"We made some history here. We put the first planned hole on Mars," said Stephen Gorevan, a scientist handling some of Spirit's workload.

A tool equipped with small, diamond-shaped heads cut 2.7 millimeters deep into a small area of a sharply angled rock dubbed Adirondack. The circular hole, measuring about 45 millimeters wide, could give scientists clues to Mars' geologic past.

"The rock gave us a lot of resistance," Gorevan said. "We needed three hours to go this deep."

The football-sized rock is believed to be made of basalt, a volcanic material. An image of the rock shows depressions that resemble the eye and open mouth of the "Pac-Man" video game figure.

Spirit has spent more than a month on Mars as part of an $820 million mission that includes its twin, Opportunity, which is exploring the opposite end of the planet. They are looking for evidence that water -- a key condition for life -- ever existed on the planet.

One reason scientists selected Adirondack for inspection was its relatively dust-free appearance compared to other nearby rocks. The rover's rock abrasion tool first cleaned a circular patch then grinded off the weathered surface.

Data and images from Spirit about the rock were expected to be received from Mars late Saturday.