When A Planet Behaves Like A Comet


A comparison of the ionosphere of Venus under different solar wind conditions. Credit: ESA/Wei et al. (2012)

A comparison of the ionosphere of Venus under different solar wind conditions. Credit: ESA/Wei et al. (2012)

ESA’s Venus Express has made unique observations of Venus during a period of reduced solar wind pressure, discovering that the planet’s ionosphere balloons out like a comet’s tail on its nightside. The ionosphere is a region of weakly electrically charged gas high above the main body of a planet’s atmosphere. Its shape and density are partly controlled by the internal magnetic field of the planet.

For Earth, which has a strong magnetic field, the ionosphere is relatively stable under a range of solar wind conditions. By comparison, Venus does not have its own internal magnetic field and relies instead on interactions with the solar wind to shape its ionosphere. The extent to which this shaping depends on the strength of the solar wind has been controversial, but new results from Venus Express reveal for the first time the effect of a very low solar wind pressure on the ionosphere of an unmagnetised planet.

As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions.

Full Story: http://www.esa.int/Our_Activities/Space_Science/When_a_planet_behaves_like_a_comet
Also: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51315

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