Vol. 596
In section 10. Planets and planetary systems

The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present

by I. Ribas, E. Bolmont, F. Selsis, et al. A&A 596, A111

The habitability of Proxima Centauri b. II. Possible climates and Observability

by M. Turbet, J. Leconte, F. Selsis, et al. A&A 596, A112


The discovery of a planet orbiting around Proxima Centauri, our closest neighbor, is in itself a significant breakthrough. The fact that the planet has a minimum mass of only 1.3 times that of our Earth and is at approximately the right distance from its star for water to be liquid at the surface makes it even more special. In two papers, Ribas et al. and Turbet et al. examine the conditions for so-called “habitability" of this planet: could liquid water be present on its surface?

In the first paper, Ribas et al. show that the planet, Proxima b, should be either synchronously rotating, or in a 3:2 resonance between its spin and orbit as Mercury is. They also show that it should have lost less than an Earth's ocean worth of hydrogen by atmospheric escape: Thus, depending on the initial water content of the planet, it may still possess water on its surface.

In the second paper, Turbet et al. use a 3D global climate model to simulate Proxima’s b climate and water cycle. They find that a broad range of compositions allow surface liquid water, and they present reflection and emission spectra, and phase curves for the simulated climates. The observation of thermal phase curves can be attempted with JWST. They conclude that within a decade we should know whether Proxima is indeed habitable.