Gary sent in this one – Surprise! Venus may have auroras – yet it is not supposed to have a magnetic field (see www.space.com/15171-venus-auroras-magnetic-field.html). Apparently, it may explain the mysterious flashes of light from Venus and even more interesting, it may shed light on the way comet tails work.
On Earth aurorae are caused by magnetic lines of force breaking and connecting with each other. It can explosively convert magnetic energy into heat and kinetic energy. This occurs on Mercury, Jupiter and Saturn as well as on Earth. Magnetic fields deflect charged particles in the solar wind streaming from the Su. On the lee sides of planets facing away from the solar wind magetospheres elongate into magneto-tails. In spite of having no magnetic field Venus does have a magneto-tail caused by the solar wind interacting with the ionosphere, the upper atmosphere of which is loaded with electrically charged ions.
For further information on auroras – see www.space.com/15139-northern-lights-auroras-earth-facts.html and http://astronomy.swin.edu.au/cosmos/A/Aurora or even www.nasa.gov/mission_pages/themis/auroras/aurora_live.html