Captain. We’ve found an M-Class Planet [Greg Laden's Blog]

The star that is nearest our own has a planet that could be habitable by Earthlings.

This is very important news.

The news comes to us from this research paper in Nature: A terrestrial planet candidate in a temperate orbit around Proxima Centauri by Guillem Anglada-Escudé, Pedro J. Amado, John Barnes, Zaira M. Berdiñas, R. Paul Butler, Gavin A. L. Coleman, Ignacio de la Cueva, Stefan Dreizler, Michael Endl, Benjamin Giesers, Sandra V. Jeffers, James S. Jenkins, Hugh R. A. Jones, Marcin Kiraga, Martin Kürster, Marίa J. López-González, Christopher J. Marvin, Nicolás Morales, Julien Morin, Richard P. Nelson, José L. Ortiz, Aviv Ofir, Sijme-Jan Paardekooper, Ansgar Reiners, Eloy Rodríguez, Cristina Rodrίguez-López, Luis F. Sarmiento, John P. Strachan, Yiannis Tsapras, Mikko Tuomi & Mathias Zechmeister.

Abstract:

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun’s closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.

Here’s why this is important. We knew that some stars that are like ours had Earth-like planets. How did we know that? Because we live on one. But how many Sun-like stars have Earth-like planets?

Trivially, we knew that all the known Sun-like stars had Earth-like planets. But that was with a sample size of one. We needed a larger sample size to estimate the actual percentage of Sun-like stars that had Earth-like planets.

Given that, consider the following question. We have a second Sun-like star. If it has no Earth-like planets, what do you think of the overall proportion of stars that have such planets? Perhaps you would guess 50-50, but the sample size is too small. Safer to simply guess, “maybe not many, because the first time we got to increment our sample size, we got nada.” Now, if it does have an Earth-like planet, what do you think of the overall proportion of stars that have such planets? Perhaps you would guess 100%, but again, the sample size is too small. But, you would safely say something like, “Well, hell, maybe a lot of them, because of the two where we have enough information to say … both have them!”

There really is no reasonable statistical way to treat this problem, but this sort of seat of the pants conjecture isn’t bad for now. But, if we were to have, say, five or six Sun-like stars to look at, we could start making real guesses.

There is a second reason. Now that we have an Earth like planet in our sights, perhaps there will be impetus for both funding and effort to squint really really hard at it and see if any life is there. Using fancy science, not actual squinting, of course.

Let us be clear. This planet is not Earth-like in that it has an atmosphere, water, or any sign of life. The planet might be locked in its orbit around its star in such a way that one side always faces that star. That would be bad for an atmosphere and for life. We don’t know if it has an atmosphere, or water. What we do know is that if water is on the surface, it might be liquid, and if an atmosphere ever formed there, maybe (though this is highly debatable) it did not necessarily get blown away into space or otherwise destroyed.

Nature made a video about the discovery:

For more information, check out these posts:

Phil Plait: Astronomers Discover a New Planet Orbiting the Closest Star to the Sun!

Mike Wall: Found! Potentially Earth-Like Planet at Proxima Centauri Is Closest Ever

Nature Podcast, an interview with the chief author: