Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: mattyh on 14/05/2011 01:27:55
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Hello again, I watched a documentary the other evening on the planets and more specifically Venus and one thing is niggling me and that is: The unusual characteristics of Venus' surface.
Bear with me and please be kind. The following statement has been cut from wikipedia:
It is hypothesized that Venus underwent some sort of global resurfacing about 300–500 million years ago, however no Venusian rock has ever been dated. Although it is exciting to imagine the entire crust of Venus sinking into the mantle, it is probably more reasonable to discuss massive lava flows lasting thousands to millions of years.
As we know Venus is hot, very hot, The temperature on the surface is around 450°C. Would temperatures that high mean that rock would act as a semi liquid over time, much like the pitch drop experiment http://en.wikipedia.org/wiki/Pitch_drop_experiment.
Would this explain unusual characteristics of Venus' surface better?
I look foward to hearing some of your replies.
Kind regards Mattyh
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Semi fluid rock sounds interesting? A new one to me though, I know of fluid rock though, that's magma. (http://en.wikipedia.org/wiki/Magma)
Maybe you are thinking of this?
"When rocks melt they do so incrementally and gradually; most rocks are made of several minerals, all of which have different melting points, and the physical/chemical relationships controlling melting are complex. As a rock melts, its volume changes. When enough rock is melted, the small globules of melt (generally occurring in between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source.
Melts can stay in place long enough to melt to 20% or even 35%, but rocks are rarely melted in excess of 50%, because eventually the melted rock mass becomes a crystal and melt mush that can then ascend en masse as a diapir, which may then cause further decompression melting."
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Thanks for your reply. I guess the point i was trying make was is there that much difference between liquids and solids.
Pitch appears to be solid but is in fact a liquid with a viscosity 230 billion times more than water. Glass is also a liquid too at room temperature (i couldn't find the viscosity).
Are all solids actually liquids? They only appear solid as the viscosity is so high. The warmer an object is the softer if becomes. Obviously the melting point has to be considered as this amends the Viscosity on a massive scale.
The surface of Venus appears young. Maybe this is the crust slumping over time. For example, craters and meteor impacts would self heal. The hotter it is the faster it would happen (provided melting point was not reached).
Kind regards Matt
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At the right temperature everything should become 'fluid' like a plasma for example. As for if all objects will need to become soft before becoming fluid? There should be some immediate state between solidity and fluidity I agree. But I think the time-gap will differ between different solids, and temperatures of course.
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Hmm, i think i understand. The Melting point and Boiling points obviously indicate a change in matter.
What thrown me was that Pitch and Glass are liquid at room temperatures (although they appear solid). Despite already being liquid they will melt once again turning into a 'True' liquid'.
A little bit of digging and i found this:
Pitch does not go through a solid-liquid phase change when heated and therefore does not have a true melting point. As the temperature is raised, pitch softens and becomes less viscous. The softening point is arbitrarily defined and must be determined by a closely controlled method that must be carefully followed if test results are to be reproducible.
source http://www.astm.org/Standards/D2319.htm
Once again thanks for your replies, you've been very helpfull
Kind regards Matt
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I do not think that Venus is quite hot enough for rock to become plastic. That is nearer red heat at around 1000 degrees C.
The idea of the process that I have seen is that The interior of planets have heat sources, notably radioactivity. Now the earth has plate tectonics and convection to allow this heat to escape reasonably steadily but Venus has what looks like a rigid surface and the poor thermal conductivity causes heat to build up in the core and below the surface until it bursts out in a violent cataclysmic volcanic period every few hundred million years and this completely resurfaces the planet.