Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.4902o&link_type=abstract
American Astronomical Society Meeting 210, #49.02; Bulletin of the American Astronomical Society, Vol. 39, p.162
Astronomy and Astrophysics
Astronomy
Scientific paper
Coronal mass ejections (CMEs) are expelled from the sun as the result of a magnetohydrodynamic process such as magnetic shear. They can reach speeds up to 2700 km/s, accelerating some fraction of the coronal and solar-wind particles they intercept to high energies by first-order Fermi shock acceleration. The largest such event of which we have detailed information is the event of September 29-30, known as ground-level event (or enhancement) 42 (GLE 42). The Earth’s atmosphere and magnetosphere protect terrestrial life from dangerous radiation effects, however, such is not the case on the surface of the planet Mars, given its current atmospheric mass of 15 g/cm2, and large solar-particle events, GLEs if they strike the planet Earth, could produce large radiation doses on the Martian surface.
The atmosphere of Mars appears to have lost considerable mass over time. Current escape rates of atmospheric constituents indicate that the Martian atmosphere 3.5 Gy ago had a surface pressure of about 1 bar, or a mass of about 2,600 g/cm2, two and a half times the mass of the current terrestrial atmosphere. Using a modified version of the adjoint Monte Carlo code ATROPOS, radiation doses to a small mass of tissue-equivalent material on the surface of Mars has been calculated on the assumption that 1) a solar-particle event identical to GLE 42 struck the surface, and 2) a solar-particle event the size of the 1859 Carrington event, with the same spectral shapes as GLE 42, struck the surface, as a function of the age of the Martian atmosphere.
In both cases, the CME was assumed to have a radius equal to the sun’s and lie one solar radius outside the sun.. The Martian atmosphere of 3.5 Gy ago offered considerable protection GLE 42 would have deposited less than one mrad, and the Carrington event, as modelled, would have deposited 15 mrad. In the case of the modern Martian atmosphere, GLE would have deposited about 2 krad (20 J/kg of body mass) and the Carrington event would have deposited about 30 krad (300 J/kg of body mass). Repeated events of this magnitude would clearly have a serious effect on life on or near the Martian surface.
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