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January 9th, 2015: Can impact craters provide reliable surface ages on the Moon and Mars?

Posted on Jan 4, 2015 in Seminars

Jean-Pierre Williams (UCLA)

Impact craters can be used to estimate the age of a planetary surface, given knowledge of the rate of crater accumulation, and is the primary method for age dating planetary surfaces (excluding Earth). Radiometric and cosmic ray exposure ages of Apollo and Luna samples, correlated with crater populations, anchor the lunar crater chronology and provide predicted size-frequency distributions (SFD) of crater populations for a given surface age. These predicted SFDs are scaled to Mars, accounting for the ratio of meteoroids at the top of the martian atmosphere relative to the Moon and the differences in gravity and average impact velocities of intersecting orbits. Crater derived age estimates have been called into question in the last decade as it has been recognized that secondary craters formed by debris ejected by primary impact events, may constitute a large fraction of the observed craters, thus contaminating the statistics. Images from the Mars Reconnaissance Orbiter have been used to identify fresh craters that have formed over the last 10 years providing the first direct observation of the present-day primary impact crater SFD at small crater diameters on Mars. Additionally, new high-resolution images from the Lunar Reconnaissance Orbiter provide the ability to study crater populations on the Moon in greater detail. What these new observations reveal about crater populations and how they relate to surface ages will be discussed.