Sky and Telescope - April 2017 - 21

10 cm

p PROTRUDING VEINS This network of mineral veins juts up 6 cm
(3 inches) above the surrounding rock. It formed when water moved
through fractured rocks, depositing the minerals that now make up the
veins. The surrounding rocks have eroded away to expose them.

N ASA / JPL- CA LTECH / MSSS; DIAG R A M: S&T G REGG DINDER M A N, SOURCE N ASA / JPL- CA LTECH

Curiosity will soon be across the Bagnold dune ﬁeld, and
then it will still have another kilometer or so of Murray rock
to cross before it ﬁnally reaches the next major transition:
the "hematite ridge," a break in both the topography and
the mineralogy where the rock is rich in this water-made
iron oxide. Crossing that ridge, Curiosity will move up into
a rock whose clays are concentrated enough to be visible to
orbiting spectrometers. The rover will likely spend the rest of
its second 2-year-long extended mission within these three
main rock types, as it traverses and drills from site to site to
understand how the mineralogical differences record changes
in Mars's climate over time.

If Curiosity gets a third mission extension in late 2018,
it might continue studying those rocks, or it could continue
upward. The next major boundary it could encounter is a
place where a channel once cut through Mount Sharp and
emptied into Gale's ancient lake, forming what looks like a
spreading, fan-shaped delta. The sediments deposited within
that delta and the channel that fed it turned into rocks that
were more resistant to erosion than the rest of Mount Sharp,
so after eons of weathering, the channel now stands above
the surrounding rocks. Curiosity could use that channel as a
ramp to drive upward into the mountain, transitioning from
a time in Martian history where clay minerals drew from
neutral waters to a period when water was scarcer and rocks
ended up more sulfate-rich.
Or not. Several things could limit the rover's lifetime. Its
wheels are the least of its problems; with care they should last
as long as they need to. Some instruments are already showing signs of their age. And the radioisotope power source is,
inexorably, decaying. Within 14 years of fueling - or about
4,700 sols into the mission, roughly the current age of the
Opportunity rover - it will no longer provide enough power
to keep the rover alive even through sleep, and the rover's
driving days will be over. Who knows, Opportunity may yet
outlast Curiosity.
¢ Currently writing a book on Curiosity, EMILY LAKDAWALLA

has penned a Planetary Society blog at planetary.org for a
decade. She thanks mission members Ashwin Vasavada, Paul
Mahaffy, and Kathryn Stack Morgan for help with this article.

"MUDPIES" The mineral compositions of mudstones at 10 of Curiosity's
drill sites differ significantly. (The rover's other five drill sites through 2016
were in sandstone.) Each pie chart displays the minerals in a drill sample.
The diagonal represents the overall elevation change from Yellowknife Bay
to the last sample, some 200 meters (700 feet). They're not a straight stratigraphy, however: Only the last four samples (Oudam, Marimba, Quela,
and Sebina) were methodically spaced, each separated by 25 meters of
elevation. The mineralogical variations in these mudstones may be
due to differences in any or all of these factors: the source materials
deposited by water that entered lakes, the processes of
Base of Naukluft
sedimentation and rock formation, and how the rocks
were later altered.
Marias Pass

Murray Buttes

Sebina

Quela
Marimba
Oudam

Pahrump Hills
Buckskin
Yellowknife Bay
Telegraph
Peak
Mojave

John Klein

Cumberland

Confidence
Hills

Feldspar
Mafic Igneous Minerals
Magnetite
Hematite
Clay Minerals
Silica
Jarosite
Flourapatite
Calcium Sulfate

s k y a n d t e l e s c o p e .c o m

* APRIL 2017

http://www.planetary.org http://www.skyandtelescope.com

Sky and Telescope - April 2017

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