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Breezing through the Space Environment of Barnard’s Star b

posted Mar 5, 2020, 6:18 AM by Jeremy Drake
The discovery of a planet orbiting the nearby - at 6 light years - red dwarf called Barnard's Star was a major step in our growing understanding that planetary systems around stars are the norm rather than the exception. Named after Yerkes Observatory astronomer E. E. Barnard, who first noted its high "proper motion" across the sky, the star is the fourth nearest known star to the Sun, after the three members of the Alpha Centauri system.  It's planet, Barnard’s Star b, orbits at a distance similar to that of Mercury around the Sun, but just outside of the supposed "habitable zone" of the faint red dwarf where liquid water is thought sustainable. Nevertheless, the relatively low magnetic activity level and attendant atmosphere-removing X-ray and EUV flux of Barnard's star has raised questions as to whether an atmosphere might exist on the planet.

Stellar winds are also known to be destroyers of planetary atmospheres - the loss of water from early Mars due to solar wind erosion being a good example. We therefore decided to examine the likely "space weather" around Barnard's Star. Supercomputer magnetohydrodynamic stellar wind models were simulated using Barnard's Star stellar parameters and likely surface magnetic field configuration. The results were described in a paper jointly lead by Smithsonian Astrophysical Observatory scientists Julian Alvarado-Gomex and Cecilia Garraffo and published in the 2019 April edition of the Astrophysical Journal.

Barnard’s Star b experiences less intense wind pressure than the much more close-in planet Proxima b, and the planets of the TRAPPIST-1 system, with space weather conditions not too much more extreme than experienced by Earth. The milder wind conditions are more a result of its much greater orbital distance rather than in differences in the surface magnetic field strengths of Proxima and Barnard's Star. Can Barnard's Star b still retain an atmosphere? Possibly. However, it should be recalled that the planetary system is old at possibly up to 10 Gyr, or twice the age of the solar system. Barnard's star would have been much more active in its first billion years or so and it is during that era that the atmosphere of Barnard's Star b would truly have been under assault from its host star.