The Surface Features of
Venus
Our knowledge concerning the surface of Venus comes from a limited amount of
information obtained by the series of Russian Venera landers, and primarily
from extensive radar imaging of the planet. The radar imaging of the planet
has been performed both from Earth-based facilities and from space probes.
The most extensive radar imaging was obtained from the Magellan orbiter in a
4-year period in the
early 1990s. As a consequence, we now have a detailed radar picture of
the surface of Venus. The adjacent animation shows the topography of the
surface as determined using the Magellan synthetic aperture radar (black areas
are regions not examined by Magellan). An
MPEG movie (303 kB) of this animation is also
available.
Overview of Surface
The surface of Venus is rather smooth in many places, though not
nearly as smooth as originally expected . However, we find evidence for many of
the same geological features found on Earth: canyons, volcanoes, lava flows,
rift valleys, mountains, craters, and plains. There is substantial evidence for
local tectonic activity but the surface appears to be a single crustal plate,
with little evidence for large-scale horizontal motion of crustal plates as
found on the Earth. Why the two planets differ in this aspect of their geology
even though we believe them to have similar interiors is not well understood.
The usual explanation is that Venus is a little behind the Earth in geological
timescale, and its tectonic activity is just getting started.
Much of the surface of Venus appears to be rather young. The global
data set from radar imaging reveals a number of craters consistent with an
average Venus surface age of 300 million to 500 million
years.
There are two "continents", which are large regions several kilometers above
the average elevation. These are called Istar Terra and Aphrodite
Terra. They can be seen in the preceding
animation as the large
green, yellow, and red regions indicating higher elevation
near the equator (Aphrodite Terra) and near the top (Ishtar
Terra).
Hemispheric Views
The following images show 5 hemispheric views of the surface, again as
determined primarily from the Magellan mission.
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Hemispheres of Venus
(Ref)
|
The center image (a) is centered
at the North Pole. The other four images are centered
around the equator of Venus at (b) 0 degrees longitude, (c)
90 degrees east longitude, (d) 180 degrees and (d) 270
degrees east longitude. The simulated hues are based on color images
recorded by the Soviet Venera 13 and 14 spacecraft. (Here is a
more extensive discussion
of these hemispheric views.)
Examples of Surface Features
We now survey a few of the prominent types of surface features that have been
discovered on Venus.
Mountains
Venus has high mountains, many of which appear to be volcanic in origin.
The bright region near the center in
the polar hemispheric view (a) above
is Maxwell Montes,the highest mountain
range on Venus; it reaches an elevation of 11 km above average elevation (2 km
more than the elevation of Mount Everest above sea level on Earth).
Volcanos and Lava Flows
There is strong evidence that
volcanoes have erupted on Venus in the
geologically recent past, and strong indirect evidence from observations
like changing
chemical composition of the atmosphere and the detection of lightning
in certain regions that volcanoes are
presently active on Venus, though we do not yet have direct proof.
(Here is a
map of volcanic structures on Venus.) One piece
of evidence for recent volcanic activity is the presence in many regions of
features that look like relatively new lava flows. The two images shown
below
illustrates a volcano about 3 miles in diameter near Paragon Chasma (left)
and an image of apparent recent lava flows in the Sif Mons region.
In all of
these radar images you should bear in mind that bright spots correspond to
regions that reflect more radar waves than other regions. Thus, if you could
actually see these regions with your eyes the patterns of brightness and
darkness would probably not be the same as in these images. However, the basic
features would still be the same.
Rift Valleys
There are rift valleys as large as the East African Rift (the largest on
Earth). The image shown below illustrates a
rift valley
in the West
Eistla Region, near Gula Mons and Sif Mons.
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Rift valley on Venus
|
The perspective in cases like this is
synthesized from radar data taken from different positions in orbit.
The East
African Rift on Earth is a consequence of tectonic motion between the African
and Eurasian plates (the Dead Sea in Israel is also a consequence of this same
plate motion). Large rift valleys on Venus appear to be a consequence of more
local tectonic activity, since the surface of Venus still appears to be a
single plate.
Meteor Craters
The surface of Venus has been smoothed by recent lava flows and by interaction
with the corrosive atmosphere. However, there are various examples of meteor
craters. The following images show a field of craters (left)
and the largest crater
found (right).
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A Field of Craters
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The Largest Crater
(Ref)
|
The View from Venera
Finally, we show two of the images taken by the Russian Venera 14 lander. The
image is poor quality, but we can see in black and white the bottom of the
spacecraft, rocks on the surface, and a portion of the horizon.
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The surface of Venus from Venera 14
(Ref)
|
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