[X] My Assistant

[Bill Harris]

Finally, Spirit's making some progress towards Larry's Leap. It'll be refreshing to see different topography for a change.

One item I'm curious about and I've seen only a few messages here on it. What is the general concensus here about the feature called the "Ultreya Abyss"? The orbital images don't show much: there _is_ a low albedo feature there but I can't say that it is a opening. Early in the mission, I recall that Spirit was to go to Ultreya after contacting the West Spur but those plans changed by the time she got to Columbia Hills. I imagine that the planners wanted something different than the basaltic plain and wanted to examine layered exposures.

--Bill

[dvandorn]

My own personal opinion, at this point, is that Ultreya represents an ancient impact into the land that now makes up the Columbia Hills. It's a roughly circular depression, and while there are several ways to make those on Mars, by far the most common is impact cratering.

The next question is, why is there so much dark material in this depression, and why does it seem to sweep out of a linear contact along the north-northwest edge of Ultreya? My best guess is that the Ultreya impact excavated a bed of very dark material (either a continuous bed that is also exposed a few other places in the Hills, or a relatively small dark deposit). Wind comes in to the depression, swirls around in a clockwise direction, and over millions of years has eroded the very dark dust from this contact and strewn it along feather-like arcs toward the east-southeast.

So, I am *really* looking forward to seeing the side of Ultreya that will remain obscured the longest... because that's where this contact appears to be located.

-the other Doug