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Science 4 July 2008:
Vol. 321. no. 5885, pp. 79 - 81
DOI: 10.1126/science.1159317
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Reports

Mercury Cratering Record Viewed from MESSENGER's First Flyby

Robert G. Strom,1* Clark R. Chapman,2 William J. Merline,2 Sean C. Solomon,3 James W. Head, III4

Morphologies and size-frequency distributions of impact craters on Mercury imaged during MESSENGER's first flyby elucidate the planet's geological history. Plains interior to the Caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages. Smooth plains exterior to Caloris exhibit a crater density ~40% less than on interior plains and are thus volcanic and not Caloris impact ejecta. The size distribution of smooth-plains craters matches that of lunar craters postdating the Late Heavy Bombardment, implying that the plains formed no earlier than 3.8 billion years ago (Ga). At diameters less than or equal to 8 to 10 kilometers, secondary impact craters on Mercury are more abundant than primaries; this transition diameter is much larger than that on the Moon or Mars. A low density of craters on the peak-ring basin Raditladi implies that it may be younger than 1 Ga.

1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
2 Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA.
3 Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA.
4 Department of Geological Sciences, Brown University, Providence, RI 02912, USA.

* To whom correspondence should be addressed. E-mail: rstrom{at}lpl.arizona.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
The Evolution of Mercury's Crust: A Global Perspective from MESSENGER.
B. W. Denevi, M. S. Robinson, S. C. Solomon, S. L. Murchie, D. T. Blewett, D. L. Domingue, T. J. McCoy, C. M. Ernst, J. W. Head, T. R. Watters, et al. (2009)
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Evolution of the Rembrandt Impact Basin on Mercury.
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Return to Mercury: A Global Perspective on MESSENGER's First Mercury Flyby.
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Reflectance and Color Variations on Mercury: Regolith Processes and Compositional Heterogeneity.
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Science 321, 66-69
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Volcanism on Mercury: Evidence from the First MESSENGER Flyby.
J. W. Head, S. L. Murchie, L. M. Prockter, M. S. Robinson, S. C. Solomon, R. G. Strom, C. R. Chapman, T. R. Watters, W. E. McClintock, D. T. Blewett, et al. (2008)
Science 321, 69-72
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Geology of the Caloris Basin, Mercury: A View from MESSENGER.
S. L. Murchie, T. R. Watters, M. S. Robinson, J. W. Head, R. G. Strom, C. R. Chapman, S. C. Solomon, W. E. McClintock, L. M. Prockter, D. L. Domingue, et al. (2008)
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