The robotic explorer has now found similar signs of past water in Victoria, a crater some 3.5 miles (6 kilometers) away.

Opportunity also spotted unique rock layers in the sides of Victoria Crater, which are likely the petrified remnants of ancient sand dunes.

The new findings confirm suspicions that water once shaped the Martian landscape on a regional scale instead of forming isolated oases, said rover project leader Steven Squyres of Cornell University in New York State.

"Given that we've seen the same stuff at places that are miles apart, it is a reasonable conjecture that those processes operated over most of this region," Squyres said.

Many scientists consider water to be a vital ingredient for life, Squyres noted.

Got the Job Done

The decision to send Opportunity down into Victoria Crater was one the rover team wrestled with for a long time in 2006.

Rough terrain leading into the crater could have damaged the aging probe's steering system or broken its wheels.

At the time, mission managers were worried that any damage would mean Opportunity would never make it back out of Victoria Crater.

But the risky maneuver has proved well worth it, Squyres said. Opportunity clambered safely out of the crater last August and is now trekking to Endeavor, an even larger crater some 8 miles (13.5 kilometers) away.