NEO 2003 EH_1, the Quadrantid Shower Parent

Near Earth Object 2003 EH_1, first seen by LONEOS on 2003 March 6, was identified in early December as the parent of the Quadrantid shower based on the orbit calculated from 48 days of observations following its discovery [1]. The Quadrantids is our most intense annual shower and was until now the only major shower with no parent body. The orbit matches the inclination, semi-major axis, and argument of perihelion of the Quadrantid meteoroids, but has a perihelion distance outside of Earth orbit. It was shown that frequent close encounters with Jupiter result in a rapid dispersion of perihelion distances, accounting for the current orbit of the parent body. The dispersion of orbits in the meteor shower implies a young ˜ 500 year age and the large mass in the stream suggests formation during a comet breakup. This leaves open the possibility that comet C/1490 Y1 was a sighting of the object shortly after it broke up near aphelion, but to match the perihelion time with that of the backward integrated orbit of 2003 EH_1, a better orbit solution is needed. In December and January of 2003, we recovered the object with the ESO New Technology Telescope and computed a much improved orbit. We used that new orbit to study the formation of the Quadrantid stream for various epochs of ejection. In the context of evaluating the NEO impact hazard, those meteoroids trace the orbital evolution of other possible fragments from the breakup 500 years ago that may now be on a collision course with Earth. [1] P. Jenniskens, B.G. Marsden (2003) IAU Circular 8252 - December 08, 2003 (D.W.E. Green, ed.); P. Jenniskens (2004) 2003 EH_1 is the Quadrantid shower parent comet. Astronomical Journal (in press); http://leonid.arc.nasa.gov