Hubble, Cassini See Auroras on Saturn

Feb 15, 2014 by Sci-News.com

Detailed images of auroras at Saturn’s north and south poles have been captured by astronomers using NASA’s Hubble Space Telescope and Cassini spacecraft.

Saturn's northern ultraviolet aurora taken by the Hubble Space Telescope. Image credit: J.D. Nichols / University of Leicester / NASA / ESA.

Saturn’s northern ultraviolet aurora taken by the Hubble Space Telescope. Image credit: J.D. Nichols / University of Leicester / NASA / ESA.

Saturn’s auroras glow when energetic electrons dive into the planet’s atmosphere and collide with hydrogen molecules.

Sometimes a blast of fast solar wind, composed of mostly electrons and protons, creates an active aurora at the sixth planet from the Sun.

“The auroras at Saturn are some of the planet’s most glamorous features – and there was no escaping NASA’s paparazzi-like attention,” said Dr Marcia Burton from NASA’s Jet Propulsion Laboratory in Pasadena, California.

“Saturn’s auroras can be fickle – you may see fireworks, you may see nothing,” said team leader Dr Jonathan Nichols from the University of Leicester, UK.

Dr Nichols and his colleagues used Hubble telescope to observe the northern auroras in ultraviolet wavelengths and NASA’s Cassini spacecraft to capture images of the north and south in infrared, visible-light and ultraviolet wavelengths.

While the curtain-like auroras we see at Earth are green at the bottom and red at the top, NASA's Cassini spacecraft has shown astronomers similar auroras at Saturn that are red at the bottom and purple at the top. Image credit: NASA / JPL-Caltech / SSI.

While the curtain-like auroras we see at Earth are green at the bottom and red at the top, NASA’s Cassini spacecraft has shown astronomers similar auroras at Saturn that are red at the bottom and purple at the top. Image credit: NASA / JPL-Caltech / SSI.

The Hubble and Cassini images help shed light on an unsolved mystery about the atmospheres of giant outer planets.

“Scientists have wondered why the high atmospheres of Saturn and other gas giants are heated far beyond what might normally be expected given their distance from the Sun,” said Dr Sarah Badman from Lancaster University.

“We know there must be other energy interactions going on to cause this heating, but we can’t yet say for sure what they are.”

“From the Earth, we can only see part of the picture, but by looking at these amazing new movies from the vantage points of both Cassini and the Hubble Space Telescope, we can see exactly where the aurora is heating Saturn’s atmosphere and for how long.”

“Being able to track the aurora all around Saturn’s poles is vital if we are to discover how its atmosphere is heated.”

The new images also help astronomers figure out the colors of Saturn’s auroras.

While the curtain-like auroras we see at Earth are green at the bottom and red at the top, Cassini’s imaging cameras have shown us similar curtain-like auroras at Saturn that are red at the bottom and purple at the top

The color difference occurs because auroras on our planet are dominated by excited nitrogen and oxygen molecules, and Saturn’s auroras are dominated by excited hydrogen molecules.

“While we expected to see some red in Saturn’s aurora because hydrogen emits some red light when it gets excited, we also knew there could be color variations depending on the energies of the charged particles bombarding the atmosphere and the density of the atmosphere. We were thrilled to learn about this colorful display that no one had seen before,” explained team member Dr Ulyana Dyudina from the California Institute of Technology in Pasadena, California.