HR: 1340h
AN: P13A-0977    [Abstracts]
TI: The Long-Term Evolution of Transient Liquid Water on Mars
AU: * Mischna, M A
EM: michael.a.mischna@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S 183-401, Pasadena, CA 91109 United States
AU: Richardson, M I
EM: mir@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd. M/S 150-21, Pasadena, CA 91125 United States
AB: Liquid water is not currently stable on the surface of Mars but transient liquid water, generated by the melting of ice, may occur if surface temperatures are between the melting and boiling points and the surface pressure exceeds the triple point. Such conditions can be met on Mars with current-day surface pressures and obliquity due to the large diurnal range of surface temperatures, yielding the potential for liquid water. A general circulation model is used to undertake an initial exploration of the variation of this ``liquid water potential'' (LWP) for different obliquities and over a range of increased atmospheric CO$_{2}$ abundances representing progressively earlier phases of Martian geological history. At higher obliquities and slightly higher surface pressures ($<$50 mb) possible in the relatively recent past ($<$10$^{8}$ yr), the LWP conditions are met over a very large fraction of the planet. However, as the surface pressure is increased above about 50--100 mb, the increased atmospheric heat capacity and greenhouse effect reduce the diurnal surface temperature range, resulting in daytime temperatures rarely exceeding the melting point. This reduction of peak daytime temperatures below the melting point greatly reduces the possibility of even transient liquid water. The modeling presented here does not extend to a state of stable liquid water for early Mars---how Mars may have yielded a ``warm, wet'' early climate is currently an open research question. However, if Mars had an early ``warm, wet'' stage, then the potential for liquid water on Mars has not decreased monotonically from that state to the present day, as the atmosphere was lost. Instead, a distinct minimum in LWP will have occurred during the extended period for which pressures were in the middle range of about 0.1 and 1 bar. These results suggest that the current climate and recent paleoclimate may be more conducive for liquid water than paleoclimate states corresponding to much thicker atmospheres. The existence of this ``dead zone'' for liquid water, likely extending over a large fraction of Martian history has direct and restrictive implications for chemical weathering and life. The fundamental conclusion of this study is insensitive to invocation of brines and to more detailed treatment of atmospheric radiative processes.
DE: 5409 Atmospheres--structure and dynamics
DE: 5445 Meteorology (3346)
DE: 5450 Orbital and rotational dynamics
DE: 3344 Paleoclimatology
DE: 3319 General circulation
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting