Venus craters are mostly what type why

The dark terrain around these craters is covered by a layer of fine material pulverized by the meteorite impact.

Perhaps because of the high surface temperature, meteorite impacts cause large amounts of rock to melt and flow like lava. If this molten material spills from the crater, it can form flows like those shown here around the crater Markham.

The thick atmosphere keeps material thrown aloft by meteorite impacts from traveling far. And so, all the craters that scientists do see on the surface of Venus are relatively young. Craters on Venus are different from craters on other planets. There are about craters identified on the surface of Venus. Crater Mead is the largest known crater on Venus, named after the American anthropologist, Margaret Mead. It measures km in diameter, and contains several concentric rings.

Suddenly, a whole host of topographic features on Venus became accessible to our view. As you look at the radar images throughout this chapter, bear in mind that these are constructed from radar reflections, not from visible-light photographs.

For example, bright features on these radar images are an indication of rough terrain, whereas darker regions are smoother. Having finally penetrated below the clouds of Venus, we find its surface to be naked, revealing the history of hundreds of millions of years of geological activity. Superficially, these plains resemble the basaltic ocean basins of Earth, but they were not produced in quite the same way. There is no evidence of subduction zones on Venus, indicating that, unlike Earth, this planet never experienced plate tectonics.

Although convection the rising of hot materials in its mantle generated great stresses in the crust of Venus, they did not start large continental plates moving. The formation of the lava plains of Venus more nearly resembles that of the lunar maria. Both were the result of widespread lava eruptions without the crustal spreading associated with plate tectonics. Rising above the lowland lava plains are two full-scale continents of mountainous terrain.

The largest continent on Venus, called Aphrodite, is about the size of Africa you can see it stand out in Figure 1.

Aphrodite stretches along the equator for about one-third of the way around the planet. Next in size is the northern highland region Ishtar, which is about the size of Australia. Ishtar contains the highest region on the planet, the Maxwell Mountains, which rise 11 kilometers above the surrounding lowlands. The Maxwell Mountains are the only feature on Venus named after a man. They commemorate James Clerk Maxwell, whose theory of electromagnetism led to the invention of radar.

All other features are named for women, either from history or mythology. One of the first questions astronomers addressed with the high-resolution Magellan images was the age of the surface of Venus. Remember that the age of a planetary surface is rarely the age of the world it is on.

A young age merely implies an active geology in that location. Such ages can be derived from counting impact craters. Figure 2 is an example of what these craters look like on the Venus radar images. The more densely cratered the surface, the greater its age. The largest crater on Venus called Mead is kilometers in diameter, slightly larger than the largest known terrestrial crater Chicxulub , but much smaller than the lunar impact basins.

Figure 2. Because they are rough, the crater rims and ejecta appear brighter in these radar images than do the smoother surrounding lava plains. The largest of these craters has a diameter of 50 kilometers. The triple impact was caused by the breaking apart of the incoming asteroid during its passage through the thick atmosphere of Venus.

The projectile had an initial diameter of between 1 and 2 kilometers. You might think that the thick atmosphere of Venus would protect the surface from impacts, burning up the projectiles long before they could reach the surface.

But this is the case for only smaller projectiles. Crater statistics show very few craters less than 10 kilometers in diameter, indicating that projectiles smaller than about 1 kilometer the size that typically produces a kilometer crater were stopped by the atmosphere.

Those craters with diameters from 10 to 30 kilometers are frequently distorted or multiple, apparently because the incoming projectile broke apart in the atmosphere before it could strike the ground as shown in the Stein crater in Figure 2. If we limit ourselves to impacts that produce craters with diameters of 30 kilometers or larger, however, then crater counts are as useful on Venus for measuring surface age as they are on airless bodies such as the Moon.

The large craters in the venusian plains indicate an average surface age that is only between and million years.