Skip Navigation: Avoid going through Home page links and jump straight to content
Date: 21 May 1996 -- For immediate release

Ref. PN 96/19
Issued by: Dr Jacqueline Mitton, RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914 FAX: Cambridge ((0)1223) 572892


First Image of Extreme-Ultraviolet Emission from a Comet: Another 'First' for Comet Hyakutake

Astronomers using the UK's Wide Field Camera (WFC) on board Germany's ROSAT X-ray satellite made the first ever extreme ultraviolet (EUV) image of a comet when they observed Comet Hyakutake on 27 March 1996. The observation was simultaneous with the X-ray measurements made from the US-provided High Resolution Imager, reported in April. It was part of a sequence of ROSAT measurements of the comet over the period 26 to 28 March.

These first ever X-ray/EUV images of a comet are remarkable because of the great - and quite unexpected - brightness, and the large changes in brightness over a few hours. The combination of simultaneous X-ray and EUV measurements provides a powerful means of investigating the physical mechanism responsible for the observed emission. This important discovery shows that there must be previously unsuspected 'high-energy' processes taking place in the comet, probably due to the influence of the Sun's radiation and/or the solar wind.

In addition to providing two close, but clearly separated, wavelength bands, the HRI and WFC are complementary in terms of the area of sky that they can see at any one time. The HRI has very good spatial resolution (roughly 10-20 times better than the naked eye) and a 'field of view' of about half a degree across, while the WFC has rather lower resolution but covers a much larger field - five degrees. The WFC images show faint diffuse emission extending beyond the edge of the HRI field of view - out to at least three-quarters of a degree from the centre of the comet nucleus, and forming an arc around the bright central region.

The ROSAT observation was proposed as a 'Target of Opportunity' by planetary scientists Drs Carey Lisse and Mike Mumma of NASA's Goddard Space Flight Center (GSFC). The research is being conducted in collaboration with Drs Konrad Dennerl, Jakob Englhauser and Juergen Schmitt of the Max- Planck-Institut fuer extraterrestrische Physik, Garching, Germany; Dr. Richard G. West of Leicester University, UK; Mr Mike Harden and Dr Martin Ricketts of the Rutherford Appleton Laboratory, UK; and the German, US, and UK Project Scientists, Professor Joachim Truemper (MPE), Dr Robert Petre (GSFC) and Dr John Pye (Leicester University), respectively.


ROSAT is a joint German, British and United States space project. ROSAT provides a fully stabilised satellite in earth orbit, carrying an X-ray telescope and an extreme-ultraviolet (EUV) telescope. ROSAT will complete six years of in-orbit operations on 1st June 1996.

The Wide Field Camera (WFC) extreme-ultraviolet telescope was designed and built by a consortium of UK research groups led by Leicester University, and including Birmingham University, Mullard Space Science Laboratory of University College London, Imperial College of Science, Technology and Medicine London, and the Rutherford Appleton Laboratory.

ROSAT activities in the UK are funded by the Particle Physics and Astronomy Research Council (PPARC). PPARC has recently awarded the UK Project team (at Leicester University, Birmingham University, and the Rutherford Appleton Laboratory) continued funding for a further two years, from 1st April 1996.

Further information on the ROSAT observations of comet Hyakutake can be found on the Internet World Wide Web at:


UK: Dr. John Pye, Department of Physics & Astronomy, Leicester University
Phone: +44 (0)252 3552
Fax: +44 (0)252 3311

Germany: Dr. Konrad Dennerl, Max-Planck-Institut fuer extraterrestrische Physik, Garching
Phone: +49 89 3299 3862
Fax: +49 89 3299 3569

USA: Dr. Carey M. Lisse, University of Maryland / NASA Goddard Space Flight Center
Phone: +1 301 405 1563
Fax: +1 301 314 9067

Caption to illustration:

This false-colour image of Comet Hyakutake at extreme- ultraviolet (EUV) wavelengths (at around 10 nanometres, equivalent to a photon energy of about 120 eV) was obtained by the UK's Wide Field Camera (WFC) on-board Germany's ROSAT satellite. The observation was made on 27 March 1996, simultaneously with X-ray measurements from the US-provided High Resolution Imager. The most intense regions of EUV emission are shown in white. Blue and black indicate background noise.

[Credit: R. G. West & J. P. Pye, Leicester University ]