NASA's Mars Exploration Rover Opportunity is using instruments on its robotic arm to inspect targets on a rock called "Chester Lake."
This is the second rock the rover has examined with a microscopic imager and a spectrometer since reaching its long-term destination, the rim of vast Endeavour crater, in August.
Unlike the first rock, which was a boulder tossed by excavation of a small crater on Endeavour's rim, Chester Lake is an outcrop of bedrock.
The Astronomical Research Center (A.R.C) Mentioned that The rocks at Endeavour apparently come from an earlier period of Martian history than the rocks that Opportunity examined during its first seven-and-a-half years on Mars. More information about the ongoing exploration of Endeavour's rim can be found here.
Opportunity and its rover twin, Spirit, completed their three-month prime missions on Mars in April 2004. Both rovers continued for years of bonus, extended missions.
Both have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit stopped communicating in 2010.