Proxima Centauri b Update

Proxima Centauri B has recently shot to the top of the list as far as interesting exoplanets go. Not only is it the closest exoplanet to our solar system, it's also about the size of earth and within the habitability zone of its star. This is potentially earthshaking because this planet is so close to us that it's possible, maybe even probable, that some day humans will set foot on it or even colonize it, assuming that it's uninhabited of course.

Unfortunately, at least until the James Webb Space Telescope launches, we don't know much about this world other than what we can infer. We also don't know much about the conditions of life arising in a red dwarf star system. But a recent paper by Laura Kreidberg and Abraham Loeb of Harvard University gives some tantalizing hints of what Proxima B might be like.

The paper's overall purpose is to present the case that the James Webb space telescope will be able to determine if there is liquid water on Proxima B. This is the first step in establishing whether life can exist there. Where there's water, there could be life. But on Proxima b, it's a bit more complicated than that and nothing is guaranteed.

Firstly, they lay out that this planet may have no atmosphere at all. It orbits a star very different from the sun and it orbits it very closely in comparison to earth. More, it's probably tidally locked which means it's like our moon, one side of the planet always faces its star. This creates some unique conditions where one side of the planet is always in night and one side is always in day. That means quite a very unearthlike mix of a permanently scorching hot day side and a frozen solid night side.

With one side always in night, that means that the planet's atmosphere may have frozen out and locked itself up as ice on the dark side. If so, that would mean that life on this world is highly unlikely. But it also makes it a target for terraforming if we ever make it there. Frozen out atmospheres can be melted and restored, which is one of the main things we'd have to do if we were to ever terraform Mars and make it habitable for humans.

But if it does have an atmosphere, the researchers point out that atmospheres tend to redistribute heat. Warm air moves around with wind and weather, so the dark side of Proxima b may just be warm enough to have prevented an atmospheric freeze out. If so, then we're back to an environment that can have liquid water on the surface of the planet.

But there's another problem, Proxima b is so close to its star that it would be subject to stellar erosion of its atmosphere. The solar wind and radiation might literally have blown the planet's atmosphere off into space. That alone may have been enough to deprive this planet of an atmosphere early on before life had a chance to arise, or it may have survived but we just don't know enough yet to say. The good news is that we'll know a lot more in just two years with the launch of the James Webb telescope.

While Proxima b is too close to its star to directly image, it's year is only 11.2 days, the James Webb Space Telescope will be powerful enough to tell us much. We should be able to use the JWST to detect the distinctive infrared emissions that would be produced by the planet and watch how it changes as it orbits Proxima Centauri. From those observations, we should be able to determine if it has an atmosphere and how it's redistributing heat, and by extension if it's warm enough for liquid water there.

But as far as life goes, other factors may also play a role. One of these would be the presence of a moon. Life on earth is thought to have arisen in tidal pools. Tides are caused by the moon. No moon, no tides, and that changes the equations on whether life can arise on a planet. Other factors include the chemical makeup of the atmosphere if it exists, the geology of the planet, weather, magnetic fields, plate tectonics and so on.

But in a best case speculative scenario, Proxima B would be a world that has a ring of habitability rather than a global habitability like earth. If life exists there, it would be centered on the twilight zone of the planet where the light is not so strong as to create a permanently lit desert, but not so weak as to prevent liquid water. This kind of a habitable world is sometimes referred to as an 'eyeball planet'.

But if it did have life, what would it look like? Well, if such a planet had foliage, it would need to adapt to a completely different light profile than earth. As a result, instead of the distinctive green of earth's planet life, leaves on Proxima b would probably be black. Given the environment, animals would probably evolve to rely on seeing infrared rather than visible light. But it may not be possible for that sort of life to exist on that planet and perhaps the best we could hope for would be algae and microbes.

It has been suggested that worlds such as Proxima b, even if it did have liquid water, it would have conditions very different from earth and would present different challenges to life. These include permanent torrential downpours in certain areas of the planet and constant high winds that scour the planet's surface. The presence of an ocean may change that however, and allow for a protected underwater zone where life could flourish. Another factor would be the presence of geothermal vents underneath the frozen side of the planet and the potential for a protected liquid water environment under the ice.

So there you have it, while we may not know much about Proxima b yet, the James Webb Space Telescope will be powerful enough to reveal much more. In just two years, we should have a better understanding of our nearest exoplanet neighbor and determine whether it is to be the first interstellar object humans will visit.