The European Space Agency said its Solar and Heliospheric Observatory has sighted -- for the first time -- the third passage of a specific comet.

The space observatory, called SOHO -- a joint ESA project with the National Aeronautics and Space Administration -- has found more than 1,350 comets. But this is the first time it's found a rare type of comet called a periodic comet -- meaning it flies by the sun at regular intervals. While many SOHO-discovered comets are believed to be periodic, this is the first that's been officially declared as such, the ESA said.

The most famous periodic comet is Halley's Comet, returning every 76 years, with its last close pass to the sun occurring in 1986.

SOHO's newly spotted comet is probably no more than about 650 feet in diameter and takes approximately four years to travel once around the sun, the ESA said. It was first seen in September 1999 and again in September 2003.

The ESA said the comet is expected to return in September 2011.