An image of the nucleus of Comet LINEAR as seen on the Jacobus Kapteyn Telescope on July 26th. This is the raw, unprocessed image that the astronomer saw straight off the telescope. The unusual elongated shape was the first evidence of the comet's complete break-up. Photo: Dr. Mark Kidger, Instituto de Astrofisica de Canarias.

Nightly observations made since July 23 in different broadband filters with the 1-m Jacobus Kapteyn Telescope on La Palma, Canary Islands, Spain show what appears to be the complete disruption of the nucleus of comet LINEAR, the brightest comet of the year.

Dr. Mark Kidger, Instituto de Astrofisica de Canarias reports from the Jacobus Kapteyn Telescope: "The central condensation was highly condensed and showed the typical 'teardrop' form in the evening of July 23rd and July 24th, although its brightness decreased by a factor of about 3 between the two nights. In the evening of July 25th something very odd was happening to the comet: the central condensation was seen to be strongly elongated, with a very flat brightness distribution. The condensation's brightness faded further and its length increased on the following nights. On July 27 there was no evidence of any local brightness peaks that would indicate the presence of sub-nuclei."

In other words, it does not appear to have broken into individual fragments in the way that Comet Shoemaker-Levy 9 did in 1993. Instead, it has completely blown apart.

The expansion velocity of the condensation is about 40 m/s, indicating that it is solid particles and not gas. The gas tail, which virtually disappeared between July 23rd and 24th, has reformed as an extension of the major axis of the central condensation.

Comet LINEAR, or C/1999 S4 (LINEAR) as it is called in correct astronomical nomenclature, is a by-product of the automated LINEAR minor-planet survey. Discovered nearly as far out as Jupiter last September, this comet passed 114 million kilometres from the Sun on July 26 and only 56 million kilometres from Earth on July 22. Comet LINEAR is a "new" comet which means that it is making its very first passage through the inner solar system. The surfaces of new comets are believed to be covered almost completely by a very thin, fragile layer of highly volatile ices such as carbon dioxide intermixed with dust.

When discovered, Comet LINEAR was immediately regarded as a candidate likely to reach naked eye visibility based on its relative brightness and large heliocentric distance. New comets though are notoriously difficult to predict as far as their light curve behaviour is concerned, particularly many months in advance.

The 1-m Jacobus Kapteyn Telescope. Photo: Nik Szymanek and Ian King.

At present Comet LINEAR is diving southward from the constellation Ursa Major into Leo. It will be about 20 degrees above the west-northwest horizon as evening twilight deepens. Although not visible to the naked eye, the comet will continue to be in northern skies until the second week of August, when it will dip below the horizon. The observations with the Jacobus Kapteyn Telescope suggest though that the comet is dying very quickly and may disappear completely within a few days

The Jacobus Kapteyn Telescope will continue to observe its disintegration over the next few nights, hopefully giving new insights into the nature of comet nuclei and their structure.

The Jacobus Kapteyn Telescope is part of the Isaac Newton Group of Telescopes (ING). The ING is an establishment of the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands. Apart from the Jacobus Kapteyn Telescope, the ING also operates the 4.2 metre William Herschel Telescope and the 2.5 metre Isaac Newton Telescope. The telescopes are located in the Spanish Observatorio del Roque de Los Muchachos on La Palma which is operated by the Instituto de Astrofisica de Canarias (IAC).