X-rays from Venus observed with Chandra

X-ray observations of Venus are so challenging that the first detection of Venusian X-rays succeeded only in January 2001, with the Chandra satellite. The X-rays from Venus were found to result from fluorescent scattering of solar X-rays in the Venusian thermosphere. An additional component, caused by charge exchange of highly charged heavy ions in the solar wind with atoms in the Venusian exosphere, was suspected, but could not be unambiguously detected. This was hampered by the fact that the observation occurred during solar maximum, when the solar X-ray flux is highest. In order to investigate the presence of an additional charge exchange component, Venus was observed again in March 2006 and October 2007 with Chandra, taking advantage of the fact that the solar X-ray flux had decreased considerably on its way to solar minimum. In fact, these subsequent observations were able to show that also the Venusian exosphere is emitting X-rays, due to its interaction with the solar wind. Here an overview of all the existing X-ray observations of Venus is presented, including first results from the most recent one, which took place after the arrival of Venus Express, providing the first ever opportunity to combine a remote X-ray observation of a planetary exosphere with simultaneous in situ measurements of the solar wind.