Charge-Exchange Mechanism of X-ray Emission V. Kharchenko ITAMP Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 02138 The charge-exchange mechanism of X-ray emissions induced by the Solar Wind (SW) ions form the cometary and planetary atmospheres and from the interstellar gas is discussed. The X-ray photon spectra of individual highly charged SW ions (Oq+, Cq+, Nq+, Neq+, and other ions) are described in detail. Spectra of cascading X-ray and EUV emissions of heavy SW ions are calculated for various ion velocities and compared with the results of laboratory measurements. Relative intensities of different spectral lines of the charge-exchange X-ray/EUV emission are used for the remote diagnostic of the compositions and velocities of the SW plasma. The synthetic X-ray spectra, computed for the slow and fast solar winds, are applied for the analysis of the observed cometary and planetary X-rays and for predictions of X-ray spectra from the interstellar gas. The contribution of the charge-transfer emission into the X-ray diffuse background is discussed.