PASADENA, Calif. -- NASA's Mars rover Opportunity, well into its
ninth year on Mars, will work for the next several weeks or
months at a site with some of the mission's most intriguing
geological features. The site, called "Matijevic Hill,"
overlooks 14-mile-wide (22-kilometer-wide) Endeavour Crater.
Opportunity has begun investigating the site's concentration of
small spherical objects reminiscent of, but different from, the
iron-rich spheres nicknamed "blueberries" at the rover's landing
site nearly 22 driving miles ago (35 kilometers). The small
spheres at Matijevic Hill have different composition and
internal structure. Opportunity's science team is evaluating a
range of possibilities for how they formed. The spheres are up
to about an eighth of an inch (3 millimeters) in diameter. The
"blueberries" found earlier are concretions formed by the action
of mineral-laden water inside rocks, but that is only one of the
ways nature can make small, rounded particles. One working
hypothesis, out of several, is tha