From: James Ganong (JGanong@webtv.net)
Date: Fri Feb 19 1999 - 02:15:31 MST
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.
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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?
*************************************************
Don Turcotte explains his theory to cover these
facts:
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.
****************************************************
The full transcript is available on the link below;
sorry if it's a bit long, but I thought it might be interesting to the
group. It also shows that reality is weirder than anything
pseudoscience
ever came up with.
http://www.pbs.org/plweb-cgi/fastweb?getdoc+nova+nova+1926+0+wAAA+venus
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