Suggested Searches

The illustration shows radiation from flares from a red dwarf eroding the atmosphere of an orbiting, rocky planet.

h-867-barnards_star_ill

Recent work has demonstrated that high levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape on temperate, terrestrial planets orbiting within the habitable zone. However, secondary atmospheres on planets orbiting older, less active M dwarfs may be stable and present more promising candidates for biomarker searches. In order to evaluate the potential habitability of Earth-like planets around old, inactive M dwarfs, we present new Hubble Space Telescope and Chandra X-ray Observatory observations of Barnard’s Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part of the Mega-MUSCLES program. Despite the old age and long rotation period of Barnard’s star, we observe two FUV (δ130 ≈ 5000s; E130 ≈ 1029.5 erg each) and one X-ray (EX ≈ 1029.2 erg) flares, and estimate a high-energy flare duty cycle (defined here as the fraction of the time the star is in a flare state) of ∼ 25%. A 5 ˚A – 10 µm spectral energy distribution of GJ 699 is created and used to evaluate the atmospheric stability of a hypothetical, unmagnetized terrestrial planet in the habitable zone (rHZ ∼ 0.1 AU). Both thermal and non-thermal escape modeling indicate (1) the quiescent stellar XUV flux does not lead to strong atmospheric escape: atmospheric heating rates are comparable to periods of high solar activity on modern Earth, and (2) the flare environment could drive the atmosphere into a hydrodynamic loss regime at the observed flare duty cycle: sustained exposure to the flare environment of GJ 699 results in the loss of ≈ 87 Earth atmospheres Gyr−1 through thermal processes and ≈ 3 Earth atmospheres Gyr−1 through ion loss processes, respectively. These results suggest that if rocky planet atmospheres can survive the initial ∼ 5 Gyr of high stellar activity, or if a second generation atmosphere can be formed or acquired, the flare duty cycle may be the controlling stellar parameter for the stability of Earth-like atmospheres around old M st

Download