NASA's Hubble space telescope has captured the first images of auroras on the ice giant Uranus.
Uranus, the seventh planet from the sun, is an oddball world. At some point in its past, the planet appears to have been knocked on its side, so now its "North Pole" sits where the equator on most planets is located.
The newly observed auroras -- seen as tiny white dots in the image above -- underscore just how strange Uranus really is.
Auroras, also known as the Northern Lights, appear on Earth when the solar wind – a stream of charged particles emanating from the sun -- interacts with our planet's magnetic field. While terrestrial auroras appear as giant green curtains of light and may last hours, the auroras seen recently on Uranus were relatively small and stuck around only a few minutes.
Scientists don't know much about Uranus' magnetic field because it has only been investigated in detail once, 25 years ago when the Voyager 2 satellite zoomed by. At that time, Voyager detected auroras but Earth-based attempts to reexamine the atmospheric phenomenon on Uranus have all failed since.
Conditions on Uranus were very different when Voyager flew past. The planet's magnetic north pole was then facing straight into the solar wind, producing auroras that lasted longer and were mainly located on the night side, similar to observations of earthly Northern Lights.
Now, Uranus has entered its spring equinox season, and its axis is perpendicular to the flow of charged particles from the sun. Astronomers suspect this weird orientation is responsible for the peculiar auroras Hubble spotted.
A paper on the Uranian aurora observation will appear Apr. 14 in Geophysical Research Letters.
*Image: *Laurent Lamy
