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2014 GSA PRESIDENTIAL ADDRESS

Figure 7. False-color image of the walls
of Endurance crater, Mars, imaged by
the Opportunity rover. Interpreted
stratigraphic column modified from
Grotzinger et al. (2005).

Gusev GRS assumes Gusev average Na/ K
GRS assumes SNC average Na/ K
Rock RAT
Rock Brush Trachyte

Na2O+K2O Gale Basaltic Trachy- Rhyolite
(wt. %) trachy- andesite
Tephrite andesite
6
Trachy- GRS

basalt

Foidite GRS

3 Basalt Andesite Dacite
Basaltic
Picrobasalt andesite Martian Meteorites
OBal-spahlytircicssh9heergrgootttittiete

Lherzolitic shergottite
Nakhlite
NWA 7635/8159
NWA 7034 breccia

Figure 8. Global map of hydrogen on asteroid Vesta, based on neutron 0
absorption measurements by the Dawn spacecraft. Also shown is a 35 45 55 65 75
photomicrograph of a Vestan meteorite breccia containing dark, hydrous
chondrite clasts. Map adapted from Prettyman et al. (2012). SiO2 (wt. %)

Large impacts have had disastrous consequences on life, and Figure 9. Geochemical classification diagram for volcanic rocks on Mars,
unraveling this history has prompted the realization that showing the compositions of martian meteorites, Gusev and Gale crater rocks
modern humans still live in the fast lane. analyzed by the Spirit and Curiosity rovers, respectively, and orbital analyses by
• Among the terrestrial planets, only the lithospheres of Earth the Mars Odyssey gamma-ray spectrometer (colored rectangles labeled GRS).
and Mars have interacted with a hydrosphere. Other planetary GRS does not measure sodium, so its abundance was estimated from Na/K
surfaces are covered by impact-comminuted regolith. ratios in Gusev rocks or martian (SNC) meteorites. Gusev rocks were either
• Active or past sedimentary processes, once thought to be brushed or ground (RAT) by the Rock Abrasion Tool before analysis. Adapted
unique to Earth, are now known on Mars, which hosts both from McSween et al. (2009), with additional data.
clastic rocks and evaporates, and on Titan, where fluids other
GSA TODAY | JANUARY 2015 than water produce and distribute sediments. scratched the surface. Science by spacecraft is complex and expen-
As an aside, it is worth mentioning that all of geology benefits sive, and large, multidisciplinary (often international) teams of
from the interest that the public displays for planetary explora- scientists and engineers have to work together seamlessly. Mission
tion, where the application of geologic principles is played out on a operations can last for decades, requiring several generations of
large stage. It helps recruit the next generation of earth scientists investigators. This can be a new experience for geoscientists used
and provides new data sets for our own planet. Terrestrial to working in isolation and on projects of limited duration.
processes at a planetary scale can sometimes be better visualized
or monitored from orbit. Understandably, an important goal for planetary exploration is
the search for extraterrestrial life. Efforts so far have focused on
WHAT THE FUTURE MAY HOLD recognizing paleoenvironments that might have been conducive
to organisms. The methods used by terrestrial paleontologists to
The reconnaissance phase of solar system exploration is well study the distribution and evolution of organisms have not yet
along, but geologic understanding of most planets has only found application on other worlds. But life’s signals, especially of
primitive life forms far removed from us in time, may be more
readily recognized by geochemistry or biomarkers than in

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