A US-European satellite launched nearly 10 years ago has helped astronomers to spot 1,000 comets, nearly half of all officially recorded comets in history, the European Space Agency (ESA) said on Tuesday.
The 1,000th comet was identified by Italian teacher Toni Scarmato on August 5, after he pored over images sent back by the satellite, it said. Just five minutes earlier, Scarmato spotted the 999th comet.
ESA and NASA launched the Solar and Heliospheric Observatory (SOHO) satellite in December 1995. Its prime mission is to observe the Sun and its surface, but the word quickly spread among astronomers that pictures sent back by one of its instruments, a coronagraph, could also be useful for spotting comets.
The overwhelming majority of sightings have been so-called Kreutz Group comets, which hurtle into the Sun on a suicidal trajectory.
Some experts suggest that Kreutz Group comets may be parts of a huge comet that broke apart in the distant past.
One such candidate is a comet, spotted by the Greek thinker Ephorus in 372 BC, which broke into two pieces during one of its orbits around the Sun.
Scientists believe that comets are primeval material left over from the making of the Solar System - an assembly of rocks and dust smothered with ice or frozen gas.
As the comet nears the Sun, the ice melts, leaving a dusty trail that is illuminated by solar rays and appears, from the Earth, as the comet's tail.