Lecturer: Herbert Gunell (IRF)
Date: 2006-09-07 10:00
Place: Aniara

X-rays from Solar Wind Charge Exchange at Unmagnetized Planets

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. We review the fundamentals of solar wind-Mars interaction in general and the generation of charge exchange X-rays in particular.
X-rays from Mars were first observed in 2001 using the Chandra telescope. Mars was also observed in X-rays in 2003 by XMM-Newton.
The X-ray emissions from the disc of Mars are caused by fluorescence of X-rays from the sun. Around Mars there is a ring shaped halo of X-ray emissions that can be explained by the solar wind charge exchange (SWCX) process. We have studied these emissions using a hybrid simulation of the solar wind-Mars interaction and a test particle simulation of heavy ion trajectories near Mars. A comparison with the observations 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 on the day of the observation were estimated. 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+ . 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.
Finally, we compare Mars to Venus, which has also been observed in X-rays.

Created 2006-05-16 08:09:22 by Mats Holmström
Last changed 2006-08-31 19:16:26 by Mats Holmström