Many of our galaxy’s suns have destroyed the atmospheres of orbiting Earth-like planets—or so astrobiologists have long feared. But a new study of one of the msot violent outburst from such stars,  indicates that these planets may be unexpectedly shielded from solar activity, keeping life safe.

The Milky Way, they note, is dominated by M dwarf stars: violent, unpredictable suns that frequently hurl high-energy particles and solar flares into space. Because they are much cooler than our sun, any potentially habitable planet would need to orbit them much closer than Earth does, putting it smack in the danger zone. But a new study from NASA's Virtual Planetary Laboratory Team indicates that these planets may be unexpectedly shielded from solar activity, keeping life safe.

They studied the impact of the 1985 April 12 flare from the M dwarf, AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect we estimated a proton flux associated with the flare  for particles  with energies >10MeV. Then they calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the “Carrington event”.

The simulations were performed using a one-dimensional (1D) photochemical model coupled to a 1D radiative/convective model. The results indicate that the ultraviolet radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reached a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 seconds.

Flares may therefore not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically-active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity.

Source: NASA NAI

Further reading: arXiv