Venus comes to life at wavelengths invisible to human eyes

New images provide insight into Venus' atmosphere.Provided by ESA, Noordwijk, Netherlands
By | Published: December 3, 2008
Venus Monitoring Camera image taken in the ultraviolet (0.365 micrometers), from a distance of about 30,000 km. It shows numerous high-contrast features, caused by an unknown chemical in the clouds that absorbs ultraviolet light, creating the bright and dark zones.
December 3, 2008
A pale yellow dot to the human eye, Venus comes to life in the ultraviolet and the infrared. New images taken by instruments on board the European Space Agency’s (ESA) Venus Express provide insight into our neighboring planet’s turbulent atmosphere.

Venus Express lets scientists compare what the planet looks like in different wavelengths, giving them a powerful tool to study the physical conditions and dynamics of the planet’s atmosphere.

Observed in the ultraviolet, Venus shows numerous high-contrast features. The cause is the inhomogeneous distribution of a mysterious chemical in the atmosphere that absorbs ultraviolet light, creating the bright and dark zones.

The ultraviolet reveals cloud structure and the atmosphere’s dynamical conditions in the atmosphere and the infrared provides information on the cloud tops’ temperature and altitude.

venus' atmosphere
A Venus Monitoring Camera ultraviolet image with a superimposed color mosaic, showing the altitude of the cloud tops. The color mosaic was derived from simultaneous pressure measurements by the Visible and Infrared Thermal Imaging Spectrometer.
With data from Venus Express, scientists have learned that the equatorial areas on Venus that appear dark in ultraviolet light are regions of relatively high temperature, where intense convection brings up dark material from below. In contrast, the bright regions at mid-latitudes are areas where the temperature in the atmosphere decreases with depth. The temperature reaches a minimum at the cloud tops suppressing vertical mixing. This band of cold air, nicknamed the cold collar, appears as a bright ring in the ultraviolet images.

Infrared observations have been used to map the altitude of the cloud tops. Surprisingly, the clouds in both the dark tropics and the bright mid-latitudes are located at about the same altitude of about 45 miles (72 kilometers). At 60° south, the cloud tops start to sink, reaching a minimum of about 40 miles (64 kilometers), and form a huge hurricane at the pole.

Infrared images overlaid on ultraviolet images bring the giant hurricane’s eye at the planet’s south pole to life. Its center is displaced from the pole and the whole structure measures about 1,243 miles (2,000 kilometers) across, rotating around the pole in about 2.5 days.

This study reveals that variable temperature and dynamical conditions at the Venus cloud tops are the cause of the global ultraviolet pattern.

But the exact chemical species that creates the high-contrast zones still remains elusive, and the search is on.