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Venus Express press conference November 28th, Venus: a more Earth-like planetary neighbour
hendric
post Nov 30 2007, 07:44 PM
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QUOTE (Juramike @ Nov 30 2007, 12:15 PM) *
Maybe Venus is what Earth should look like if it hadn't been for a lucky strike or two?


I don't think it's the lucky strike syndrome, but more "location location location". Once a terrestrial planet gets warm enough that it's H2O starts significantly evaporating, the endgame looks like Venus. In a billion years or so, once the Sun's output increases enough, Earth will rapidly evolve into a Venus near-twin.

The hardest part of this scenario to explain, for me, is why the massive cloud cover generated by an ocean starting to evaporate wouldn't block enough sunlight to keep it in equilibrium. I recall reading somewhere that the actual solar heat input at the surface of Venus is less than Earth due to the clouds, but the percentage kept is of course much higher.

QUOTE (nprev @ Nov 30 2007, 12:28 PM) *
Seriously, though, to me this seems as if Venus had a very slow rotation period from the outset, and the fact that it comes fairly close to Earth (25 million miles) might have been just enough to brake its rotation into the current resonance. Maybe all that went wrong is that it didn't get smacked in the right way to get it spinning right (in fact, it probably got smacked the wrong way to slow it down in the first place.)


I think the big player in Venus rotational evolution has got to be the Sun. Any effect from Earth would have to be very very small. That said, it's possible, and the fact that there is a very close synchronicity is interesting. But given that the other reasonably large objects in the inner solar system (excluding Mercury, but including Earth, Mars, Ceres and Vesta) have fast rotations, I'd lean towards Venus starting at a similar rate.

Here's a wild hypothesis. What if Venus was just like Earth, but never got hit by that last Mars-sized object to strip away it's outer crust & volatiles? Perhaps this left Venus with a <b>larger</b> amount of water than Earth, setting it up for a massive runaway greenhouse at the right time in the Sun's evolution? To be a worthwhile theory though, it needs to make a prediction...Umm, on the one piece of Venusian ground at the top of Maxwell Montes is a giant titanium sign written in Venusian that says "Don't burn carbon based fuels Earthlings". smile.gif

QUOTE (elakdawalla @ Nov 30 2007, 12:31 PM) *
All that atmosphere is just a pesky obstruction to Venus' cool geology.


Pesky obstruction? That atmosphere caused much of that cool geology, if present theories are accurate. smile.gif


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Juramike
post Nov 30 2007, 08:03 PM
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QUOTE (hendric @ Nov 30 2007, 02:44 PM) *
Here's a wild hypothesis. What if Venus was just like Earth, but never got hit by that last Mars-sized object to strip away it's outer crust & volatiles? Perhaps this left Venus with a <b>larger</b> amount of water than Earth, setting it up for a massive runaway greenhouse at the right time in the Sun's evolution?


blink.gif Wow! That's a really cool hot concept!


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Julius
post Nov 30 2007, 09:26 PM
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QUOTE (Juramike @ Nov 30 2007, 09:03 PM) *
blink.gif Wow! That's a really cool hot concept!



I kinda like that!AWESOME smile.gif
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vjkane
post Dec 1 2007, 12:30 AM
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As I remember, one of the puzzles of planetary science is why the Earth has just enough water to fill its major basins but not flood the entire surface. Apparently, it would have been easy to have sufficiently more water to flood the entire surface. Perhaps this comes down to the special pleadings case: most earth like worlds that don't orbit too close to their star have entirely water covered surfaces. We are having this discussion only because we happen to be on one of the few that has significant exposed land.


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JRehling
post Dec 1 2007, 01:00 AM
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QUOTE (vjkane @ Nov 30 2007, 04:30 PM) *
As I remember, one of the puzzles of planetary science is why the Earth has just enough water to fill its major basins but not flood the entire surface. Apparently, it would have been easy to have sufficiently more water to flood the entire surface. Perhaps this comes down to the special pleadings case: most earth like worlds that don't orbit too close to their star have entirely water covered surfaces. We are having this discussion only because we happen to be on one of the few that has significant exposed land.


Of course, if the Earth were sufficiently flat, there would be more than enough water to flood the surface, so the flip side is why the Earth has enough topography that some of it rises above the water. There could be a feedback system there: The diversification of new rock into lighter granite and heavier basalt possibly depending crucially on some crust being above water and some below.

Obviously, if the planet had 10 times as much water, or alternately 0.1 times as much, the topographical requirements to reach that feedback might be unattainable, but we might have a situation where the two nevertheless interact and create a larger attractor for some-land/some-sea.
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mcaplinger
post Dec 1 2007, 02:33 AM
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QUOTE (JRehling @ Nov 30 2007, 05:00 PM) *
Of course, if the Earth were sufficiently flat, there would be more than enough water to flood the surface, so the flip side is why the Earth has enough topography that some of it rises above the water.

This is a significant part of the "Rare Earth" hypothesis of Ward and Brownlee.

http://en.wikipedia.org/wiki/Rare_Earth_hypothesis


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Tom Tamlyn
post Dec 1 2007, 02:38 AM
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So also is the existence of a large moon (product of the "big whack"), which stabilizes the earth's rotation.

TTT

This post has been edited by Tom Tamlyn: Dec 1 2007, 02:39 AM
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brellis
post Dec 1 2007, 06:11 AM
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The other day, I found a copy of David Grinspoon's Venus Revealed at the used book store. It's been on my night table since. Tomorrow, I'm going down to the magazine stand, hoping to find the new issue of Nature. I feel like a kid on Christmas eve! smile.gif
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JRehling
post Dec 1 2007, 08:08 AM
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QUOTE (brellis @ Nov 30 2007, 10:11 PM) *
The other day, I found a copy of David Grinspoon's Venus Revealed at the used book store. It's been on my night table since. Tomorrow, I'm going down to the magazine stand, hoping to find the new issue of Nature. I feel like a kid on Christmas eve! smile.gif


Venus Revealed is a very good read, which is almost entirely responsible for rekindling my childhood interest in astronomy here in the age of Internet coverage of space exploration. It captures a lot of the mystery of Venus, and is also very witty (Section titles like "Alternative Rock" and "But It's a Dry Heat"). About all of my childhood books on the planets were third-hand buys at garage sales, so all of the "upcoming opposition/maximum elongation" tables were far out of date by the time I got my hands on them. I emailed David and told him that I liked the idea of some kid in 2015 perceiving his book that way and he said he also had the outdated books as a kid and liked that idea, too.

This VEx release is also very stimulating, and offers a rare (for me; also this board) emphasis on atmospheric science, for a planet that's got quite a bit of one. Strange to say, but in some ways, Venus's atmosphere is the one in the solar system that most resembles ours (Titan is really the only other candidate). If you just start 60 km up, Venus's atmosphere has pressure/temperature curves that are pretty earthlike. I think a good outreach opportunity would be to format the gists of this issue into a Weather Channel program. If weather geeks can listen to analysis of the jet stream for 5 minutes, they might enjoy hearing about Venus's Hadley cells.
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edstrick
post Dec 1 2007, 10:26 AM
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Regarding the lack of magnetic field...

1)
Venus is smaller and less dense then Earth. This is partly, but models indicate not entirely, due to the lower compression of the interior due to the planet's lowre mass.
Venus also has a higher surface temperature than Earth. This raises the starting point for temperatures to rise due to the "geothermal" heat-flow as you go inward.

Models, as of maybe 15 years ago, indicated that Venus probably is not compressed enough and too warm for a solid, crystaline iron inner core to have started forming. This means the liquid core lacks a heat source from the freeze-out of the inner core and is considerably more stagnant than Earth's core, reducing convection that could drive a dynamo.

2)
The surface temperature is above the "curie point" of magnetic minerals that can hold a permanent magnetic field. There can't be magnetic anomalies like on Earth and Mars and the Moon from magnetic minerals in the crust.

these are additional points, adding to but not replacing above discussion of dynamo field generation.
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AndyG
post Dec 1 2007, 02:00 PM
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QUOTE (hendric @ Nov 30 2007, 07:44 PM) *
...at the top of Maxwell Montes is a giant titanium sign written in Venusian that says "Don't burn carbon based fuels Earthlings". smile.gif


Wouldn't those metal snows on the tops of these mountains make lightning strikes probable, at the very least?

Andy (edit for spelling)
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JRehling
post Dec 1 2007, 04:30 PM
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QUOTE (AndyG @ Dec 1 2007, 06:00 AM) *
Wouldn't those metal snows on the tops of these mountains make lightning strikes probable, at the very least?

Andy (edit for spelling)


I would guess that they would contribute almost zero. A cloud-ground discharge will take place if the resistance is overcome. Adding a thin layer of conductor doesn't reduce the total resistance (from air, mainly).

By analogy, it's like wondering if your money would go farther if an expense of zero were added to your budget. That neither hurts nor helps. If it REPLACED some other positive expense, then it would help. So a tall tower of copper might increase the probability of a lightning strike, but a thin flat layer shouldn't.

In any event, the best chance for lightning on Venus is cloud-cloud, with the resistance being a lot less than in the huge vertical groundtrack. There are no cumulus clouds on Earth ever nearly as high as all of the clouds are on Venus.

Even on Earth, I'm not sure that metal towers really increase the number of lightning strikes in a given locale significantly. Only to the extent that the height of the tower was a significant fraction of the cloud height (like the Empire State Building). Otherwise, they mainly just determine where it hits. (Eg, the tower instead of 20 meters north of the tower.)
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