LONDON (Reuters) - Finnish scientists have spotted a new and previously undetected comet that passed through the solar system three years ago.

Teemu Makinen and his colleagues at the Finnish Meteorological Institute in Helsinki found the comet known as C/1997 K2 while examining old images from an instrument called SWAN on the SOHO satellite.

``From May to July 1997, five comets were visible...only four of which were previously known. The one passing through the southern ecliptic pole had been missed by all observers until it was identified from the SWAN images,'' they said in a letter published in the science journal Nature Wednesday.

Although K2 should have been easily spotted from the ground the Finnish researchers said there were no reports of sightings.

The main purpose of SWAN is to study sun and solar wind, but Makinen and his associates said its images of the whole sky could be a helpful tool for spotting comets and other near-Earth objects that could cause a catastrophe if they collided with Earth.

Another comet passed the same region as K2 just a month earlier and was not detected early -- a fact that the scientists said underlines the need for full-sky surveillance of comets.

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