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.

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.

A Volcano (Ref) Apparent Lava Flows (Ref)


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.

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).

A Field of Craters 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.

The surface of Venus from Venera 14 (Ref)


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