of the two scientists who made the essential confirmation of that first exoplanet, and he played an important supporting role in the Proxima b detection as well.

“We’ll continue finding planets, but this may well be the last big deal detection,” Butler said.  “There may be even more important planets out there, but it’s pretty hard to imagine what they might be.”

The Doppler method is particularly useful and effective in studying or red dwarf stars. Because these stars are cooler than our sun, their potentially habitable planets would orbit much close to the host star (about one-tenth of the sun–Earth distance,) and so are potentially easier to detect.

These red dwarf stars are also less massive than the sun, and so are more visibly affected by the presence of an orbiting planet.  A Doppler wobble for a red dwarf with exoplanets is large enough (about 1 meter per second) to be detected by current instruments. By comparison, Earth causes a Doppler wobble of the sun of 0.09 meters per second.

Anglada-Escudé and colleagues first detected a possible signal of their exoplanet using Doppler measurements taken by the Ultraviolet and Visual Echelle Spectrograph at the European Southern Observatory (ESO) in Chile between 2000 and 2008.

These data showed a hint — but not an entirely convincing one — of a Doppler wobble of 1.38 meters per second.  With the help of Butler, they also re-analyzed date from an earlier Proxima run using the ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph in Chile.

The authors confirmed the signal by using many more Doppler measurements taken in 2016 with the same spectrometer and telescope. Nonetheless, to be on the safe side, Proxima b is still formally called a “candidate” exoplanet.

The European Southern Observatory's La Silla facility in Chile. The "Pale Red Dot" campaign used previous data collected at La Silla, and updated with new observations there this year. (ESO)
The European Southern Observatory’s La Silla facility in Chile’s Atacama Desert. The “Pale Red Dot” campaign used previous data collected at La Silla, and updated with new observations there this year. (ESO)

The Pale Red Dot campaign has been aimed at Proxima, but plans to continue looking for exoplanets orbiting nearby red dwarf stars.  The group includes 31 scientists from eight international and national organizations, and shares its news on this site: https://palereddot.org/.

The name of the campaign plays on the “pale blue dot” image of the Earth taken in 1990 by Voyager 1 on its way to interstellar space. The phrase was later used by Carl Sagan, who lobbied for Voyager to make the necessary maneuvers to take the images,  for his essay, “Pale Blue Dot: A Vision of the Human Future in Space.”

I spoke recently with Anglada-Escude´ about the campaign and its breakthrough Proxima b detection. Both clearly flow from his deep interests and drives.

“I’m a scientist and I’ve been excited about exoplanets for a long time.  But when I was young I read a lot of science fiction, I was a geek I guess.  Proxima and the Centauri system always seemed like the next place to go — not now, but in a few hundred years.  But to do this we had to learn all about the stars and hopefully the planets around them.  So you could say that none of this happened by chance.

“So this is all about detection and characterizing the planet and star, but about exploration as well.  It’s the nearest object outside of our solar system, and that makes it a natural destination.

“We know the planet is there, so now is the time for people to get creative about imaging it, and learning how to search for life there, and ultimately set out on interstellar expeditions in that direction.”

Proxima Centauri, it should be noted, is 266,000 times as far away as the distance from the Earth to our sun.

his image of the sky around the bright star Alpha Centauri A B also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The picture was created from pictures forming part of the Digitized Sky Survey 2. The blue halo aroun d Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in co lour like the Sun. Credit: Digitized Sky Survey 2 Acknowledgement: Davide De Martin/Mahdi Zamani
While Alpha Centauri AB (very bright in the image) and Proxima Centauri (much fainter and reddish) are considered part of a single system, it remains unclear whether they are subject to the gravitational tugs of each other — a key issue in understanding the possibile evolution of the stars and detected and potential exoplanets. This image was created from pictures forming part of the Digitized Sky Survey 2. The blue halo aroun d Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in color like the sun. (Digitized Sky Survey 2/Davide De Martin/Mahdi Zamani)

 

 

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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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