Mars rover meteorite find

Sylvia Else wrote:

From the article it appears the dating is based on the fact that the
meteorites managed to land intact, and without creating large craters.
The implication is that they landed when Mars had a thicker atmosphere
than it does now. While the 3 billion number may look overly precise,
the event could hardly be geologically recent unless you can find a
mechanism that would have recently thinned Mars's atmosphere.

One person commenting on it had a interesting theory that neatly
explained both why it survived entry and why it's just sitting around
intact on the surface, rather than having made a crater; they suggested
that the meteorite had landed on either water or CO2 ice which had later
sublimated into the Martian atmosphere, in a process similar to the way
Antarctic meteorites are found sitting on the ground at the base of
melting glaciers.
Given that the Martian axis of rotation has apparently wandered all over
the place in its past due to the lack of a large moon to keep its poles
stable in relation to the planet's surface in the way Earth's moon does,
the meteorite may have fallen onto one of the polar caps, only to have
the pole migrate away from under it as time passed, leaving it sitting
on bare ground. Snow and ice (water or CO2) could have cushioned the
impact enough to prevent it from breaking up on impact even at low
atmospheric pressures.
Another interesting thought is that instead of falling in from deep
space, the meteorite may have decayed out of Martian orbit, as several
ovoid craters on the Martian surface are thought to be the impact points
of small decaying Martian moonlets (impactors have to hit at a very
shallow angle to create anything other than a circular crater) and it is
suspected that in another 50 million years Phobos is going to come
flying out of the Martian sky also.

Pat