The storms had delayed Opportunity's planned descent into Mars' giant Victoria Crater and NASA said the exploration might start this week.

The rovers are 43 months into missions originally planned to last three months. Last Wednesday Spirit climbed onto its long-term destination called Home Plate -- a plateau of layered bedrock bearing clues to an explosive mixture of lava and water.

"These rovers are tough," said Alan Stern, associate administrator of NASA's Science Mission Directorate. "They faced dusty winds, power starvation and other challenges -- and survived. Now they are back to doing groundbreaking field work on Mars. These spacecraft are amazing,"

Victoria Crater contains an exposed layer of bright rocks that scientists said might have preserved evidence of interaction between the Martian atmosphere and surface from millions of years ago.

Martian dust storms in July blocked so much sunlight that researchers grew concerned the rovers' daily energy supplies could plunge too low for survival. Although the skies above both rovers remain dusty, they have been clearing gradually since early August.