The breakup of a long-period comet is not a likely match to the Chicxulub impactorOPEN ACCESS 

Steven J. Desch, Alan P. Jackson, Jessica L. Noviello & Ariel D. Anbar

Scientific Reports, Volume 12, Article number: 10415 (2022)
Published: 21 June 2022


The Original Article was published on 15 February 2021

“Since the discovery of Ir in the clay layer at the K-Pg boundary1, scientists have sought to constrain the origin of the extraterrestrial impactor that triggered the end-Cretaceous mass extinction of the non-avian dinosaurs and other species. While the first proposal was for an asteroid1, for a while some theories invoked a cometary impactor to explain perceived periodicities in mass extinctions2. Such models have long been disfavored by the mass of Ir in the layer, inferred to be 2.0−2.8×1011g3. The size of the Chicxulub crater leads to an estimated asteroid impactor diameter, D≈10km1,4,5. Comets typically impact at higher speeds, reducing the impactor mass for the same impact energy4. Although it is increasingly recognized that a continuum exists between comets and asteroids, ’comets’ are considered to be more ice-rich (estimates for 67P/Churyumov-Gerasimenko are about 20%;6), implying lower Ir contents per impactor mass. A carbonaceous chondrite-like asteroid of the appropriate size would likely deliver ≈2.3×1011g of Ir4, in the center of the estimated mass range of the global Ir layer; but a comet would only deliver ∼0.1×1011g, because it would be less massive. Although these conclusions are long standing, Siraj and Loeb7 have recently argued anew in favor of a comet over an asteroid, based on dynamical and geochemical evidence. Here we demonstrate that their arguments are based on misinterpretations of the literature, and that an asteroid is in fact still highly favored over a comet.”