Comets, Mars and Venus

This chapter deals with recent insights gained by X-ray observations of comets, Mars and Venus. It starts with the discovery of cometary X-ray emission, which has revealed the importance of the process of charge exchange. This process will then be described before proceeding to X-ray observations of comets, where observational aspects and data analysis methods will be covered and results will be presented. The next section deals with Mars, starting with a comparison with comets and explaining why its X-ray emission contains scattered solar X-rays as an additional component. Then specific Mars observations will be presented together with the results which they have provided, before the section about Mars will conclude with a short summary of the scientific value of such observations. The last section will be devoted to Venus, starting with a comparison with Mars, providing details about the observational challenges, and presenting results.