Scientists stressed that finding the minerals, called carbonates, does not immediately prove the lake theory. Instead, the carbonate dust could have formed through interactions with the tiny amounts of water vapor found in the martian atmosphere.
Scientists continue to debate the various working hypotheses.
"We've got a bunch of ideas and we don't know which one is right yet,'' said Steven Squyres, of Cornell University, and the mission's main scientist. Another NASA spacecraft previously has spotted carbonates from orbit as well.
Spirit remained parked on its lander, nearly a week after safely arriving on Mars.
Engineers said the six-wheeled robot won't roll off the lander and onto Mars until late Jan. 15 or early Jan. 16 at the earliest.
A last-ditch effort failed to draw in two sections of the air bags that cushioned Spirit's landing. The sections of tough fabric still block the safest path the rover could follow to the surface.
Engineers will now command Spirit to turn in place 120 degrees to its right and roll off a secondary, unobstructed ramp, said Matt Wallace, mission manager.
While immobile, Spirit has continued to carry out science work, including snapping a sweeping panorama of its surroundings with its color camera. NASA has received 73 percent of that 360-degree view as the rest trickles in, said Albert Haldemann, deputy project scientist.
Spirit also has begun measuring the temperature and makeup of the rocks and soil around it with its mini-thermal emission spectrometer.
The instrument sees infrared radiation _ heat _ emitted by objects, including rocks and soil. It can measure that radiation in 167 different "colors,'' information that scientists use to deduce the mineralogical composition of what Spirit sees.
Determining what the rocks and soil are made of opens up the martian geological history book they contain, and allows scientists to begin in earnest the job of picking targets they want Spirit to examine up close, once it rolls off its lander.
On Friday, scientists displayed the first of that data, showing off psychedelically colored views of the surface of Mars.
The rover also completed the first step in standing up to its full height, unfolding its two front wheels and locking them into place.
The $820 million Mars Exploration Rover project includes a second, identical rover named Opportunity, which is expected to land on the Red Planet on Jan. 24.
NASA sent the two robotic geologists to prospect for evidence that Mars may have been a wet world conducive to life in its ancient past.
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