The Early Climate and Geologic Evolution of Mars
Alan D Howard
Department of Environmental Sciences
The resemblance of the Martian valley networks to terrestrial runoff channels, and their almost exclusive occurrence in the planet's ancient cratered terrain, has suggested to some that the networks are the relics of a substantially warmer and wetter greenhouse climate that may have existed throughout much of the Noachian (e.g., Craddock and Maxwell, 1993).
Additional support for this possibility is provided by the apparent deficit of craters with diameters < 30 km, and the poor preservation state of most large craters, within the intercrater plains (Hartmann, 1966). These observations have been cited as possible evidence of a dense early atmosphere that both warmed the early climate and accelerated the rates of fluvial and eolian erosion (Pollack et al., 1987).Skeptics of the warm early Mars hypothesis have noted the theoretical difficulty of creating and sustaining an atmospheric greenhouse sufficient to raise surface temperatures above 273 K - particularly in light of the early Sun's expected ~25% lower luminosity (Haberle, 1998).
Here we propose to explore another possibility: that the valley networks, as well as other frequently cited geomorphic evidence of a warm early Mars, are simply the byproducts of the geologic evolution of a water-rich planet - created by a variety of processes, including rainfall, that may have occurred under ambient global atmospheric and climatic conditions no different than those we observe on Mars today. Specifically, we propose to investigate how impact cratering (and, to a lesser extent, volcanism and tectonism) may have affected the geomorphic evolution of a water-rich Mars on the local, regional and global scale - focusing on the potential effects of impact-generated liquefaction and hydrothermal systems.
Our intent is to assess the extent to which these processes may have contributed to the morphologic evolution of the Noachian landscape, utilizing an enhanced landform evolution model (developed by Co-I Howard) in combination with atmospheric precipitation estimates derived from the NASA/Ames Mars General Circulation Model (GCM). The latter will be used to investigate the consequences of impact-generated hydrothermal systems (of various sizes) on both the atmospheric circulation and ultimate fate of released H2O - including the areal distribution, phase, duration and intensity of any resulting precipitation.
Through the application of these state-of-the-art tools, and the knowledge of our interdisciplinary team, we propose to pursue four tasks: (1) the development of physical, phenomenological, and empirical models to describe the first-order seismic and hydrothermal effects of large impacts; the investigation of the local, regional and global consequences of these processes using (2) the Ames GCM and (3) the landscape evolution model of Howard; and (4) by conducting morphometric analyses of the output of these simulations to determine how closely they reproduce the observed properties of the Martian valley networks and global topography.
This investigation is expected to yield important new insights regarding the extent to which geomorphic interpretation is capable of discriminating between a warm and cold early Mars (i.e., one with a long-lived, massive greenhouse atmosphere vs. one with ambient atmospheric and climatic conditions much like today, but subject to enormous local, regional and global perturbations due to impacts and other energetic geologic processes).
More information at www.evsc.virginia.edu
Project Sponsored By: Universities Space Research Association
Start Date: 3/1/2004
- End Date: 11/30/2004
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