|Venus in the ultraviolet|
3 December 2008
pale yellow dot to the human eye, Earth’s twin planet comes to life in
the ultraviolet and the infrared. New images taken by instruments on
board ESA’s Venus Express provide insight into the turbulent atmosphere
of our neighbouring planet.
Using Venus Express, it is
possible to compare what the planet looks like in different
wavelengths, giving scientists a powerful tool to study the physical
conditions and dynamics of the planet’s atmosphere.
|Venus in the ultraviolet and the infrared|
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
The ultraviolet reveals the structure of the clouds and the
dynamical conditions in the atmosphere, whereas the infrared provides
information on the temperature and altitude of the cloud tops.
|Altimetry of the cloud tops|
data from Venus Express, scientists have learnt 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 annulus of cold air, nicknamed the ‘cold collar’,
appears as a bright band in the ultraviolet images.
Observations in the infrared 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 height of about
At 60° south, the cloud tops start to sink, reaching a minimum of about 64 km, and form a huge hurricane at the pole.
Venus’s southern hemisphere
In this mosaic, the infrared image is overlaid on an ultraviolet image,
bringing the giant hurricane’s eye at the planet’s south pole to life.
Its centre is displaced from the pole and the whole structure measures
about 2000 km across, rotating around the pole in about 2.5 days.
This study, carried out by D. Titov and colleagues has revealed that
variable temperature and dynamical conditions at the Venus cloud tops
are the cause of the global ultraviolet pattern.
Venusian cloud top structure
But the exact chemical species that creates the high-contrast zones still remains elusive, and the search is on.
Notes for editors:
These results appear in ‘Atmospheric structure and dynamics as the
cause of ultraviolet markings in the clouds of Venus’ by D. Titov et
al., published in the 4 December 2008 issue of the journal Nature.
For more information:
Dmitri Titov, Max Planck Institute for Solar System Research
Email: Titov @ mps.mpg.de
Håkan Svedhem, ESA Venus Express Project Scientist
Email: Hakan.Svedhem @ esa.int