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    Re: We may be due to go out with a bang
    From: Hewitt Schlereth
    Date: 2009 Jun 11, 09:18 -0400

    No sense making a will. Just as well spend it all while there's still time. :-)
    On 6/11/09, Peter Fogg  wrote:
    > A force known as orbital chaos may cause our solar system to go haywire,
    > leading to a possible collision between earth and Venus or Mars, according
    > to a study released on Wednesday.
    > The good news is that the likelihood of such a smash-up is small, around
    > one-in-2500.
    > And even if the planets did careen into one another, it would not happen
    > before another 3.5 billion years.
    > Indeed, there is a 99 per cent chance that the sun's posse of planets will
    > continue to circle in an orderly pattern throughout the expected life span
    > of our life-giving star, another five billion years, the study found.
    > After that, the sun will likely expand into a red giant, engulfing earth and
    > its other inner planets - Mercury, Venus and Mars - in the process.
    > Astronomers have long been able to calculate the movement of planets with
    > great accuracy hundreds, even thousands of years in advance. This is how
    > eclipses have been predicted.
    > But peering further into the future of celestial mechanics with exactitude
    > is still beyond our reach, said Jacques Laskar, a researcher at the
    > Observatoire de Paris and lead author of the study.
    > "The most precise long term solutions for the orbital motion of the solar
    > system are not valid over more than a few tens of millions of years," he
    > said in an interview.
    > Using powerful computers, Laskar and colleague Mickael Gastineau generated
    > numerical simulations of orbital instability over the next five billion
    > years.
    > Unlike previous models, they took into account Albert Einstein's theory of
    > general relativity. Over a short time span, this made little difference, but
    > over the long haul it resulted in dramatically different orbital paths.
    > The researchers looked at 2,501 possible scenarios, 25 of which ended with a
    > severely disrupted solar system.
    > "There is one scenario in which Mars passes very close to earth," 794
    > kilometres to be exact, said Laskar.
    > "When you come that close, it is almost the same as a collision because the
    > planets get torn apart."
    > Life on earth, if there still were any, would almost certainly cease to
    > exist.
    > To get a more fine-grained view of how this might unfold, Laskar and
    > Gastineau ran an additional 200 computer models, slightly changing the path
    > of Mars each time.
    > All but five of them ended in a two-way collision involving the sun, earth,
    > Mercury, Venus or Mars. A quarter of them saw earth smashed to pieces.
    > The key to all the scenarios of extreme orbital chaos was the rock closest
    > to the sun, found the study, published in the British journal Nature.
    > "Mercury is the trigger, and would be the first planet to be destabilised
    > because it has the smallest mass," explained Laskar.
    > At some point Mercury's orbit would get into resonance with that of Jupiter,
    > throwing the smaller orb even more out of kilter, he said.
    > Once this happens, the so-called "angular momentum" from the much larger
    > Jupiter would wreak havoc on the other inner planets' orbits too.
    > "The simulations indicate that Mercury, in spite of its diminutive size,
    > poses the greatest risk to our present order," noted University of
    > California scientist Gregory Laughlin in a commentary, also published in
    > Nature.
    >  >
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