156 Encyclopedia of the Solar System
FIGURE 6 Four views of Venus, with centers at 0◦,90◦, 180◦, and 270◦E. Topography is in color,
withMagellanradar images overlain on top.
relatively hot regions in the mantle. Clearly some highlands,
such as tessera plateaus (see section VII), are compensated
by crustal roots. Many other highlands appear to be com-
pensated by mantle plumes.
In addition to plumes, conduction through the litho-
sphere must contribute to the heat loss on Venus. The thin-
ner the lithosphere, the more rapidly the planet loses heat.
Estimates of the thickness of the lithosphere on Venus,
derived from gravity and topography, are typically 100–
200 +km. This is comparable to the lithospheric thickness
on Earth, and is too large to account for the majority of
Venus’ heat loss. There is growing evidence that the re-
cycling of the lower lithosphere back into the mantle may
help cool Venus, just as subduction helps cool the Earth.
New models for corona formation show that at least some
coronae may form above sites where the thickening, cold