Roque de Los Muchachos Observatory, La Palma

Press Release ING 2/2000

Date: Friday 28 July 2000

For immediate release

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.

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).


Disruption of the nucleus of Comet LINEAR


Caption: 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.

Picture credit: Dr. Mark Kidger, Instituto de Astrofisica de Canarias.

The Jacobus Kapteyn Telescope


Caption: The 1-m Jacobus Kapteyn Telescope.

Picture credit: Nik Szymanek and Ian King.


Dr. Mark Kidger

Instituto de Astrofisica de Canarias


Phone: +34 922 605200

Fax: +34 922 605210

Mr. Javier Mendez

Public Relations Officer

Isaac Newton Group of Telescopes


Phone: +34 922 425464, +34 616 464111

Fax: +34 922 425401

More information on ING:

More information on this news can be found in IAU Circular 7467.