UCL News


New Jupiter discovery

8 February 2007

An international team of astrophysicists, led by Dr Graziella Branduardi-Raymont (UCL Mullard Space Science Laboratory) has discovered the presence of high energy X-ray auroral emissions in Jupiter's atmosphere.

Reported in the current issue of 'Astronomy and Astrophysics', the emissions were detected by the XMM-Newton observatory. Equipped with three highly sensitive X-ray cameras - and an optical/UV telescope which was designed and built at UCL - it can detect much more than any other X-ray satellite.

As on Earth, Jupiter displays spectacular aurorae across its polar skies. The Jovian aurorae, at times pulsating  at approximately 45-minute intervals, cover thousands  of kilometres. They are caused by electrically charged particles, precipitating along Jupiter's magnetic field lines and striking atoms in the planet's upper atmosphere.

With X-ray images and spectra from XMM-Newton, the team found the presence of a high energy component in the spectra of the Jovian aurorae.

Scientists have been aware of the emission lines at lower energy, caused by heavy, energetic ions undergoing 'charge exchange' - when they collide with hydrogen molecules in Jupiter's upper atmosphere.

However, the newly discovered high energy component has a continuum spectrum - indicative of 'bremsstrahlung emission', a phenomenon that was suggested 25 years ago, but never conclusively proven until now.

Dr Branduardi-Raymont said: "Electron bremsstrahlung is radiation originating from high speed electrons slowing down in the Coulomb field of ions. Prior to XMM-Newton, we never had sensitive enough space X-ray observatories to detect the electron bremsstrahlung."

The team observed the emission for three and a half days, during which the high energy component varied significantly, thought to be in response to solar activity.

"High resolution X-ray spectra taken during the same observations allow us to measure the speeds of the ions producing the line emission, which travel at thousands of kilometres per second, and these are compatible with expectations from theoretical models proposed recently," added Dr Branduardi-Raymont. "All in all, these results give us more clues to try and understand the complex magnetosphere of the giant planet, and its interactions with the solar wind and solar activity. Analogies and differences with the Earth's magnetosphere can also be explored with this new found information."