Jupiter's 'northern lights'

The light show grew to the size of the Earth in 70 seconds

By BBC News Online science editor Dr David Whitehouse

Astronomers have witnessed the first auroral flare ever seen on Jupiter.

The dramatic flare occurred while they were watching Jupiter's north pole through the Hubble Space Telescope.

They were observing the so-called auroral oval, a permanent glowing ring that encircles each of the planet's poles.

It faded as quickly as it grew

They saw an expanding region of light that covered an area the size of Earth in a matter of minutes, and disappeared just as fast.

No explanation

Earth's northern lights or aurorae occur when electrons in the solar wind penetrate our planet's magnetosphere. They interact with the upper atmosphere causing it to glow.

Scientists believe that the eerie glow near Jupiter's poles is also caused by interactions between electrons and the planet's atmosphere, but the electrons come from Jupiter and not the solar wind.

Some believe that the electrons originally come from volcanoes on Jupiter's moon Io.

Charged particles given off by them spiral towards Jupiter and are energised by Jupiter's magnetosphere, releasing light at the auroral oval.

Somehow a burst of these electrons were channelled onto one particular region near Jupiter's north pole causing the dramatic rise in emissions.

However, the researchers, describing their observations in the journal Nature, do not yet have an explanation for the precise mechanism that caused the dramatic flare.