Vénus et la Terre seraient-elles des planètes jumelles ?


Interaction between Venus and the solar wind
 
Mars, Earth and Venus are immersed in a flow of plasma, an ionised and highly variable gas originating from the Sun, called the solar wind.

While Earth has a planetary magnetic field, which can deviate the flow of solar wind, Venus (and Mars) don’t. Gases in the upper atmospheres of these planets are ionised and can thus interact with the solar wind.

Venus is as large as Earth and it is difficult for its atmosphere to escape due to the planet’s gravity. The solar wind is the best source of energy to accelerate the upper atmosphere’s charged particles, giving them enough energy to escape. This is why Venus loses its atmosphere due to interaction with the solar wind.

To understand this phenomenon, the key questions that the instruments studying plasma on Venus Express must answer are: what and how much of the atmosphere is lost, and where is it lost?

Right now, solar activity is at its minimum in the 11-year cycle, making the solar wind weaker than average. The critical question now is how solar wind interacts with Venus when solar activity is low.

Terrific south polar vortex
 
This beautiful set of infrared images of the south polar vortex at Venus was obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express. The images, taken during four different observations performed over three orbits in August 2007, show variations in the shape of the vortex and also provide clues on the temperature variation in the clouds. They were obtained at a distance of about 66 000 km from the planet’s surface, at wavelengths of 3.8 micrometres (top left, down left, top right) and 5 micrometres (bottom right).

High-resolution versions of the individual images in the composite:

5_VIRTIS_polar_vortex_1, 5_VIRTIS_polar_vortex_2, 5_VIRTIS_polar_vortex_3, 5_VIRTIS_polar_vortex_4

Venus Express detects evidence of lightning
 
The magnetometer (MAG) on board ESA’s Venus Express detected wave signals that show evidence of lightning in the atmosphere.

Global view of Venus
 
This composite image of Venus is a combination of ultraviolet images obtained by the Venus Monitoring Camera (VMC) and infrared images obtained by the Visual and Infrared Thermal Mapping Spectrometer (VIRTIS) on board ESA’s Venus Express.



Release date: 4 décembre 2007