The rock, which scientists have dubbed "Peace," is contained in bedrock in the Columbia Hills of Gusev Crater. Spirit has been investigating the hills for months and landed at Gusev 13 months ago.
"This may be what the bones of this mountain are really made of; it gives us even more compelling
evidence for water playing a major role for altering the rocks here," Squyres added.
The new rock contains more sulfate salt than any other rock that Spirit has looked at during its mission.
"Usually when we have seen high levels of sulfur in rocks at Gusev, it has
been at the very surface. The unusual thing about this rock is that deep
inside; the sulfur is still very high. The sulfur enrichment at the
surface is correlated with the amount of magnesium, which points to
magnesium sulfate," said Ralf Gellert, of Max-Planck-Institut für Chemie in Mainz, Germany.
The presence of sulfate salt means the salt had to get into the rock somehow.
Peace, a volcanic rock, "looks as if you took volcanic rocks that were ground into little
grains, and then formed a layered rock with them cemented together by a
substantial quantity of magnesium-sulfate salt," Squyres said.
"Where did
the salt come from? We have two working hypotheses we want to check by
examining more rocks. It could come from liquid water with magnesium
sulfate salt dissolved in it, percolating through the rock, then
evaporating and leaving the salt behind.
"Or it could come from weathering
by dilute sulfuric acid reacting with magnesium-rich minerals that were
already in the rock. Either case involves water."
Spirit's observations also revealed significant amounts of the
minerals olivine, pyroxene and magnetite, all of which are common in some
types of volcanic rock.
Meanwhile, the rover Opportunity closely examined a cross-section of the heat shield that it wore on the way to the Martian surface. The shield slammed into the planet's surface, and now Opportunity is taking a closer look. Engineers expect the observations to help in designing future missions.
"We are examining the images to
determine the depth of charring in the heat shield material. In the
initial look, we didn't see any surprises. We will be working for the next
few months to analyze the performance of the heat shield," said Christine Szalai, a spacecraft engineer at NASA's Jet Propulsion
Laboratory (JPL), Pasadena, Calif. in the press release.
