Ever since astronomers announced the discovery of an Earth-sized exoplanet less than five light years down the cosmic street, the question on every good space cadet's mind has been whether or not we can colonise it. We aren't going to know if Proxima b is habitable until we can point some very powerful telescopes at it, which won't happen until next year. But until then, scientists are playing around with models -- and one such modelling effort recently came to some promising conclusions.
Artist's rendition of the surface of Proxima b, our nearest neighbouring exoplanet. Image: ESO/M. Kornmesser
If Proxima b has an Earth-like atmosphere, researchers found, it might just be a comfortable place to live. A (probably) rocky planet located a measly 40 trillion km away, Proxima b lies squarely in the "habitable zone" of its star -- a tempestuous red dwarf called Proxima Centauri -- meaning it might be able to support liquid water, and even life. The latter is still a big question mark, but as we wait for more data, a UK-based team of scientists is trying to figure out whether Proxima b might have the stable climate and reasonable temperatures necessary for life.
So the researchers turned to the Met Office Unified Model, one of the foremost models for studying the climate here on Earth. The team modified this model for extraterrestrial forecasting by considering two potential atmospheres: An Earth-like one rich in nitrogen and oxygen, and a simple nitrogen atmosphere containing trace amounts of CO2. Then they ran their simulations considering a few hypothetical orbits for Proxima b, including one in which the planet is tidally locked, with a permanent dayside and a permanent nightside, and an orbit similar to that of Mercury. The researchers also considered differences in the star's light output, which produces more infrared and less visible light than our Sun.
Overall, the findings published this week in Astronomy and Astrophysics were promising. In both tidally locked and Mercury-like orbits, the planet's hypothetical climate featured stable surface temperatures conducive to liquid water, supporting and extending the results of previous studies. Although not all parts of Proxima b were habitable in all simulations (the night side in the tidally locked scenario hovered around a nice, balmy -129C), the models pointed to enough warmish regions to make our neighbouring exoplanet a very acceptable interstellar holiday spot.
Caveats abound, however. First and foremost, these models assume Proxima b has an atmosphere, which might not be the case at all. In fact, as another recent modelling study demonstrated, planets in tight orbits around red dwarf stars might be getting lashed by an incredible number of high-energy solar flares, stripping their atmospheres faster than they can be replenished. No atmosphere, no rivers, lakes or oceans, no life as we know it.
The model has other limitations, too -- for instance, it didn't consider what the surface of Proxima b is like at all. As we know from studying Earth's climate, the mixture of land, water and ice coating a planet has an enormous impact on its temperature.
Avi Loeb, chair of Harvard's astronomy department and an adviser for Breakthrough Starshot, an effort to send an interstellar probe to the Alpha Centauri system (which includes Proxima Centauri), called the study's results "encouraging" but agreed that the results are "predicated on an atmosphere being present which remains to be seen". The way forward, Loeb told Gizmodo, is to figure out whether Proxima b actually has an atmosphere by observing it, and if so, to figure out what it's made of.
Both questions require more powerful telescopes than our current state of the art, but the technology is on its way. In the meantime, studies like this inject hope in the quest to find habitable worlds beyond Earth, serving to inspire scientists and motivate further investigations. Maybe we'll even make that interstellar voyage to settle the matter once and for all.