Smaller and More Recent Features on Mars Can Now Be Dated

The crater-counting system that scientists have used since the 1970s to determine the age of large geologic features on Mars will also allow them to date small features, such as riverbeds and lava flows, according to William K. Hartmann, a senior scientist at the Tucson-based Planetary Science Institute.

Hartmann, who works out of PSI's Tucson office, presented the results of his study at the Division of Planetary Sciences meeting, which began yesterday and is running through Wednesday at Cornell University in Ithaca, N.Y.

Crater counting relies on the density, or crowding, of craters to determine the age of planetary surfaces. It works on the assumption that older landforms have been exposed for a longer periods and have been hit by more meteorites than younger surfaces.

While the method is widely recognized as valid for large, miles-wide craters, some scientists had questioned whether the rate at which small craters form is well enough understood and constant enough to be trusted in predicting the age of a landform.

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