Surprise!  What are those people doing there?

Science team members at JPL were surprised to see FIDO field crew members in one of their rear Hazcam images, because no humans of course will appear in the pictures from Mars.

"This image was taken by the rover's hazard avoidance camera as it completed a commanded drive towards the Kaibab feature. All we were expecting was the lander and some wheel tracks," said Scientist Lutz Richter. "We don't think they meant to be in the camera field of view, but we're pretty sure they were watching to ensure that the rover was driving properly."

Scientist Lutz Richter

This unexpected peek at the remote crew might make you wonder "what are they doing out there anyway?" Science and Engineering crews in the desert are vital to ensuring a successful test. From acting as the human RAT (Rock Abrasion Tool) to keeping the rover cool with umbrellas during the summer desert heat (which isn't necessary in the frigid temperatures of Mars), they make possible the science investigations that the mission team wishes to complete.

Unfortunately, when the Mars Exploration Rovers land on Mars, there will be no field crew to protect and look out for the rovers. Just the opposite, the rovers will be on their own, contributing to the four science goals of the Mars program, including preparation for human exploration. For example, scientists will study rover tracks like the ones in this image to determine the depth of sinkage of the wheels. That information will be valuable in part because it would assist in the design of vehicles that might someday support human weight.

This particular image shows wheel sinkage of about five millimeters (about two-tenths of an inch). Richter was not surprised by this depth. "We knew from the visual appearance of the surface material that it was a rather coarse-grained soil that would exhibit large strength and therefore a small sinkage. Had this been a finer soil like beach sand, I would have anticipated sinkage three times greater."

Richter and the rest of the science team also study the reflectivity of the tracks made by the rover. Reflectivity tells us quite a bit about the processes that formed the soil. "These tracks are not reflective. If the rover were driving over soil with properties more like baking flour, the particles would be more packed, and reflect more light. A less reflective surface like the one here indicates particles that do not pack down well, or, coarse particles." Coarse particles - like the ones shown in yesterday's Microscopic Imager image - are evidence that the processes that formed the soil were most likely water-based, and not wind-based.

Images like this one might inspire you to imagine a future picture returned from Mars in which human astronauts will be working alongside their rover partners. The humans in that eventual picture, however, wouldn't be there by accident!