Sunday, August 15, 2010

Gullies at the Edge of Hale Crater

Several years ago gullies carved into hill-slopes and the walls of impact craters like the ones pictured here were discovered. Scientists are excited to study these features because, on Earth, they usually form through the action of liquid water - long thought to be absent on the Martian surface. Whether gullies form under today's cold dry conditions is a major question that planetary scientists are trying to answer.

The gullies pictured here are great examples of what a typical Martian gully looks like. You can see wide V-shaped channels running downhill (from top to bottom) where the material that carved the gully flowed. At the bottom of the channel this material empties out onto a fan-shaped mound. Several gullies are visible here and the fans from each gully overlap one other in complicated ways.

At the tops of the channels, large amphitheater-shaped alcoves are carved in the rock. The material removed from these alcoves likely flowed downhill to the aprons through the gullies.

Gullies at this site are especially interesting because scientists recently discovered examples at similar locations to be still active. Images separated by several years showed changes in the appearance of some of these gullies. Today, planetary scientists are using the HiRISE camera to examine gullies for ongoing change and investigate what that might mean for the occurrence of liquid water on the surface of Mars.

Photo credit: NASA/JPL/University of Arizona

Note: Hale Crater is located in the massifs north of Argyre Planitia.

1 comment:

Herbert Highstone said...

What really happens when liquid water is released into a vacuum and flows down a dirt slope? Nobody has actually tried this, so let's do the experiment. We have large vacuum chambers here on earth that can be pumped down to the atmospheric pressure of Mars. Let's build a few dirt slopes in such a chamber, pull a vacuum, and then dump some water down these slopes. Maybe we can match the Mars gullies by doing this, or maybe we can't, but in either case the results will be highly interesting. In fact, somebody could make a very good Ph.D. thesis out of this idea. Will it be you?
Herbert in Oakland California