Ancient oceans on Venus, Possible detection of surface granite by Venus Express |
Ancient oceans on Venus, Possible detection of surface granite by Venus Express |
Jul 14 2009, 02:33 PM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
space.com article on the possible detection of granite by IR signature on some of the ancient-looking plateaus:
http://www.space.com/scienceastronomy/0907...-venus-map.html Granite is formed by chemical processing with water in the mantle. The lower density granite bloops up and forms continental material. The argument is that if there was processing of subsurface rock by water, there may have been oceans and plate tectonics. -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Jul 15 2009, 12:32 AM
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Exciting & interesting, but gotta play skeptic.
For one thing, there's certainly nothing like a definitive spectral signature of granite here, just a putative compositional difference based on thermal emission (with a strong correlation to altitude... ) Second, exposed granite on Earth weathers away relatively quickly; I've seen some pretty rotten granite in the Rocky Mountains. Admittedly, water's not a serious player on Venus' surface, but it seems reasonable to assume that H2SO4 is pretty common, perhaps even more so at higher elevations from atmospheric precipitates? I dunno. Guess we have to build a lander or two & go find out for sure! -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Jul 15 2009, 12:58 AM
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Member Group: Members Posts: 384 Joined: 4-January 07 Member No.: 1555 |
Exciting & interesting, but gotta play skeptic... Me too, but for additional reasons. Large bodies of granitic rocks on Earth commonly are believed to have used subducted water as a flux (dissolved substance that lowers the melting point), but such a process cannot yet be demonstrated for Venus, which may have lacked both a granitic continental crust and liquid water. In addition, many other dissolved substances besides H2O, including sulfates and carbonates, can act as fluxes in magma (molten rock). Furthermore, if higher elevations on Venus have a different spectral response, this presumably could be caused by temperature effects (including coatings of frost-like mineral condensates) alone. Even in the absence of fluxes, granitic and intermediate rocks, generally in small amounts, can be formed by the classical, experimentally proven "Bowen mechanism" - extreme fractional crystallization of basaltic magma. This mechanism is how small bodies of granite are believed to have formed on Earth's Moon, for example, in the virtual absence of water. It was once believed to be how all granites formed. Agree - granite problem probably needs a lander or two. -- HDP Don (edited after reading original article) |
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Jul 16 2009, 09:20 AM
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#4
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Junior Member Group: Members Posts: 57 Joined: 13-February 06 From: Brisbane, Australia Member No.: 679 |
Exciting & interesting, but gotta play skeptic. For one thing, there's certainly nothing like a definitive spectral signature of granite here, just a putative compositional difference based on thermal emission (with a strong correlation to altitude... ) Second, exposed granite on Earth weathers away relatively quickly; I've seen some pretty rotten granite in the Rocky Mountains. Admittedly, water's not a serious player on Venus' surface, but it seems reasonable to assume that H2SO4 is pretty common, perhaps even more so at higher elevations from atmospheric precipitates? I dunno. Guess we have to build a lander or two & go find out for sure! I agree with your conclusion but sulfuric acid decomposes thermally before it ever goes near the solid surface. Need those landers - especially some nuke-powered rovers. |
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