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View Full Version : Did Venus Give Earth the Moon? Wild New Theory on Lunar History



Nick Theodorakis
2013-Oct-02, 01:39 PM
See:

http://www.space.com/22966-earths-moon-from-venus.html



LONDON —The Earth's moon may be a present from Venus, which once had a moon and then lost it, a new theory suggests. Under the theory, Earth's gravity captured Venus' old moon, giving our planet its big natural satellite.
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I am not a physicist, but this idea seems completely incoherent to me. Or is it just a badly written article? I thought that capture was hard enough to model on its own, without even bringing Venus into the mix (which I still can't figure out why they are trying to do so). Is somebody able to explain what it s supposed to be being modeled?

Nick

NEOWatcher
2013-Oct-02, 01:58 PM
Or is it just a badly written article?
I think it's badly written, at least if you are looking for what the theory is. They talk about all sorts of theories and only a short mention about what this new one is.

To me, it sounds like thay are trying to assume that Venus and Earth have nearly the same makeup, but just different enough to explain any discrepencies in the Earth impactor theory.

Sounds like adding a whole lot of improbable situations to explain small discrepencies.

eburacum45
2013-Oct-04, 09:51 AM
If Venus did have a moon, it is quite reasonable to expect that moon to escape in due course, since Venus has a much smaller Hill Sphere. How it ended up here is another problem.

blueshift
2013-Oct-04, 05:47 PM
I would study orbital mechanics a bit more closely along with conservation of angular momentum, linear momentum, Newton's Third Law, eccentricity of the orbits of those things that are captured, the ratios of their relative masses to one another and how the tidal forces would affect an object being launched from the inner solar system against solar gravity (its speed would have to exceed the escape speed of the sun) to a body the mass of the earth without breaking up into moonlets for the earth to capture into Saturn-like rings (with an extremely elliptical orbit). Then look at Jupiter and try and figure out why it hasn't tossed its moonlets successfully but can assist the small mass objects like comets and toss them, perturbing its own orbit.

If you want to capture something from the solar system, it's easier to grab something inbound toward the sun with its perihelion that matches earth but whose aphelion does not.

Just an estimate, a very rough one, on my part.

publiusr
2013-Oct-13, 08:42 PM
Something happened with Venus to give it that retrograde spin...I just cannot imagine what.

Githyanki
2013-Oct-17, 12:18 AM
Something happened with Venus to give it that retrograde spin...I just cannot imagine what.


I think Venus also had a moon-formation-like impact, but until Earth's, this impact only slowed Venus' rotation and knocked it upside-down.

Noclevername
2013-Oct-17, 08:11 AM
Something happened with Venus to give it that retrograde spin...I just cannot imagine what.

The theory I heard was that the constant heat-driven directional circulation of the immense atmosphere over billions of years eventually slowed and reversed the rotation.