Oceans of the Solar System - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 221

the surface. The first images of the surface of Venus were finally gar-
nered by the specially strengthened Venera 8 , 9 , and 10 spacecraft,
which functioned for up to an hour after landing, and sent back grainy
black and white pictures of a barren rocky landscape.
Spacecraft continued to probe the physical and chemical charac-
teristics of this fantastical and hostile planet. The Magellan missions
of the 1990s used radar to map its topography in exquisite detail,
revealing a landscape of volcanoes, some bizarrely shaped like
pancakes, and lava channels thousands of kilometres long (in that
furnace heat magma takes a long time to congeal, even when at the
surface). As for water, there is almost none: merely the barest traces
as water vapour in the atmosphere. The surface is, mysteriously, only
lightly cratered, leading to suggestions that every half-billion years
or so Venus 'resurfaces' itself, almost literally turning itself out in a
welter of outpouring magma. That makes some kind of sense, for
a world without water cannot have plate tectonics (see Chapter 2).
Plate tectonics is, at heart, a gentle, steady, planetary heat release
mechanism which we on water-rich Earth are lucky to have. Venus,
therefore, seems to have evolved another, far more terrifying, form
of intermittent heat release (as if its 'normal' conditions were not
bad enough).
Venus seems not always to have been this torrid. Given that it is
much like Earth in its composition and mass, the processes that pro-
duced water on Earth should also have produced water on Venus:
from volcanoes and incoming comets from space. How then did
Venus end up with only about a thousandth of 1 per cent of the water
within the Earth's atmosphere and oceans?
There is evidence that water was once present on Venus, and was
perhaps even plentiful—and this planet might once have been akin
to the imagined world of Svante Arrhenius (if not that of Edgar Rice
Burroughs). This former hydrosphere is suggested by the unusual