Both of NASA's twin rovers are now ready to perform a scientific study of Mars with the suite of tools at the end of their robotic arms. Opportunity extended its arm for the first time today, while Spirit has been locked with its arm stretched out for the last few weeks. Controllers will have Opportunity examine a patch of soil right in front with its microscope and Moessbauer Spectrometer, and then it will turn the arm and look at another patch with its alpha particle X-ray spectrometer. This should tell scientists back at Earth what minerals are in the soil.