Scientists organise groundbreaking Saturn's Aurora observational campaign

Auroral formation on Saturn. 

Credit: Jonathan Nichols, NASA, ESA, University of Leicester 

University of Leicester planetary scientists have collaborated with an international team of researchers to organise the largest ever observational campaign of Saturn's auroras. 

The month-long project will see a host of space and ground-based telescopes focus on the ringed gas giant in order to expand our knowledge of the planet's northern lights.

A team of scientists from the University's Department of Physics and Astronomy has collaborated with NASA and the European Space Observatory (ESO) on the project.

The instruments involved include NASA and ESA's Hubble Space Telescope, the NASA/ESA/ASI Saturn-orbiting spacecraft Cassini, the ESO's Very Large Telescope (VLT) in Chile, the W. M. Keck Observatory in Hawaii and NASA's Infrared Telescope Facility (IRTF) in Hawaii.

Saturn's Aurora
Each instrument will make different observations of Saturn's aurora covering a variety of wavelengths and view points – potentially giving the most comprehensive set of data on the phenomenon to date.

The team hope the observations will tell us more about how the auroras are formed and the way energy flows from the solar wind and Saturn's magnetic field into the planet's ionosphere and atmosphere.

This could tell us more about other auroras – including those on Earth. The group of instruments will observe Saturn's northern aurora and southern aurora at several points between April 19 and May 21.

The team chose this period to observe Saturn as it is the time of year when the planet is closest to the Earth and at its largest in the night's sky.

Dr Tom Stallard is leading the ground-based observations from IRTF over 74 hours and the VLT over 15 hours – both of which will observe Saturn's northern aurora.

Dr Jonathan Nichols is leading on the Hubble, which will observe the planet's northern ultraviolet aurora for a total of 11 hours, and Dr Sarah Badman has co-ordinated with the Cassini team to help plan observations in both the northern and southern aurora over 142 hours.

In addition, Dr Kevin Baines, of NASA's Jet Propulsion Laboratory is leading on Keck observations over 24 hours, and will work closely with Dr Tom Stallard.

At the end of the observations, the findings from each instrument will be collated. The researchers will then be able to view and compare the observations of auroral events from many different angles.

Dr Stallard, of the Radio and Space Plasma Physics Group within the University of Leicester's Department of Physics and Astronomy, said: "Up until now, it's like we have been looking at the aurora in black and white – and now we're trying to look in colour."

"We're hoping to get much more depth to the observations we have taken - filling in a far more complete picture of the aurora as a whole, rather than disconnected parts."

"What we hope to gain from this observing campaign is a way to link different auroral and magnetospheric events, following the flow of energy through the system, from the solar wind and magnetic field of Saturn down into the ionosphere and atmosphere. "

"By understanding the way this energy flows at Saturn, we should also gain real insight into the interaction between the Sun and other planets."

NORUSCA II camera: First-ever hyperspectral images of Earth's auroras

The aurora as seen as a color composite image from the NORUSCA II camera.

Three bands were combined to make the image. 

Each band was assigned a different color - red, green, and blue - to enhance the features of the aurora for analysis. 

Credit: Optics Express.

Hoping to expand our understanding of auroras and other fleeting atmospheric events, a team of space-weather researchers designed and built NORUSCA II, a new camera with unprecedented capabilities that can simultaneously image multiple spectral bands, in essence different wavelengths or colors, of light.

The camera was tested at the Kjell Henriksen Observatory (KHO) in Svalbard, Norway, where it produced the first ever hyperspectral images of auroras-commonly referred to as "the Northern (or Southern) Lights" and may already have revealed a previously unknown atmospheric phenomenon.

Details on the camera and the results from its first images were published in the Optical Society's (OSA) open-access journal Optics Express.

Auroras, nature's celestial fireworks, are created when charged particles from the Sun penetrate Earth's magnetic field. These shimmering displays in the night sky reveal important information about the Earth-Sun system and the way our planet responds to powerful solar storms.

Current-generation cameras, however, are simply light buckets-meaning they collect all the light together into one image-and lack the ability to separately capture and analyze multiple slivers of the visible spectrum.

That means if researchers want to study auroras by looking at specific bands or a small portion of the spectrum they would have to use a series of filters to block out the unwanted wavelengths.

The red arrow points to the unidentified low-intensity wave pattern, which the researchers suspect is an auroral-generated wave interaction with airglow. 

For contrast, the blue arrow points to the faint emission of the Milky Way. Credit: Optics Express.

The new NORUSCA II hyperspectral camera achieves the same result without any moving parts, using its advanced optics to switch among all of its 41 separate optical bands in a matter of microseconds, orders of magnitude faster than an ordinary camera.

This opens up new possibilities for discovery by combining specific bands of the same ethereal phenomenon into one image, revealing previously hidden details.

"A standard filter wheel camera that typically uses six interference filters will not be able to spin the wheel fast enough compared to the NORUSCA II camera," said Fred Sigernes of the University Centre in Svalbard (UNIS), Norway.

"This makes the new hyperspectral capability particularly useful for spectroscopy, because it can detect specific atmospheric constituents by their unique fingerprint, or wavelengths, in the light they emit."

These spectral signatures can then reveal subtle changes in atmospheric behaviour, such as the ionization of gases during auroras. This form of multispectral imaging also will enable scientists to better classify auroras from background sky emissions and study the way they cluster in the atmosphere.

Slow Moving Solar Coronal Mass Ejection - Video

A large but relatively slow moving coronal mass ejection (CME) that erupted from the Sun on September 27 hit Earth September 30 causing a low level radio blackout and moderate geomagnetic storms.

Although the blackout has passed, storm warnings continue through October 1.

In a couple of weeks, NOAA's GOES-15 satellite, which is the primary X-ray solar sensor used to monitor solar weather, will undergo a maintenance phase as its view of the sun is eclipsed by Earth.

During that time NOAA's GOES-14 will be brought online to provide continuous coverage of solar activity.

GOES-15 is expected to be operational again around October 30.

Aurora and two Soyuz spacecraft docked to the ISS

Aurora and two Soyuz spacecraft docked to the International Space Station are seen in this photo taken by astronaut Mike Fossum.

The closest Soyuz spacecraft will be used to transport the astronauts home at the end of their mission.

The farthest Soyuz spacecraft is the Progress cargo ship. 

It is used to deliver new supplies to the ISS, and carry away waste. It is designed to burn up in the atmosphere once released from the ISS.

Picture: BARCROFT

Extreme Space Weather at Mercury Blasts the Planet's Poles

The solar wind sandblasts the surface of planet Mercury at its poles, according to new data from a University of Michigan instrument on board NASA's MESSENGER spacecraft.

The sodium and oxygen particles the blistering solar wind kicks up are the primary components of Mercury's wispy atmosphere, or "exosphere," the new findings assert.

Through interacting with the solar wind, they become charged in a mechanism that's similar to the one that generates the Aurora Borealis on Earth.

The findings are published in the Sept. 30 edition of Science.

The Fast Imaging Plasma Spectrometer (FIPS,) made by U-M scientists, has taken the first global measurements of Mercury's exosphere and magnetosphere in an effort to better understand how the closest planet to the sun interacts with its fiery neighbor.

The measurements confirmed scientists' theories about the composition and source of the particles in Mercury's space environment.

"We had previously observed neutral sodium from ground observations, but up close we've discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury's surface," said FIPS project leader Thomas Zurbuchen, a professor in the Department of Atmospheric, Oceanic and Space Sciences and Aerospace Engineering at the U-M College of Engineering.

Earth and Mercury are the only two magnetized planets in the solar system, and as such, they can somewhat deflect the solar wind around them.

The solar wind is a squall of hot plasma, or charged particles, continuously emanating from the sun. Earth, which has a relatively strong magnetosphere, can shield itself from most of the solar wind. Mercury, which has a comparatively weak magnetosphere and is 2/3 closer to the sun, is a different story.

"Our results tell us is that Mercury's weak magnetosphere provides very little protection of the planet from the solar wind," Zurbuchen said.

Studying Mercury's magnetosphere and space environment helps scientists understand fundamental science about the sun.

Space Weather Video of Auroras

More Aurora Images and Videos here

Space Weather predictions based on flawed research

For more than 25 years, our understanding of terrestrial space weather has been partly based on incorrect assumptions about how nitrogen, the most abundant gas in our atmosphere, reacts when it collides with electrons produced by energetic ultraviolet sunlight and "solar wind."

New research published today, Tuesday 8 June, in IOP Publishing's Journal of Physics B: Atomic, Molecular and Optical Physics describes how scientists from NASA's Jet Propulsion Laboratory (JPL) at the California Institute of Technology have fired electrons of differing energies through a cloud of nitrogen gas to measure the ultraviolet light emitted by this collision.

The researchers have found that well-trusted measurements published in a 1985 journal paper by researchers Ajello and Shemansky contain a significant experimental error, putting decades of space weather findings dependent on this work on unstable ground.

The difference between these contemporary findings and the 1985 researchers' work stems from the 2010 team's improved ability to create and control the collisions and avoid the analytical pitfalls that plagued the 1985 findings.

The new results from the team at JPL suggest that the intensity of a broad band of ultraviolet light emitted from the collision changes significantly less with bombarding electron energies than previously thought.

As the ultraviolet light within the so called 'Lyman-Birge-Hopfield' (LBH) band is used by the likes of NASA and the European Space Agency to better understand the physical and chemical processes occurring in our upper atmosphere and in near-Earth space, the results will give some immediate cause to reflect.

With near-Earth space playing host to our ever-growing satellite communication systems, the new more accurate measurements might unleash a greater understanding of space weather and help us better protect our space-based assets.

The findings will also help further our understanding of phenomena like Aurora Borealis (the Northern Lights) and similarly the Aurora Australis (Southern Lights), which are caused by collisional processes involving solar wind particles exciting terrestrial oxygen and nitrogen particles at the North and South Pole.

The researchers are hopeful that their findings will also assist the Cassini project understand happenings on Saturn's largest moon, Titan, as LBH emissions have been detected by the orbiting robotic spacecraft.

Author Dr Charles Patrick Malone from JPL said, "Our measurement of LBH energy-dependence differs significantly from widely accepted results published 25 years ago. Aeronomers can now turn the experiment around and apply it to atmospheric studies and determine what kind of collisions produce the observed light."

Cassini Camera Captures Aurora high over Saturn

This video shows the tallest known auroras in the solar system, rippling high above Saturn. Image credit: NASA/JPL/Space Science Institute

In the first video showing the auroras above the northern latitudes of Saturn, Cassini has spotted the tallest known "northern lights" in the solar system, flickering in shape and brightness high above the ringed planet.

The new video reveals changes in Saturn's aurora every few minutes, in high resolution, with three dimensions. The images show a previously unseen vertical profile to the auroras, which ripple in the video like tall curtains. These curtains reach more than 1,200 kilometers (750 miles) above the edge of the planet's northern hemisphere.

Auroras occur on Earth, Jupiter, Saturn and a few other planets, and the new images will help scientists better understand how they are generated.

"The auroras have put on a dazzling show, shape-shifting rapidly and exposing curtains that we suspected were there, but hadn't seen on Saturn before," said Andrew Ingersoll of the California Institute of Technology in Pasadena, who is a member of the Cassini imaging team that processed the new video.

"Seeing these things on another planet helps us understand them a little better when we see them on Earth."

Auroras appear mostly in the high latitudes near a planet's magnetic poles. When charged particles from the magnetosphere - the magnetic bubble surrounding a planet - plunge into the planet's upper atmosphere, they cause the atmosphere to glow.

The curtain shapes show the paths that these charged particles take as they flow along the lines of the magnetic field between the magnetosphere and the uppermost part of the atmosphere.

The height of the curtains on Saturn exposes a key difference between Saturn's atmosphere and our own, Ingersoll said. While Earth's atmosphere has a lot of oxygen and nitrogen, Saturn's atmosphere is composed primarily of hydrogen. Because hydrogen is very light, the atmosphere and auroras reach far out from Saturn. Earth's auroras tend to flare only about 100 to 500 kilometers (60 to 300 miles) above the surface.

The speed of the auroral changes in the video is comparable to some of those on Earth, but scientists are still working to understand the processes that produce these rapid changes. The height will also help them learn how much energy is required to light up auroras.

"I was wowed when I saw these images and the curtain," said Tamas Gombosi of the University of Michigan in Ann Arbor, who chairs Cassini's magnetosphere and plasma science working group. "Put this together with the other data Cassini has collected on the auroras so far, and you really get a new science."

Ultraviolet and infrared instruments on Cassini have captured images of and data from Saturn's auroras before, but in these latest images, Cassini's narrow-angle camera was able to capture the northern lights in the visible part of the light spectrum, in higher resolution.

The movie was assembled from nearly 500 still pictures spanning 81 hours between Oct. 5 and Oct. 8, 2009. Each picture had an exposure time of two or three minutes. The camera shot pictures from the night side of Saturn.

The images were originally obtained in black and white, and the imaging team highlighted the auroras in false-color orange.

The oxygen and nitrogen in Earth's upper atmosphere contribute to the colorful flashes of green, red and even purple in our auroras. But scientists are still working to determine the true color of the auroras at Saturn, whose atmosphere lacks those chemicals.

Aurora from Space

Auroras: What powers the greatest light show on Earth?
See New Scientist's gallery of auroras

A few times a day, a gigantic explosion shakes the Earth's magnetic shield, triggering a chain of events that lights up the polar skies with dazzling auroras. These explosions are substorms, and how they happen has long been a mystery. Until now, no one has been able to explain how they gather the energy to create such spectacular displays, or what happens to trigger them.

Now a flotilla of NASA satellites is finally providing answers. They could help us understand not only one of nature's greatest spectacles, but also help predict more serious space weather, which can endanger satellites and astronauts, and even scramble electrical systems on Earth.

The northern and southern lights have fascinated people throughout human history, and there has been no shortage of attempts to explain them. Galileo described these auroras as sunlight reflected in vapours rising from the Earth, while Descartes proposed reflections from ice crystals instead. In the late 1600s, Edmond Halley was the first to correctly link the aurora to the Earth's magnetic field, though it wasn't until the 1950s that scientists confirmed that the display is created when electrons are funnelled by magnetic fields into the upper atmosphere.

Auroras, substorms and more hazardous kinds of space weather all begin with the solar wind - a thin, hot gas of charged particles ejected from the sun, laced with magnetic fields and threaded with electric currents. This magnetic hurricane is blowing over the planet at 1.6 million kilometres per hour, but we don't feel so much as a breeze. That's because most of it is deflected by the Earth's magnetic field, which maintains a zone of relatively calm weather around the planet, called the magnetosphere. As the solar wind blows past the Earth, it pushes and stretches this protective shield out on the night side of the planet, like hair blown in the wind.

Despite this protection, the solar wind buffets and stirs up the magnetosphere, sending high-energy particles showering into the Earth's upper atmosphere. There they light up the gases like a neon tube, creating an aurora that appears as a slowly shifting curtain of green light as the charged particles smash into oxygen atoms. These "quiet auroral arcs" are usually quite faint. "People will often not realise there's an aurora. The sky will look a bit weird maybe, with a diffuse glow," says Eric Donovan of the University of Calgary, Alberta, who monitors the aurora borealis in Canada.

When a substorm rips through the magnetosphere, though, unleashing the energy of a few megatons of TNT, the effects are unmistakable. Magnetic fields whip through space, the electrical currents that circle the magnetosphere thrash wildly, and the aurora is transformed into a much brighter and more dynamic display that sweeps across the sky for 10 to 15 minutes. "It is not uncommon to get a hundred or thousandfold increase in brightness," says Donovan. The aurora also becomes more colourful, as high-energy electrons smash into molecules of the air, exciting red and green light from oxygen and blue from nitrogen.

During a substorm, it is not uncommon to get a hundred or thousandfold increase in brightness

It was already known that what makes the difference between subtle auroral arcs and the dazzling light shows caused by substorms is the direction of magnetic field in the solar wind. Most of the time the field aligns with that of the Earth, which allows the solar wind to flow uninterrupted around the planet. When the two fields point in opposite directions, though, they can become connected, and that loads the magnetosphere with the energy needed to create a substorm. It was not clear exactly how this happened, however.

Satellites such as the Geotail mission, led by the Japan Aerospace Exploration Agency, have helped tell part of the story. Since 1992, Geotail has ranged around the long tail of the Earth's magnetic field, studying its interaction with the solar wind. But a single spacecraft can only tell what's happening at one point; it can't get a big picture of the rapid and complex changes that shake the whole magnetosphere. "In the past, we only had 'pinprick' observations," says David Sibeck of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

To broaden this view, NASA launched a flotilla of satellites, collectively named THEMIS, in February 2007 to catch substorms as they happen. The five small spacecraft orbit the Earth like juggled balls, each following a different looping path, so when something interesting happens in the magnetosphere there's a good chance that they will be in a suitable arrangement to see it.

Three months after launch, THEMIS encountered the beginnings of a substorm. "We had five spacecraft lined up in a row perpendicular to the outer boundary of Earth's magnetic field, some just inside, some just outside," says Sibeck.

This position turned out to be the perfect spot to answer one of the mission's questions: how the solar wind pumps energy into the magnetosphere to power a substorm.

THEMIS's recordings revealed changes in the Earth's magnetic field as the solar wind connected with the magnetosphere. A bulge of twisted magnetic fields formed and slid along its boundary, towards the night side of the Earth. The team recognised this as a phenomenon called a flux rope, which some researchers had suggested would be linked to substorms.

Flux ropes connect the magnetic fields in the solar wind with those of the magnetosphere and the two become entwined, linking Earth's domain with that of the sun. This allows high-energy particles to stream in, loading the magnetosphere with pent-up energy (see diagram).

As the solar wind blows over the Earth, it pulls on its end of the flux rope, dragging the rope and its magnetic fields away from Earth's day side and out into the tail of the magnetosphere.

As more and more flux ropes form and are pulled into the tail, the day side of the Earth loses more and more of its magnetic field. That does not go on forever, of course. "It would completely deplete the day-side magnetic field", says Vassilis Angelopoulos of the University of California in Los Angeles, who heads the THEMIS mission. Earth's shield would disappear, leaving us exposed to carcinogenic cosmic rays. Over geological timescales, the atmosphere might even be stripped away by the solar wind.

Clearly, and luckily for us, that doesn't happen. Instead, after a few hours of building magnetic tension, a substorm strikes. Several things happen almost simultaneously: the tail snaps, hurling plasma towards the Earth, and the electric current that girdles the Earth is disrupted. But which of these triggers the substorm and the resulting aurora? To find out, the THEMIS researchers needed to know which happens first.

There are two competing theories. One school of thought has it that the impetus must come from the powerful electric current that flows around the magnetosphere about 60,000 kilometres up. The motion of magnetic fields drives this current, as in a dynamo, and it is known to be boosted when magnetic field is added to the tail. Does it get so strong that it becomes unstable and showers the atmosphere with high-energy electrons?

The other theory is that the trigger comes from the tail itself. As more magnetic field is added to it, the tail gets compressed tighter and tighter. Around the pinched core of the tail, these magnetic fields point in opposite directions, one running outwards from the north pole and the other running in towards the south pole. As these two field lines are stretched and squeezed by the solar wind, perhaps the two opposing fields spontaneously reconnect, cutting the tail in half and sparking a substorm (see diagram).

As luck would have it, on 26 February 2008, a substorm hit while the THEMIS flotilla was strung out on the night side of the Earth, straddling the region where the current would be disrupted and also where the tail would be expected to snap and reconnect. It was the perfect opportunity to settle the argument.

The first thing the satellites recorded was the tail of the magnetic field snapping off and reconnecting, suggesting that substorms do start with changes in this area. Case closed? Not quite. There was also a big surprise for the THEMIS team. Angelopoulos expected that the break in the tail would first destabilise the current encircling the planet, which in turn would spray electrons down to Earth to cause the aurora. Instead, the aurora began to intensify about a minute after reconnection in the tail, and, crucially, before the disruption of the ring current. "I was shocked," says Angelopoulos. "We never expected that within a minute you would see the aurora light up."

Not everyone is convinced that the team's findings, settle the matter, however. Indeed, Anthony Lui of Johns Hopkins University in Baltimore, Maryland, disputes the whole sequence of events. He thinks that Angelopoulos and his team have misinterpreted the THEMIS data and that reconnection in the tail happens later. "Then the sequence would be opposite to that stated in the Science article, implying that current disruption is the trigger of substorms instead," Lui says.

Although the THEMIS team have since recorded several more substorms, with the same results, Lui maintains that the spacecraft have never been in quite in the right positions to give definitive results. Angelopoulos has decided to alter their orbits to address this problem. Over the coming months, that may remove any remaining controversy about what sparks substorms and perhaps explain how their auroras appear so quickly.

The mission might also illuminate the link between substorms and full-blown geomagnetic storms, which can cause more than a pretty display. These storms are caused by violent outbursts from the sun and can play havoc with satellites, scramble GPS signals, endanger astronauts and even blow power lines on Earth. During a geomagnetic storm there are typically several substorms, but how the two are connected is unclear. So far during the mission, solar activity has been low, but it should increase over the coming year or so, giving THEMIS a chance to watch a much larger storm unfold.

Angelopoulos will be looking forward to it, and not just for the scientific opportunities. Perhaps surprisingly for someone who spends much of his time pondering substorms, Angelopoulos has seen very few with his own eyes. That is part of his motivation to understand them. "I want to go and watch them, so I'm working on predictive models," he says. "With a good model of how the trigger mechanism works, it should be possible to predict the onset of a substorm to within minutes, he says. "Then I can run outside."