Nearly three weeks after the Mars rover Opportunity encountered the first meteorite ever discovered on the surface of a foreign planet, its sibling, the Mars rover Spirit, stumbled upon a native Martian rock that scientists claim provides strong evidence of the existence of liquid water during the Martian past. The rover spent nearly 13 earth days drilling into the rock, analyzing its interior and taking pictures, despite reduced energy due to dust storms. The investigation of the rock, nicknamed Peace, revealed a large quantity of sulfate salt in the rock’s interior — a substance that may have been deposited by liquid water.
“[The sulfate salt] could come from liquid water with magnesium sulfate salt dissolved in it, percolating through the rock, then evaporating and leaving the salt behind,” said Prof. Steven Squyres ’81, astronomy, in a NASA press release.
Sulfate salt forms when positively charged metals linked to negatively charged sulfate dissociate in a polar solvent, such as water.
When the solvent evaporates, the sulfate and metal compounds form crystals, which are collectively referred to as salt.
Though substances other than water may have originally dissolved the magnesium sulfate found within “peace,” Prof. John Terry, chemistry and chemical biology, described that as doubtful.
“It is highly unlikely that something other than water would act as the solvent,” Terry said. Theoretically, other traditional solvents, such as alcohol, could be responsible for the presence of the sulfate salt, “but that would require an environment under much higher pressure,” Terry said.
Data acquired by the Mars Pathfinder, an earlier Martian probe, measured an average atmospheric pressure on the planet’s surface of about six hectopascals, several orders of magnitude less than the earth’s average surface pressure of 1013 hectopascals, where the primary solvent is water.
The sulfate salt could also have “come from weathering by dilute sulfuric acid reacting with magnesium-rich minerals that were already in the rock,” Squyres added. As with the first hypothesis, this second scenario also requires water, because sulfuric acid, a sulfate compound involving hydrogen, must first dissociate in a solvent before becoming a corrosive acid.
The rock’s discovery has been the result of an extended search for evidence of water on the Martian surface.
“We are mainly interested in the presence of water,” said NASA science team member Prof. Harry Stewart, civil and environmental engineering. If water once existed on Mars, it may have played a role in determining the shape and characteristics of the planet’s present surface.
In a process similar to what may have created the inside of Peace, evaporating water may have lead to the formation of surface crusts of dissolved salts and minerals. “If we can find cemented crusts on Mars, … we can learn more about how it formed … and the processes it has undergone” during its evolution, Stewart said.
Though some of the data collected by Spirit is under evaluation by scientists, most data analysis is being postponed until the mission is completed, according to Stewart.
“The rover is still operating, far longer than its original design life, … and [scientists] are still designing new experiments for it,” Stewart said. “We want to get as much information as we can.”
Peace is located in the Columbia Hills region of the Gusev Crator, where Spirit first landed. Spirit left Peace on Feb. 2 and has since then encountered another rock, dubbed Alligator.
Archived article by David Andrade
Sun Staff Writer