Giant Comets May Be Biggest Celestial Threat to Earth, New Study Finds

December 24,2015 at 02:46 am

Giant comets known as centaurs may pose a greater danger to Earth than asteroids, according to a newly-released study in the journal of the Royal Astronomical Society.  
 "In the last three decades we have invested a lot of effort in tracking and analyzing the risk of a collision between the Earth and an asteroid," researcher Bill Napier, a professor at the University of Buckingham, said in a press release. "Our work suggests we need to look beyond our immediate neighborhood, too … out beyond the orbit of Jupiter."

Centaurs inhabit the regions around the outer planets of Jupiter, Saturn, Uranus and Neptune and move in unstable orbits around the sun. The gravitational fields of the massive outer planets can occasionally capture these objects - Jupiter`s moon Phoebe is thought to be a centaur - but they can also deflect them towards Earth.

 Centaurs are typically 30 to 60 miles across, the study says, and a single one contains more mass than the entire population of Earth-crossing asteroids found to date. Whilst in near-Earth space they are expected to disintegrate into dust and larger fragments, flooding the inner solar system with cometary debris and making impacts on our planet inevitable.

A map, with our Sun in the center, showing the orbits of the planets (blue) and 22 of the nearly 400 known giantcomets, also known as centaurs (red). Seventeen orbits of Tans-Neptunian objects, of which more than 1500 areknown, are shown in yellow. 

The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years. A centaur arrival carries the risk of injecting, from above, a mass of dust and smoke comparable into the atmosphere to that assumed in nuclear winter, the study says. 

  "If we are right, then these distant comets could be a serious hazard," Napier said, "and it’s time to understand them better."

 There is evidence, including tiny craters in moon rocks returned to Earth during the Apollo space missions, that a centaur event struck the Earth as recently as 30,000 years ago.