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.
Without more and better data, we simply cannot know. We know very little about Proxima b. Here’s how you can separate scientific fact from mere speculation.
Despite Roasting Flares From Its Sun, Proxima b Might Still Have Life
“It’s true that stars that are very different from our Sun have restrictions on what conditions their planets can have and still be habitable. For red dwarf stars like Proxima Centauri, their worlds have conditions that make it unlikely for life to have taken the exact same evolutionary pathway that life on Earth took. But that doesn’t spell doom for life; it merely indicates that alternative pathways are required to arrive at similar outcomes. Frequent flares and excessive blasts of ultraviolet radiation may spell doom if Earth-based life were subject to those conditions, but organisms that have adapted to their environments could survive these outbursts routinely. A few solar hiccups a year should pose no problem for life forms that developed under those exact. harsh conditions. On every world, after all, it should be the organisms most robust against the adversarial conditions they face that will survive.”
The nearest star to us, Proxima Centauri, was discovered to have an Earth-sized planet in its habitable zone just two years ago. In that time, scientists have observed catastrophic flares comfing from the red dwarf star, fearing for the survival of any life on the planets orbiting it. Many now claim that planets orbiting red dwarfs are completely inhospitable to life, since the combination of tidal locking, ultraviolet-rich flares, ozone depletion, and a lack of higher-energy light in general would make photosynthesis and life-as-we-know-it an impossibility. How narrow-minded of us to go down that road! In reality, the energy source is there, the conditions are right for liquid water, the atmosphere as a whole will stick around, and there are many, many adaptations that could lead to life not only surviving, but thriving on a world like Proxima b.
It’s easy to look at a world that’s different from ours and declare how life like ours wouldn’t do well, but the key is to figure out what kind of life would do well there. That’s where the greatest chances for success are. That’s where we need to look.