[meteorite-list] Wet and Mild: Caltech Researchers Take the Temperature of Mars' Past (ALH84001)

From: Steve Dunklee <steve.dunklee_at_meteoritecentral.com>
Date: Thu, 13 Oct 2011 10:12:26 -0700 (PDT)
Message-ID: <1318525946.24846.YahooMailClassic_at_web113911.mail.gq1.yahoo.com>

If the carbonates formed under the surface it may have taken years for them to form in a warm aquifer under the surface. At this time we still don't know enough to be certain. What I do know is the carbonates almost always form in the presence of water. At higher tempratures they tend to form soda lime glass. I'm not sure what happens over time at lower tempratures.
Cheers
Steve Dunklee

--- On Thu, 10/13/11, Ron Baalke <baalke at zagami.jpl.nasa.gov> wrote:

> From: Ron Baalke <baalke at zagami.jpl.nasa.gov>
> Subject: [meteorite-list] Wet and Mild: Caltech Researchers Take the Temperature of Mars' Past (ALH84001)
> To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
> Date: Thursday, October 13, 2011, 4:49 PM
>
> http://news.caltech.edu/press_releases/13462
>
> Wet and Mild: Caltech Researchers Take the Temperature of
> Mars' Past
> California Institute of Technology
> October 12, 2011
>
> PASADENA, Calif. - Researchers at the California Institute
> of Technology
> (Caltech) have directly determined the surface temperature
> of early Mars
> for the first time, providing evidence that's consistent
> with a warmer
> and wetter Martian past.
>
> By analyzing carbonate minerals in a four-billion-year-old
> meteorite
> that originated near the surface of Mars, the scientists
> determined that
> the minerals formed at about 18 degrees Celsius (64 degrees
> Fahrenheit).
> "The thing that's really cool is that 18 degrees is not
> particularly
> cold nor particularly hot," says Woody Fischer, assistant
> professor of
> geobiology and coauthor of the paper, published online in
> the
> Proceedings of the National Academy of Sciences (PNAS) on
> October 3.
> "It's kind of a remarkable result."
>
> Knowing the temperature of Mars is crucial to understanding
> the planet's
> history - its past climate and whether it once had liquid
> water. The Mars
> rovers and orbiting spacecraft have found ancient deltas,
> rivers,
> lakebeds, and mineral deposits, suggesting that water did
> indeed flow.
> Because Mars now has an average temperature of -63 degrees
> Celsius, the
> existence of liquid water in the past means that the
> climate was much
> warmer then. But what's been lacking is data that directly
> points to
> such a history. "There are all these ideas that have been
> developed
> about a warmer, wetter early Mars," Fischer says. "But
> there's precious
> little data that actually bears on it." That is, until
> now.
>
> The finding is just one data point - but it's the first and
> only one to
> date. "It's proof that early in the history of Mars, at
> least one place
> on the planet was capable of keeping an Earthlike climate
> for at least a
> few hours to a few days," says John Eiler, the Robert P.
> Sharp Professor
> of Geology and professor of geochemistry, and a coauthor of
> the paper.
> The first author is Itay Halevy, a former postdoctoral
> scholar who's now
> at the Weizmann Institute of Science in Israel.
>
> To make their measurement, the researchers analyzed one of
> the oldest
> known rocks in the world: ALH84001, a Martian meteorite
> discovered in
> 1984 in the Allan Hills of Antarctica. The meteorite likely
> started out
> tens of meters below the Martian surface and was blown off
> when another
> meteorite struck the area, blasting the piece of Mars
> toward Earth. The
> potato-shaped rock made headlines in 1996 when scientists
> discovered
> tiny globules in it that looked like fossilized bacteria.
> But the claim
> that it was extraterrestrial life didn't hold up upon
> closer scrutiny.
> The origin of the globules, which contain carbonate
> minerals, remained a
> mystery.
>
> "It's been devilishly difficult to work out the process
> that generated
> the carbonate minerals in the first place," Eiler says. But
> there have
> been countless hypotheses, he adds, and they all depend on
> the
> temperature in which the carbonates formed. Some scientists
> say the
> minerals formed when carbonate-rich magma cooled and
> crystallized.
> Others have suggested that the carbonates grew from
> chemical reactions
> in hydrothermal processes. Another idea is that the
> carbonates
> precipitated out of saline solutions. The temperatures
> required for all
> these processes range from above 700 degrees Celsius in the
> first case
> to below freezing in the last. "All of these ideas have
> merit," Eiler says.
>
> Finding the temperature through independent means would
> therefore help
> narrow down just how the carbonate might have been formed.
> The
> researchers turned to clumped-isotope thermometry, a
> technique developed
> by Eiler and his colleagues that has been used for a
> variety of
> applications, including measuring the body temperatures of
> dinosaurs and
> determining Earth's climate history.
>
> In this case, the team measured concentrations of the rare
> isotopes
> oxygen-18 and carbon-13 contained in the carbonate samples.
> Carbonate is
> made out of carbon and oxygen, and as it forms, the two
> rare isotopes
> may bond to each other???clumping together, as Eiler
> calls it. The lower
> the temperature, the more the isotopes tend to clump. As a
> result,
> determining the amount of clumping allows for a direct
> measurement of
> temperature.
>
> The temperature the researchers measured -? 18 ? 4
> degrees Celsius - rules
> out many carbonate-formation hypotheses. "A lot of ideas
> that were out
> there are gone," Eiler says. For one, the mild temperature
> means that
> the carbonate must have formed in liquid water. "You can't
> grow
> carbonate minerals at 18 degrees other than from an aqueous
> solution,"
> he explains. The new data also suggests a scenario in which
> the minerals
> formed from water that filled the tiny cracks and pores
> inside rock just
> below the surface. As the water evaporated, the rock
> outgassed carbon
> dioxide, and the solutes in the water became more
> concentrated. The
> minerals then combined with dissolved carbonate ions to
> produce
> carbonate minerals, which were left behind as the water
> continued to
> evaporate.
>
> Could this wet and warm environment have been a habitat for
> life? Most
> likely not, the researchers say. These conditions wouldn't
> have existed
> long enough for life to grow or evolve - it would have
> taken only hours to
> days for the water to dry up. Still, these results are
> proof that an
> Earthlike environment once existed in at least one
> particular spot on
> Mars for a short time, the researchers say. What that
> implies for the
> global geology of Mars - whether this rock is
> representative of Martian
> history or is just an isolated artifact - is an open
> question.
>
> The research described in the PNAS paper, "Carbonates in
> the Martian
> meteorite Allan Hills 84001 formed at 18 ? 4 ??C in a
> near-surface
> aqueous environment," was supported by a Texaco
> Postdoctoral Fellowship,
> NASA, and the National Science Foundation.
>
> Written by Marcus Woo
>
> Deborah Williams-Hedges
> 626-395-3227
> debwms at caltech.edu
> <mailto:debwms at caltech.edu>
>
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Received on Thu 13 Oct 2011 01:12:26 PM PDT