Solar wind interaction with comets, Venus, Earth, and Mars: soft x-ray emission from charge exchange

Many objects in the solar system produce x-rays, including the Sun, Venus, Earth, Mars, Jupiter, and comets. A particularly important x-ray emission mechanism operates whenever highly solar wind ions (e.g., O7+ , C6+ , Fe12+ ,. . . .) undergo charge transfer collisions with neutral atoms and molecules they might encounter in space. The ions resulting from such collisions are almost always highly-excited and emit extreme ultraviolet (EUV) or soft x-ray photons. X-ray emissions from comets, from the terrestrial geocorona, from Mars, and from the heliosphere have been attributed to this solar wind charge exchange (SWCX) mechanism. X-ray emission from this mechanism should also take place at Venus. This x-ray emission can be used to probe how the solar wind interacts with these different solar system environments, and relevant model and observational results will be reviewed in this talk. For example, we demonstrate that for a time period when a major coronal mass ejection was impacting the Earth's magnetosphere, X-rays should be emitted from the subsolar magnetosheath and from the cusp regions.