Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
|The "crater farm", a cluster of three young craters. The dense atmosphere of Venus has little effect on objects big enough to form craters tens of kilometers across. The ejecta forms distinct lobes, probably as a result of dense debris flows in the thick atmosphere. There are also other flows around the craters, more faintly visible. These are apparently flows of impact melt, which probably remained molten a long time due to the high temperatures on Venus.|
|It doesn't help in the least that NASA colors all the surface images of Venus in these lurid orange hues, giving the impression the surface is red hot. It's plenty hot all right, but not that hot.
This is an oblique view of the "crater farm."
Below: some craters appear to have material flowing away from them, possibly impact melt.
|A peak-ring crater with ejecta lobes.|
|Malformed craters like this are common on Venus, possibly because the thick atmosphere is effective at breaking up large bodies.|
|This is Mead, named for anthropologist Margaret Mead, the largest crater on Venus, 280 km (168 miles) in diameter. Although it looks like it has a rounded, wide raised rim, that's an optical illusion. There are actually two concentric rings with downdropped interiors.|
There are collapse pits and sinuous channels on Venus reminiscent of those in lunar maria, and probably also due to lava flows. However, some of the channels on Venus are thousands of kilometers long. The problem is, it's very difficult to come up with a way for lava to make channels that long. Even as hot as it is, Venus is still 600 degrees cooler than basalt lava, so how can lava remain fluid long enough to flow so far? One suggestion is that exotic composition lavas like carbonatites might have the necessary combination of fluidity and low melting point.
|Features like those above are called arachnoids from their spider-like form and are believed to result from doming of the surface by magma. The one at right has been nicknamed a "tick."||Below are oblique computer generated views of two shield volcanoes. The foreground of the right image is cut by numerous parallel faults.|
|These "cow pie" volcanoes are common on Venus. They are a few kilometers wide with a tiny crater in the top. Similar volcanoes occur on the deep ocean floors of Earth. Where external pressures are too great for explosive volcanism, small volcanoes seem to form domes rather than cones.|
|Rift valley and lava flows|
|Oblique view of cow pies, very reminiscent of lava domes on earth.|
|You might think that with an atmosphere 90 times denser than Earth's, that Venus would have ferocious winds. Actually thick atmospheres are less effective at wind erosion simply because it's so hard to get them moving. Think stirring cake batter versus stirring water. Nevertheless, there are places where there appear to be wind-driven plumes of material. Some might be due to atmospheric blast waves due to impacts.|
|Here's a crater with a debris plume downwind.|
The only pictures ever returned from the surface of Venus were sent back by the Soviet Venera spacecraft. A number of early missions failed to survive the atmospheric pressure of Venus and were crushed before reaching the surface. Venera 9, 10, 13 and 14 survived to transmit pictures. Venera 11 and 12 landed but failed to transmit pictures.
These pictures are awesome achievements. It's 450 C and 90 atmospheres (1250 psi) out there, a pressure equivalent to 900 meters of water. The rocks look like basalt and have the same chemistry from the simple measurements made by the surface chemistry probes. There are processes on the surface of Venus that break rocks down and move the pieces. With no ice or water, such as operate on Earth, Venusian surface processes are a riddle. I used to joke that Russia excelled in exploring Venus because it was the one place so horrible not even a Russian would want to defect there, but these are magnificent achievements.
Created 6 April 1999, Last Update 13 September 2018