While studying a red dwarf star—the Proxima Centauri—located 25 trillion miles away, an international team of scientists discovered an Earth-sized planet called Proxima b orbiting it. After publishing their findings in the journal Nature last week, a public dialogue ensued on whether or not the newly discovered planet could sustain life since Proxima b is Earth sized and located in a “habitable zone”—an area where liquid water can exist on Earth-like planets.
Is Proxima b habitable? According to Guillem Anglada-Escudé, lead author of the study from Queen Mary, University of London, it is possible. “There is a reasonable expectation that this planet might be able to host life, yes,” said Anglada-Escudé.
But for Rory Barnes, University of Washington research assistant professor of astronomy, the answer is not so clear cut. "The short answer is ‘It’s complicated,’" writes Barns on palerreddot.org, a website dedicated to Proxima Centauri. "Our observations are few, and what we do know allows for a dizzying array of possibilities."
According to Barnes, questions surrounding whether Proxima b is habitated and whether or not it can be habitable are “impossible to answer” since scientists know too little about the planet. What is known is that it is comparable in size to Earth and it takes 11 days for the planet to orbit its star. That said, Barnes says it is possible to speculate on the planet’s history using theoretical models and by looking into our Solar System.
“If Proxima b is in fact habitable, meaning it possesses liquid water or even inhabited, meaning life is currently present, then it will have traversed a very different evolutionary path than Earth,” writes Barnes.
There are several variables working against life on the planet including the lack of season, solar flares from the sun and whether or not there is water. Then there is the possibility that the planet is tidally locked (read: one hemisphere is constantly facing the host star). Barnes adds that the brightness of the planet’s host star, which may be 4 trillion years old, is relatively dim but once upon a time, it was so hot that the planet’s surface would have been too hot for life.
“Proxima’s brightness evolution has been slow and complicated,” Barnes writes. “Stellar evolution models all predict that for the first one billion years Proxima slowly dimmed to its current brightness, which implies that for about the first quarter of a billion years, planet b’s surface would have been too hot for Earth-like conditions.”
Essentially, the only real answer there is about habitability on Proxima b is that more research is required and there is no definitive answer.
“If Proxima b is habitable, then it might be an ideal place to move,” concludes Barnes. “Perhaps we have just discovered a future home for humanity! But in order to know for sure, we must make many more observations, run many more computer simulations, and, hopefully, send probes to perform the first direct reconnaissance of an exoplanet. The challenges are huge, but Proxima offers a bounty of possibilities that fills me with wonder. Whether habitable or not, Proxima b offers a new glimpse into how planets and life fit into our universe.”