https://www.jpl.nasa.gov/news/news.php?feature=6863

Curiosity Peels Back Layers on Ancient Martian Lake
Jet Propulsion Laboratory
June 1, 2017

Fast Facts:

o NASA's Curiosity Mars rover mission has provided an unprecedented
level of detail about an ancient lake environment on Mars that offered favorable conditions for microbial life.

o A lake in Mars' Gale Crater long ago was stratified, with oxidant-rich shallows and oxidant-poor depths.

o The lake offered multiple types of microbe-friendly environments simultaneously.

A long-lasting lake on ancient Mars provided stable environmental conditions that differed significantly from one part of the lake to another, according
to a comprehensive look at findings from the first three-and-a-half years
of NASA's Curiosity rover mission.

Different conditions favorable for different types of microbes existed simultaneously in the same lake.

Previous work had revealed the presence of a lake more than three billion
years ago in Mars' Gale Crater. This study defines the chemical conditions
that existed in the lake and uses Curiosity's powerful payload to determine that the lake was stratified. Stratified bodies of water exhibit sharp
chemical or physical differences between deep water and shallow water.
In Gale's lake, the shallow water was richer in oxidants than deeper water
was.

"These were very different, co-existing environments in the same lake,"
said Joel Hurowitz of Stony Brook University, Stony Brook, New York, lead author of a report of the findings in the June 2 edition of the journal Science. "This type of oxidant stratification is a common feature of lakes
on Earth, and now we've found it on Mars. The diversity of environments
in this Martian lake would have provided multiple opportunities for different types of microbes to survive, including those that thrive in oxidant-rich conditions, those that thrive in oxidant-poor conditions, and those that inhabit the interface between those settings."

Whether Mars has ever hosted any life is still unknown, but seeking signs
of life on any planet -- whether Earth, Mars or more-distant icy worlds
-- begins with reconstruction of the environment to determine if it was
capable of supporting life.

Curiosity's primary goal when it landed inside Gale Crater in 2012 was
to determine whether Mars has ever offered environmental conditions favorable for microbial life. In its first year, on the crater floor at "Yellowknife Bay," the rover found evidence of ancient freshwater river and lake environments
with all the main chemical ingredients for life and a possible energy
source for life. Curiosity has since driven to the base of Mount Sharp,
a layered mountain inside the crater, and inspected rock layers that grow progressively younger as the rover gains elevation on lower Mount Sharp.

Differences in the physical, chemical and mineral characteristics of several sites on lower Mount Sharp at first presented a puzzle to the rover team.
For example, some rocks showed thicker layering with a larger proportion
of an iron mineral called hematite, while other rocks showed very fine
layers and more of an iron mineral called magnetite. Comparing these properties suggested very distinctive environments of deposition.

Researchers considered whether these differences could have resulted from environmental conditions fluctuating over time or differing from place
to place.

"We could tell something was going on," Hurowitz said. "What was causing
iron minerals to be one flavor in one part of the lake and another flavor
in another part of the lake? We had an 'Aha!' moment when we realized
that the mineral information and the bedding-thickness information mapped perfectly onto each other in a way you would expect from a stratified
lake with a chemical boundary between shallow water and deeper water."

In addition to revealing new information about chemical conditions within
the lake, the report by Hurowitz and 22 co-authors also documents fluctuations in the climate of ancient Mars. One such change happened between the time crater-floor rocks were deposited and the time the rocks that now make
up the base of Mount Sharp were deposited. Those later rocks are exposed
at "Pahrump Hills" and elsewhere.

The method the team used for detecting changes in ancient climate conditions
on Mars resembles how ice cores are used to study past temperature conditions on Earth. It is based on comparing differences in the chemical composition
of layers of mud-rich sedimentary rock that were deposited in quiet waters
in the lake. While the lake was present in Gale, climate conditions changed from colder and drier to warmer and wetter. Such short-term fluctuations
in climate took place within a longer-term climate evolution from the
ancient warmer and wetter conditions that supported lakes, to today's
arid Mars.

"These results give us unprecedented detail in answering questions about ancient environmental conditions on Mars," said Curiosity Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California.
"I'm struck by how these fascinating conclusions on habitability and climate took everything the mission had to offer: a set of sophisticated science instruments, multiple years and miles of exploration, a landing site that retained a record of the ancient environment, and a lot of hard work by
the mission team."

In mid-2017, Curiosity is continuing to reach higher and younger layers
of Mount Sharp to study how the ancient lake environment evolved to a
drier environment more like modern Mars. The mission is managed by JPL,
a division of Caltech in Pasadena, for NASA's Science Mission Directorate, Washington. Curiosity and other Mars science missions are all part of
ambitious robotic exploration to understand Mars, which helps lead the
way for sending humans to Mars in the 2030s. For more about Curiosity,
visit:

https://www.nasa.gov/curiosity

https://mars.nasa.gov/msl/

News Media Contact
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov

Gregory Filiano
Stony Brook University, Stony Brook, N.Y.
631-444-9343
gregory.filiano@stonybrookmedicine.edu

Robert Perkins
Caltech, Pasadena, Calif.
626-395-1862
rperkins@caltech.edu

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov

2017-158

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