Date: 14 September 2017
Satellite: Venus Express
Copyright: ESA/VIRTIS/J. Peralta and R. Hueso

This pair of images, taken with the VIRTIS instrument on Venus Express, shows stationary waves in the clouds above the night side of the planet.

Observing the thermal emission from clouds in the upper layers of Venus's atmosphere has been difficult because the contrast in infrared images was low. A team of scientists, led by Javier Peralta of the Japan Aerospace Exploration Agency (JAXA), used the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on ESA's Venus Express spacecraft to see the clouds properly for the first time, allowing them to explore what previous teams could not.

Night side upper clouds form different shapes and morphologies than those found elsewhere–large, wavy, patchy, irregular, and filament-like patterns, many of which are unseen in dayside images–and are dominated by unmoving phenomena known as stationary waves.

These waves are concentrated over steep, mountainous areas of Venus; this suggests that the planet's topography is affecting what happens up above in the clouds.

This pair show cloud cover at 13:35:23 UTC on 29 April 2008 and one hour later, and was taken with the 3.9 micron filter. Careful examination shows that some of the cloud features do not move.

This research is reported in 'Stationary waves and slowly moving features in the night upper clouds of Venus', by J. Peralta et al., published on 24 July 2017 in Nature Astronomy. doi: 10.1038/s41550-017-0187.