Weak solar wind gives Venus’ ionosphere a comet-like tail

"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)

European Space Agencies’ Venus Express recently observed the “tail of Venus”.  The Venus Express news release states:

“Measurements obtained with ESA’s Venus Express spacecraft have shed new light on the interaction between the solar wind and the second planet from the Sun. During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet.   

Scientists have long known about the existence of the solar wind, a continuous outflow of electrons and protons which flows at high speed across interplanetary space. However, this stream of charged particles is highly variable, both in speed and density.

Under normal conditions, the solar wind has a density of 5 – 10 particles per cubic cm at Earth’s orbit, but occasionally the solar wind almost disappears, as happened in May 1999. Although such unusual episodes have been studied near Earth, which is surrounded by a strong magnetic field, there have been very few opportunities to study what happens near planets with negligible magnetic fields, such as Venus.”

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