The Spirit rover on has been stuck in Martian soil, going nowhere, but that doesn’t mean she hasn’t been busy or hasn’t been making new discoveries. Just the opposite. Scientists have taken advantage of what could be a bad situation to learn more about the Red Planet’s environmental history. “By serendipity, Troy (the region where Spirit is stuck) is one of the most interesting places Spirit has been,” said Ray Arvidson, deputy principal investigator for the science payloads on the two Mars rovers. “We are able here to study each layer, each different color of the interesting soils exposed by the wheels.”
While the rover team remains optimistic about getting Spirit unstuck, they have also acknowledged the possibility that the rover might not ever be able to leave Troy. But engineers at JPL are pulling out all the stops, and will be conducting test at the Mars Yard with the engineering rover. (More on that below.)
But Spirit is also benefiting from increased power from wind events in April and May that blew away most of the dust accumulated on the rover’s solar panels. “The exceptional amount of power available from cleaning of Spirit’s solar arrays by the wind enables full use of all of the rover’s science instruments,” said Richard Moddis of the Johnson team. “If your rover is going to get bogged down, it’s nice to have it be at a location so scientifically interesting.”
While engineers are working on a plan for getting Spirit extracted from her predicament, scientists have been studying images and data the rover has sent back. One of the rover’s wheels tore into the site, exposing colored sandy materials and a miniature cliff of cemented sands. Some disturbed material cascaded down, evidence of the looseness that will be a challenge for getting Spirit out. But at the edge of the disturbed patch, the soil is cohesive enough to hold its shape as a steep cross-section.
Spirit has been using tools on its robotic arm to examine tan, yellow, white and dark-red sandy soil at Troy. Stretched-color images from the panoramic camera show the tints best.
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“The layers have basaltic sand, sulfate-rich sand and areas with the addition of silica-rich materials, possibly sorted by wind and cemented by the action of thin films of water. We’re still at a stage of multiple working hypotheses,” said Arvidson. “This may be evidence of much more recent processes than the formation of Home Plate…or is Home Plate being slowly stripped back by wind, and we happened to stir up a deposit from billions of years ago before the wind got to it?”
Water seems to have played a role in the different colors seen at the location, and perhaps differences in tints at Troy observed by the panoramic camera may come from differences in the hydration states of iron sulfates.
Meanwhile back on Earth, the rover team has developed a soil mix for testing purposes that has physical properties similar to those of the soil under Spirit at Troy. This soil recipe combines diatomaceous earth, powdered clay and play sand. A crew is shaping a few tons of that mix this week into contours matching Troy’s. The test rover will be commanded through various combinations of maneuvers during the next few weeks to validate the safest way to proceed on Mars.
Spirit’s right-front wheel has been immobile for more than three years, magnifying the challenge. Diagnostic tests on Spirit in early June provided encouragement that the left-middle wheel remains useable despite an earlier stall.
“With the improved power situation, we have the time to explore all the possibilities to get Spirit out,” said JPL’s John Callas, project manager for Spirit and Opportunity. “We are optimistic. The last time Spirit spun its wheels, it was still making progress. The ground testing will help us avoid doing things that could make Spirit’s situation worse.”