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Title: Curiosity Rover Finds Hints of a Carbon Cycle on Ancient Mars

Link: https://science.slashdot.org/story/25/04/19/2...

Billions of years ago Mars "had a warm, habitable climate with liquid water
in lakes and flowing rivers," writes Ars Technica. But "In order for Mars to
be warm enough to host liquid water, there must have been a lot of carbon
dioxide in the atmosphere," says Benjamin Tutolo, a researcher at the
University of Calgary. "The question we've been asking for at least 30 years
was where the record of all this carbon is." Tutolo led a new study of rock
samples collected by the Curiosity rover that might have answered this
question... Curiosity rover was called Mars Science Laboratory for a reason.
It went to the red planet fitted with a suite of instruments, some of which
even the newer Perseverance was lacking. These enabled it to analyze the
collected Martian rocks on the spot and beam the results back to Earth. "To
get the most bang for the buck, NASA decided to send it to the place on Mars
called the Gale Crater, because it was the tallest stack of sediments on the
planet," Tutolo says. The central peak of Gale Crater was about 5 kilometers
tall, created by the ancient meteorite impact... The idea then was to climb
up Mount Sharp and collect samples from later and later geological periods at
increasing elevations, tracing the history of habitability and the great
drying up of Mars. On the way, the carbon missed by the satellites was
finally found... It turned out the samples contained roughly between 5 and 10
percent of siderite... The siderite found in the samples was also pure, which
Tutolo thinks indicates it has formed through an evaporation process akin to
what we see in evaporated lakes on Earth. This, in turn, was the first
evidence we've found of the ancient Martian carbon cycle. "Now we have
evidence that confirms the models," Tutolo claims. The carbon from the
atmosphere was being sequestered in the rocks on Mars just as it is on Earth.
The problem was, unlike on Earth, it couldn't get out of these rocks... A
large portion of carbon that got trapped in Martian rocks stayed in those
rocks forever, thinning out the atmosphere. "While it's likely the red planet
had its own carbon cycle, it was an imperfect one that eventually turned it
into the lifeless desert it is today," the article points out. But the study
still doesn't entirely explain what warmed the atmosphere of Mars - or why
Martian habitability "was seemingly intermittent and fluctuating".

Read more of this story at Slashdot.

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