Endurance has its rewards: exposed rock, for example, and lots of it. That's what Mars rover Opportunity saw when it rolled up to the rim of 130-meter Endurance crater last week. The layered outcrops may contain hints about what predated the salty sea at Eagle crater.Endurance has its rewards: exposed rock, for example, and lots of it. That's what Mars rover Opportunity saw when it rolled up to the rim of 130-meter Endurance crater last week. The layered outcrops may contain hints about what predated the salty sea at Eagle crater.
Opportunity had already spent weeks analyzing the outcrop at 20-meter-wide Eagle crater, its landing site. That curb-high chunk of finely layered rock told of an acid, salty sea on early Mars, perhaps more of an intermittent puddle (ScienceNOW, 2 March). With just one sliver of martian history to read, rover team scientists had no idea how long that water stuck around on the surface of ancient Mars or what preceded it.
Endurance crater may provide some clues. "We see enormous outcrops of layered rock," says science team leader Steven Squyres of Cornell University in Ithaca, New York. Perhaps as many as five layers record what happened before water arrived at Eagle crater. If Opportunity's first look across Endurance at its bare cliffs is any indication, the time before the Eagle crater sea was a varied chapter of Mars history. So far, remote spectral analysis of the older layers shows no trace of the salts detected in the Eagle outcrop, just the basaltic rock typical of Mars. Hints of cross-cutting layers suggest to team member James Rice of Arizona State University in Tempe that some of the older beds may be sandstone laid down by ancient winds, much as wind has shaped the dark sand that Opportunity has already traveled. "It may be a dune environment," says Squyres, "it may be a beach. It isn't what we saw at Eagle crater."
Opportunity will be sizing up Endurance from its rim in coming weeks, but duplicating its earlier success will likely require some gutsier roving. The odd rock blasted onto the rim might allow some hands-on detailed analysis, but for a reliable reading of martian history, Opportunity will have to edge down to rock exposures on the crater's steep inner walls. "If we go in," says Squyres, "it will have enormous scientific potential, but there will be risk as well." Rolling the rover or just getting it stuck in soft soil would spell the end of the mission. Before Opportunity took such risks, it would take care of unfinished business on the less exciting but safer plains.
NASA's Mars rover site