Updated 11 March: Infrared observations of 2009 DD45 suggest it is a member of a class of rocky asteroids called «S - type». (newscientist.com)
They were performing a routine sky survey on Sept. 21, 2012, as part of the International Scientific Optical Network, or ISON, a project that normally tracks rocky asteroids and space debris. (discovermagazine.com)
That's because the higher speed of comets and the high volatility of their constituents would create giant plumes on impact, so more of the iridium would escape into space, compared with impacts by rocky asteroids. (newscientist.com)