Comparing the Oxidation State of Fe in Comet 81P/Wild 2 and CP-IDPs

Chondritic-porous interplanetary dust particles (CPIDPs) are widely thought to originate in comets [1]. The collisional history of asteroids makes it unlikely that these fragile particles are asteroidal [2]. Cometary material is thought to be made of porous aggregates of small grains which is consistent with the structure of CP-IDPs. The atmospheric entry speed of CP-IDPs (deduced from heat alteration of the stratospherically collected particles) is consistent with cometary, rather than asteroidal, orbits [3]. Anhydrous CP-IDPs, showing very little parentbody alteration, originate from either anhydrous objects or hydrous objects that have been kept at very low temperature, again consistent with a cometary origin. With the return of cometary samples by NASA’s Stardust mission, it is now possible to compare CP-IDPs with material from comet Wild 2. Ishii et al. [5] reported several differences between CP-IDPs and the Wild 2 material such as a lack of GEMS and elongated enstatite whiskers and platelets. They concluded that the Wild 2 material was dissimilar to CP-IDPs and more closely resembled asteroidal material. Meteorite groups are distinguished from each other by their differing Fe oxidation states, as Urey and Craig first reported more than fifty years ago [10]. We report on the oxidation state of Fe in 15 CP-IDPs, and directly compare these measurements to the Fe oxidation state of comet Wild 2, deduced from 194 Stardust fragments in 11 aerogel tracks.