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Teresa L. Segura,1*Owen B. Toon,1Anthony Colaprete,2Kevin Zahnle2
The martian valley networks formed near the end of the
period of heavy bombardment of the inner solar system, about 3.5 billionyears ago. The largest impacts produced global blankets of veryhot ejecta, ranging in thickness from meters to hundreds of meters.Our
simulations indicated that the ejecta warmed the surface,keeping it
above the freezing point of water for periods rangingfrom decades to
millennia, depending on impactor size, and causedshallow subsurface or
polar ice to evaporate or melt. Large impactsalso injected steam into
the atmosphere from the craters or fromwater innate to the
impactors. From all sources, a typical 100-,200-, or
250-kilometers asteroid injected about 2, 9, or 16 meters,respectively, of precipitable water into the atmosphere, whicheventually rained out at a rate of about 2 meters per year. Therains
from a large impact formed rivers and contributed to rechargingaquifers.
1 Program in Atmospheric and Oceanic Sciences,
Laboratory for Atmospheric and Space Physics, University of Colorado,
Campus Box 392, Boulder, CO 80309-0392, USA.
2 NASA-Ames Research Center, MS 245-3, Moffett
Field, CA 94035, USA.
*
Present address: NASA-Ames Research Center, MS 245-3, Moffett
Field, CA 94035, USA.
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[DOI: 10.1126/science.298.5600.1866a] |Summary »|Full Text »|PDF »
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