Comet Enthusiast

The greatest risk to Earth comes from comets, which have proved harder for NASA to keep tabs on.Many comets swing into the inner solar system every 200 to 300 years. The origin of such so-called "short-period comets" is unknown but the immediate source is thought to be the Centaurs -a collection of an estimated million icy objects more than 1 kilometre across on elliptical orbits that come closest to the sun between the orbits of Jupiter and Neptune.  A new study of the Trojan asteroids that exist around the orbit of Neptune concludes that material from these may go on to become comets that could strike our planet.