Author(s): E.F. Guinan, S. Engle, Astrophysics and Planetary Science, Villanova University, Glen Mills, Pennsylvania, UNITED STATES|I. Ribas, Institut de Ciències de l’Espai (ICE, CSIC),, Bellaterra, Pennsylvania, SPAIN|
Institution(s): 1. Astrophysics and Planetary Science, Villanova University, Glen Mills, PA, United States. 2. Institut de Ciències de l’Espai (ICE, CSIC),, Bellaterra, Spain.
Contributing team(s): (none)
Barnard’s Star (GJ 699) is a dim old red dwarf M4 V star. At 6 LY it is the 2nd nearest star system. Until recently Barnard Star’s claim to stardom is having the largest proper motion (mu = 10.4”/yr). Adding to its fame, Ribas et al. (2018 Nature 563, 365) recently found that Barnard’s Star hosts a super-Earth exoplanet (Mp sini = 3.2 Me). Barnard b has an orbital period of 233-d and semi-major axis of a = 0.40 au- i.e. at the same distance of Mercury from the Sun. However Barnard’s Star is very dim (Lbol = 0.0033Lo) thus Barnard b with an irradiance (relative to the Earth) of S/Se ~0.020 and thus it is cold (-170 C). So that there is little chance of liquid water and life on its frigid surface. Barnard’s Star is a founding member of the Villanova Living with a Red Dwarf program (Engle & Guinan 2011, ASPCS 451) From photometry started in 2003 we determined a rotation period of Prot = 142+/-8 days. Utilizing our Period-Age relation for red dwarfs (Engle & Guinan 2018 RNAAS 2, 34) indicates an age of 8.5+/-0.9 Ga. This gyro-chronological age agrees well with other age indicators that include large UVW space motions and low chromospheric Ca II HK and coronal X-ray emissions. From the available X-ray and UV data, we compute the X-ray and UV irradiances of the planet. All hope for life on Barnard b may not be lost. As a super-earth, if not too massive, Barnard b could have a large hot (iron?) core and possibly enhanced geothermal activity. Geothermal heating could support “life zones” under its surface. We note that the surface temperature on Jupiter’s icy moon Europa is similar to Barnard b but because of tidal heating Europa probably has liquid oceans under its icy surface. However, if the actual mass of the Barnard b is much higher than ~5 Me, its higher gravity could result in a thick H-He atmosphere and thus be a dwarf gas giant / mini-Neptune. The angular separation of the Barnard b from its star is ~220 mas. Although very faint, it may be possible for the planet to be imaged by future very large telescopes. Such observations will shed light on the nature of the planet’s atmosphere/surface and potential habitability. This research is supported by grants from NASA that we gratefully acknowledge.