Proxima’s progress: Why it’ll take years to learn what closest exoplanet is really like
University of Washington astronomer Rory Barnes says Proxima Centauri b is the biggest discovery in 20 years for planet hunters like himself, but it could take another 20 years to find out just how livable it is.
The alien planet orbits a red-dwarf star at a distance that puts it in a zone where liquid water could conceivably exist. The fact that such a world circles the sun’s nearest stellar neighbor, 4.2 light-years away, puts it on top of the list of potentially habitable planets beyond our solar system.
Barnes, however, emphasizes the word “potentially.” During a lecture at Seattle’s Pacific Science Center, set for 7:30 p.m. tonight, the UW astronomer will delve into the opportunities and obstacles for life on Proxima Centauri b.
“We’re looking at a 15- to 20-year time frame before we can answer this question of whether it’s habitable,” Barnes told GeekWire in advance of the talk.
Over the course of the past 16 years, astronomers have determined that the planet is at least 1.3 times as massive as Earth. Its orbit brings it far closer to its parent star, Proxima Centauri, than Mercury is to our own sun. But because Proxima Centauri is so much dimmer than our sun, Proxima b is in what’s known as the star’s habitable zone.
That checks off an essential box for life as we know it. But only one box.
“We found it, but we know next to nothing about it,” Barnes said. “Being in the habitable zone doesn’t mean it’s habitable. It just means we have a shot at it.”
Astronomers need to know whether the planet is rocky, like Earth. (They think it is.) They also need to know whether it has a protective atmosphere and magnetic field. (They hope it does.)
If Proxima b’s atmosphere is thick enough, it can distribute the wan heat from its parent star around the planet. A strong magnetic field would help Proxima b fend off stellar radiation flares and keep its atmosphere, as is the case for Earth. But there are also scenarios in which Proxima b is an airless Mercury-type world, or a gassy Neptune-type world.
How will we know which scenario is correct? If Proxima b happens to line up just right, it might pass across Proxima Centauri’s red-dwarf disk as seen from Earth. In that case, next-generation instruments such as NASA’s James Webb Space Telescope might be able to detect the ingredients of the planet’s atmosphere. Or not.
Barnes said it’s more likely that the job will be up to the “next, next generation” of telescopes. Maybe it’ll be a 100-foot-wide telescope on the ground, like the Thirty Meter Telescope that’s being planned in Hawaii. Or maybe it’ll be a 50-foot-wide telescope in space, like the proposed ATLAST or HDST projects. (UW astronomer Julianne Dalcanton is co-chair of the HDST study committee.)
The discovery of Proxima Centauri b is likely to heighten interest in telescopes that are designed to produce direct images of exoplanets rather than relying on indirect stellar observations. “The field was already moving toward direct imaging,” Barnes said.
Astronomers are considering at least two telescopes that could fill the bill: the Habitable-Exoplanet Imaging Mission, or HabEx; and the Large Ultraviolet-Optical-Infrared Surveyor, or LUVOIR. Both are among four mission concepts that are being studied as part of the 2020 Decadal Survey.
Once the analyses are in, NASA will have to figure out which concepts to pursue. It may take another decade or more to translate the winning concepts into space missions.
By that time, you’re getting into Barnes’ 15- to 20-year time frame. You’re also getting into the time frame when the scientists and engineers behind the Breakthrough Starshot Project aim to be ready to launch nano-probes in the direction of the Alpha Centauri system, potentially including Proxima Centauri.
Everything points to the 2030s as prime time for Proxima b. And that gives us plenty of time to think about the implications of identifying what could be the first known interstellar haven for life.
“The ‘habitable zone’ has always been just the first hurdle you have to clear in this race,” Barnes said. “This planet makes us start thinking about habitability in more concrete terms.”
For much more about Proxima b, check out Barnes’ posting to PaleRedDot.org, and show up at 7:30 p.m. PT tonight at the Pacific Science Center’s Paccar IMAX Theater. Admission is free for science center members, and $5 for everyone else.