Vision and Voyages for Planetary Science in the - Solar System ...

FIGURE 6.6 Geologic time sequence of events on Mars. Martian geologic eras are not well constrained
in terms of absolute age. SOURCE Modified from S.L. Murchie, J.F. Mustard, B.L. Ehlmann, R.E.
Milliken, J.L. Bishop, N.K. McKeown, E.Z. Noe Dobrea, F.P. Seelos, D.L. Buczkowski, S.M. Wiseman,
R.E. Arvidson, et al., A synthesis of martian aqueous mineralogy after one Mars year of observations
from the Mars Reconnaissance Orbiter, J. Geophys. Res. 114:E00D06, 2009, doi:
10.1029/2009JE003342, copyright 2009 American Geophysical Union, modified by permission of
American Geophysical Union.
The diversity of minerals detected from orbit has increased significantly as the spectrometers
have improved dramatically in spatial and spectral resolution. A myriad of hydrated minerals have been
discovered, including iron and magnesium clays, chlorite, prehnite, serpentine, kaolinite, potassium mica,
opaline, analcime, and magnesium carbonate (Figure 6.2). 57 Exposures of the mineral serpentine have
been identified in a variety of martian outcrops, 58 with potential significance for the formation of the
reported methane as a product in alteration of olivine to serpentine. Another key discovery is the
occurrence of carbonate rocks in Mars’s ancient strata using data from the CRISM aboard Mars
Reconnaissance Orbiter 59 and the suite of instruments on the Spirit rover. 60 Through most of its history
Mars has had very acidic surface chemistry, rarely wet and usually dry. Finding old carbonates informs
us that some ancient Martian environments could have been less acid and therefore more conducive to
life’s emergence.
Ancient rocks also record processes in the planet’s interior such as heat transfer from the mantle,
and magnetism in the core. Radiogenic isotopes in martian meteorites and data from magnetic regions
show that Mars differentiated relatively quickly (25-100 million years). Hypotheses for how the martian
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