The Solar and Heliospheric Observatory (SOHO) has spotted an unusual comet that flies around the sun at regular intervals.

Dubbed P/2007 R5 (SOHO), the object belongs to a rare class of comets called periodic comets. Only 190 of the thousands of known comets are periodic. The most famous periodic comet is Halley's Comet, which can be seen from Earth every 76 years and last passed close to the sun in 1986.

While many of SOHO's 1,350 detected comets are suspected of being periodic, this is the first one conclusively proven and declared as such. The new comet has a much smaller orbit than Halley, taking only about four years to travel once around the sun. It was first seen in September 1999, and then again in September 2003. In 2005, Ph.D. student Sebastian Hoenig at the Max-Planck-Institute for Radioastronomy in Bonn, Germany, speculated the two comets were actually the same object.

http://www.space.com/scienceastronomy/070925_soho_comet.html