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13 Volcanism on other

planets

13.1 Introduction we might expect to see evidence for volcanism on
any other bodies in the Solar System that are similar
As seen in earlier chapters, the Earth exhibits vol- to the Earth. It is now known from investigations
canic activity because this is a major mechanism by using manned and unmanned spacecraft since the
which it can lose internal heat. On Earth heat loss early 1960s that volcanism has indeed occurred
through volcanism can be thought of as consisting on many other bodies; those for which there is
of three parts: volcanism at divergent margins, vol- unambiguous evidence are Venus, Mars, our Moon,
canism at convergent margins and volcanism asso- Jupiter’s satellite Io and the asteroid 4 Vesta (aster-
ciated with hot spots. The first two are associated oids are referred to by their numbers as well as
with the plate tectonic system while the third names). We also strongly suspect that volcanism
occurs well away from plate boundaries and is has occurred on the planet Mercury. Figure 13.1
driven by deeper mantle convection not directly shows all of these bodies to scale.
linked to surface plate motions. Thus volcanism One fundamental observation that emerges is
associated with the plate tectonic system accounts that the Earth appears to be the only one of these
for about 60% of volcanic heat loss and hot spots bodies that has unambiguous evidence of plate
only 40%. As volcanic activity is such a fundamental tectonics. We still do not entirely understand why
mechanism by which the Earth loses internal heat this is so, but many arguments have been made

Fig. 13.1 Shown to scale, from left to right are the planets Mercury, Venus, Earth with its Moon, and Mars; Jupiter’s satellite
Io; and the asteroid 4 Vesta. These are the bodies in the Solar System known (suspected in the case of Mercury) to have been
volcanically active. (NASA images.)