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from the 'habitable-zone'-is-more-of-a...guideline dept.
Venus is believed to have once been a much more hospitable place with a cooler atmosphere and liquid oceans. However tidal braking in a large ocean could have slowed Venus to its current rate of rotation (243 Earth Days to complete a Venusian day) within 10-50 million years taking it away from being habitable in a short time frame.
[The relatively habitable climate on Venus] changed billions of years ago as Venus experienced a runaway greenhouse effect, changing the landscape into the hellish world we know today. According to a NASA-supported study by an international team of scientists, it may have actually been the presence of this ocean that caused Venus to experience this transition in the first place.
On Earth, tidal torque changes the length of our day by around 20 seconds every million years.
The team simulated what Venus would be like with oceans of varying depth and a rotational period ranging from 243 to 64 sidereal Earth days. They then calculated the tidal dissipation rates and associated tidal torque that would result from each. What they found was that ocean tides would have been enough to slow it down by up to 72 Earth [days] every million years, depending on its initial rate of rotation.
This suggests that the tidal brake could have slowed down Venus to its current rotation in just 10 to 50 million years. Since it was this reduced rotation rate that caused Venus' oceans to evaporate on its Sun-facing side, leading to the runaway greenhouse effect, this tidal disruption effectively robbed Venus of its habitability in what was (from a geological standport) a pretty short time frame.
The study provide an alternative explanation of why Venus rotates the way it does which previously was assumed to be due to a massive impact slowing its rotation, additionally
These findings could also have implications for the study of extrasolar planets, where many "Venus-like" worlds have already been found.
Journal Reference : Consequences of Tidal Dissipation in a Putative Venusian Ocean (pdf)
(Score: 2, Interesting) by Anonymous Coward on Sunday May 26 2019, @04:12PM (6 children)
There is no warming in their model. That seems to be stuff added by the press.
I mean I would be interested in a model where there is an ocean and the the tides slow the rotation so the ocean evaporates for some reason leading to a thick atmosphere that becomes 99% CO2 and .005% H20 somehow. That is what the headline and lay press article implies this is, but it isn't.
(Score: 1) by RandomFactor on Sunday May 26 2019, @07:06PM (4 children)
Ahhh, I get you now. Yes, even in the original article the word hydrogen does not appear at all so the process of H20 breaking down, oxygen bonding with Carbon and Hydrogen off gassing, or H2O just being lost as whole molecules is not addressed. Thermal decomposition of H2o occurs at 2200C or higher, so that's right out. There would need to be another process in play. Still the water on Venus was once believed to be "as abundant as on Earth" which fits well enough with the oceanic braking view.
Here's an article that discusses the loss of Venusian atmospheric water over time and fingers the lack of magnetic field and solar wind for at least some of that: https://www.esa.int/Our_Activities/Space_Science/Venus_Express/Where_did_Venus_s_water_go [esa.int]
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(Score: 0) by Anonymous Coward on Sunday May 26 2019, @07:51PM (3 children)
They also say mars has little atmosphere due to lack of a magnetic field, although Venus has a very thick atmosphere. Seems like a "dark matter" type explanation to me.
(Score: 1) by RandomFactor on Sunday May 26 2019, @08:12PM (1 child)
Dark Matter - Is there anything it can't do?
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.
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Now we wait for the inevitable connection between Graphene and Dark Matter.
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(Score: 0) by Anonymous Coward on Tuesday May 28 2019, @03:28PM
You ask and we deliver. Graphene must be packed in Dark Matter to ensure safety and non-reactivity during transport.
(Score: 3, Interesting) by dry on Monday May 27 2019, @02:32AM
Venus has an induced magnetosphere, https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Induced_magnetosphere [wikipedia.org] which helps. It is also has close to 3 times the gravity compared to Mars and it seems, much more volcanic activity, including a resurfacing event in the last few billion years.
Mars loses most gases to the solar wind while Venus loses H, He and O, leaving the relatively heavy CO2.
As for the heating, my understanding that was caused by the Sun getting hotter until it boiled the oceans and water vapour is a powerful greenhouse gas. Similar will happen to the Earth in perhaps a billion years as the Sun continues to get hotter.
(Score: 1) by khallow on Monday May 27 2019, @01:08AM
The Earth too would have very little water, if water didn't freeze about 10-15 miles up. Venus probably had high water content in the top of its atmosphere. Even if it had a magnetic field to shield against the solar wind, it would still lose that water vapor to space as a result (as molecules achieve escape velocity and don't return).