73P/Schwassmann–Wachmann, also known as Schwassmann–Wachmann 3, is a periodic comet in the Solar System that is in the process of disintegrating. Starting the 2011 perihelion passage the primary component 73P-C was recovered on 28 November 2010 near apparent magnitude 21.3; it came to perihelion (closest approach to the Sun) on 16 October 2011.
Comet Schwassmann–Wachmann 3, one of the comets discovered by astronomers by Arnold Schwassmann and Arno Arthur Wachmann, working at the Hamburg Observatory in Bergedorf, Germany, broke into fragments on its re-entry to the inner Solar System, May 1, 2006, in a reaction triggered by the Sun's heating the comet as it emerged from the frozen space of the outer Solar System.
Comet 73P is a parent body of meteor shower Tau Herculids.
The comet was discovered as astronomers were exposing photographic plates in search of minor planets for a minor planet survey, on May 2, 1930. The comet was lost after its 1930 apparition, but was observed several more times.
73P/Schwassmann–Wachmann has an orbital period of slightly less than 5 1/3 years so that it comes nearest to the Earth every 16 years. The primary fragment 73P-C has an Earth-MOID of 0.04 AU (6,000,000 km; 3,700,000 mi). 73P was originally estimated to have a core diameter of 1100 meters.
In 1995, 73P began to disintegrate. It was seen to break into four large pieces labeled 73P-A, B, C, & D. As of March 2006, at least eight fragments were known: B, C, G, H, J, L, M & N. On April 18, 2006, the Hubble Space Telescope recorded dozens of pieces of fragments B and G. It appears that the comet may eventually disintegrate completely and cease to be observable (as did 3D/Biela in the 19th century), in which case its designation would change from 73P to 73D. It is now known to have split into at least 66 separate objects. Nucleus C is the largest and the presumed principal remnant of the original nucleus.
The fragments were passing the Earth in late April and early May 2006, coming nearest to the Earth around May 12 at a distance of about 11.9 million km (7.4 million miles), a close pass in astronomical terms (0.08 AU) though nothing to be concerned about. In 1930 when it passed the Earth that close, there were meteor showers with as many as 100 meteors per minute. However, analysis by P. A. Wiegert et al. suggested that a recurrence of that spectacle was unlikely.
The comet was to have been visited by the CONTOUR comet nucleus probe on June 18, 2006. Unfortunately, contact with the probe was lost on August 15, 2002 when it fired its Star 30BP solid rocket motor to inject itself into solar orbit.