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Jay200MPH
2008-Feb-18, 07:49 PM
Okay, so we know about 500 My. ago Venus was completely resurfaced. Right now we have no predominant theory how or why - or even the scale of the resurfacing event.

What's everyone's favourite hypotheses for this? I like the idea of a giant impactor hitting it nearly dead-on (i.e. the debris goes up and comes back down rather than forming a ring or a moon.) This can account for the planet's slow, retrograde rotation, and - if you give it enough energy to liquify the whole surface - the lack of giant craters. It's still got some problems though - I'd think there would be a lot of Venus-derived material ending on Earth, which we haven't found, and I'm not convinced it can account for the present day atmosphere which is 98% CO2. Not to mention the big unknown of where the impactor came from in the first place. We're talking something the size of the Moon or even Mars. As much as I like smashing planets into each other I'd have to say this is probably not what happened.

What do you guys think?

- J

Noclevername
2008-Feb-18, 09:24 PM
This can account for the planet's slow, retrograde rotation,

The solar tide's effect on the mass of Venus' atmosphere is what's currently believed to account for the retrograde rotation.

As for the impact, how would Venus retain so much atmosphere if such an impact had occurred? And why would it have so little water and an atmosphere of such uniform composition, if the impact were only a few hundred MY ago, probably releasing a lot of internal gasses and vapor?

aurora
2008-Feb-19, 03:46 AM
Another idea is that Venus has a thick crust, and the heat could not easily escape until it had built up and reached a critical level.

Ara Pacis
2008-Feb-19, 10:30 PM
I think Venus went to the powder room to change her makeup...

Romanus
2008-Feb-20, 02:00 PM
http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/ilt/000f0edd.gif

(Runs!)

trinitree88
2008-Feb-20, 04:07 PM
I think Armand Hammer should send a great big box of baking soda, washing soda, and sodium oxide to Venus to neutralize all the sulfuric acid in the clouds...making lots of Glauber's salt. Then, with the SO3 and the CO2 scrubbed and the H2SO4 neutralized, it can slowly cool off, leaving room for evolving lifeforms....send them a bottle of extremeophiles... pete

zraith
2008-Feb-20, 04:44 PM
Can it be due to the extreme temperature of the atmosphere at the surface of Venus that it effects the edges of the continental plates (if there is any) of the planet. The heat making the crust not entirely solid lets the pressure beneath it build up until it reaches a critical level.

Another thing might be is that there is no evidence of plate tectonics on Venus that the pressure in the planet's mantle builds up to critical pressure releasing lava/magma on a global scale. Similar to what aurora has said but without the thick crust.

ravens_cry
2008-Feb-20, 04:47 PM
I think we should send in a bunch of colonists in oxygen nitrogen balloons, have them over time build more and more floating habitats as needed, extracting the sulfuric acid and carbon dioxide for water, sulphur, carbon nanotubes and related materials, and oxygen. Materials inextricable from the atmosphere could be mined and refined on the surface by tele-robots, then sent by balloon. Over the generations, the colonies would both provide a solar shade, as well as removing the atmosphere. Though this would take longer then if you could find a big enough box baking soda,(sodium bicarbonate) washing soda (borax?), and sodium oxide, it has the advantage of much less money needed up front and in fact is the result of the natural growth of the planets human population.

Ara Pacis
2008-Feb-20, 08:47 PM
Trinitree and Raven's Cry, this is a thread about what physical process caused Venus to be resurfaced in the past, not how humans might resurface/terraform Venus in the future.

Romanus
2008-Feb-20, 10:16 PM
On a more serious note, though, relevant to the OP:

1.) Impactor: I rather doubt this one. As already mentioned, an impact massive enough to change Venus's rotation from prograde to retrograde in the last billion years (the estimated age of Venus's current surface) would definitely leave some kind of mark, IMO. There's also the question of whether Venus's atmosphere itself would survive a cataclysm like that...

2.) IIRC, there are two competing models for a Venusian resurfacing: a gradual, global process of volcanic flows that basically covers craters at a rate similar to their formation, skewing the crater age to youth. The other is the more well-known catastrophic resurfacing event, which I favor; the other model seems more scientifically parsimonious, but I find it hard to believe that a global process could be even or efficient enough to produce the more or less random crater distribution we find on Venus.

Just my two bits.

Cosmonaut3030
2008-Feb-20, 10:24 PM
Perhaps there was a small planet in orbit around the sun that was close to Venus? The orbital drift the smaller planet was slower than that of venus, (meaning venus would be in orbit closer to the sun but moving outward faster) until their own gravities intertwined and caused impact.

Just a random thrown out guess.

Noclevername
2008-Feb-20, 10:29 PM
But there's still no evidence of any recent impact at all, and lots of factors are present that couldn't exist if there were a recent impact. So it seems unlikely based on the available evidence.

Cosmonaut3030
2008-Feb-20, 10:46 PM
Venus's largest impact crater named Meade indicates a 200 mile wide body collided with the planet. Would this be enough to wipe the surface well enough?

Noclevername
2008-Feb-20, 11:12 PM
Venus's largest impact crater named Meade indicates a 200 mile wide body collided with the planet. Would this be enough to wipe the surface well enough?

Actually, Mead (no -e) crater itself is around 280 miles wide, meaning the impactor was much smaller than that. And even then, a 200-mile diameter impactor would still be much too small to effect the entire surface.

ravens_cry
2008-Feb-21, 01:55 AM
I thought maybe the resurfacing was from volcano's, from what I remember of a video of a 3D flyby rendered from radar studies, there is maybe evidence of present volcanic activity. Am I right in that Venus also lacks plate tectonics, like mars? If so, maybe a massive eruption flowed over the entire surface, or maybe it was several volcanos, I don't know, but with the low-viscosity lava spreading out, like a pile of caramel in a hot oven, oozing to the far corners of tray. And sorry for deviating from topic, the idea of Venusian colonisation excites me.

Noclevername
2008-Feb-21, 01:59 AM
Maybe the surface hasn't been resurfaced; we don't really know the long-term effects of 500+ degree heat on light stone. Maybe it just "caramelized" and created a similar surface composition and form.

Ara Pacis
2008-Feb-21, 09:32 AM
Ahh, the Affy Tapple theory of Planet Formation.

Eroica
2008-Feb-21, 11:34 AM
I like the lithospheric overturn model.

Jay200MPH
2008-Feb-21, 03:22 PM
Maybe the surface hasn't been resurfaced; we don't really know the long-term effects of 500+ degree heat on light stone. Maybe it just "caramelized" and created a similar surface composition and form.

I'd think if it were "soft" enough to eliminate craters (even over millions of years) the Soviet landers would have detected this. I don't really accept any "gradual process" theories because the purported resurfacing is just too uniform. I really think it has to be a catastrophic event. Either that or you need active plate tectonics which we just haven't seen any evidence of.

I'm still hung up on the homogeneous atmosphere though. Seems to me anything that covers the surface in enough magma (flood volcanism, giant impact, etc.) should leave a lot more volcanic-derived elements (nitrogen, sulpher, etc.) than what we see. I'm assuming whatever caused the catastrophe significantly changed or replaced entirely the existing atmosphere.

For comparison, half a billion years ago the Earth's atmosphere was mostly anoxic and CO2 levels have fluctuated a lot in the interim - but that was mostly biotic processes. The nitrogen never went anywhere though.

[Edit: there IS sulphur in Venus' atmosphere - in the form of nasty sulphuric acid vapour - but I have no idea how the amount that there is compares to how much would be expected from planet-wide volcanism.]

- J

Ara Pacis
2008-Feb-21, 08:32 PM
How do rocks generally act under a uniform temperature of 900F+? Will they be more apt to deform and rebound in a geologically rapid timeframe?

I suspect it's less about geology (venerology? aphroditology?) and more about meteorology. The atmosphere is really hot and dense. That might prevent all but the largest impactors from getting through. However, a smaller meteor that falls in might burn up or detonate in the atmosphere, transferring its momentum, and create a shockwave that could create massive lithographic perturbations when it reaches the surface.

This could result in rocks that are shattered and scattered but not melted or deformed into a crater. At the surface, the dense atmosphere is thought to move rocks around on its own, so it might not be a stretch to think that a shock front wouldn't carry them quite a distance to erode and fill in any surface craters. The rocks might surf the shock front in the thick atmosphere. Moreover, an oblique trajectory might create a precursor wave, which has been shown to create a much higher lateral component to shockwaves. This process would result in a surface that reveals fewer craters but does not show massive lava flows.

BigDon
2008-Feb-22, 12:11 AM
Ara, (peace BTW)

I believe I saw a good demonstration on how the heat acts like a kiln and actually makes the material harder than it would be on Earth. Analogous to fired clay. That would explain why various mountains are steeper and taller than they should be considering their makeup and the gravity.

FriedPhoton
2008-Feb-22, 03:40 AM
The truth is that at one time Venus was a beautiful utopia with rainbows and unicorns until one day a really big comet sort of cruised up along side and was dragged into Venus's gravity well. The comet tried to escape but could only whirl around in a tight orbit that had a horrible braking effect on the planet's rotation, tearing the surface apart, killing all the rainbows and unicorns, and as the orbit tightened up it actually dragged Venus into a retrograde rotation. Venus rapidly sucked mass off the comet and the comet finally succumbed to Venus's gravitational pull and slammed into the planet. A few unicorn and rainbow bits were flung into space only to land on a crummy planet called Earth which had an atmosphere that smelled like rotten eggs, but eventually those bits replicated and made Earth an almost-utopia but it had the unfortunate side effect of creating intelligent monkeys running around with iPods.

BigDon
2008-Feb-22, 08:47 PM
Wow Photon.

Can I have some too?

Noclevername
2008-Feb-25, 08:48 PM
I had Unicorn Bits for breakfast this morning. No prize inside, though.

William
2008-Mar-01, 04:10 AM
This is another instance of a body where there is evidence of controlled fracturing of the crust. In the case of Venus there is evidence of ridges across the planet's surface which is were the planet fractured. (The ridges are in some case covered with magna flow which would indicate Venus' surface fractured repeatedly.)

For Iapetus, the same mechanism perhaps fractured the moon's surface, however, Iapetus, must have had a structural weakness at the equator of the moon, which explains why the moon fractured at its equator. (See pictures in the attached link.)

http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1270


The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.

William
2008-Mar-01, 04:17 AM
The following is a hypothesis that Venus' crust was repeatedly fractured.

http://gsa.confex.com/gsa/2006AM/finalprogram/abstract_115427.htm


The catastrophic resurfacing hypothesis—which permeates textbooks, popular science, and is rarely questioned—emerged relatively early in Magellan data analysis; it calls for global volcanic burial of all craters formed prior to the massive outpouring of lava. The separate but related global stratigraphy hypothesis deems that catastrophic resurfacing involved emplacement of 1-3 km thick lava flows that buried pre-flood craters across ~80% of Venus, with high standing crustal plateaus, marked by ribbon-tessera fabrics preserving older terrain. Both of these hypotheses predict that ribbon-terrain, a unique tectonic fabric comprised of typically orthogonal folds and ribbons (marked by periodic ridges and troughs), predated, and therefore underlies, catastrophically emplaced plains material across Venus' lowlands. If these hypotheses are viable ribbon-terrain must be buried to a depth of >1 km globally.