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      The case for rainfall on a warm, wet early Mars : RAINFALL ON MARS

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      Journal of Geophysical Research: Planets
      American Geophysical Union (AGU)

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          Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life.

          Sources of organic molecules on the early Earth divide into three categories: delivery by extraterrestrial objects; organic synthesis driven by impact shocks; and organic synthesis by other energy sources (such as ultraviolet light or electrical discharges). Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources. Which sources of prebiotic organics were quantitatively dominant depends strongly on the composition of the early terrestrial atmosphere. In the event of an early strongly reducing atmosphere, production by atmospheric shocks seems to have dominated that due to electrical discharges. Organic synthesis by ultraviolet light may, in turn, have dominated shock production, but only if a long-wavelength absorber such as H2S were supplied to the atmosphere at a rate sufficient for synthesis to have been limited by ultraviolet flux, rather than by reactant abundance. In the apparently more likely case of an early terrestrial atmosphere of intermediate oxidation state, atmospheric shocks were probably of little importance for direct organic production. For [H2]/[CO2] ratios of approximately 0.1, net organic production was some three orders of magnitude lower than for reducing atmospheres, with delivery of intact exogenous organics in interplanetary dust particles (IDPs) and ultraviolet production being the most important sources. At still lower [H2]/[CO2] ratios, IDPs may have been the dominant source of prebiotic organics on the early Earth. Endogenous, exogenous and impact-shock sources of organics could each have made a significant contribution to the origins of life.
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            A detachment-limited model of drainage basin evolution

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              Evidence for recent groundwater seepage and surface runoff on Mars.

              Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs.
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                Author and article information

                Journal
                Journal of Geophysical Research: Planets
                J.-Geophys.-Res.
                American Geophysical Union (AGU)
                01480227
                November 2002
                November 2002
                : 107
                : E11
                : 21-1-21-36
                Article
                10.1029/2001JE001505
                1f719b1c-fadc-44e2-8c9d-a17c21138d92
                © 2002

                http://doi.wiley.com/10.1002/tdm_license_1.1

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