October 10, 2014

VIRTIS results

Venus observed from its surface to the high atmosphere

First map of Venus' southern hemisphere at infrared wavelengths

First temperature map of Venus' southern hemisphere at infrared wavelengths

This new map comprises over a thousand individual images, recorded between May 2006 and December 2007, from a distance of about 60 000 km. It is centred at the South Pole. The measured temperatures range from 442°C (or 715K), red to 422°C (or 695K) blue; higher temperatures correspond to lower altitudes, while lower temperature correspond to higher altitudes.

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Emission of carbon dioxide at 4.3 microns. Maximal altitude of emission at 110 km

Emission of carbon dioxide at 4.3 micronsEmission of carbon dioxide at 4.3 microns

The comparison of the spectra at 4.3 microns between the day (in blue) and night side (in red) shows a high emission of CO2 on the day side due to the high atmosphere fluorescence, high altitude molecular excitation. The imaging at this wavelength (on the left) enables to follow the variations of these emissions, responsive to the atmospheric structure.


Detection of OH by VIRTIS

Detection of OH by VIRTIS

Mean spectrum from 90 to 100 km
green: synthetic spectrum,
black: measured spectrum
The emission of OH is identified by its spectral lines.


Mean of O2 emissions

Mean of O2 emissionsMean of O2 emissions

A Mean of O2 emissions observed during numerous orbits enables to map the statistical maximum of the emission. An emission peak found at midnight (local time) in mean, corresponds to the models of formation of O2 emissions.


Emission of the high atmosphère (O2)

Emission of the high atmosphère (O2)

An instantaneous measurement of the O2 observations gives a very different image: the diffuse emission structures have a high spatial and temporal variability on this image of Venus south nocturnal hemisphere.


Drawing of the principle of O2 emissions

Drawing of the principle of O2 emissions

Drawing of the principle of O2 emissions: the photolysis on the day sider (on the left) of CO2 molecules forms atomic oxygen O, which is transported to the night side by large scale circulation. The recombination occures on the night side at the convergence point, around the local midnight.


The south pole vortex

The south pole vortexThe south pole vortex

The 6 images on the right give a vision of the rotation of the south pole vortex of Venus observed in thermal emission. The enlargement shows the cloud structure in reversed S characteristic of this "double vortex", image of the north pole vortex observed by Pioneer Venus in 1979.


Clouds velocity depending on the wavelength

Clouds velocity depending on the wavelength

Graph of the variation of the clouds velocity (in abscissa) with the latitude (in ordinate) for different wavelengths, sounding the clouds at different altitudes.


Movement of the clouds
(insertion orbit on the 11/04/2006)

Movement of the clouds (insertion orbit on the 11/04/2006)

Images of thermal emissions at 2.3 microns of Venus showing the movement of the clouds (night side); the measurement of the movement enables to build the graphs of the previous figure.


Variations of CO at 35 km

Variations of CO at 35 km

Chemical composition variations of Venus low atmosphere. The carbon monoxide is observed at 2.3 microns at an altitude of about 35 km; its variation in latitude is linked to Venus general circulation (Hadley cell).


Measurements of the composition by spectroscopy

Measurements of the composition by spectroscopy

Molecular absorptions: CO2, CO, H2O, OCS, SO2


IR and UV images correlations (VIRTIS / VMC)

IR and UV images correlations (VIRTIS / VMC)IR and UV images correlations (VIRTIS / VMC)IR and UV images correlations (VIRTIS / VMC)

Morphology of the clouds between UV (VMC) and IR (VIRTIS): day/night combination.


Measurement of the clouds altitude (VIRTIS / VMC combination)

Measurement of the clouds altitude (VIRTIS / VMC combination)Measurement of the clouds altitude (VIRTIS / VMC combination)

Spectral bands of CO2
The band depth is linked to the gas column above the clouds
=> measurement of the pression
=> measurement of the altitude.


Characterisation of the differents dynamic states

Characterisation of the differents dynamic states

Differents kinds of clouds observed function of the latitudes: laminar area near 60° where gravity waves can be observed. Convective area, where clouds show the dynamic activity of the atmosphere linked to the convection towards the medium latitudes.


Detection of the surface with VIRTIS

Détection de la surface avec VIRTIS

On the right: altitude map of the surface retrieved from Magellan data. On the left: observations of VIRTIS at 1.05 microns: the variations of surface temperature, linked to the altitude can be observed directly in the image, and produce an altimetry image of the surface in negative.