X-rays from Comets, Venus and Mars
Konrad Dennerl (MPE)
The discovery of cometary X-ray emission has demonstrated that X-rays provide a powerful tool for studying the interaction between the solar wind and low density gas in the solar system. This is due to the fact that the solar wind contains a small fraction of highly charged heavy ions, which capture electrons with a high cross section whenever they encounter neutral or weakly ionized atoms. As a consequence of the charge exchange, the solar wind ions attain highly excited states and radiate a large fraction of the excitation energy in the X-ray range. Thus, these X-rays contain a wealth of information: the distribution of low density gas can be globally mapped with high sensitivity, details of the interaction are revealed by spatially resolved X-ray spectroscopy, and temporal studies provide additional information about the dynamic properties of the interaction. The talk will present X-ray observations of the solar wind interaction with gas around objects where this process can be studied in an environment which is not affected by the presence of an intrinsic magnetic field. These are the comets and the planets Venus and Mars. For planets, the study of solar wind induced X-rays is more challenging than for comets, because planetary atmospheres also scatter solar X-rays. While the presence of solar wind induced X-rays could already be well established for Mars, the talk will present the first evidence that this component is also present in the X-ray emission of Venus.