A major step in understanding the X-ray generation in comets:: recent progress obtained with XMM-Newton

The observation of comet C/2000 WM1 (LINEAR) with XMM-Newton is a highlight in the field of cometary X-ray research. During 17 hours of almost uninterrupted observations, more than one million photons were recorded with unprecedented spectral resolution. The results obtained so far clearly demonstrate that the X-ray emission is caused by charge exchange reactions between highly charged heavy ions in the solar wind-mainly oxygen and carbon-and cometary gas. Due to the high number of detected photons, an investigation of the X-ray morphology is also possible in unprecedented detail. The observation is also a highlight from the technological point of view, demonstrating that XMM-Newton has more capabilities than are currently utilized. In order to follow the comet, the orientation of the satellite had to be adjusted several times. This was done by just changing the guide star offsets, leaving the X-ray instruments switched on. Compared to the usual procedure with regular slews, where the X-ray instruments are reinitialized afterwards, this new technique increased the time available for scientific observations by 34% for MOS and by 83% for PN. The capability of performing quick attitude adjustments during an observation may be of interest also for other astrophysical applications.