Artist’s impression of NASA's Van Allen Probes mission studying Earth's radiation belts.
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
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 neighborhood.
(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.)
PHOTOS: Epic Aurora Photos From the Space Station
Image: Aurora detections made by the Mars Express spacecraft between 2004 and 2014. Credit: Based on data from J-C. Gérard et al (2015)
Because Mars doesn't have a global magnetic field like Earth, we don't expect to see auroras that often. But the Red Planet
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.PHOTOS: Solar Storm Leads to Stunning Aurora Displays
Image: This picture from the Hubble Space Telescope shows auroras coiled around Jupiter's north pole. Credit: John Clarke (University of Michigan) and NASA
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 (center) 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 locationwhere auroras are located
.PHOTO: Sun Storm Supercharges Northern Lights
Image: A NASA Cassini mission view of an aurora on Saturn as seen in ultraviolet light. Credit: NASA
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.PHOTOS: Spectacular Displays of Dancing Aurora
Image: Auroras spotted on Uranus in 2011. This image is a combination of Hubble's view of the aurora, 2011 Gemini Observatory pictures of Uranus' ring system in infrared light, and 1986 Voyager 2 pictures of Uranus in visible light. Credit: NASA, ESA, and L. Lamy (Observatory of Paris, CNRS, CNES)
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."PHOTOS: Stunning Auroras Seen Over Swedish Mountains
Image: While you can't see storms in this Voyager 2 image of Neptune, the spacecraft did gather data in 1989 showing auroras at the large planet. Credit: NASA
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."
Satellites can short-out if they encounter a surge of radiation in Earth orbit and a new study of the Van Allen belts’ shape — an intensely charged region surrounding our planet — could help better protect them from this highly-charged environment, researchers say.
Astronauts in orbit are mostly protected from the Van Allen belts as these radiation-filled volumes start at 600 miles above the Earth’s surface — generally, astronauts in low-Earth orbit travel around 250 miles high. These belts extend as far as the altitude of geosynchronous satellites, at 25,000 miles. We’ve known this for decades, but scientists have just found a new link between charged particle (specifically electrons) behavior and the shape of the belts.
“The shape of the belts is actually quite different depending on what type of electron you’re looking at,” said lead author Geoff Reeves, of Los Alamos National Laboratory’s intelligence and space research division, in a statement. “Electrons at different energy levels are distributed differently in these regions.”
The shape of the Van Allen belts can vary widely depending on how energetic the individual electrons are, and general conditions in the Earth’s magnetic environment. During geomagnetic storms (4), all three regions in the belts can balloon. NASA Goddard/Duberstein
The belts were discovered by Explorer 1, the first American satellite that went into space in 1958. They are named after James Van Allen, the space scientist who designed a cosmic ray instrument on that satellite. (He detected fewer cosmic rays than expected and suggested it may be due to radiation belts, which were confirmed in a later mission.) The belts’ shape changes depending on many factors, such as if the sun has recently sent a solar flare that hit the Earth’s magnetic environment.
Initially, scientists built up a very simple picture of the belts: a small inner belt, an empty space (called the “slot region”), and an outer belt that has a lot of electrons and is highly changeable.
The new research shows that these belts change frequently. If there’s a big solar storm, for example, the region merges into one large belt. Sometimes you’ll see a large inner belt and a small outer belt. Sometimes there will be an outer belt, but no inner belt at all.
There also are different energies of electrons throughout the belts. The inner belt has more electrons with low energies (generally) while the outer belt usually has more electrons with high energies. The level of electron energy varies with geomagnetic storms, causing the belts to dynamically change size and shape with respect to one other.
Launched in 2012, the current NASA Van Allen Probes are able to measure more levels of electron energy than previously detected, both because of their sensitive instruments and position above the atmosphere. With more study, scientists are hoping to start building a better picture of how the Van Allen belts change, with an eye to protecting satellites.
The study was published in the Journal of Geophysical Research.