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Epic Auroras Throughout the Solar System: Photos
By Elizabeth Howell,
Discovery News, 17 November 2015.

When you live in the extreme north or south regions of Earth, there is a special astronomical phenomenon to enjoy besides an extra-long winter. That's auroras (or aurorae), sometimes called the northern or southern lights. This happens when charged particles from the sun interact with Earth's magnetic field lines, and "excite" molecules high in the atmosphere.

Luckily for future explorers of the solar system, they will have similar light shows to enjoy on other planets and moons. Here's a brief overview of some of the aurora research going on around our planetary neighbourhood. (We should note that auroras or associated magnetic activity for them are discussed as possibilities in some locations, such as Venus, but this will focused on confirmed observations.)

1. Mars


Because Mars doesn't have a global magnetic field like Earth, we don't expect to see auroras that often. But the Red Planet does happen to have "residual magnetism" in its crust, which is just enough to create the light show, according to the European Space Agency. During about 10 years of observations reported earlier this month, a handful of auroras were detected near where open and closed magnetic field lines intersect.

Auroras, which shine on Mars in the ultraviolet, were also detected for five days before Dec. 25, 2014 by NASA's MAVEN (Mars Atmosphere and Volatile Evolution Mission) spacecraft. In this case, the auroras seem to have been sparked by an outburst on the sun with energetic particles deep enough to penetrate into the atmosphere of the planet, further down than what you would see on Earth.

2. Jupiter (and its Moons)


A decade after NASA's Galileo mission, which ended in 2003, scientists are keen to further research the mysteries of Jupiter's magnetic field. Luckily, NASA's Juno spacecraft is on its way there, scheduled to arrive in 2016. Among its instruments is an ultraviolet spectrometer that will give a detailed look at auroras on the planet.

There should be a nice light show if past research is any indication. An amazing picture (above) from the Hubble Space Telescope shows auroras dancing around Jupiter's north pole, built on emissions from its largest moons - Io (left), Ganymede (centre) and Europa (right). The emissions happen as the moons create electric current that interacts with Jupiter's magnetic field.

Some of Jupiter's moons also have aurora-like features. Galileo spotted collisions between charged particles and Io's atmosphere that created emissions similar to aurora. Auroral features on Europa happen because Jupiter has such a strong magnetic field; these are just visible by Hubble. And we can't forget years of observations on Ganymede, which not only has a magnetic field, but also a stable location where auroras are located.

3. Saturn


Saturn has been under a long-time watch from NASA's Cassini spacecraft, which arrived there in 2004. And what a view we've had. Last year, Cassini and Hubble teamed up to provide a 360-degree view of auroras on the planet, which you can view above (and in this video). "The result is a kind of step-by-step choreography detailing how the auroras move, showing the complexity of these auroras and how scientists can connect an outburst from the sun and its effect on the magnetic environment at Saturn," NASA wrote at the time.

A couple of the major findings: It appears there is a strong link between solar activity, specifically the amount of charged particles making its way into Saturn's magnetic environment. Storms are likely also sustained as magnetic field lines forge connections between each other, which are linked to movements of the moons Enceladus and Mimas.

4. Uranus


The Voyager 2 spacecraft captured some information about auroras on Uranus when it zoomed by in 1986, but little is known to this day about the planet's magnetosphere. It is so far away, and was only visited by the one spacecraft very briefly, so it is difficult to get much information about auroras and other signs of magnetic activity. A brief exception to that came in 2011, when auroras shone so brightly on the planet that they were captured by Hubble.

"The ultraviolet images were taken at the time of heightened solar activity in November 2011 that successively buffeted the Earth, Jupiter, and Uranus with a gusher of charged particles from the Sun," NASA wrote at the time. "Because Uranus' magnetic field is inclined 59 degrees to its spin axis, the auroral spots appear far from the planet's north and south poles."

5. Neptune


Neptune is another planet that we know little about. It's far away from Earth and telescope time is precious, so we only have relative glimpses here and there into the gas giant's science. Our best close-up look came from a single spacecraft flyby in 1989, when Voyager 2 briefly zoomed by the cool, blue planet.

Voyager 2 found a much different magnetic field on Neptune than on Earth. "Because of Neptune's complex magnetic field, the auroras are extremely complicated processes that occur over wide regions of the planet, not just near the planet's magnetic poles," NASA wrote in a summary page about the planet. "The auroral power on Neptune is weak, estimated at about 50 million watts, compared to 100 billion watts on Earth."

Top image: A view of an auroral display over Earth as seen from the International Space Station during a solar storm in September 2015. Credit: NASA/Scott Kelly.

[Source: Discovery News. Edited. Some links added.]