Geology Reference
In-Depth Information
Figure 6.1. (cont.)
Venus on the way to rendezvous with Comet Halley. Both
Ve ga 1 and Ve ga 2 ejected balloons into the venusian
atmosphere and provided additional information on atmos-
pheric characteristics, including wind patterns through
careful tracking of the balloon paths. Ve ga 1 and 2 also
sent landers to the surface, which provided additional meas-
urements of surface compositions.
NASA
'
s Magellan spacecraft began orbiting Venus in
1990 and returned 12.6 cm wavelength SAR images with
spatial resolution 120
-
300m. A spare antenna from
the earlier Voyager mission was used both for radar map-
ping and for data return to Earth. As shown in
Fig. 6.6
,the
spacecraft was in a near-polar orbit, with radar mapping
taking place when the Magellan spacecraft was closest to
the planet and data return to Earth occurring for
the remainder of each orbit. In addition to high-quality
images, data were returned on surface emissivity (which
is partly a function of composition), surface roughness at
the sub-meter scale, and ground elevations with 80m
vertical resolution and ~10 km spatial resolution. The
obtaining of
SAR data on one orbit and
“
left-looking
”
SAR data on a subsequent orbit meant that
some images can be viewed stereoscopically and used for
detailed topographic and stratigraphic studies. At the con-
clusion of the mission, more than 98% of the planet had
been imaged, and the absence of signs of plate tectonics
was con
rmed. The Magellan data remain the primary
source for understanding the geomorphology of Venus.
Missions following Magellan include the ESA
'
s
Venus Express and
flybys of Venus by the MESSENGER
spacecraft, both of which returned additional information
on the atmosphere but little geologic data for the
surface. However, the Visible Infrared Thermal Imaging
Spectrometer (VIRTIS) on Venus Express returned
low-spatial-resolution information for surface composi-
tions over some areas. In May 2010, JAXA launched
the Venus Climate Orbiter, named Akatsaki, but in 2011
the spacecraft failed to go into orbit.
“
right-looking
”
