"The overall aim of our project is to better characterize the impactor that produced the crater in the Yucatan peninsula [in Mexico],” Jason R. Moore, an Obering Postdoctoral Fellow in Dartmouth’s Department of Earth Sciences, tells BBC.
Moore and his colleague, Mukul Sharma, an associate professor of earth sciences, found that a comet, rather than an asteroid, was likely the culprit that produced the crater. Moore explains to BBC, "You'd need an asteroid of about 5 kilometer diameter to contribute that much iridium and osmium. But an asteroid that size would not make a 200 kilometer-diameter crater. So we said: how do we get something that has enough energy to generate that size of crater, but has much less rocky material? That brings us to comets."
Read the full story, published 3/22/13 by BBC.