Sky and Telescope - April 2017 - 14

MARS ROVER UPDATE

by Emily Lakdawalla

Curiosity's
Discoveries
on Mars
After four Earth years on the Red Planet, the intrepid rover has
found evidence of long-gone water and habitable environments.

osity rover, is the most complex machine ever sent beyond
Earth. Since its 2012 daredevil landing inside a broad crater
called Gale, it has ventured 15 kilometers (9 miles) across the
crater's interior, trundling 17 cameras, several spectrometers,
a suite of weather sensors, and two miniature laboratories
along as it investigates whether Mars was ever habitable.
A habitable environment needs three things: liquid water
to facilitate chemical reactions, sources of energy and organic
(that is, carbon-bearing) material, and long-term stability
- time in which chemistry can take place in that water. It's
better if the water is not so acidic or saline that it inhibits
chemical reactions, and if a thick atmosphere or magnetic
ﬁeld (or both) shields the surface from harmful radiation.
Geochemists think the Red Planet had all these conditions
early in its history. Evidence from recent orbiters suggests
that the place to conﬁrm such clement environments once
existed is in Mars's oldest rocks, speciﬁcally in places where
we can see clay minerals from orbit (S&T: Sept. 2013, p. 16).
These clays formed when volcanic rocks were drenched in
neutral or alkaline water, an environment in which microbial life could originate and prosper.

SAY CHEESE Curiosity took this self-portrait at Buckskin in August 2015. The rover team white-balances
images to make rock types easily identiﬁable, so landscapes shown here look slightly different on Mars.

A P R I L 2 0 1 7 * SK Y & TELESCOPE

But the mission's scientists hoped to do more than study
clays; they hoped to ﬁnd sedimentary environments like
placid ancient lakes, whose rocks would have had a chance of
preserving any organic molecules that may have been in the
ancient environment.
Curiosity's landing site offered a place to do that. One
of the deepest holes on Mars, Gale is located just south of
the equator, punching about 4 km deep into the boundary
between Mars's southern highlands and northern lowlands.
Gale displays clear evidence that water once ﬂowed down its
rim, depositing fans of sediment on the crater ﬂoor, and it
also possesses a 5-km-tall central mound of layered sediments formally named Aeolis Mons. NASA's Mars Reconnaissance Orbiter had spotted spectral signs of clays, sulfates,
and hematite (an iron oxide) in the mound's lowermost
layered rocks, all of which form in different kinds of wet
environments. Also, the stack was the thickest section of
sedimentary rock seen on Mars, recording several potentially
habitable environments that went, from bottom to top, in a
roughly wet-to-dry order.
The grand challenge for Curiosity would be getting to
those rocks.

N ASA / JPL- CA LTECH / MSSS

NASA's Mars Science Laboratory, a.k.a. the Curi-

Sky and Telescope - April 2017

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