Unseen comets may raise impact risk for Earth
Mark Peplow
Thousands of dark objects could be hiding in our Solar System.
The Solar System could be teeming with almost invisible comets, according to some astronomers' calculations. If they are right, such extra comets would significantly increase the risk of a catastrophic impact with Earth.
These objects have never been observed, but the astronomers argue that 'dark comets' provide a likely explanation for an astronomical puzzle: we can only see a tiny fraction of the comets that theory predicts.
The rest is at: Nature