Is the New Planet Proxima b Really Habitable?

It depends on water, radiation, and other factors still unknown.

Artist's conception of the surface of Proxima b.

Yesterday’s announcement of a newly discovered planet in the solar system closest to us has scientists excited, and with good reason. Proxima Centauri b is now the closest exoplanet yet found. In fact, it’s the closest that can be found outside of our solar system (give or take a few million kilometers).

Current data indicate that the planet, named Proxima b, is nearly the size of our own planet, with about 1.3 Earth masses. It orbits its faint central star, a red dwarf or M star, in 11.2 days. Given its orbital location, liquid water could be present on its surface. We have now detected close to 50 planets in the so-called “habitable zone” of their suns, but laudably, the authors chose more cautious wording, and said that the new planet is in a “temperate” orbit around Proxima Centauri.

This makes sense, as we cannot distinguish based on current data whether the planet may be like Mercury, Venus, or Earth, or perhaps unlike anything in our solar system. Proxima Centauri, like other M stars, emits strong solar flares and X-ray emissions that would make the origin of life challenging on the surface of a nearby planet. We don’t know about the initial water endowment of the planet around Proxima Centauri, but modeling (as reported in a paper posted just yesterday) indicates it should have lost less than an Earth’s ocean of water during its history. So if Proxima b originally received around the same amount of water that Earth did, there should still be plenty of water around, which increases the potential for life.

We also don‘t know whether the planet has a geomagnetic field to protect its surface from Proxima Centauri’s extreme radiation. This may be a critical factor for life, since it would be so close to the star. Other parameters have to be right for life to originate and evolve, as well, including the availability of organic compounds and the presence of an effective mechanism for recycling nutrients, such as plate tectonics.

Nevertheless, the discovery marks a significant step forward. A potentially habitable exoplanet so close to us will spur development of spectroscopic tools to probe whether the planet has an atmosphere, and if so, what type. It will also provide momentum to those thinking about ways to travel to the next solar system, as envisioned by the 100-Year Starship Initiative.

But don’t be fooled. I attended the first 100-Year Starship meeting and came away thinking that we are still light years from developing any type of warp drive, if that’s even possible. If we have to use today’s propulsion, we would quickly realize that 4.2 light years is a really, really long way to go. Anything in our solar system would seem a stone’s throw away in comparison.

I don’t mean to be a downer, though. This discovery is awe-inspiring, and at least for the short-term we can expect some good science-fiction movies. In the long-term we should gain more and more insight into our closest solar system, until some day, hopefully, we’re able to send a robotic probe to Proxima b—perhaps even in our lifetime.

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