On Jan 6, 3:32 pm, Alastair <[email protected]> wrote:
> On Jan 5, 1:06 pm, Tom Adams <[email protected]> wrote:
>
> > Can you cite something, anything, that claims that Earth protected
> > Venus from icy asteroids?
>
> Following from my previous post, it is not that Earth acted as a
> backstop. It is that the eccentricity only extended the orbits inwards
> as far Earth.
>
> I have found a paper which may have been the first I read about this:
> Nature 435, 466-469 (26 May 2005) | doi:10.1038/nature03676; Received
> 6 December 2004; Accepted 18 April 2005
>
> Origin of the cataclysmic Late Heavy Bombardment period of the
> terrestrial planets
>
> R. Gomes1,2, H. F. Levison2,3, K. Tsiganis2 & A. Morbidelli2
>
> It says on page 467:
>
> "However, our scheme probably also produced an in flux of material
> from the asteroid belt. As Jupiter and Saturn moved from 1:2 MMR
> towards their current positions, secular resonances (which occur when
> the orbit of an asteroid processes at the same rate as a planet) swept
> across the entire belt. These resonances can drive asteroids onto
> orbit with eccentricities and inclinations large enough to allow them
> to evolve into the inner Solar System and hit the Moon."
>
> From that I assumed that the inclinations were large enough to hit
> Earth but not large enough to hit Venus.
>
> Cheers, Alastair.
There are currently a good many asteroids known to have Venus crossing
obits:
http://en.wikipedia.org/wiki/List_of_Venus-crossing_minor_planets
Planets and asteroids don't all orbit in the same plane. The planets
obital planes vary by 1-7 degrees. Obits are elliptical and not in
the same plane, so the probability of Earth colliding with a Earth-
crossing asteroid can can be small or even zero:
"An asteroid with an Earth-crossing orbit is not necessarily in danger
of colliding with the Earth, far from it. The orbit of an Earth-
crossing asteroid may not even intersect with the orbit of the Earth.
This apparent contradiction arises because many asteroids have highly
inclined orbits, so although they may have a perihelion less than that
of the Earth, their paths can never cross."
http://en.wikipedia.org/wiki/Earth-crosser_asteroid
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