The data flowing from Mars has been impressive the past two weeks. Each day brings hundreds of new images many of which contain scenes like no others ever sent back to Earth before. I have followed the travels of previous rovers and looked at 10s of thousands of pictures they have beamed back over the years. Those pictures have been fascinating but I have been stunned by how varied and interesting the geology of the Gale Crater floor that Curiosity is now traversing has been. I had expected little variation in rocks and sandy landscapes prior to reaching the foot of the large mountain in the center of the crater. Now it appears there is such a diversity of geological formations that the angst to get to the good stuff is giving way to the wonder of just exploring right were the rover is at now. I had to share some of the pictures with you now even if I don’t have a lot of time to make comments. There are so many great pictures that tell stories to choose from but here are a few images that will give you an idea of what the rover is seeing in its immediate surroundings. There are an especially good number of interesting picts from the MastCam on Sol 64 if you want to see lots of pictures. To appreciate the images below you really must click on them and view them at full scale to appreciate the detail of the rocks.
First up is an image from soon after Curiosity began its travels. These rocks are what is called conglomerate because they are composed of many smaller stones (gravel) that have been cemented together. As this cementing agent erodes the harder original stones of what appears to have a been an area of gravel is now reappearing on the ground. This gravel is composed of a mixture of rounded and angled stones indicating that many of these stones experiences a lot of tumbling in their history but that some came to this position without that same history. This suggests the possibility of a flash flood type of deposit where a mixture of rocks were brought to this location and deposited together. The fairly even size of theses stones almost completely eliminates wind as a source of the stones (unless there were frequent wind storms of of many hundreds of miles per hour) and the water transport must have included a large volume to have sorted these stones in this way. If you read my prior post on the Curiosity rover and what it might find you may remember that I said I thought that some of the rocks at the land site itself looked like conglomerate to me and with this find they rover team has said that in fact the surface rocks at that site were also conglomerate. So Opportunity is likely driving on the top of a ancient river bed or flood deposit. But this raises some questions such as, how did the gravel come to be cemented together into conglomerate? This is very unlikely to happen with gravel sitting at the surface. One possible history of this site is that the gravel was buried by addition deposits and that some water remained in the ground for long enough that the cementing process could occur. After conglomerate rock was formed this area then underwent some erosion (probably by wind) revealing the layers that we see today.
Wow, I really didn’t expect to see all these thin layers of a sedimentary type rock on the crater floor. In other pictures these appear to be composed of some very fine material and the layers are not all completely horizontal but join each other if traced horizontally. This suggests either a very dynamic beach type of setting or, I think more likely, wind deposits. If I have been following the locations right I believe these layers are exposed as rocks that are blow the conglomerates that were seen below as the rover has been driving a bit downhill since it left the conglomerate rocks. Below is another picture of the same area showing these amazing thin layers of rock that have been eroded by wind. The fact that small shelves of rock are sticking out demonstrates that the rock is composed of altering layers of different compositions (probably different sized particles with differing strengths of cementing agents).
Now if we look North over the “lighter” terrain as seen in satellite images we see these amazing vistas of lighter toned eroded smooth-0ff rock. In the distance are the foothills of the mountains that make up the crater wall and between the two looks to be another area of rubble strewn surface similar to the picture just above this one. The contrast between these landscapes is really amazing and quite curious. Why do few stay boulders here? Looks like a lot of thin layers in these rocks as well but how did this valley in the foreground get eroded? Why isn’t this valley just filled up with sand blow in from higher ground? Fascinating and complex geology here.
This is is a closer (telephoto) image of this light-tone layered rock that forms some amazing mounds of rock and wide valley. I really find this and the next picture to be quite mind-boggling to think about with respect to how did this scene form? The distance that darker layer looks to be the same strewn boulders, sand and probably conglomerates that have already been seen on the other side of this lower ground. How then did this valley form. The next picture may be even clearer but it is tempting to imagine a large flood of water coming through and scouring out this valley and since that time some wind erosion has sculpted the rocks to their present form. But where did this water come from and where did it go? The rover may find out as it may just take a trip down this valley on its way to the base of the mountain that is its final destination.
The diversity of rock types and landscapes that they are found in is just amazing. This attests to a complex history of events that the Curiosity rover hopes to sort out over the next year. By examining the composition of the rocks the rover will be able to test a number of hypotheses that have been proposed to explain what we are seeing. I will provide updates as new findings are revealed.
Addendum: I’ve added one more image (below) which is a false color image of a rock that was examined for its composition. What was significant about this rock is that is a type of igneous rock is fairly uncommon on earth. How these form on earth suggest a complex long-term history of Mar’s rocks. What I found interesting about this rock is that it is just sitting on top of some form of bedrock that is probably the conglomerate that we are seeing in the area. So how did it get here? How does a igneous rock end up sitting on various sedimentary rocks? One hypothesis I would suggest is that it was thrown there from a impact somewhere in the region. I guess it could have eroded out of the rock layers that were above the conglomerate but this rock is not the type that would be found in a simple lava flow at the surface but rather produced a bit deeper in the crust. For much more detail about this rock and its analysis see this article: First science reports from Curiosity’s APXS and ChemCam: Petrology on Jake Matijevic.