Computer Science – Numerical Analysis
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u11b0031z&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U11B-0031
Computer Science
Numerical Analysis
5405 Atmospheres (0343, 1060), 5462 Polar Regions, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
The Phoenix lander touched down on May 25, 2008 at 68.16°N 233.35°E, an area that is fairly typical of the Vastitas Borealis plains. The high latitude regolith is a reservoir for substantial near-surface ground ice, and appears to play a significant role in the seasonal H2O cycle. The Phoenix landing site is within the circumference of the seasonal CO2 cap, and surface energy balance at the site is key to characterize in understanding the seasonal volatile cycles. Nighttime soil temperatures reach lows of ~ 203K at Ls = 98 -100°, dropping to 199K by Ls 107°. Maximum daytime temperatures are not measured directly, due to self-shadowing by the instrumentation on the end of the Robotic Arm. Numerical analysis suggests that peak temperatures at the visible surface may reach 265 K. The thermal inertia of the materials measured by Phoenix is considerably higher than observed from orbit, and appears to be out of thermal equilibrium with ground ice, which was excavated at depths of a few centimeters. Along with the detection of a visible dark halo around the Phoenix lander from HiRise, these results indicate that the pre-existing surface was heavily disturbed during landing. Atmospheric H2O is variable during the day, averaging just under 2 Pa. During the evening hours, the variability disappears, and the abundance of H2O tracks the falling temperatures. The temperature- dependent behavior begins long before either the soil or atmosphere reaches the frost point, which argues against H2O ice as the buffer. In addition, a plot of PH2O against the soil temperature yields an estimate of ΔH H2O = 30 kJ/mole, which is too low for the enthalpy of ice sublimation, but is characteristic of hydrogen bonds. Electrical conductivity measurements in the regolith detect no measureable changes associated with the exchange of H2O, but simultaneous dielectric permittivity measurements record abrupt discontinuities associated with the onset of adsorptive H2O scavenging. These data support the hypothesis that the Martian boundary layer collapses in the evening, and that the regolith adsorptively buffers the H2O content of the atmosphere overnight.
Cobos D.
Hecht Martin
Hudson Thomas
Milkovich S.
Smith Patrick
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