If you've been following along, you'll already know we think it is a volcanic feature formed when lava met wet terrain, like a maar volcano (hey! Maars on Mars!). If lava interacts with groundwater, the water can flash into steam and make shallow eruptions. These eruptions don't make normal volcanic cones, but looke like low rings or craters. Zuni Salt Lake in New Mexico is a well-preserved example of a maar, which is why it was a stop on our MER field trip last summer. Check out team intern Megan Ennis' terrific poster comparing Zuni Salt Lake to Home Plate to see some of the interesting and diagnostic features of each.
It's good to keep an open mind among the team, though, and we're doing all a lot of new work with the rover to look for more evidence that would help us rule scenarios in or out. For instance, one of the things many people find compelling is this photo, which shows a dark rock and some apparently bending layers. To many, this is a bomb sag, formed when the lighter rock was still wet or deformable, and the dark rock got plunked down onto the layers, bending them under it like when you sit on a soft chair. I'm still a little skeptical though - to me the dark rock looks like the other dark rocks in this frame, which might be weathering out of the light rock or might just be rolled onto the light rock later. We can't tell which from this photo and we didn't have time last fall to investigate more thoroughly. It would be great to find another example like this one!We are planning a throrough characterization of the rocks as we guide Spirit up the side of Home Plate in the next couple of weeks. And then we've got an exciting area ahead of us - the Home Plate surface itself! We just scooted on by as we headed for Winter Haven and we're all anxious to get on up there and check it out.
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