[meteorite-list] Reports Detail Mars Rover Clues to Atmosphere's Past
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 18 Jul 2013 13:09:13 -0700 (PDT)
Reports Detail Mars Rover Clues to Atmosphere's Past
Jet Propulsion Laboratory
July 18, 2013
PASADENA, Calif. - A pair of new papers report measurements of the
Martian atmosphere's composition by NASA's Curiosity rover, providing
evidence about loss of much of Mars' original atmosphere.
Curiosity's Sample Analysis at Mars (SAM) suite of laboratory
instruments inside the rover has measured the abundances of different
gases and different isotopes in several samples of Martian atmosphere.
Isotopes are variants of the same chemical element with different atomic
weights due to having different numbers of neutrons, such as the most
common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.
SAM checked ratios of heavier to lighter isotopes of carbon and oxygen
in the carbon dioxide that makes up most of the planet's atmosphere.
Heavy isotopes of carbon and oxygen are both enriched in today's thin
Martian atmosphere compared with the proportions in the raw material
that formed Mars, as deduced from proportions in the sun and other parts
of the solar system. This provides not only supportive evidence for the
loss of much of the planet's original atmosphere, but also a clue to how
the loss occurred.
"As atmosphere was lost, the signature of the process was embedded in
the isotopic ratio," said Paul Mahaffy of NASA Goddard Space Flight
Center, Greenbelt, Md. He is the principal investigator for SAM and lead
author of one of the two papers about Curiosity results in the July 19
issue of the journal Science.
Other factors also suggest Mars once had a much thicker atmosphere, such
as evidence of persistent presence of liquid water on the planet's
surface long ago even though the atmosphere is too scant for liquid
water to persist on the surface now. The enrichment of heavier isotopes
measured in the dominant carbon-dioxide gas points to a process of loss
from the top of the atmosphere -- favoring loss of lighter isotopes --
rather than a process of the lower atmosphere interacting with the ground.
Curiosity measured the same pattern in isotopes of hydrogen, as well as
carbon and oxygen, consistent with a loss of a substantial fraction of
Mars' original atmosphere. Enrichment in heavier isotopes in the Martian
atmosphere has previously been measured on Mars and in gas bubbles
inside meteorites from Mars. Meteorite measurements indicate much of the
atmospheric loss may have occurred during the first billion years of the
planet's 4.6-billion-year history. The Curiosity measurements reported
this week provide more precise measurements to compare with meteorite
studies and with models of atmospheric loss.
The Curiosity measurements do not directly measure the current rate of
atmospheric escape, but NASA's next mission to Mars, the Mars Atmosphere
and Volatile Evolution Mission (MAVEN), will do so. "The current pace of
the loss is exactly what the MAVEN mission now scheduled to launch in
November of this year is designed to determine," Mahaffy said.
The new reports describe analysis of Martian atmosphere samples with two
different SAM instruments during the initial 16 weeks of the rover's
mission on Mars, which is now in its 50th week. SAM's mass spectrometer
and tunable laser spectrometer independently measured virtually
identical ratios of carbon-13 to carbon-12. SAM also includes a gas
chromatograph and uses all three instruments to analyze rocks and soil,
as well as atmosphere.
"Getting the same result with two very different techniques increased
our confidence that there's no unknown systematic error underlying the
measurements," said Chris Webster of NASA's Jet Propulsion Laboratory,
Pasadena, Calif. He is the lead scientist for the tunable laser
spectrometer and the lead author for one of the two papers. "The
accuracy in these new measurements improves the basis for understanding
the atmosphere's history."
Curiosity landed inside Mars' Gale Crater on Aug. 6, 2012 Universal Time
(on Aug. 5 PDT). The rover this month began a drive of many months from
an area where it found evidence for a past environment favorable for
microbial life, toward a layered mound, Mount Sharp, where researchers
will seek evidence about how the environment changed.
More information about Curiosity is online at:
http://www.jpl.nasa.gov/msl , http://www.nasa.gov/msl and
You can follow the mission on Facebook at:
http://www.facebook.com/marscuriosity and on Twitter at
Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov
Nancy Neal Jones 301-286-0039
Goddard Space Flight Center, Greenbelt, Md.
nancy.n.jones at nasa.gov
Received on Thu 18 Jul 2013 04:09:13 PM PDT