Geoscience Reference
In-Depth Information
areas of specific interest with spatial resolutions better of up to 5 m. The
near- and thermal-infrared spectrometers will obtain the global mineralog-
ical surface composition with a spatial resolution of 500 m, comparable to
the regolith mixing length. The X-ray spectrometer will provide a global
mapping of the elemental surface composition at a scale of about 50 km,
and during higher solar activity measure with high spatial resolution of up
to 500 m. The combination of these five instruments allows the morphologi-
cal and compositional characterization of individual surface features, hence
the identification of compositional variations between surface features. This
is absolutely necessary in order to conclude on whether specific landmarks
have been produced by endogenic processes (e.g., volcanism) or exogenic
processes (e.g., impacting objects). Knowledge of Mercury's surface com-
position will provide a key test of competing models for the formation and
evolution of Mercury and with that of all the terrestrial planets. Elements
not accessible through X-ray spectroscopy as well as the sub-surface ele-
mental composition will be measured by the
γ
-ray-neutron spectrometer,
albeit at lower spatial resolution. The neutron spectrometer and will addi-
tionally take measurements of the radar-bright spots observed from ground
in the polar regions
3
,
4
to identify their composition. If these spots, originally
suspected to be due to water ice, are composed of sulphur,
5
this will sup-
port the planet's core to be composed of Fe-FeS alloys, which are liquid at
lower temperatures than pure iron.
6
Mercury's interior structure will be investigated by the radio science
experiment in combination with the laser altimeter and the high-resolution
camera. Together these instruments will provide an accurate determination
of the global gravity field and the rotational state of the planet as well
as the amplitude of the physical libration. These parameters allow con-
straining its internal structure. A recent discussion of Mercury's interior
and strategies for its exploration using gravity and topography data can
be found in Ref. 7. The question whether the solid crust of the planet is
decoupled from the inner core by some liquid layer will also be tackled by
accurate measurements of the planetary magnetic field.
The exosphere will be studied by remote sensing as well as
in situ
measurements. It is expected that the six elements observed to date (Ca,
Na, K, H, He, and O) only constitute a fraction of Mercury's exosphere.
8
Spectrometers in the visible and ultraviolet will provide large-scale mea-
surements of its composition, vertical structure and dynamics, while the
neutral and ion particle analyzers will perform an
in situ
analysis of the
exosphere and its interactions with the surface and the magnetosphere to
