A few months ago Proxima Centauri b, an exoplanet in the constellation of Centaurus located “only” 4.22 light-years from Earth, got a lot of attention, since it orbits its sun within the habitable zone and will be probably the first in the target list in the search for alien life.
The studies have continued since then, focussing especially on observing the planet’s climate. The parent star itself is an M-dwarf star with a mass about one-tenth the Sun’s mass and a luminosity about one-thousandths of the Sun’s; this makes the planet’s habitable zone twenty times closer than the Earth’s is to the Sun, exposing it, however, to hazards like extreme UV, and X-rays and heavy stellar wind – with pressures of 2,000 times more than the Sun and resulting into an uncomfortable experience for life. However, there’s evidence that the surface might even be liquid water instead of rocks and dust only.
This is, at least, what a recent paper, appeared on Astronomy & Astrophysics, suggests.
“We present results of simulations of the climate of the newly discovered planet Proxima Centauri B, performed using the Met Office Unified Model (UM). We examine the responses of both an ‘Earth-like’ atmosphere and simplified nitrogen and trace carbon dioxide atmosphere to the radiation likely received by Proxima Centauri B. Additionally, we explore the effects of orbital eccentricity on the planetary conditions using a range of eccentricities guided by the observational constraints. Overall, our results are in agreement with previous studies in suggesting Proxima Centauri B may well have surface temperatures conducive to the presence of liquid water. Moreover, we have expanded the parameter regime over which the planet may support liquid water to higher values of eccentricity (& 0.1) and lower incident fluxes (881.7 W m−2 ) than previous work. This increased parameter space arises because of the low sensitivity of the planet to changes in stellar flux, a consequence of the stellar spectrum and orbital configuration. However, we also find interesting differences from previous simulations, such as cooler mean surface temperatures for the tidally-locked case. Finally, we have produced high resolution planetary emission and reflectance spectra, and highlight signatures of gases vital to the evolution of complex life on Earth (oxygen, ozone and carbon dioxide).” [ From Boutle et al., 2017, “Exploring the climate of Proxima B with the Met Office Unified Model”, Astronomy & Astrophysics, available at https://arxiv.org/pdf/1702.08463.pdf]
M dwarf-types are the most abundant type of stars, and their small radii make them easier targets (relatively speaking) to spot transiting exoplanet signatures: this explains the great interest in Proxima Centauri.