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

BOX 5.2 The Discovery Program’s Value to Exploring the Inner Planets
The Discovery program continues to be an essential part of the exploration and scientific study of
the inner planets. Their proximity to Earth and the Sun enable easy access by spacecraft in the Discovery
class.
During the past decade inner planets science has benefited greatly from the Discovery program.
Past and ongoing missions include:
• MESSENGER—The first mission to orbit Mercury; and
• GRAIL—An effort to use high-quality gravity field mapping of the moon to determine the
moon’s interior structure (scheduled for launch in 2011).
In addition, recent and planned missions to the Moon, although not Discovery missions, are
generally equivalent to other missions in that program. The orbital LRO and impactor LCROSSE
missions address both exploration and science goals for characterizing the lunar surface and identifying
potential resources, while LADEE will characterize the lunar atmosphere and dust environment.
The proximity and ready accessibility of the inner planets provides opportunities to benefit from
the frequent launch schedule envisioned by this program. Although Discovery missions are competitively
and not strategically selected, Mercury, Venus and the Moon offer many science opportunities for
Discovery teams to seek to address. The most recent Discovery announcement of opportunity attracted
over two dozen proposals, including a number of inner planets proposals.
At Mercury, orbital missions that build on the results from MESSENGER could characterize
high-latitude, radar-reflective volatile deposits, map the chemistry and mineralogy of the surface, measure
the composition of the atmosphere, characterize the stability and morphology of the magnetosphere, and
precisely determine the long-term planetary rotational state. At Venus, platforms including orbiters,
balloons, and probes could be used to study atmospheric chemistry and dynamics, surface geochemistry
and topography, and current and past surface and interior processes. The proximity of the Moon makes it
an ideal target for future orbital or landed Discovery missions, building on the rich scientific findings of
recent lunar missions, and the planned GRAIL and LADDE missions. The variety of tectonic, volcanic
and impact structures, as well as chemical and mineralogical diversity offer significant opportunity for
future missions.
REFERENCES
1. The term inner planets is used here to refer to Mercury, Venus and the Moon. Whereas, the
term terrestrial planets is used to refer to Earth, Mercury, Venus, Mars, and the Moon.
2. Although scientific and programmatic issues relating to Mars are described in Chapter 6, it is
not always possible to entirely divorce martian studies from studies of the other terrestrial planets.
Therefore, when issues concerning Mercury, Venus, or the Moon naturally touch upon corresponding
issues relevant to Mars they are mentioned in the spirit of comparative planetology.
3. R. Jeanloz, D.L. Mitchell, A.L. Sprague, and I de Pater. 1995. Evidence for a basalt-free
surface on Mercury and implications for internal heat. Science 268(5216):1455-1457, doi:
10.1126/science.7770770.
D.T. Blewett, M.S. Robinson, B.W. Denevi, J.J. Gillis-Davis, J.W. Head, S.C. Solomon, G.M.
Holsclaw, and W.E. McClintock. 2009. Multispectral images of Mercury from the first MESSENGER
flyby: Analysis of global and regional color trends. Earth Planet. Sci. Lett. 285:272-282, doi:
10.1016/j.epsl.2009.02.021.
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