Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p31b0204k&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P31B-0204
Mathematics
Logic
5405 Atmospheres (0343, 1060), 5415 Erosion And Weathering, 6225 Mars
Scientific paper
Climate change on Mars during the Amazonian is thought to be driven by intrinsic climate instabilities, astronomical climate forcing (change of obliquity of the spin axis, eccentricity of the orbit, and season of the perihelion), catastrophic events (large meteoritic impacts, outflows, large volcanic eruptions), secular increase of the Sun luminosity, and loss of volatiles. Neither these factors nor their effects on the climate system can be calculated accurately. For example, calculations of the astronomic forcing are not predictive due to the chaotic nature of the Solar System dynamics; the secular evolution of volatile inventory is poorly constrained; the atmospheric pressure response to the obliquity increase is not known. These and many other questions of the climate history are addressed to the geological record. Here we infer two new general constraints of this kind. (1) We have found a strong asymmetry of steep north - south slopes in mid-latitude zones of Mars. This asymmetry has been attributed to the enhanced erosion of pole-facing slopes due to seasonal freezing and thawing cycles at extremely high obliquities. The asymmetry indicates that the day-average temperature of tilted surface was sensitive to the local insolation, which means that the thermal coupling between the surface and the atmosphere was minimal and hence the atmospheric pressure was not high even at maximal obliquity. The same conclusion follows from the absence of any apparent elevational trend of steep slope occurrence. (2) We have systematically studied morphology and morphometry of 10-25 km craters in the Northern Lowlands. These craters were accumulated through the whole Amazonian. Among these craters, all craters with steep or moderately steep walls have recent gullies that effectively erode the walls. All craters, however, including the oldest, have well preserved rims. This indicates that the total amount of erosion through the Amazonian was not large, which means that climate conditions favorable for gullies formation occurred rather infrequently. This may be the case, if the high obliquity periods occurred infrequently, especially in the Late Amazonian, when the Sun luminosity was maximal. Alternatively, the recent gullies may be related to some rare event.
Head James
Kreslavsky Mikhail
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