An Earth-like stellar wind for Proxima Centauri c

Proxima Centauri is the closest star to the Sun and its planet, Proxima Cen b (“Proxima b”), is in its habitable zone (the distance range within which surface water can be liquid), making the planet a main target for exoplanet characterization. The star is a dwarf M with a mass of only 0.12 solar masses and an effective surface temperature of about 3000 Kelvin. The relatively low surface temperature means that its habitable zone is very close to the star and Proxima b, with its mass of about 1.2 Earth masses, is about twenty times closer to the star than the Earth is to the Sun , orbiting only 11.2. days. Being as close to its star as possible, Proxima b (like all habitable exoplanets around M dwarf stars) is susceptible to stellar flare, winds, X-rays and other types of activity that could disrupt its atmosphere and the possibilities of life. These activities are linked to the strong magnetic fields of M dwarfs and remain active in dwarf stars on much longer time scales than in higher-mass stars such as the Sun, so that cumulative exposures are proportionately greater. All these problems have been studied in detail for Proxima b; one conclusion, for example, is that it is likely subject to wind pressures ten thousand times greater than those exerted by the Sun on Earth.

A new planet was recently discovered in the Proxima Cen system, Proxima c, after astronomers identified slight variations in the orbital velocity of Proxima b (since it does not pass the star, its discovery was made by monitoring its velocity, not the curve of star light). Subsequent studies of Proxima c determined that it was a planet of about six Earth masses and orbited at 1.44 AU every 5.3 years, and is much further away from the star than Proxima b. (There are also hints of the presence of a third planet). CfA astronomers Jeremy Drake and Cecilia Garraffo, and their colleagues, have studied the effects that the star’s activity could have on the atmosphere of Proxima c.

Scientists built the most complete numerical simulation of the Proxima Cen system’s space environment that has been done to date, including models for the stellar corona and realistic surface magnetic field configurations during the star’s minimum and maximum activity states. Their results indicate that Proxima c experiences Earth-like conditions, at least in terms of stellar wind effects. It is not known whether Proxima c actually has an atmosphere, but the new models indicate that the conditions are not overly corrosive and are conducive to the persistence of any existing atmosphere.