Proxima Centauri B: Our Future Home?

By John Michael Godier

Yesterday, scientists confirmed the existence of yet another exoplanet. But this one stands out and will quickly become the most important exoplanet yet found. The reason for that is simple; it's close by. In fact, it's practically as close as an exoplanet can get to the sun given that it orbits Proxima Centauri, the closest star system to our own at just 4.2 light years away. But that's not the most interesting thing, the planet also happens to be earth-sized and located within the habitability zone of its star. Not only do we have an exoplanet that is close and potentially habitable, it's close enough for us to eventually visit.

While not much is known yet about Proxima Centauri B, we do know a little. Proxima Centauri itself is a red dwarf star, rather dim and small and slightly older than our sun and about one seventh the size. That means its zone of habitability is very close to the star, and indeed Proxima B orbits at just .05 astronomical units out. Compare this to Mercury which orbits at .38 astronomical units from our sun. Even though Proxima B orbits very close to its star, given how dim the star is the planet receives only about 65% of the energy from its star that we get from the sun. Its distance from its star is within the zone where liquid water can exist. But that closeness also raises the likelihood that the planet is tidally locked, that is to say that one side of it is always in light and the other hemisphere is always in dark. That creates a special situation for potential life.

While by no means is this planet guaranteed be able to host life, there are many, many factors involved with that, if it did it would congregate at the terminator between the light and dark hemispheres rather than globally as it does on Earth. This zone may be very thin, or somewhat thicker if the atmosphere is right to distribute heat to the dark side. There's also an uncertainty about the conditions in which this system exists, we do not know for example if Proxima Centauri is part of a larger system that includes the nearby stars Alpha Centauri A and Alpha Centauri B.

If it is gravitationally bound to them and formed with them, then this affects the distribution of water within the system due to the fact that the larger stars would have driven comets into the Proxima system that would have enriched it with water. If Proxima is merely passing by, then this factor changes and Proxima B may have very little water at all and probably no life.

Also working against life is the amount of X-Ray radiation the planet receives, about 400 times more than what we have here on earth. Depending on the conditions on that world, that amount could make it impossible for life to gain a foothold, we simply don't have enough information to say.

One thing we do know however is that the planet's orbital eccentricity is low, which would allow for a more stable environment and perhaps even temperatures similar to those on earth within the areas that might be habitable.

So while we don't know much about this world yet, and cannot make any claims as to whether its earth-like and habitable or very different from earth and hostile to all forms of life, it does have certain features that make it extremely intriguing. But perhaps the most interesting aspect of Proxima B is how close it is. While most exoplanets we find are hopelessly distant, this one is reachable with sufficient technology. It would take years to get there, there's no question of that, but it also took nearly a decade for the New Horizons probe to reach Pluto, so we humans are no strangers to long-term exploration missions.

Eventually, we'll send a probe when we gain the ability to travel at speeds approaching half the speed of light or more. There are already concepts out there on just how to do that. And possibly, just possibly, at some time in the far future humans may one day set foot on Proxima Centauri B.