Dating planetary surfaces

Martian mysteries Robbins and co-author Brian Hynek, also of CU Boulder, sifted through huge piles of data from a number of Mars orbiters and landers to compile the new database.

"I basically analyzed maps and drew crater rim circles for four years," Robbins said.

Some of them have orbits that cross the orbits of the planets and moons.

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“Knowing what it is makes me excited to see it every time,” Anderson says.

What Anderson wants from these far-flung fragments of the Solar System is elementary: their ages.

Terrestrial planets have hard surfaces that can be re-shaped by several different processes: impact cratering, volcanism, erosion, and tectonics.

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The craters on all of the moons except Io, Mercury, and most of the ones on Mars are from impacts.

The kinetic energy of the impacting meteorite or asteroid is converted into heat, sound, and mechanical energy---the projectile explodes on impact.

The authors tested dating by counting small craters in a variety of presumed “old” and “young” regions of the moon, and got widely divergent results despite using standard methods and software.

They urged a high degree of caution, therefore, when trying to infer the age of a planetary surface.

The bits of rock on Scott Anderson's shelf are not much to look at, but they have stories to tell.

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