September 25, 2007—Like an interplanetary ninja, a stealthy comet has been making regular visits to our neck of the solar system undetected—until now.
Researchers working with the ESA/NASA Solar and Heliospheric Observatory (SOHO) announced today that a body first glimpsed in 1999 is a periodic comet—one that flies by the sun at predictable intervals.
This is the first comet proved to be periodic of the more than 1,350 comets seen so far by the probe.
Of the thousands of known comets in the solar system, only 190 are periodic, including the famed Halley's comet that last flew by in 1986 and is slated to appear again in 2061.
German doctoral student Sebastian Hoenig noticed in 2004 that a bright body in a September 1999 SOHO image (top) looked remarkably similar to one in an image snapped in September 2003 (middle).
Hoenig correctly predicted the body's return on September 10, 2007 (bottom)—proving that it swings past the sun every four years and providing sufficient evidence for an official designation: P/2007 R5 (SOHO).
The distant body displayed the right characteristics to be dubbed a comet, but it is missing the most well-known cometary feature—a tail.
"It is quite possibly an extinct comet nucleus of some kind," Karl Battams, who runs SOHO's comet discovery program, said in a press release. Extinct comets are those that have shed most of their volatile ice and no longer form tails.
Comet P/2007 R5 (SOHO) is too small for observers on Earth to see with the naked eye. But now astronomers eager to spot the repeat visitor will know where to look in September 2011.
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