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| This picture shows a lab demonstration of the measurement chamber inside the Tunable Laser Spectrometer, an instrument that is part of the Sample Analysis at Mars investigation on NASA's Curiosity rover. [PHOTO: NASA/JPL-Caltech] |
Pasadena, California: NASA's car-sized rover, Curiosity, has taken significant
steps toward understanding how Mars may have lost much of its original
atmosphere.
Learning what
happened to the Martian atmosphere will help scientists assess whether the
planet ever was habitable. The present atmosphere of Mars is 100 times thinner
than Earth's.
A set of instruments
aboard the rover has ingested and analyzed samples of the atmosphere collected
near the "Rocknest" site in Gale Crater where the rover is stopped
for research. Findings from the Sample Analysis at Mars (SAM) instruments
suggest that loss of a fraction of the atmosphere, resulting from a physical
process favoring retention of heavier isotopes of certain elements, has been a
significant factor in the evolution of the planet. Isotopes are variants of the
same element with different atomic weights.
Initial SAM results
show an increase of 5 percent in heavier isotopes of carbon in the atmospheric
carbon dioxide compared to estimates of the isotopic ratios present when Mars
formed. These enriched ratios of heavier isotopes to lighter ones suggest the
top of the atmosphere may have been lost to interplanetary space. Losses at the
top of the atmosphere would deplete lighter isotopes. Isotopes of argon also
show enrichment of the heavy isotope, matching previous estimates of atmosphere
composition derived from studies of Martian meteorites on Earth.
Scientists theorize
that in Mars' distant past its environment may have been quite different, with
persistent water and a thicker atmosphere. NASA's Mars Atmosphere and Volatile
Evolution, or MAVEN, mission will investigate possible losses from the upper
atmosphere when it arrives at Mars in 2014.
With these initial
sniffs of Martian atmosphere, SAM also made the most sensitive measurements
ever to search for methane gas on Mars. Preliminary results reveal little to no
methane. Methane is of interest as a simple precursor chemical for life. On
Earth, it can be produced by either biological or non-biological processes.
Methane has been
difficult to detect from Earth or the current generation of Mars orbiters
because the gas exists on Mars only in traces, if at all. The Tunable Laser
Spectrometer (TLS) in SAM provides the first search conducted within the
Martian atmosphere for this molecule. The initial SAM measurements place an
upper limit of just a few parts methane per billion parts of Martian
atmosphere, by volume, with enough uncertainty that the amount could be zero.
"Methane is
clearly not an abundant gas at the Gale Crater site, if it is there at all. At
this point in the mission we're just excited to be searching for it," said
SAM TLS lead Chris Webster of NASA's Jet Propulsion Laboratory (JPL) in
Pasadena, Calif. "While we determine upper limits on low values,
atmospheric variability in the Martian atmosphere could yet hold surprises for
us."
In Curiosity's first
three months on Mars, SAM has analyzed atmosphere samples with two laboratory
methods. One is a mass spectrometer investigating the full range of atmospheric
gases. The other, TLS, has focused on carbon dioxide and methane. During its
two-year prime mission, the rover also will use an instrument called a gas
chromatograph that separates and identifies gases. The instrument also will
analyze samples of soil and rock, as well as more atmosphere samples.
"With these
first atmospheric measurements we already can see the power of having a complex
chemical laboratory like SAM on the surface of Mars," said SAM Principal
Investigator Paul Mahaffy of NASA's Goddard Space Flight Center in Greenbelt,
Md. "Both atmospheric and solid sample analyses are crucial for
understanding Mars' habitability."
SAM is set to analyze
its first solid sample in the coming weeks, beginning the search for organic
compounds in the rocks and soils of Gale Crater. Analyzing water-bearing
minerals and searching for and analyzing carbonates are high priorities for
upcoming SAM solid sample analyses.
Researchers are using
Curiosity's 10 instruments to investigate whether areas in Gale Crater ever
offered environmental conditions favorable for microbial life.