HR: 0800h
AN: P21A-0218    [Abstracts]
TI: Explaining Meridiani Planum: The Modeled Frequency and Spatial Extensiveness of Episodes Warm Enough to Allow Ponding in Hesperian Mars
AU: * Manning, C V
EM: cmanning@astro.berkeley.edu
AF: Department of Astronomy Curtis V. Manning, 600 Campbell Hall University of California, Berkeley, CA 94720 United States
AU: * Manning, C V
EM: cmanning@astro.berkeley.edu
AF: Nasa-Ames Reserch Center, MS 245-3 Moffett Field, Mountain View, CA 94035-1000 United States
AU: McKay, C P
EM: cmckay@mail.arc.nasa.gov
AF: Nasa-Ames Reserch Center, MS 245-3 Moffett Field, Mountain View, CA 94035-1000 United States
AU: Zahnle, K J
EM: Kevin.J.Zahnle@nasa.gov
AF: Nasa-Ames Reserch Center, MS 245-3 Moffett Field, Mountain View, CA 94035-1000 United States
AB: We have compounded a model of the evolution of Mars' inventories of CO$_2$ over its lifetime [1] in an effort to understand the likely path of evolution of Mars' climate from an apparently wet early Hesperian [2], suggestive of a large inventory of free CO$_2$, to what is expected to be a very low CO$_2$ inventory at present. Here we investigate the opportunity for diurnally averaged temperatures greater than the melting point of water on Mars during the Hesperian by utilizing sub-seasonal insolation patterns, especially during periods with high eccentricity. While recent MER Opportunity observations suggest an extensive body of water [2], observations of Hesperian valley networks suggest they are immature [3]. Hypsometric analysis [4] confirms that martian drainage basins are systematically different from terrestrial drainage basins, with very little erosion. The immaturity of martian drainage basins suggests they were formed by infrequent episodic fluvial action. Our evolutionary model was used to investigate the frequency of such episodes by incorporating obliquity and eccentricity variations consistent with recent Laskar et al. findings [5]. We develop a measure of the trend in the frequency of ponding by calculating the area-normalized fraction of degree-days above 273 K over 10 Myr time bins. Models that produce ponding in the Hesperian and reproduce the atmospheric pressure of the present show a rapid decline in ponding during the Hesperian, a result of sequestration of CO$_2$ into carbonate rocks. {\bf References} [1] Manning, C. V., et al. (2004) \emph{Icarus} submitted [2] Hynek, B. M. (2004) \emph{Nature} {\bf 431}, 156. [3] Irwin, R. et al. (2004) \emph{LPI Conf.} {\bf 35}, 1991. [4] Stepinski, T. F., (2004) \emph{JGR} {\bf E18}, 2005 [5] Laskar, J. et al. (2004) \emph{Icarus}, {\bf 170}, 343.
DE: 5407 Atmospheres--evolution
DE: 5415 Erosion and weathering
DE: 5418 Heat flow
DE: 5420 Impact phenomena (includes cratering)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting