For the first time ever, astronomers may have seen the light from a world in a life-friendly orbit around another star.
The planetary candidate remains unverified and formally unnamed, little more than a tiny bunch of pixels on a computer screen, a potential signal popping up from a sea of background noise. If it turns out to be genuine, the newly reported find would not be particularly remarkable in most respects: a ‘hot Neptune’ estimated to be five to seven times larger than Earth, a kind of world that takes scores like NASA ‘s Kepler and Transiting Exoplanet Survey. Satellite missions appear to be common in the Milky Way.
But even though it would be shrouded in gas and actually get rid of any surface to rise, the distance from its star would place it in the so-called ‘habitable zone’ where liquid water could exist. No other planet has been seen directly in this star-soaked area around any other star, due to the associated luster. And the world’s celestial coordinates are directly from astronomers’ wildest dreams – it will orbit a twin of the sun called Alpha Centauri A, who also happens to be a member of a triple galaxy that is only 4.5 light – years away. , is closest to our own.
Due to its proximity, the other members of the system – a slightly smaller solar star called Alpha Centauri B, and the small red dwarf star Proxima Centauri – are also high priority targets for astronomers, already indirectly representing the presence of two worlds around Proxima. detected. (including one that is probably rocky and within the star’s habitable zone). Whether you are looking for property in the city or another star, location is everything. The Centauri system is so close that it provides a unique front seat for scientists who want to study the atmosphere and surfaces of any worlds out there, especially to look for possible signs of life. And astronomers long ago learned that planets are like domestic pests in some respects: where one is seen, others are likely to be found. Therefore, as tentative as it may be, the budding harvest of Centauri worlds points to countless discoveries yet to be made and can profoundly change our view of our place in the universe.
The new findings were reported Wednesday in the journal Nature Communications. They are descended from an international consortium of planetary hunters called Breakthrough Watch, via the first scientific course of a unique direct imaging tool called NEAR (New Earths in the AlphaCen region), which works on the European southern observatory. (ESO) Very Large Telescope (VLT) in Chile. The effort is named after its main funding organization, Breakthrough Initiatives – the brainchild of billionaire Yuri Milner of Silicon Valley, which also sponsors related projects to search the heavens for signs of alien civilizations and to pint-sized interstellar sins to the Alpha Centauri system. send. .
“Alpha Centauri offers us a magical opportunity because there is no better place in the sky to try to image small, potentially habitable planets directly,” said Pete Klupar, chief engineer at Breakthrough Initiatives. ‘It was, in a sense, a low-hanging fruit – for just $ 3 million we could build with our international partners a tool to take advantage of the billions of dollars that ESO has invested in its telescopes. But it’s also like walking behind a needle in a haystack, which is why no one has ever done it. Governments tend to build measuring instruments, look at a large number of stars and guarantee a return on investment, while NEAR was determined to do just this one, risky thing. ”
“As we work together globally, we discover new worlds and we’re still advancing,” says Milner. “Identifying a candidate-habitable zone planet in our heavenly backyard will continue our curiosity.”
The Blip
The candidate’s seductive signal stemmed from 100 hours of observations on the VLT, which lasted a total of ten nights in the spring of 2019. By June of this year, when members of the Breakthrough Watch team sifted through their observations, they began to realize that they might have found something. Kevin Wagner, lead author of the study and a postdoctoral fellow Sagan fellow at the University of Arizona, first saw evidence of a planetary blip far above NEAR’s instrumental noise. It happened while processing a bundle of data remotely during a family vacation in Lake Jocassee, South Carolina. The Breakthrough Watch team measured its brightness and calculated it between limits on planet masses and sizes, calculated in previous studies by other groups, and estimated that if the blip was indeed a planet, it was probably somewhere between Neptune and Saturn would be in size. By November, he and his colleagues were sure the find was worth publishing, even though it did not appear to be a world at all. (This would not be the first time our neighboring galaxy has deceived astronomers. Peer-reviewed claims of a small planet around Alpha Centauri B in 2012 evaporated a few years later, apparently products of stellar noise.)
“In a way, I hope we didn’t notice anything this time either,” Wagner said. ‘Because what I like most is an earthy planet in the habitable zone. The presence of a Neptune in the habitable zone of Alpha Centauri A would not exclude anything smaller in the area, but it would limit a part of the area in which we could in the first place hope that rocky worlds would exist there. ‘
There is no shortage of other possible explanations for the weak signal, which is essentially a thermal sound of infrared photons – that is, of heat – apparently coming from a source outside the habitable zone of Alpha Centauri A. In visible light, a sunny star shines on a small, rocky planet with a factor of billions. But in infrared, the star is dimmer, and this contrast ratio is measured ‘only’ in millions. The difficulty of obtaining even this more modest measurement has for decades been limited to direct giant planets orbiting far from their stars. That is, until NEAR is built. It is a medium-infrared coronograph, a specialized instrument designed to erase most of the thermal glow of a star with a tight wavelength of 10 microns. Supplemented by adaptive optics to compensate for the fading of the Earth’s atmosphere, it shifts the focus between Alpha Centauri A and B every tenth of a second by helping observations of each star to calibrate those of the other. It gradually unwinds starlight and stacks frame after frame so that any faint planetary light can accumulate and eventually be seen. But rather than betraying the presence of a planet, a blip could be a distant background object, a bunch of star-warmed dust or an asteroid belt orbiting a star, or even the wandering game of stray photons emanating from ray line leak. and spray over sensitive optics in the instrument. Wagner and his co-authors have already ruled out the first possibility (no well-known background star or galaxy can explain the blip), but the others remain in varying degrees.
Confirming the blip’s planetary status should have been relatively simple: just try to observe it again after sufficient time has passed; if it were in fact a planet, its orbital motion would have swept it to a new and very different position around its star. Subsequent, more time-intensive studies with NEAR were able to accurately measure the colors of the blip to eliminate the hypothesis of the “dust cloud”. But that would not be the case anyway, as the ensuing Covid pandemic shut down astronomical observatories and most others worldwide. Wagner says the team has applied for extra time to use NEAR on the VLT, but the proposal has yet to be approved.
“The timing is so unfortunate,” said Debra Fischer, a veteran planetary fighter at Yale University. She is not involved in the study, but her work with her student Lily Zhao has placed the best constraints on the planets that may or may not exist in the Alpha Centauri system. “If it’s in the habitable area around Alpha Centauri A, it’s an earthy orbit. If you observe it six months later, it would probably be nailed down,” says Fischer. ‘Without it, it’s not a planet tracking site, it’s proof of NEAR’s ability to monitor Alpha Centauri in mid-infrared. But if it turns out to be right – oh my God, it’s great. ”
Brave new worlds
For now, NEAR is the only corona grave on Earth with a realistic chance of depicting Alpha Centauri’s hidden worlds. But other instruments and facilities are already waiting in the wings to apply their own investigation to the system. Fischer’s high-precision spectrograph EXPRES radial velocity – and an even more advanced European counterpart, ESPRESSO – are both already in operation. They could indirectly help confirm the planetary candidate and others, and could estimate their masses by looking for periodic wobbles of each world’s orbit caused by its host. A related technique, astrometry, can do much the same, detecting planetary masses by measuring how the gravity of each world shifts its star’s position slightly into the sky. Such observations using the Atacama Large Millimeter Array in Chile, or even a modest, breakthrough-funded space mission, could take place later this decade.
According to a recent study led by one of Webb’s leading scientists, Charles Beichman of the California Institute, James Webb’s James Webb Space Telescope, which would be launched in late October, could also directly image the candidate planet. of Technology. “Because Alpha Centauri A is a twin of our own sun and less than five light-years away, it is our closest solar neighbor,” says Beichman. ‘This makes it the first place among equals, of all the stars in the sky. No other system will lend itself to more detailed studies over the next decades. ”
The space agency’s follow-up mission to Webb, the Nancy Grace Roman Space Telescope, will also carry a coronary shaft as a technology demonstration that (with some modifications now being actively considered) could possibly take photos of the candidate.
And about the same time as Roman may begin, a new generation of sophisticated coronary graves coupled with giant observatories on the ground should begin operations that could deliver images of Centauri planets within minutes that are currently hours upon hours of NEAR’s time on the VLT need. Armed with stellar mirrors 30 meters or more across, ESO’s European extraordinarily large telescope and its American counterpart, the Giant Magellan Telescope, can both in theory collect enough light from a habitable zone of Neptune around Alpha Centauri A to study its atmosphere and sniff. find out what known or alien chemistry is there. (A third hemotope, the US 30-meter telescope, is currently planned for a site in the northern hemisphere from which Alpha Centauri is not visible.) Finally, NASA and other space agencies are now studying billion-dollar space telescope concepts for the 2030s and beyond . Some of these can image on small rocky planets around Alpha Centauri as well as many other stars in the area and look for signs of life.
All of this means that, even if this latest candidate from Alpha Centauri turns out to be false, it’s still something real: a looming sea change in which planetary astronomers move from safe, statistical surveys to the more daring in-depth study of individual worlds. life can house.
“Whether this thing is real is almost secondary to me,” said co-author of the study, Olivier Guyon, an innovator in direct imagery and chairman of Breakthrough Watch. ‘Because it shows in any case that we are clearly opening a new area in the history of astronomy, where we can finally, after more than 20 years of hard work, finally get a direct picture of another star’s habitable zone . This is the ‘game on’ moment for the field. ”