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Paper: X-rays from Venus discovered with Chandra
Volume: 262, The High Energy Universe at Sharp Focus: Chandra Science
Page: 21
Authors: Dennerl, K.; Burwitz, V.; Englhauser, J.; Lisse, C.; Wolk, S.
Abstract: In January 10-13, 2001, Venus was observed for the first time with an X-ray astronomy satellite. The observation, performed with the ACIS-I and ACIS-S/LETG instruments on Chandra, yielded data of high spatial, spectral, and temporal resolution. Venus was observed at an elongation of 47 degrees and a phase angle of 86 degrees. At a geocentric distance of 0.72 AU, the apparent diameter of the planet was 23 arcsec. In X-rays Venus is clearly detected as a half-lit crescent, with considerable brightening on the sunward limb. The morphology agrees well with that expected from fluorescent scattering of solar X-rays in the planetary atmosphere. The emission is observed at discrete energies, mainly at the oxygen K-alpha energy of 0.53 keV. Emission is also detected from carbon K-alpha at 0.28 keV and, marginally, from nitrogen K-alpha at 0.39 keV. The X-ray flux was variable by up to a factor of five on time scales of minutes. All these findings are fully consistent with fluorescent scattering of solar X-rays. No other source of X-ray emission is detected, in particular none from charge exchange interactions between highly charged heavy solar wind ions and atmospheric neutrals, the process which causes cometary X-ray emission.
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