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Saturday, September 28, 2013
Curiosity's SAM Instrument Finds Water and More in Surface Sample on Mars
SAM Instrument Finds Water and More in Surface Sample
The first scoop of soil analyzed by the analytical suite in the belly of
NASA's Curiosity rover reveals that fine materials on the surface of the planet
contain several percent water by weight. The results were published today in
Science as one article in a five-paper special section on the Curiosity
"One of the most
exciting results from this very first solid sample ingested by Curiosity is the
high percentage of water in the soil," said Laurie Leshin, lead author of
one paper and dean of the School Science at Rensselaer Polytechnic Institute.
"About 2 percent of the soil on the surface of Mars is made up of water,
which is a great resource, and interesting scientifically." The sample
also released significant carbon dioxide, oxygen and sulfur compounds when
Curiosity landed in
Gale Crater on the surface of Mars on Aug. 6, 2012, charged with answering the
question: "Could Mars have once harbored life?" To do that, Curiosity
is the first rover on Mars to carry equipment for gathering and processing
samples of rock and soil. One of those instruments was employed in the current
research: the Sample Analysis at Mars (SAM) instrument suite, which includes a
gas chromatograph, a mass spectrometer and a tunable laser spectrometer. These
tools enable SAM to identify a wide range of chemical compounds and determine
the ratios of different isotopes of key elements.
"This work not
only demonstrates that SAM is working beautifully on Mars, but also shows how
SAM fits into Curiosity's powerful and comprehensive suite of scientific
instruments," said Paul Mahaffy, principal investigator for SAM at NASA's
Goddard Space Flight Center in Greenbelt, Md. "By combining analyses of
water and other volatiles from SAM with mineralogical, chemical and geological
data from Curiosity's other instruments, we have the most comprehensive
information ever obtained on Martian surface fines. These data greatly advance
our understanding surface processes and the action of water on Mars."
researchers, all members of the Mars Science Laboratory Science Team,
contributed to the paper.
In this study,
scientists used the rover's scoop to collect dust, dirt and finely grained soil
from a sandy patch known as Rocknest. Researchers fed portions of the fifth
scoop into SAM. Inside SAM, the "fines"—the dust, dirt and fine
soil—were heated to 1,535 degrees F (835 C).
Baking the sample also
revealed a compound containing chlorine and oxygen, likely chlorate or
perchlorate, previously found near the north pole on Mars. Finding such
compounds at Curiosity's equatorial site suggests they could be distributed
more globally. The analysis also suggests the presence of carbonate materials,
which form in the presence of water.
In addition to
determining the amount of the major gases released, SAM also analyzed ratios of
isotopes of hydrogen and carbon in the released water and carbon dioxide.
Isotopes are variants of the same chemical element with different numbers of
neutrons, and therefore different atomic weights. SAM found that the ratio of
some isotopes in the soil is similar to the ratio found in atmospheric samples
analyzed earlier, indicating that the surface soil has interacted heavily with
ratios, including hydrogen-to-deuterium ratios and carbon isotopes, tend to
support the idea that as the dust is moving around the planet, it's reacting
with some of the gases from the atmosphere," Leshin said.
SAM can also search
for trace levels of organic compounds. Although several simple organic
compounds were detected in the experiments at Rocknest, they aren't clearly
Martian in origin. Instead, it is likely that they formed during the
high-temperature experiments, when the heat decomposed perchlorates in the
Rocknest samples, releasing oxygen and chlorine that then reacted with
terrestrial organics already present in the SAM instrument.
A related paper,
published in the Journal of Geophysical Research-Planets, details the findings
of perchlorates and other chlorine-bearing compounds in the Rocknest sample.
This paper is led by Daniel Glavin, a Mars Science Laboratory Science Team
member at Goddard.
Glavin notes that SAM
has the ability to perform another kind of experiment to address the question
of whether organic molecules are present in the Martian samples. The SAM suite
includes nine fluid-filled cups which hold chemicals that can react with
organic molecules if present in the soil samples. "Because these reactions
occur at low temperatures, the presence of perchlorates will not inhibit the
detection of Martian organic compounds," said Glavin.
The combined results
shed light on the composition of the planet's surface, while offering direction
for future research.
"Mars has kind of
a global layer, a layer of surface soil that has been mixed and distributed by
frequent dust storms. So a scoop of this stuff is basically a microscopic Mars
rock collection," said Leshin. "If you mix many grains of it
together, you probably have an accurate picture of typical Martian crust. By
learning about it in any one place you're learning about the entire
Above is a
Mosaic Image of Curiosity
Credit: NASA/JPL-Caltech/Malin Space Science Systems