X-ray probes of magnetospheric interactions with Jupiter's auroral zones, the Galilean satellites, and the Io plasma torus

Abstract

Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the jovian system is a source of X-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are both powerful sources of X-ray emission. Chandra observations revealed X-ray emission from the Io plasma torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from the moons is due to bombardment of their surfaces by highly energetic magnetospheric protons, and oxygen and sulfur ions. These ions excite atoms in their surfaces leading to fluorescent X-ray emission lines. These lines are produced against an intense background continuum, including bremsstrahlung radiation from surface interactions of primary magnetospheric and secondary electrons. Although the X-ray emission from the Galilean moons is faint when observed from Earth orbit, an imaging X-ray spectrometer in orbit around one or more of these moons, operating from 200 eV to 8 keV with 150 eV energy resolution, would provide a detailed mapping of the elemental composition in their surfaces. Surface resolution of 40 m for small features could be achieved in a 100-km orbit around one moon while also remotely imaging surfaces of other moons and Jupiter's upper atmosphere at maximum regional resolutions of hundreds of kilometers. Due to its relatively more benign magnetospheric radiation environment, its intrinsic interest as the largest moon in the Solar System, and its mini-magnetosphere, Ganymede would be the ideal orbital location for long-term observational studies of the jovian system. Here we describe the physical processes leading to X-ray emission from the surfaces of Jupiter's moons and the properties required for the technique of imaging X-ray spectroscopy to map the elemental composition of their surfaces, as well as studies of the X-ray emission from the planet's aurora and disk and from the Io plasma torus.

Modeling spectra of the north and south Jovian X‐ray auroras

“…The Chandra ACIS‐S instrument obtained spectra of the Jovian polar X‐ray emission during the February 2003 observations. A general description of the Chandra observational data has been reported in earlier papers [ Elsner et al , 2005a, 2005b; Bhardwaj et al , 2006]. In Figures 7 and 8we show the X‐ray photon spectra obtained with the Chandra X‐ray telescope for the North and South polar regions respectively.…”

“…They have been inferred from least square fitting of observational data. Modeling with the charge‐exchange spectra is different from a standard fitting of observational data by arbitrary variations of intensities of individual emission lines [ Elsner et al , 2005a; Branduardi‐Raymont et al , 2007a, 2007b]. Individual line fitting includes a larger number of variable parameters (degrees of freedom) and may yield relatively small values of χ 2 .…”

“…The resolving power of the latest observations of the Jovian X‐ray spectra with Chandra and XMM‐Newton telescopes was sufficient to distinguish the radiation of highly‐charged excited ions from bremsstrahlung and yield data on the composition of the precipitating ion flux [ Elsner et al , 2005a; Branduardi‐Raymont et al , 2004, 2007a, 2007b; Kharchenko et al , 2006]. Although recent observations support strongly the charge‐exchange mechanism for Jovian X‐ray auroras, the detailed characteristics of polar X‐ray spectra have not been determined.…”

Low‐ to middle‐latitude X‐ray emission from Jupiter

“…These initial observations were followed about a decade later by a series of ROSAT observations spanning a period of about 6 years [ Waite et al , 1994, 1995, 1997; Gladstone et al , 1998]. More recently, both X‐ray cameras on the Chandra X‐ray Observatory (CXO), the spectroscopy array of the Advanced CCD Imaging Spectrometer (ACIS‐S) and the imaging array of the High‐Resolution Camera (HRC‐I), have observed Jupiter [ Gladstone et al , 2002; Elsner et al , 2002, 2005a, 2005b, 2005c], as has the XMM‐Newton X‐ray Observatory [ Branduardi‐Raymont et al , 2004, 2006a, 2006b; Bhardwaj et al , 2005a]. These observations have stimulated theoretical studies of X‐ray emission from Jupiter [ Metzger et al , 1983; Barbosa , 1990; Waite , 1991; Singhal et al , 1992; Cravens et al , 1995, 2003, 2006; Kharchenko et al , 1998; Liu and Schultz , 1999; Maurellis et al , 2000; Bhardwaj et al , 2002; Bhardwaj , 2003, 2006; Bunce et al , 2004].…”

Geant4 Applications in Space

“…Full-scale geometrical and magnetosperic structure of a planet is modeled in Geant4 to simulate the trapped solar particles to the Earth [22], Mercury [23], Mars [24] and Jupiter [25]. Geant4 is also used successfully for simulation of even larger scale and in higher energies such as particle accelerations in solar flare [26] and gamma-ray burst [27].…”