Spectrum of Atomic Carbon Produced in Photodissociation of CO on Mars: Implications for Atmospheric Evolution

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Photodissociation of CO proceeds via line absorptions into predissociating states between the photodissociation threshold at 111.8 nm and 88.9 nm, and by continuum absorption shortward of 88.9 nm. The atoms produced may be very energetic. Photodissociation has been shown to be an important source of C on Venus and Mars, and on Mars it is an important source of escaping carbon. At moderate solar activity, photodissociation is comparable to dissociative recombination of CO+ as a source of escaping C, and to sputtering, as computed by other investigators. We present here calculations of the energy distributions of C produced in photodissociation near the exobase of Mars at both high and low solar activities. Although the spectrum of C peaks near 1 eV, carbon atoms with energies of up to 5 eV are produced, and a significant fraction have energies in excess of the escape energy of about 1.47 eV at exobase altitudes. We also present estimates of the total escape fluxes due to this source and to other non-thermal sources, and the implications for the escape of carbon from Mars, and to the time evolution of the atmosphere.


Presented at the 32nd Annual Meeting of the Division of Planetary Sciences (DPS) of the American Astronomical Society, Pasadena, CA.

Presentation Number 51.24.

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