This grey-scale image, obtained by the VIRTIS instrument on board ESA’s Venus Express, shows the atmospheric region of Venus over which NASA’s MESSENGER passed on 5 June 2007. The region of MESSENGER’s closest approach is in the night side (marked by a circle).
VIRTIS obtained this image at 2.3 micrometres from about 35 000 kilometres from the planet, on the night side. This wavelength makes it possible to probe the atmosphere down to about 30 kilometres from the surface. Much of the contrast in this image is due to the structure of the lower clouds.
The bright areas correspond to radiation from the lower atmospheric layers, indicating that the clouds are thinner in those areas. At the 2.3-micrometre wavelength it is possible to study not only the morphology of the cloud layers, but also its chemical composition (carbon monoxide, water, sulphur-dioxide, etc).