Double aurorae shine on Saturn (slideshow)

Credit: NASA, ESA and Jonathan Nichols (University of Leicester)

Few sights on Earth are more stunning that the atmospheric light show displayed by the aurora borealis and aurora australis. But Earth isn’t the only planet to dazzle with northern and southern lights. Early last year Hubble snapped a shot of Saturn’s own polar light show. The image of the shining lights around Saturn’s poles, seen above, was released today.

The picture is a straight-on view of Saturn taken in ultraviolet (hence the blue coloring). The black line of the rings is sharply defined, but for once, the rings aren’t the focal point of the image. The real stars are the sparks of light seen on both poles, caught at the perfect moment just as Saturn was approaching the equinox of its orbit.

At equinox the sun’s light shines at a planet’s equator at a direct 90-degree angle. On Earth, there are two equinoxes a year, one in the fall and another in the spring. Saturn’s equinoxes are 15 years apart—so for the dying Hubble, this is a once-in-a-lifetime image. While there are a handful of images of one pole’s aurora (see slideshow), it is rare to see both at the same time.

The phenomenon of aurorae is more than just pretty lights. It can tell astronomers a great deal about a planet’s chemical make-up and magnetic field. Aurorae occur when particles sloughed off by the sun in the form of solar wind interact with the particles in a planet’s atmosphere. Solar wind particles are electrically charged, meaning they mingle with the magnetic field as well. Since the magnetic field is the strongest at the poles, that is where the most interaction occurs. The myriad of colors that appear reflect the sorts of particles that exist, such as red for nitrogen and green for oxygen.

From the images (and videos) taken by Hubble, astronomers were able to pinpoint differences in the northern and southern aurorae of Saturn. In the north, the “auroral oval is slightly smaller and more intense than the southern one, implying that Saturn's magnetic field is not equally distributed across the planet.” [EurekAlert] It is stronger in the north, a factiod first suggested by data taken by Cassini in 2004.

As scientists continue to study the images, take a look at a slideshow of some of Saturn’s greatest picture moments, as well as some Earthly aurorae shots.  Also, over on MSNBC, check out a video compilation of the lights in action.