Venus comes to life at wavelengths invisible to human eyes
Wed Dec 3, 2008 at 19:39 UTC
A 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.
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 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.
With 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.
Credit: ESA/MPS/DLR/IDA.
High resolution image (1.1 MB)
Venus Monitoring Camera image taken in the ultraviolet (0.365 micrometres), 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.
With 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.
Credit: VMC ultraviolet image: ESA/MPS/DLR/IDA; VIRTIS infrared image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.
High resolution image
Using Venus Express, it is possible to compare what the planet looks like at different wavelengths, giving scientists a powerful tool with which to study this planet's turbulent atmosphere.
The lower left shows a differential temperature map (not absolute values) of the venusian cloud tops, derived from the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, on the planet's night-side. The darker the region, the colder the cloud tops. To the upper right is an ultraviolet image of the venusian day side, captured by the Venus Monitoring Camera, VMC, simultaneously with the night-side infrared image.
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.
Credit: VMC ultraviolet image: ESA/MPS/DLR/IDA; VIRTIS infrared image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.
High resolution image
A Venus Monitoring Camera ultraviolet image with a superimposed colour mosaic, showing the altitude of the cloud tops. The colour mosaic was derived from simultaneous pressure measurements by the Visible and Infrared Thermal Imaging Spectrometer.
Credit: VMC ultraviolet image: ESA/MPS/DLR/IDA; VIRTIS infrared image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.
High resolution image
In this mosaic, infrared images taken at a wavelength of 5 micrometres (in red) are overlaid on ultraviolet images, taken at 0.365 micrometres.
The bright areas in the infrared images represent the temperatures at the cloud tops (dark regions denote lower temperatures). The oval feature that stands out in these images is the giant eye of a hurricane, or the polar vortex, at the planet's south pole. Its centre is displaced from the south pole and the structure measures about 2000 km across, rotating around the pole in about 2.5 days. The atmosphere rotates anticlockwise in the figure.
Credit: Titov et al., 2008.
High resolution image
The lines indicate regions of constant temperature. They were derived from spectrometry data from the soviet Venera-15 spacecraft, taken in the northern hemisphere of Venus. Bright blue regions show areas that appear bright in the ultraviolet whereas dark blue regions indicate areas that appear dark.
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 72 km.
At 60° south, the cloud tops start to sink, reaching a minimum of about 64 km, and form a huge hurricane at the pole.
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.
But the exact chemical species that creates the high-contrast zones still remains elusive, and the search is on.
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.
| Source: European Space Agency | |
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