X-RAYING THE DARK SIDE OF VENUS-SCATTER FROM VENUS' MAGNETOTAIL?

Abstract

We analyze significant X-ray, EUV, and UV emission coming from the dark side of Venus observed with Hinode/XRT and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) during a transit across the solar disk that. occurred in 2012. As a check we have analyzed an analogous Mercury transit that. occurred in 2006. We have used the latest version of the Hinode/XRT point spread function to deconvolve Venus and Mercury X-ray images, to remove instrumental scattering. After deconvolution, the flux from Venus' shadow remains significant while that of Mercury becomes negligible. Since stray light contamination affects the XRT Ti-poly filter data we use, we performed the same analysis with XRT Al-mesh filter data, not affected by the light leak. Even the latter data show residual flux. We have also found significant EUV (304 angstrom, 193 angstrom, 335 angstrom) and UV (1700 angstrom) flux in Venus' shadow, measured with SDO/AIA. The EUV emission from Venus' dark side is reduced, but still significant, when deconvolution is applied. The light curves of the average flux of the shadow in the X-ray, EUV, and UV bands appear different as Venus crosses the solar disk, but in any of them the flux is, at any time, approximately proportional to the average flux in a ring surrounding Venus, and therefore proportional to that of the solar regions around Venus' obscuring disk line of sight. The proportionality factor depends on the band. This phenomenon has no clear origin; we suggest that. it may be due to scatter occurring in the very long magnetotail of Venus.