The demise of Comet 85P/Boethin, the first EPOXI mission target

Abstract Comet85P/Boethin was selected as the original comettarget for the Deep Impact extended mission, EPOXI . Because this comethad been only observed at two apparitions in 1975 and 1986 and consequently had a large ephemeriserror, an early intense recovery effort similar to that of 1P/Halley was undertaken beginning in 2005 using the ESO Very Large Telescopes(VLTs) in a distant comet program. These were challenging observations because of the low galactic latitude, and an error ellipse (the line of variations) that was larger than the CCD FOV, and the cometwas not seen. Dedicated recovery observing time was awarded on the Subaru telescopein April and May 2006, and June 2007, in addition to time on the VLT and Canada–France–Hawaii telescopesduring July–August 2007 with wide field mosaics and mosaicing techniques. The limiting V magnitudes from these observing runs ranged between 25.7 and 27.3 and again the cometwas not seen in the individual nights. A new image processing technique was developed to stack images over extended runs and runs after distorting them to account for dilations and rotations in the line of variations using modifications of the world coordinate system. A candidate at V ∼ 27.3 was found in the CFHT data along the LOV, 2.5′ west of the nominal ephemerisposition. The EPOXI mission was unwilling to re-target the spacecraft without a confirmation. Additional time was secured using the Spitzer Space Telescope, the Gemini South 8-m telescope, the Clay and Baade (Magellan 6.5 m), CTIO 4 m, and SOAR 4 m telescopesduring 2007 September and October A composite image made by stacking the new data showed no plausible candidate nucleus to a limiting magnitudeof V = 28.5, corresponding to a nucleus radius between 0.1 and 0.2 km (assuming an albedo of 0.04). The cometwas declared lost, presumably having disintegrated. Searches in the WISE data set revealed no debris trail, but no constraints on the possible time of disruption can be made. NASA approved the trajectory correction maneuver to go to Comet103P/Hartley 2 on 2007 November 1. Many observers searched for the cometas it came to its December 2008 perihelion, but no trace of the nucleus was found. Based on observations collected at the Very Large Telescope, Chile, in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, in part using data gathered with the 6.5 m Magellan Telescopeslocated at Las Campanas Observatory, Chile, in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope(CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii, in part using data collected at the Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which are operated by the Association for Research in Astronomy, under contract with the National Science Foundation, and in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministerio da Ciencia, Tecnologia, e Inovacao (MCTI) da Republica Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). This work is also based in part on observations taken with the Spitzer Space Telescope, which is operated by JPL/Caltech under a contract with NASA.