By Dr David Whitehouse BBC News Online science editor

Astronomers in the Czech Republic and Hawaii have seen Comet 57P/du Toit-Neujmin-Delporte splinter into at least 19 fragments.

Initial observation from the 1.2-metre (3.9-foot) telescope at Mount Palomar in California, US, on 11 July appeared to show a companion to the comet.

Further work done the following day at the Klet Observatory in the Czech Republic then confirmed the comet had actually split apart.

Pictures taken from Mauna Kea in Hawaii with the University of Hawaii 2.2-metre (7.2-ft) telescope on the nights of 17 and 18 July revealed a host of tiny mini-comets strung out in a line trailing behind the parent body.

Thermal stress

The fragmentation of Comet 57P/du Toit-Neujmin-Delporte was probably triggered by thermal stresses within the nucleus due to it being warmed by sunlight.

Astronomers believe that as the comet neared the Sun, the heat from the star was sufficient to start evaporating the water-ice and other ices bound up in the rocky nucleus.

Linear's demise was caught by Hubble

Since the ice and rock are intimately mixed, the warming and evaporating ice produces great thermal and physical stresses on the body of the nucleus.

Under normal circumstances, only vapour and tiny dust grains fly off the surface of the nucleus, producing a long tail. Occasionally, however, the stress is great enough that entire chunks of the nucleus also break away.

It is not uncommon for one or two companions to be seen near a comet that has fragmented.

A similar situation was seen some years ago with observations of Comet Linear C/1999 S4 made by the Hubble Space Telescope. In that case, the fragments were short-lived, and fizzled out after only a few days.

Fragile object

The fragments from Comet 57P/du Toit-Neujmin-Delporte are trailing alongside and behind the comet over an apparent distance equivalent to the apparent size of the full Moon.

At the comet's distance this means that some of the fragments are about one million kilometres (620,000 miles) from the main nucleus.

Researchers believe that the fragments are large enough to be around for several weeks, allowing astronomers to watch how they evolve, which should give some insight into the make-up and fragility of the comet.

Detailed measurements reveal that some of the components are 250,000 times fainter than can be seen with the unaided eye and others some 10 million times fainter. This suggests that the fragments are a few hundred metres in size.

Comet 57P/du Toit-Neujmin-Delporte was discovered in 1941 by the three people for whom it is named. The 57P just means it is the 57th comet in the list of comets that have been seen on two of their passages around the Sun. (The first comet in this list, 1P, is the famous Comet Halley's.)