JUPITER has long been thought to defend the inner planets by kicking dangerous comets and asteroids out into interstellar space. Now it seems the planet could have been responsible for the greatest pounding in Earth鈥檚 history.
Kevin Grazier of NASA鈥檚 Jet Propulsion Lab in Pasadena, California, and colleagues built a computer model comprising 40,000 small objects in circular orbits between the outermost planets, similar to the disc of material present in the early solar system. As the simulation progressed, Jupiter hurled over 95 per cent of the objects out of the solar system. But in the process its gravitational tug stretched their circular orbits into loops that crossed the paths of the inner planets.
The model, presented at the Division of Planetary Sciences meeting in Ithaca, New York, this week, provides a possible mechanism for the 鈥渓ate heavy bombardment鈥�, a controversial theory which says that some craters on the moon and inner planets were caused by a massive influx of small bodies around 4 billion years ago. The deflection of comets may also explain how volatile substances like water arrived on the inner planets.
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The paper ends the myth of a purely protective Jupiter, says Jonathan Horner of the Open University in Milton Keynes, UK. 鈥淲e鈥檙e finally making sense of something we should have already known.鈥�
