Comet LINEAR was discovered on January 3, 2001, and designated by the International Astronomical Union (IAU) as ‘C/2001 A2’.

Six weeks ago, it was suddenly observed to brighten. Amateurs all over the world saw the comparatively faint comet reaching naked-eye magnitude and soon thereafter, observations with professional telescopes indicated the reason for this strange behaviour: the comet’s “dirty snowball” nucleus had split into two pieces.

During the splitting of the nucleus, fresh material from the interior of this frozen body is suddenly exposed to the sunlight, causing a rapid increase in the evaporation process. More cometary material is released and the overall brightness increases, as more sunlight is reflected off the dust around the nucleus.

New images from the VLT show that one of the two nuclei of Comet LINEAR, now about 100 million km from the Earth, has just split into at least two pieces. The three fragments are now moving through space in nearly parallel orbits while they slowly drift apart.

This comet will pass through its perihelion (nearest point to the Sun) on May 25, 2001, at a distance of about 116 million kilometres. It has brightened considerably due to the splitting-up of its ‘dirty snowball’ nucleus and can now be seen with the unaided eye by observers in the southern hemisphere as a faint object in the southern constellation of Lepus (The Hare).

Comet LINEAR moves in an exceedingly elongated orbit and it is making one of its first approaches to the Sun, perhaps even the first one. It is therefore a “new” comet in which unaltered material from the formation of the solar system some 4.5 billion years ago may still be present. For this reason, the splitting of its nucleus is of particular interest to the astronomers: by spectroscopic observations, they may be able to observe directly such material and hence to learn more about the processes that took place at the time of the formation of the solar system.

Last year, the nucleus of another Comet LINEAR (designated C/1999 S4) disintegrated completely. It was observed extensively with the ESO VLT and the Hubble Space Telescope (HST), cf. ESO PR Photo 20/00. Quite by chance, a series of research papers based on those and other observations of that comet are being published in today’s issue (May 18) of the research journal Science.

The full text of this communication from ESO, with photos and all weblinks,is available at:


Dr Richard West

European Southern Observatory