We Know Almost Nothing About Proxima b, The Closest Exoplanet To Earth
“In reality, we do not even know whether this planet is Earth-like or Neptune-like. The typical border between an Earth-like world, where you have a rocky surface with a thin atmosphere, and a Neptune-like world, where you have a large gas envelope surrounding your world, is about 2 Earth masses. Proxima b has a minimum mass of about 1.3 Earths, but that’s if the alignment is perfectly edge-on. Since there’s no transit, we know the alignment cannot be exactly perfect, but how imperfect is it? That’s gloriously unknown.
If the alignment is inclined at more than about 25° from our line-of-sight, it’s likely to be a gaseous world, not a rocky, Earth-like one. But at this point, without further information, we cannot know.”
Two years ago, some amazing news came in from the astronomical world: the closest star beyond our Sun, Proxima Centauri, has a planet orbiting it. Named Proxima b, it has an orbital period of 11.2 days around a star just 0.17% as luminous as our Sun. This places it into what we call the habitable zone, as it receives approximately 65% of the energy that Earth receives from the Sun. It also has a mass that’s touted as 1.3 times the mass of Earth, but that figure is very suspect. We can claim that as the minimum mass, but can do no better than that. As far as life, water, oceans, or even an atmosphere goes, we have no idea. It could be a completely airless, barren world, or could have a thick gas envelope like Neptune.