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500th Comet Discovered by SOHO

The 500th comet discovered by the joint European-US Solar and Heliospheric Observatory (SOHO), a space probe launched in December 1995 to study the Sun, was announced today.

The discovery of so many comets passing close to, or falling into, the Sun was unexpected. There seem to be at least half a dozen separate groups of bodies on orbits that collide with the Sun, each presumably fragments of a larger body that strayed too close to the Sun's powerful gravity and heat, and was broken up.

Many of these new comets have been found by amateurs, who scan the SOHO images as soon as they are posted on the internet. This is just one area where amateur astronomers have made a significant contribution to their subject, the highest tally, in excess of 135 objects, currently going to the British amateur astronomer Michael Oates.

Most SOHO comets belong to the famous Kreutz sun-grazing family of comets, a few of which (like Comet Ikeya-Seki in 1965) are some of the brightest comets ever seen. However, many of the recent discoveries are relatively small objects, perhaps only 10 - 100 m across. They are thought to be the fragments of a giant comet progenitor, possibly the one seen by the Greek Ephorus in 372 BC. Although several of these 'pygmy' sungrazers have been observed to fall directly into the Sun, astronomers are divided as to whether these impacts on the Sun cause any significant disturbance to its outer layers and atmosphere.

The SOHO space probe is located at a distance of about 1.5 million kilometres on a line between the Earth and the Sun. It was designed to provide continuous monitoring of the Sun and its outer atmosphere from X-rays through to ultraviolet and visual wavelengths. During its six-year operation, SOHO has observed many indicators of solar activity, including bright spots, flares, and highly energetic coronal mass ejections which can leave the Sun at speeds up to several thousand km per second and cause auroral displays on Earth.

These data have led to significant new understanding of our Sun, the nearest star, and the mechanisms by which energy is transferred to Earth from its hot interior through its nearly equally hot outer atmosphere or corona.

Images of the Sun, updated approximately every 30 minutes, can be obtained as a screen saver from the SOHO website.

FOR FURTHER INFORMATION CONTACT: Mark Bailey or John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; e-mails: meb@star.arm.ac.uk or jmf@star.arm.ac.uk; URL: http://star.arm.ac.uk/.

Last Revised: 2002 August 19th
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