Geologic story of landing site

Ron Greeley video
Ron Greeley audio

The geology of the landing site is extremely complex. We see an interaction of processes. Obviously we see the results of the flood--the rounded boulders. But we also see the work of the wind. We see the soil that has been shaped and molded by the wind. We see rocks that have been sculpted by the wind. Other rocks that have been sandblasted and have their faces on one side, the up wind side, swept free. All of this means that wind is a very active process, in fact it's probably the dominant process shaping the current surface. In addition to this we see rocks that are probably ejecta from impact craters, material that has been thrown in from impact craters. The closest one is a little over a mile away and its thrown in ejecta blocks that are littering the site in addition to the stream-washed boulders.

Matt Golombek audio

Well, it's almost perfect. Here's this site that we thought would look pretty much the way it did. We thought from the remote sensing data that it would be less dusty than Viking I, and it certainly seems to be the case. There are many more rocks that are darker and deeper in blue and appear less dust covered. And in fact, we kind of predicted what the site would look like from the analog that I described, as well as the Viking orbital images and other remote sensing tools such as the thermal inertia and the Earth-based radar data from this site. And so that's one of the strongest things. We found a place that we were able to infer from the remote sensing data at a scale that's wildly different from what you see down on the surface. Down on the surface, you're seeing centimeters- and meters-scale things, and from orbit you're seeing kilometers-scale things, if you will. That's remarkable and unbelievable that we were so fortunate. In addition, we found an area that had much more relief than either of the Viking sites. We have hills on the horizon and that allowed us to locate ourselves in the Viking images within a day. And it took Viking I a year to do that. And in Viking II, they were never able to locate themselves because it was so flat and fairly featureless.

Now, what we really wanted at the landing site was a grab-bag sweep, a diversity of rock types. It's too soon to tell. It looks like there is a variety of rocks there, but we don't have enough of them with the APXS yet to really tell whether, in fact, that has borne out. We certainly see indications that there are a variety of different rocks. There are textures and fabrics and things that indicate they might be different, but we don't know yet. We certainly have a variety of different soil materials. We see those. There are different colors and textures. Even though the composition seems to be remarkably similar, it looks like we have a much wider diversity of soil than we saw at either of the two Viking sites.

So I'm very gratified that the site is kind of like what we expected. It's, again, among the rockier places on Mars. About 18% of the surface is covered with rocks, which is fairly similar to Viking II, although the distribution of those rocks probably looks a little different. It is a rocky area; that's what we wanted. There are lots of rocks there; that's what we wanted. They are not dust-covered; that's what we wanted. We wanted an area that was tractable by the rover, and we got it. All those fundamental things that really enable us to even begin to do the science, we got, and we're tremendously gratified by that.