The idea of Jupiter as protector was first proposed by planetary scientist George Wetherill in 19941. Wetherill showed that the planet's enormous mass — more than 300 times that of the Earth — is enough to catapult comets that might hit Earth, like a slingshot ,out of the Solar System. Other astronomers have postulated that Jupiter's gravitational pull would thin the crowd of dangerous asteroids and other objects, making Earth less impact prone. Other research has suggested that, in the past, changes in Jupiter's orbit might have actually increased the number of objects on a collision course with earth. Until now, Horner says, little work was done to test either idea.