Return to web version

UK Astronomers Home in on Exploding Comet

UK astronomers using the Isaac Newton Telescope (INT) in La Palma have been tracking a comet that has brightened by a factor of a million over the last week, enabling it to be seen with the naked eye.

Comet Holmes enhanced to show the expanding cloud of dust.
(Credit: T Naylor / A Fitzsimmons / C Brunt / ING)

Last Monday night, Comet Holmes was a very faint object that needed a large telescope to see it. On Tuesday night, two amateur astronomers in the Canary Islands spotted it had suddenly got much brighter. Over the next 24 hours it continued the trend until it had brightened by a factor of a million and could clearly be seen without a telescope!

The comet is easy to see with by eye, as long as you are not in the centre of a large town or city. It appears as a small fuzzy object as bright as a medium-brightness star in the constellation Perseus. It is visible in the early evening after dark in the north east sky, and is directly overhead by 1 o'clock in the morning.

As word spread around the globe, Professor Alan Fitzsimmons of Queen's University Belfast knew this was a once in a lifetime event and scrambled to find a telescope that could observe this phenomenon. "Although comets have been seen to undergo outbursts before, the scale of this dwarfed anything seen in the past century", he said.

Luckily, Professor Tim Naylor and PhD student Cameron Bell from The University of Exeter were using the 2.5m Isaac Newton Telescope (INT) that evening. "Comets are not normally my thing" said Prof. Naylor who usually studies star formation, "but it was an interesting technical challenge to observe something so bright with a large telescope."

“On the first night we were only able to do it thanks to a filter left over from an old cosmology project which we used to cut down the light. It’s the first time I've walked out of the control room, estimated by eye how bright an object is, and then set my exposure time accordingly. The most fascinating bit was watching the nucleus gradually separate from the cloud of dust, and realising just how far out of the ordinary this comet is."

The images from the INT show an expanding circular cloud of gas and dust emanating from the nucleus of the comet, together with a brighter cloud of material. Professor Fitzsimmons said "From these images we can see the ejecta moving away from the comet at 2,000 km per hour (1,300 miles per hour). The total amount of material ejected is probably about 1% of the total mass of the comet. On a smaller scale, it is like the Earth suddenly threw off its crust."

It is not clear what caused this explosive event. One possibility is that it was hit by a meteoroid. More probably there has been a build-up of gas under part of the surface that catastrophically ruptured the surface last week.

Astronomers are now studying the event to try and determine the cause. There is always the possibility of another outburst as well. "When this comet was discovered in 1892 it was also undergoing an outburst" noted Professor Fitzsimmons. "It underwent another one just ten weeks later. We'll have to keep an eye on this one."

Also taking part in this study are Dr. Colin Snodgrass of the European Southern Observatory, Dr. Hermann Boehnhardt of the Max-Planck Institute for Solar System Research, and Dr. Tim Lister of the Las Cumbres Observatory.

  • Gill Ormrod
    Science and Technology Facilities Council
    Press Office
    Tel: +44 (0)1793 442 012
    Mobile: 0781 8013 509

  • Prof Alan Fitzsimmons
    Astrophysics Research Centre
    Queen's University Belfast
    Tel: +44 (0)2890 973 124

  • Prof Tim Naylor
    School of Physics
    University of Exeter
    Tel: +44 (0)1392 264 151

  • Javier Mendez
    ING Public Relations Officer

Image - Comet Holmes enhanced to show the expanding cloud of dust from the outburst more clearly. The Earth is shown to scale at the lower right.
Credit: T. Naylor/A.Fitzsimmons/C.Brunt/ING

Further images of the comet, the telescope and a sky map showing where the comet can currently be observed are available from Gill Ormrod in the STFC press office (contact details above).

Further information

Comets are small icy bodies that orbit our Sun. When near the Sun, the comet warms and ices on the surface 'boil off' to form its atmosphere and tails. Over a thousand comets have been discovered orbiting our Sun.

Comet 17P/Holmes was discovered in 1892 by British amateur astronomer Edwin Holmes. It takes 6.9 years to orbit the Sun once, and does not come close to the planet Earth. Comet Holmes is currently 244 million kilometres from Earth and 368 million kilometres from the Sun.

The Isaac Newton Group of Telescopes (ING) operates the 4.2m William Herschel Telescope (WHT), the 2.5m Isaac Newton Telescope (INT) and the 1.0m Jacobus Kapteyn Telescope (JKT) on behalf of the Science and Technology Facilities Council (STFC) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands, and the Instituto de Astrofísica de Canarias (IAC) in Spain. The ING is located at the Roque de Los Muchachos Observatory, La Palma.

About STFC

Page last updated: 31 October 2007 by Gill Ormrod