Planetary surfaces

Abstract:

Physical weathering induced by heating and cooling may cause rock breakdown on Mars and Earth. We report results from parallel weathering simulations on basalt blocks exposed to diurnal cycles representing Mars-like (two simulation runs from -55 to +20 ^oC and -75 to +10 ^oC, 1-100% relative humidity, 4-8 mbar pressure, CO2 atmosphere) and hot arid Earth (23-72^o C, 30-100% relative humidity) conditions. Under Earth conditions, thermally pre-stressed blocks showed measurable strength declines, whilst salt pre-treated blocks showed strength gains. Under Mars-like conditions, pre-stressed blocks recorded greater or similar strength declines and salt pre-treated blocks showed more muted strength declines than under Earth conditions. The results imply that on Earth and Mars diurnal cycling of temperature alone can cause deterioration of basalt with a pre-existing stress history. The type of stress history is important, with salt pre-treatment affecting the response of thermally pre-stressed blocks under both Earth and Mars conditions. Copyright © 2010 by the American Geophysical Union.

Abstract:

The first Martian year and a half of observations by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter has revealed new details of the thermal structure and distributions of dust and water ice in the atmosphere. The Martian atmosphere is shown in the observations by the Mars Climate Sounder to vary seasonally between two modes: a symmetrical equinoctial structure with middle atmosphere polar warming and a solstitial structure with an intense middle atmosphere polar warming overlying a deep winter polar vortex. The dust distribution, in particular, is more complex than appreciated before the advent of these high (∼5 km) vertical resolution observations, which extend from near the surface to above 80 km and yield 13 dayside and 13 nightside pole-to-pole cross sections each day. Among the new features noted is a persistent maximum in dust mass mixing ratio at 15-25 km above the surface (at least on the nightside) during northern spring and summer. The water ice distribution is very sensitive to the diurnal and seasonal variation of temperature and is a good tracer of the vertically propagating tide. Copyright 2010 by the American Geophysical Union.