Soil analysis finds organic compounds of uncertain origin
SAN FRANCISCO — It took more than three months, but NASA’s Curiosity rover has sent back its first complete tests of Mars’ windswept soil. In it, mission scientists have spotted chemical compounds that include chlorine, hydrogen and, tantalizingly, carbon.
Organic compounds contain carbon and are sometimes associated with life. But scientists can’t say yet whether the carbon Curiosity detected came from Mars or was carried from Earth by the rover.
Curiosity also found that the Martian surface is five times richer than Earth’s in deuterium, a heavy version of hydrogen that contains an extra neutron. Radiation probably blasted water containing the lighter version of hydrogen into space early in the planet’s history, mission scientists reported December 3 at a meeting of the American Geophysical Union.
The announcement is the first from the last of Curiosity’s arsenal of instruments to be deployed, the Sample Analysis at Mars, or SAM, suite. “The most exciting thing is that this thing works,” said mission scientist Laurie Leshin, a planetary geologist at Rensselaer Polytechnic Institute in Troy, N.Y.
Curiosity now has full chemical specifications for a small dune in the area called Rocknest. This place will serve as a touchstone to help scientists analyze everywhere the car-sized rover drives in the future — including its ultimate destination, possibly ancient rock layers on the flanks of a peak known as Mount Sharp.
“This baseline of what we see on the modern planet gives us a frame of reference to go looking billions of years older,” said Caltech geologist John Grotzinger, the mission’s chief scientist.
To deploy SAM, Curiosity scientists scooped soil from Rocknest and dumped it into one of SAM’s 59 quartz cups. Ovens heated the dirt sample, and three tools analyzed the gases coming off of it.
Oxygen detected this way probably comes from chlorine-oxygen compounds known as perchlorates, which NASA’s Phoenix mission spotted in 2008 at a different landing site near the Red Planet’s north pole. Perchlorates are normally very reactive and destroy anything around them, including organics. But a 2010 paper suggested ways in which perchlorates could form chlorinated organic compounds when heated. Similar compounds were spotted by the Viking landers in 1976 but dismissed at the time as being contamination from Earth (SN: 10/9/10, p. 9).
Next SAM sniffed out chlorinated hydrocarbons, molecules containing chlorine, hydrogen and carbon. These compounds were probably made as perchlorates in the scoop of dirt reacted with other materials present — including carbon. “It’s very likely that they were made as we heated the sample up,” said Paul Mahaffy, a mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
That carbon had to come from somewhere. “We have detected organic compounds,” said Grotzinger. “We simply don’t know if they are indigenous to Mars or not.”
Finding organic compounds native to Mars wouldn’t be a huge surprise. After all, meteorites that fell from Mars to Earth contain organic compounds. And having organics doesn’t necessarily mean having life; the MESSENGER spacecraft recently detected what is likely organic-rich matter in icy craters near Mercury’s poles (SN Online: 11/30/12).
Further tests should distinguish where the carbon comes from, Grotzinger said, but they could take a while. “Curiosity’s middle name is patience, and we should all have a healthy dose of that,” he said.
Finally, SAM’s measurements of heavy versus light hydrogen are the first hard numbers on exactly how much more deuterium Mars has than Earth. “That’s just terrifically interesting,” said Mahaffy. The discovery will help scientists better understand Mars’ early atmosphere and climate.
Curiosity’s main goal is to figure out whether its landing site, in a region called Gale Crater, was ever capable of supporting life. After landing in August, Curiosity drove to Rocknest and worked there for more than a month. Since then Curiosity has driven a little farther, taking panoramic shots at a place called Point Lake. Soon the rover will test its rock drill and then move on to Mount Sharp.
That may take some time. Curiosity can drive up to 100 meters a day, and the mountain lies about 10 kilometers away.
J. Grotzinger. The Mars Science Laboratory mission: early results from Gale Crater landing site. American Geophysical Union Fall Meeting, San Francisco, Dec. 3, 2012.
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