Field Report from Mars: Sol 4577 - December 9, 2016

Opportunity is continuing its great 21^st century natural history expedition on Mars, exploring the complex geology and record of past climate here on the rim of the 22-km-diameter Endeavour impact crater. Opportunity has begun the ascent of the steep slopes here in the inner wall of Endeavour impact crater after completion of a survey of outcrops close to the crater floor. The goal now is to climb back to the rim where the terrain is less hazardous, drive quickly about 1 km south, and arrive at the next major mission target on the rim before the next Martian winter.

The traverse thus far has been over 43 kilometers, the last 10 km of which have been along the rim of Endeavour crater (named after the ship the HMS Endeavour). Endeavour crater dates from the earliest Martian geologic history, a time when water was abundant and erosion was relatively rapid and somewhat Earth-like. So, in addition to exploring the geology of a large crater—a type of feature that no one has ever explored in its preserved state—the mission seeks to take a close look at the evidence in the rocks for the past environment. Thus we are trying to stick to the crater rim, where the oldest rocks are.

The image above shows the segment of the crater rim where Opportunity is currently working. The yellow line is the traverse from the rim down the Marathon Valley to the foot of the inner crater wall. Opportunity is just beginning the drive back out. The green line is the proposed path in the coming months. The objective is to drive back up the rather steep slopes and through rugged terrain of the crater wall to the rim. From there the drive will be south to the head of a water-cut valley.

Above is a closer look at the crater wall. Previously we had no understanding of the geologic complexity of a large impact crater and how it related to the actual terrain of a large crater. The only large craters that we have here on Earth are all eroded to the point of essentially being flat. The complexity that we are seeing on Mars is too great to describe completely here, but observations of outcrops along the traverse have shown that it is a structural geologist’s challenge of faulting, diverse lithologies, variable types and timing of alterations, and a long history of erosion and deposition. The green line is the route that we will likely be driving over the next month or so up and out of the crater.

Since the Navcam panoramas are in stereo, it is routine to turn them into digital elevation models into which a model of Opportunity can be placed, thus showing the physical situation of the rover. So the image above is what the terrain looks like on the inner crater wall, and in the upper right shows the far wall 22 km away. The floor of the crater is the dark streaky area. Notice that the summer dusty season makes the crater floor near the base of the far wall look hazy. Since this picture was acquired, Opportunity has continued to drive up the slope and is, as of this writing, in the far upper right of this scene.

The view south and west upper the crater wall with Pancam shows that Opportunity has a rocky obstacle course. Again, that is a nineteen to twenty degree slope and there are a lot of rocks. Most people would have trouble walking on a slope like this with all the loose rocks. Twenty degrees actually is a fairly steep slope.