Let me introduce myself and tell you my impressions of the mission so far: I lead the SuperCam remote sensing instrument on Perseverance’s mast. Early this year I had a hard time tearing myself away from my previous Mars mission to focus on this one. I had high hopes for exploring the river delta features, but I was not sure that this early part of the mission would be earthshaking. From our current vantage point, I can now say that the mission has been totally exciting. The chemistry and mineralogy are very different from other landing sites. In contrast to my previous exploration, the mineral grains here are large, which makes it easier to understand the make-up of these rocks. However, the rock surfaces are heavily weathered, cloaking the rocks in a veil of mystery. That veil was lifted when we got our first glimpse of the abraded (“Guillaumes”) and then drilled (“Roubion”) targets the first week of August. And, WOW, what a sight! Our team chat lines went crazy, with something over a thousand posts over the weekend. But, true to its nature, Mars never yields its secrets easily, and our first sample tube ended up being an atmospheric sample (no rock).
While scratching our heads over this new challenge, on Sol 168, Perseverance drove to a new location, “Mure,” named for a village in southeastern France. Voila! There in front of Percy lay the first clear strata (layered rocks) up close and personal. Back on Sol 116, in June, we had first spotted stratigraphic layers over half a kilometer away in an outcrop called “Artuby.” Remote images of “Mure” suggested that it also might contain layered rocks, and indeed, it does.
Visibly layered rock outcrops most often occur in sedimentary rocks. In the range of sub-millimeter to centimeter thick, they can signal annual deposition layers. The shapes of the layers—whether they pinch out at points, whether they slope or are flat—and the size of the grains help geologists understand whether the material was deposited by wind, placid water such as in a lake, or flowing water. Lava flows can also produce layered deposits, but usually with thicker layers and other telltale features. Rock layers are very important because they reveal the sequence of events that occurred when the rocks formed. If apparent igneous rocks overlie apparent sedimentary layers, we might surmise that a volcanic event happened after the deposition of rocks in a watery or wind environment. Perseverance is in a lake basin where one would normally expect sedimentary rocks. We know that fact from the elevation contours and the river delta deposits in the distance. But the floor of Jezero was mapped from orbit with apparent igneous mineral compositions. So we’re trying to piece together the history.
Perseverance has now driven several hundred meters further, scouting out “Artuby” ridge, which contains a number of outcrops showing different styles of layering. This reconnaissance is useful, as the rover is likely to eventually come back this way after checking out some more terrain up ahead and carrying out another sampling campaign.
