X-ray observations of Jupiter
The current generation of X-ray observatories, with their unprecedented spatial resolution (Chandra) and sensitivity (XMM-Newton), coupled to moderate (CCD) to high (gratings) spectral resolution, have made it feasible for the first time to study solar system objects in detail. Jupiter has a particularly complex magnetospheric environment, which is governed by its fast rotation and by the presence of Io and its dense plasma torus. Not surprisingly the giant planet became a target of observations since the earliest attempts at X-ray studies of the solar system: Jupiter was first detected in X-rays with the Einstein observatory (Metzger et al. 1983), and was later studied with ROSAT (e.g. Waite et al. 1994).
I have been involved with observations of Jupiter in collaboration with a team led by Graziella Branduardi-Raymont of MSSL. Jupiter was observed for 110 ksec in April 2003 and for 245 ksec in Nov 2003. The first set of data showed auroral regions at both the north and south poles. Their spectra could be modelled using a combination of emission lines. In contrast, X-ray emission from the low-latitude regions of Jupiter matched that of solar X-rays scattered in the atmosphere of Jupiter.
In our second observation we found the existance for a higher energy component to the spectra taken from the auroral regions. This component can be modelled using an electron bremmsstrahlung emission component. This is first time that this predicted component has been detected. The strength of this component was found to vary significantly over the duration of the observation which maybe linked to variations on the solar activity. Full details of these observations can be found in:
Branduardi-Raymont et al (2007), A&A, 463, 761, A study of Jupiter's aurorae with XMM-Newton
Branduardi-Raymont et al (2007), P&SS, 55, 1126 Latest results on Jovian disk X-rays from XMM-Newton
Branduardi-Raymont et al (2004), A&A, 424, 331 First observation of Jupiter by XMM-Newton
Bhardwaj et al (2005), GeoRL, 3203, S08B Solar control on Jupiter's equatorial X-ray emissions: 26-29 November 2003 XMM-Newton observation
Smoothed XMM-Newton EPIC images of Jupiter in narrow spectral bands: From top left, clockwise: OVII, OVIII, Mg XI, Fe XVII. The colour scale bar is in units of EPIC counts. The image of the planet appears slightly smaller than in Fig. 1 because of the different colour contrast. A graticule showing Jupiters orientation with 30 degree intervals in latitude and longitude is overlaid. The circular mark with a dot indicates the sub-solar point; the sub-Earth point is at the centre of the graticule. Taken from Branduardi-Raymont et al (2007).