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Billy Brown wrote:
So far as we can tell, Venus is completely dead in a geological sense. There is no molten core, no tectonic activity, and no recent volcanism. It looks like it once had the same kind of geological activity as Earth, but the internal heat that drives the system ran out many millions of years ago. The calculations I've seen on cooling rates for planet-sized objects suggest that it should take several billion years for a molten globe to reach this state. A contrarian might argue that we can't be sure there is no molten core (although circumstantial evidence argues against this view). Even then, you need at least a few hundred million years worth of cooling time.
This is from a NOVA program about Venus
from a couple of years ago, dealing with theories on the geological features of Venus:
We were all proven wrong. The Venus surface turned out to be more mysterious than any of us had anticipated and all of our ideas, which after all had been based on our understanding of how the Earth worked, were tossed out the window. It was a strange and alien place we were looking at. There was a river formed by running lava longer than the Nile. There were huge mountain belts. The sides of the mountains ran up so steeply that they were unlike anything we had seen on Earth. We looked searchingly for features that we could identify, that looked familiar, that looked like something close to home. We were just blown away by how different that planet looked. NARRATION: Among all the strange and inexplicable features, there seemed to be none of the usual geological signs of heat loss: no tell-tale ridges and fault lines of plate tectonics, and no large active volcanoes. Most of the volcanoes, in fact, looked like they had been dormant for hundreds of millions of years. So Venus had to be losing internal heat in some unknown and un-Earth-like way. The key to solving the puzzle turned out to be hidden in an unexpected place on the planet's surface. Like the moon, all solid bodies in the solar system are hit by meteorites. Such collisions scar the surface with impact craters which can tell us about its age. Older land has more craters because it has had more time to accumulate meteorite strikes. Fresh land is formed when volcanoes erupt, coating the surrounding landscape in a new skin of lava. This younger land will have fewer impact craters. When a team of specialists sat down to count, measure and plot every crater on the surface of Venus, they were in for the surprise of their careers. ROBERT STROM: This is the surface of Venus after it has been fully mapped by the Magellan mission. And when we plotted all of the craters on the surface, lo and behold, it was extremely uniform, they were extremely uniformly distributed across the surface. Just totally random. Truly astounding. NARRATION: Such an even distribution of impact craters across the whole planet could only mean one thing: there was no old or new land. The whole surface was the same age. Judging from the number of craters, it was young for a planet - only about 500 million years old. GERALD SCHABER: It was quite amazing. ROBERT STROM: It was incredible to me. I had never seen anything like this in the thirty years that I've been looking at solid bodies in the solar system. I've counted craters from Mercury to Triton at Neptune and this is the first time I've ever seen a crater population that was completely random. It just absolutely blew my mind. No place else in the solar system. One simple way of explaining this is to have a complete resurfacing of Venus and then starting all over again, building up the cratering record. What this actually means: is that Venus has turned itself inside out. How do you do that? You know, how do you do that?
Basically the theory that evolved in my mind at that time was that this planet today is basically dead, as far as its surface is concerned. But the net result is that the interior is heating up and getting hotter and more active like a pot of porridge if you turn up the heat. And eventually the surface will become disrupted and it will catastrophically sink into the interior. And then there will be a period of totally catastrophic surface volcanism with a time of flame and you have virtually a complete magma ocean on the entire surface of the planet. This extracts so much heat from the interior of the planet that the interior cools off until the point that it is sufficiently cool that again the planet dies and starts to form a solid surface, very quiet and peaceful for 500 million years, and looks like the planet is totally dead with no volcanism, earthquakes or other activity of that sort. But it then heats up in the interior until you're ready for another catastrophe. As the interior heats up, eventually this process repeats. The whole surface founders and sinks into the interior and this episodicidity repeats again.
X-URL-Title: NOVA Online | Transcripts | Venus Unveiled
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