Article

X rays from solar wind charge exchange at Mars: A comparison of simulations and observations

Institutet för rymdfysik, Kiruna, Norrbotten, Sweden
Geophysical Research Letters (Impact Factor: 4.2). 11/2004; 31(22). DOI: 10.1029/2004GL020953

ABSTRACT

A hybrid simulation of the solar wind-Mars interaction and a test particle simulation of heavy ion trajectories near Mars are used to compute the contribution from solar wind charge exchange processes to the X-ray emission from Mars. It is found that the X-ray halo observed by the Chandra X-ray observatory can be explained by emissions from heavy, highly charged, ions in the solar wind undergoing charge exchange collisions in the upper atmosphere of Mars.

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    • "In a detailed computer model, adjusted to the specific circumstances of the Chandra Mars observation, Gunell et al. (2004) confirmed that the contribution from the solar wind charge exchange process to the X-ray emission from the halo is large enough to explain the observed X-ray flux. A direct comparison of the azimuthally averaged radial X-ray brightness profiles, however, showed some discrepancies: the calculated count rates for the halo were higher than the observed ones by a factor between one and three. "
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    ABSTRACT: During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies. At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1- 2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles. This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun.
    Full-text · Article · Dec 2010 · Planetary and Space Science
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    • "In our previous paper (Gunell et al., 2004) the calculations were performed for a large number of ion species. In this work we concentrate on the two species that generate the highest luminosity, and study the effects of changes in the parameters of the solar wind and the exosphere. "
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    ABSTRACT: A hybrid simulation of the solar wind–Mars interaction and a test particle simulation of heavy ion trajectories near Mars are used to compute the contribution from solar wind charge exchange processes to the X-ray emission from Mars. Here, we study how the simulated X-ray emissions depend on the parameters of the simulation model. Solar wind parameters are estimated using a ballistic model based on data from the WIND satellite and using an MHD model that uses inputs from interplanetary scintillation measurements. These two models produce X-ray images with significantly different structure. The intensity of the X-ray emissions and the size of the X-ray halo are also found to increase with an increasing exobase neutral temperature.
    Full-text · Article · Dec 2005 · Advances in Space Research
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    • "These simulations show that the contribution from the solar wind charge exchange process to the X-ray emissions from the halo is large enough to explain the observed X-ray flux [3]. "
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    ABSTRACT: Wherever the solar wind meets a neutral atmosphere, X-rays are emitted by a charge exchange process between the neutrals and heavy solar wind ions. A hybrid simulation of the solar wind-Mars interaction and a test particle simulation of heavy ion trajectories near Mars is used to compute the contribution from charge exchange processes to the X-ray emission from Mars. The results are compared to observations of X-rays from Mars made with the Chandra telescope (Dennerl, K., Astronomy & Astrophysics, vol. 394, pp. 1119--1128, 2002). The comparison indicates that the solar wind charge exchange process is a likely candidate for the production of the X-ray halo at Mars. The calculations were performed in three steps. First the solar wind parameters were estimated from data obtained by the WIND spacecraft. Since Mars was near opposition the plasma that was sampled by WIND near the earth on 2 July 2001 arrived at Mars two days later during the X-ray observation. The data was scaled with the distance from the sun, and the average parameter values over the period of the observation were used as input parameters for a hybrid simulation. The second step was running a hybrid simulation of the interaction between the solar wind and Mars to obtain the electric and magnetic fields around Mars. As a third step a test particle simulation was run, calculating the trajectories of heavy solar wind ions in the electric and magnetic fields that were obtained from the hybrid simulation. The X-ray emission density was saved on a grid for each time step of the test particle simulation. A hundred thousand trajectories were calculated for each of the ion species O7+, C6+, O6+, O8+, Mg10+, Mg9+, Si9+, N6+, C5+, Ne8+, Fe9+, S9+, Si8+, Fe11+, and Mg8+.
    Preview · Article · Jan 2004
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