(Editor: BTW is it the 26th anywhere on the Earth? PST 3/22/05)

Crater count led Mars historians astray
26 March 2005
NewScientist.com news service
David L. Chandler

THE method used by planetary scientists to estimate the ages of various regions of Mars is flawed.

"This really changes things," says Nadine Barlow of Northern Arizona University in Flagstaff. For instance, the findings will significantly change our understanding of when Mars may have been volcanically active.

To estimate the age of any region on Mars, geologists count the number of meteor craters they can see in images of the area. The idea is that the older a surface, the more craters should have accumulated over time. Crater counts give an indication of the relative age of different Martian regions.

To determine absolute ages, these counts are then compared with crater counts from regions of the moon, some of which have been precisely dated thanks to the rocks brought back by the Apollo astronauts. Assuming that the rate of meteor impacts at any given time was roughly uniform throughout the inner solar system, those ages should translate directly to Mars.

More at: http://www.newscientist.com/channel/space/mg18524925.100