[X] My Assistant

[djellison]

Looks quite Fram-ish

Doug

[ilbasso]

Any guesses as to the relative age of this crater (even relative to Eagle)? It looks "fresh" and well-defined from the MGS image, but there's a lot of sand inside the crater. Does that build up over thousands, or millions, of years?

Do we assume that the vast majority of the impact craters are very ancient? Obviously Vostok was a real old one. However, with Mars' proximity to the asteroid belt and thinner atmosphere relative to Earth, I would expect that there would be a lot more meteors the size of a car or house striking Mars every year and making craters this size.

Did we ever get a guesstimate on the age of the meteor near the heatshield? Had that one been sitting there for hundreds, or thousands, or millions of years?

[dvandorn]

Do we assume that the vast majority of the impact craters are very ancient? Obviously Vostok was a real old one.  However, with Mars' proximity to the asteroid belt and thinner atmosphere relative to Earth, I would expect that there would be a lot more meteors the size of a car or house striking Mars every year and making craters this size.

Did we ever get a guesstimate on the age of the meteor near the heatshield?  Had that one been sitting there for hundreds, or thousands, or millions of years?

First off, a meteor the size of a car would blast a crater a mile or more wide. A meteor the size of a house would blast a crater something like five to ten miles wide. Viking was made by a meteor more the size of your fist (by the time it impacted, anyway).

Secondly, the rovers don't carry the kind of equipment needed to come up with wild-ass guesses as far as absolute ages of rocks are concerned. There is no way at all of even guessing how old that meteorite was, or how old any of the rocks that have been analyzed are. (There is a good thread in the MSL category on the kinds of equipment needed to date rocks even close to accurately.)

Finally, I don't know that anyone has ever calculated the difference in the number of Mars-orbit-crossing objects and the number of Earth-orbit-crossing objects, but I'd be willing to bet that the difference is fairly minor. Over billions of years, the population of objects thrown towards the inner system from the asteroid belt has probably evened out and is relatively constant from the inner edge of the belt all the way in to the Sun.

You do make a decent point that Mars has a thinner atmosphere than Earth's, and therefore more smaller objects reach the ground there than here. But remember that a vast majority of the meteorites seen on Earth are the size of a grain of sand (or smaller), most of which are the remnants of broken-up comets -- which will burn up in Mars' atmosphere just as easily as they do in ours. And while there more fist-sized objects that reach Mars' surface than ours, I'm sure, I doubt the rate of impact is any higher than we see, say, on the Moon. And the seismometers we left on the Moon showed that such impacts are pretty rare -- only a very few were seen in the years the ALSEPs were operated. And only a single impact of a car-sized object was recorded on the Moon in those years. (Not counting man-made objects, of course.)

We really don't have good enough empirical data to characterize the meteor flux at Mars. I'd be willing to bet, though, that any crater at Meridiani where the rocks of the exposed evaporite layer are semi-rounded and have shed a bunch of concretions (as Viking appears in the images) wasn't made in the last few hundred years. A few hundred thousand to a few million, I'd buy...

-the other Doug