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Could life exist on Proxima b, the closest Earth-like planet in the universe?

A planet that could be Earth's cousin is circling the nearest star beyond our sun. Could Proxima b also host cousins of a different sort?

This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system.

ESO/M. Kornmesser

Today the world knows something it didn't know yesterday: the nearest star to our solar system is orbited by a rocky planet in the habitable zone.

Like many big-deal discoveries, this one leads to more questions than answers. Could there be life on Proxima b? How could we get there to find out for sure?

"The discovery is inspiring," said Lisa Kaltenegger, Cornell astronomy professor and director of the Carl Sagan Institute. "What more can we ask for than a potentially habitable world around our closest neighbor, to get everyone inspired to try to get there?"

Of course, physically getting there isn't going to happen overnight. In fact, it would take thousands of years with our current rocket technology. The Breakthrough Starshot initiative has already proposed sending a tiny nanocraft to Proxima Centauri at 20 percent of the speed of light. That craft still needs to be developed, but it provides hope we could at least lay digital eyes on Proxima b within our lifetimes.

Meanwhile, there's plenty of work that can be done to try and figure out what exactly might be waiting to greet us on Proxima b if we ever make it. Just because a planet lies in the habitable zone of its star doesn't mean it's actually habitable.

In a press conference Tuesday, prior to Wednesday's big announcement of the Proxima b discovery, team leader Guillem Anglada-Escudé from Queen Mary, University of London explained that the planet probably receives 100 times more radiation from its star than we do on Earth from the sun.

You might assume this is a deal breaker for life, but Anglada-Escudé says that's not the case. The planet's history is actually more important. For example, have conditions been right for a strong magnetic field and atmosphere that could block all that radiation to develop?

"Chances are good...there are models (for the evolution of Proxima b) that lead to a viable Earth-like planet today," he said.

Keep in mind that "Earth like" certainly doesn't mean "Earth identical." There are plenty of reasons to think it would still be a very alien world compared to ours.

Any star around a red dwarf is likely to be illuminated by light with a more crimson hue, but that's just the beginning of the possible weirdness afoot on Proxima b.

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Because of its close proximity to its small star, the planet could be tidally locked, which means it always shows the same side to its sun, just as the moon does to Earth. That would create a constantly light and warm side of the planet and a constantly dark side with no sunrises or sunsets.

"Until recently, exoplanet hunters thought that tidal locking would be a deal breaker for habitability," said Doug Vakoch, president of METI International.

"One side of the planet would be scorched, while the other side would be perpetually frozen. But in recent years, new models of exoplanet atmospheres and oceans suggest that heat might be distributed around a tidally locked planet, leaving the door open for habitability. Even if the newly discovered exoplanet around Proxima Centauri is tidally locked, it could still be prime real estate for life."

Harvard astronomy professor David Charbonneau concurs.

"Last night when the sun set in Boston, the temperature did not fall to absolute zero. Any planet with a decent ocean and atmosphere has a means to redistribute energy," he said via email.

The early consensus seems to be that despite some potentially fundamental challenges to the development of life on Proxima b, it's still feasible and definitely worth investigating. Doing that right away poses other obstacles, however.

"The biggest question now, and the one my team has been trying to solve, is does it transit?" explained Columbia University's David Kipping. "Characterizing this planet will be very difficult if Proxima b does not transit."

He's referring to the method of observing an exoplanet as it passes in front of, or "transits," its star and then analyzing the way the transiting planet affects the spectrum of the starlight to determine what elements are present in its atmosphere, if it has one. If that analysis picks up elements needed for life like oxygen or methane, that's a good sign for a planet's potential habitability.

Kipping says Anglada-Escudé's team shared their findings on Proxima b a few weeks ago to aid in his quest to find a way to observe the planet in transit. He hopes to be able to share the results of that effort in the coming weeks after a little more analysis and review.

The reality, though, is that we should expect to wait years or even decades before we can say for sure that there might be interesting critters roaming the newly discovered planet. New observatories like the James Webb Space Telescope launching in the coming years will surely help this effort.

Despite all the challenges to life making it on Proxima b and the obstacles to even being able to study the possibility of life there, researchers are already adjusting their work plans based on today's announcement.

"The discovery of a potentially habitable planet around Proxima Centauri is a game changer for METI (Messaging Extraterrestrial Intelligence)," Vakoch said. "If we sent a message today, we might get a reply in less than nine years. We could have several back-and-forth exchanges with any civilizations there over the course of a human lifetime."

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