Signs of past water on the surface of Mars just keep getting clearer, with new discoveries from both NASA rovers.
Spirit has discovered hematite, an iron mineral that is usually formed in water. It is abundant at Opportunity鈥檚 site, but not seen before on the other side of the planet. Opportunity, meanwhile, has extended its evidence of water further back in time, through possible past cycles of wet and dry climate.
The rover鈥檚 missions have both entered new phases. Opportunity has descended more than five metres into Endurance crater, while Spirit has begun its reconnaissance at the base of Columbia hills. The prospects are so exciting, says lead scientist Steve Squyres, that 鈥渋t felt to us in the last couple of weeks like the [five-month-long] mission has started all over again鈥�.
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Spirit鈥檚 discovery of the first hematite seen at Gusev crater came from a peculiar rock dubbed 鈥減ot of gold鈥�. The fist-sized rock has strange round nodules that stick out on the end of stalks and also has very distinct planar layering.
Despite detailed inspection with the microscopic imager, 鈥渨e have not got this thing figured out yet,鈥� Squyres admitted at a press conference at NASA鈥檚 Jet Propulsion Laboratory, in Pasadena, California on Friday. 鈥淚 don鈥檛 know how these things formed, and it鈥檚 driving me nuts!鈥�
What is clear, Squyres said, is that Spirit is now in a very different geological zone and so has a good chance of learning about very different episodes in Martian history.
Hazardous drive
Opportunity鈥檚 hazardous drive down into Endurance crater has taken it to lower rock strata and hence back in geological time. And the team鈥檚 risk taking has already paid off with further evidence that water existed on the surface in the past. That shows water was present not just at one point in time, but over an extended period.
Opportunity landed in the much smaller Eagle crater, and found a whole suite of evidence for liquid water. But the stadium-sized Endurance crater is much deeper.
In Endurance, the rover found a layer that matched the one at Eagle, and then delved down beyond it, past a geological 鈥渃ontact鈥� with a separate, older layer of rock. And conditions during the deposition of that rock seem to be essentially the same, indicating that water either persisted on the surface for a long time, or else returned during repeated wet spells.
The layers close by and some within immediate reach of Opportunity鈥檚 instrument arm have been divided by the team into geological units A through to E. So far, only A and B have been examined, so the coming days will quickly extend the record further back in time.
