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Orbiters suggest
early Mars water
was underground
analysis disputes warm, wet
picture of planet’s surface
STORY ONE
By Nadia Drake
Four billion years ago, the Mar- tian surface may have been cold and dry — not warm, watery and more Earthlike than it is today,
as many scientists have suggested.
Instead of saturating the dusty surface, fluids appeared only occasionally,
quickly shaping channels and other
landforms that bear watery footprints.
Tucked beneath the planet’s reddish,
rocky sands lurked a warm and wet
subterranean environment, a potential
incubator powered by hydrothermal
activity and revealed when meteorite
impacts blasted telltale minerals from
the planet’s crust.
At least, that’s the picture painted in
the Nov. 3 Nature . An international team
of researchers developed this scenario
after synthesizing recent mineral data
gathered by the Mars Express and Mars
Reconnaissance Orbiter, two spacecraft
orbiting Earth’s small neighbor. If the
authors are right, scientists hunting for
evidence of past Martian life might be
better off using a shovel than sniffing
around the ruddy surface.
When the team studied the locations and identities of minerals on the
Martian surface, looking for clues to
the environments in which ancient clays
Layered mineral deposits (blue) in the Noctis Labyrinthus region of Mars appear to
have been created by hydrothermal activity inside the planet. Recent evidence sug-
gests water existed on early Mars, but could not have lasted long on its surface.
formed, “ ‘warmer and wetter’ is one of
the things we saw that wasn’t being
borne out by the evidence,” says planetary geologist and study author Bethany
Ehlmann of Caltech.
Ehlmann and her coauthors concluded
that Mars’ most ancient clay miner-
als — those dating back to the Noachian
epoch, or the period between roughly 3. 7
billion and 4. 1 billion years ago — formed
within the planet’s crust when warm
water interacted with rock five to 10 kilo-
meters below the surface. Minerals such
as iron-magnesium clays, chlorite and
serpentine need water and heat to form.
Some form when temperatures are in a
broad range above freezing; others, like
the calcium-aluminum blend known as
prehnite, require baking at particularly
high temperatures (between 200˚ and
400˚ Celsius).
