Mapping Venus
ATLAS OF THE UNIVERSE
B
ecause we can never see the surface of Venus, the only
way to map it is by radar. It has been found that Venus
is a world of plains, highlands and lowlands; a huge
rolling plain covers 65 per cent of the surface, with low-
lands accounting for 27 per cent and highlands for only
8 per cent. The higher regions tend to be rougher than the
lowlands, and this means that in radar they are brighter (in
a radar image, brightness means roughness).
There are two main upland areas, Ishtar Terra and
Aphrodite Terra. Ishtar, in the northern hemisphere, is
2900 kilometres (1800 miles) in diameter; the western
part, Lakshmi Planum, is a high, smooth, lava-covered
plateau. At its eastern end are the Maxwell Mountains,
the highest peaks on Venus, which rise to 11 kilometres
(nearly 7 miles) above the mean radius and 8.2 kilometres
(5 miles) above the adjoining plateau. Aphrodite straddles
the equator; it measures 9700 3200 kilometres (6000
2000 miles), and is made up of several volcanic massifs,
separated by fractures. Diana Chasma, the deepest point
on Venus, adjoins Aphrodite.
(En passant, it has been decreed that all names of fea-
tures in Venus must be female. The only exception is that
of the Maxwell Mountains. The Scottish mathematician
James Clerk Maxwell had been placed on Venus before
the official edict was passed!)
A smaller highland area, Beta Regio, includes the
shield volcano, Rhea Mons and the rifted mountain Theia
Mons. Beta, which is cut by a huge rift valley rather like
the Earth’s East African Rift, is of great interest. It is
likely that Rhea is still active, and there can be no doubt
that the whole surface of Venus is dominated by vul-
canism. Venus’ thick crust will not slide over the mantle
in the same way as that of the Earth, so that plate tectonics
do no apply; when a volcano forms over a hot spot it will
remain there for a very long period. Lava flows are found
over the whole of the surface.
Craters are plentiful, some of them irregular in shape
while others are basically circular. The largest, Mead, has a
diameter of 280 kilometres (175 miles), though small craters
are less common than on Mercury, Mars or the Moon.
There are circular lowland areas, such as Atalanta
Planitia, east of Ishtar; there are systems of faults, and
there are regions now called tesserae – high, rugged tracts
extending for thousands of square kilometres and charac-
terized by intersecting ridges and grooves. Tesserae used
to be called ‘parquet terrain’, but although the term was
graphic it was abandoned as being insufficiently scientific.
Venus has been contacted by fly-by probes, radar-
carrying orbiters and soft-landers; in 1985 the two Russian
probes en routefor Halley’s Comet even dispatched two
balloons into the upper atmosphere of the planet, so that
information could be sent back from various levels as the
balloons drifted around. The latest probe, Magellan, has
confirmed and extended the earlier findings that Venus is
overwhelmingly hostile.▲ Topographic globes
of Venus.Pioneer Venus 2
visited Venus in 1978. The
mission involved an entry
probe and a ‘bus’ which
dispatched several small
landers which sent back
data during their descent.
The map was compiled as
a false-colour representation
with blue indicating low
levels and yellow and
red higher areas. Ishtar
and Aphrodite stand out
very clearly. It has been
suggested that in the future
it may be possible to ‘seed’
the atmosphere, breaking
up the carbon dioxide and
sulphuric acid and releasing
free oxygen.The topography of
Venus, in perspective views
generated by computer
using Magellan data. They
are, of course, false colour.
The image immediatelybelow shows lowland plain
in Sedna Planitia. The other
two images show the
typically Venusian highland
terrain of Ovda Regio,
bordered by plains.C Atl of Univ Phil'03stp 2/4/03 2:58 pm Page 72