Jupiter: friend or foe?

Jonti Horner and Barrie W Jones re-examine the role of giant planets in the evolution of life – specifically, whether Jupiter has in fact shielded Earth from excessive extraterrestrial bombardment. Abstract The idea that Jupiter has shielded the Earth from potentially catastrophic impacts has long permeated the public and scientific mind. But has it shielded us? We are carrying out the first detailed examination of the degree of shielding provided by Jupiter and have obtained some surprising results. Rather than Jupiter acting as a defensive presence, we found that it actually makes little difference – but if Jupiter were significantly smaller, the impact rate experienced by the Earth would be considerably enhanced. Indeed, it seems that a giant planet in the outer reaches of a planetary system can actually pose a threat to the habitability of terrestrial worlds closer to the system's parent star.