Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusm.p41a..10w&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #P41A-10
Other
1621 Cryospheric Change (0776), 3305 Climate Change And Variability (1616, 1635, 3309, 4215, 4513), 3322 Land/Atmosphere Interactions (1218, 1631, 1843), 5220 Hydrothermal Systems And Weathering On Other Planets, 6225 Mars
Scientific paper
We present a modeling study of a mechanism that has not previously been considered but is likely to have generated significant subsurface warming during the periodic intervals when Mars' obliquity was lower than 25°. Orbital dynamics calculations show that Mars' obliquity, which is currently 25°, oscillates between 10° and 45° - with a dominant periodicity of ~120,000 years and a modulation period of ~1.3 million years - due to long-term perturbations by the other planets [1]. The present Martian atmosphere is 95% CO2 with a mean surface pressure of 6 mbar, but model calculations [2] show that it could drop to as low as 0.3 mbar at low obliquity because the global surface pressure would be controlled by the annual-average temperature of the perennial CO2 ice at the poles [3]. At such low pressures, the thermal conductivity of a porous regolith can be significantly reduced as the mean free path of gas molecules approaches the size of pore spaces [4]. This decreased conductivity leads to increased subsurface temperatures as the geothermal gradient steepens to maintain a constant internal heat flux (estimated to be ~ 30 mW/m2). We have performed model simulations of the resulting time evolution of subsurface temperatures, ground ice, and adsorbed volatiles. This mechanism could explain many of the geomorphological features attributed to liquid water without invoking a thicker atmosphere or increased geothermal heat flow. [1] Laskar, J. et al., Icarus 170, 343-364, 2004. [2] Manning, C. V. et al., Icarus 180, 38-59, 2006. [3] Toon, O. B., et al., Icarus 44, 552-607, 1980. [4] Presley, M. A. and P. R. Christensen, JGR 102, 6535-6549, 1997.
Griffiths S. G.
Wood Stephen E.
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