The National Aeronautics and Space Administration said the lander, during the past two weeks, used its 8-foot-long robotic arm to move a rock nicknamed "Headless" about 16 inches and snapped an image of the rock with its camera.

The robotic arm scraped the soil under the rock and delivered a few teaspoonfuls of soil onto the lander's optical and atomic-force microscopes.

The soil piqued scientists' interest because it might contain a high concentration of salts, said Diana Blaney, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

As water evaporates in arctic and arid environments on Earth, it leaves salt, which can be found under or around rocks, Blaney said. "That's why we wanted to look under 'Headless,' to see if there's a higher concentration of salts there."

The Phoenix lander, originally planned for a three-month mission on Mars, is in its fifth month. As fall approaches and daylight hours wane, NASA said the lander will become primarily a weather station and will likely cease all activity by the end of the year.