Thursday, March 22, 2012

Villain in Disguise: Jupiter's Role in Impacts on Earth

Comet Shoemaker–Levy 9 Strikes Jupiter
Jupiter vacuumed up the pieces of the disrupted comet Shoemaker–Levy 9 in 1994, but the impacts were a reminder of the danger faced by Earth.


Date: 15 March 2012 Time: 12:04 PM ET

The story of Lexell's Comet was pretty much forgotten in the decades and centuries that followed. By the 1960s astronomers looked upon long period comets – comets that hail from the Oort Cloud at the very edge of our solar system and which take many millennia to orbit the sun – as the major impact hazard to Earth. A general idea developed, bolstered by computer simulations performed in 1994 by the late George Wetherill of the Carnegie Institution, that dictated how Jupiter acted as Earth's protector, sweeping up or ejecting many of the long period comets from the solar system and removing them from the population of potential impactors (Wetherill's simulations coincided with comet Shoemaker–Levy 9 colliding with Jupiter). This idea has taken hold in established theory yet few have ever really questioned it until now.
Realizing that today we know of many more short period comets and near-Earth asteroids that cross our planet's orbit than long period comets, Jonathan Horner of the University of New South Wales, Sydney and Barrie Jones of the UK's Open University have run new simulations that reveal a very different picture, one that has important consequences for the habitability of Earth and planets in general.



Glenn A. Walsh, Project Director,
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