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Mars Mystery: How Was Ancient Red Planet Warm Enough for Liquid Water?



 
 
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Old February 7th 17, 03:53 AM posted to alt.astronomy
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Default Mars Mystery: How Was Ancient Red Planet Warm Enough for Liquid Water?

Mars Mystery: How Was Ancient Red Planet Warm Enough for Liquid Water?
By Charles Q. Choi, Space.com Contributor | February 6, 2017


A simulated image of a lake filling Mars' Gale Crater in the ancient past.
Observations by NASA's Curiosity rover suggest that Gale Crater once hosted
potentially a habitable lake-and-stream system for long stretches - perhaps
millions of years at a time.
Credit: NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

The mystery of how Mars could have once had water flowing on its surface is
now deepening, as a new study reveals that the Red Planet's early atmosphere
likely possessed up to hundreds of times less carbon dioxide than needed to
keep it warm enough for liquid water to last.

Although Mars is now cold and dry, there are decades of evidence suggesting
that the Red Planet's surface was once covered with rivers, streams, ponds,
lakes and perhaps seas and oceans. Dark, narrow lines seen on Mars even hint
that water could run down some of its slopes every spring. There is life
virtually wherever there is water on Earth, so these findings raise the
possibility that Mars was once a home to life, and might host it still.

"The watery environments that once occupied the floor of Gale Crater look
like they were pretty hospitable to life - not too hot, not too cold, not
too acid, not too alkaline, and the water probably was not too salty," said
study lead author Thomas Bristow, a planetary scientist at NASA's Ames
Research Center in Moffett Field, California. [Photos: Ancient Mars Lake
Could Have Supported Life]


Bedrock at this site inside Mars' Gale Crater, which was studied by NASA's
Curiosity rover, added to a puzzle about the ancient Red Planet. Curiosity's
data indicated that a lake was present, but little carbon dioxide was
apparently in the air to help keep a lake unfrozen.
Credit: NASA/JPL-Caltech/MSSS

Ancient Mars must have been much warmer than the planet is today for such
environments to persist, many scientists think. As such, prior work sought
to look for signs that Mars once possessed ample amounts of greenhouses
gases such as carbon dioxide in its atmosphere, which trap heat from the
sun.

However, analyses of data taken from orbit above Mars suggested little in
the way of the carbonate minerals on the Martian surface that one would
expect to find if its atmosphere were once richer in carbon dioxide. To help
solve this mystery, scientists examined data collected from the Red Planet's
surface by NASA's Curiosity rover as it traversed the lower slopes of the
mountain Aeolis Mons (known informally as Mount Sharp), which rises about
3.4 miles (5.5 kilometers) high from the center of Gale Crater.

The researchers analyzed Martian mudstones, siltstones, sandstones and other
sedimentary rocks deposited by lakes and rivers on the floor of Gale Crater
about 3.5 billion years ago. They did not detect carbonates, suggesting that
atmospheric levels of carbon dioxide back then were tens to hundreds of
times lower than those required by climate models to warm early Mars enough
to keep liquid water on its surface.

These findings do not suggest that ancient Mars wasn't wet, study team
members said. "The sedimentary evidence at Gale Crater is indisputable in
showing the prolonged presence of liquid water on the surface of early
Mars," Bristow told Space.com.

One possible explanation for this discovery is that Mars once did have
carbonates on its surface that were later destroyed. However, "the nature of
the minerals in the samples we focused on don't support that conclusion,"
Bristow said. "They don't show any sign of suffering an acidic attack that
could have dissolved any carbonates there in the past."

Another possibility is that early Mars was warmed by other greenhouse gases,
such as sulfur dioxide, methane or nitrous oxide.

"The downside of all these other greenhouse gases is that they tend to be
quite reactive, so when you put them in the atmosphere, they don't hang out
an especially long time," Bristow said. "So the warming periods driven by
those kinds of greenhouse gases are relatively short-lived, which is not
consistent with observations from Gale Crater where we have evidence for
lakes and rivers that persisted for hundreds of thousands or even millions
of years."

Other scenarios that might explain the water of early Mars include ice caps
that could have kept liquid water insulated under them, or a change in the
Martian orbit that made the Red Planet warmer. "Our findings mean that
scientists have to think a bit more deeply about what kind of mechanisms
could lead to stabilization of surface water," Bristow said.

Future research will analyze more data that Curiosity is collecting as it
makes its way up Aeolis Mons.

"It looks like the rover should be sampling the rock record of ancient Mars
during a climatic transition as it dried out and cooled down," Bristow said.
"We are hoping to get more clues as to how the early Martian climate system
operated."

The scientists detailed their findings online today (Feb. 6) in the journal
Proceedings of the National Academy of Sciences.

Follow Charles Q. Choi on Twitter @cqchoi.

http://www.space.com/35595-ancient-m...r-mystery.html

 




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