Tag Archives: #aurora

Scientists Solve 40-year Mystery Over Jupiter’s X-ray Aurora (Planetary Science)

A research team co-led by UCL has solved a decades-old mystery as to how Jupiter produces a spectacular burst of X-rays every few minutes.

The X-rays are part of Jupiter’s aurora – bursts of visible and invisible light that occur when charged particles interact with the planet’s atmosphere. A similar phenomenon occurs on Earth, creating the northern lights, but Jupiter’s is much more powerful, releasing hundreds of gigawatts of energy, enough to briefly power all of human civilisation*.

In a new study, published in Science Advances, researchers combined close-up observations of Jupiter’s environment by NASA’s satellite Juno, which is currently orbiting the planet, with simultaneous X-ray measurements from the European Space Agency’s XMM-Newton observatory (which is in Earth’s own orbit).

The research team, led by UCL and the Chinese Academy of Sciences, discovered that X-ray flares were triggered by periodic vibrations of Jupiter’s magnetic field lines. These vibrations create waves of plasma (ionised gas) that send heavy ion particles “surfing” along magnetic field lines until they smash into the planet’s atmosphere, releasing energy in the form of X-rays.

Co-lead author Dr William Dunn (UCL Mullard Space Science Laboratory) said: “We have seen Jupiter producing X-ray aurora for four decades, but we didn’t know how this happened. We only knew they were produced when ions crashed into the planet’s atmosphere.

“Now we know these ions are transported by plasma waves – an explanation that has not been proposed before, even though a similar process produces Earth’s own aurora. It could, therefore, be a universal phenomenon, present across many different environments in space.”

X-ray auroras occur at Jupiter’s north and south poles, often with clockwork regularity – during this observation Jupiter was producing bursts of X-rays every 27 minutes.

The charged ion particles that hit the atmosphere originate from volcanic gas pouring into space from giant volcanoes on Jupiter’s moon, Io.

This gas becomes ionised (its atoms are stripped free of electrons) due to collisions in Jupiter’s immediate environment, forming a doughnut of plasma that encircles the planet.

Co-lead author Dr Zhonghua Yao (Chinese Academy of Sciences, Beijing) said: “Now we have identified this fundamental process, there is a wealth of possibilities for where it could be studied next. Similar processes likely occur around Saturn, Uranus, Neptune and probably exoplanets as well, with different kinds of charged particles ‘surfing’ the waves.” 

Co-author Professor Graziella Branduardi-Raymont (UCL Mullard Space Science Laboratory) said: “X-rays are typically produced by extremely powerful and violent phenomena such as black holes and neutron stars, so it seems strange that mere planets produce them too.

“We can never visit black holes, as they are beyond space travel, but Jupiter is on our doorstep. With the arrival of the satellite Juno into Jupiter’s orbit, astronomers now have a fantastic opportunity to study an environment that produces X-rays up close.”

For the new study, researchers analysed observations of Jupiter and its surrounding environment carried out continuously over a 26-hour period by the Juno and XMM-Newton satellites.

They found a clear correlation between waves in the plasma detected by Juno and X-ray auroral flares at Jupiter’s north pole recorded by X-MM Newton. They then used computer modelling to confirm that the waves would drive the heavy particles towards Jupiter’s atmosphere.

Why the magnetic field lines vibrate periodically is unclear, but the vibration may result from interactions with the solar wind or from high-speed plasma flows within Jupiter’s magnetosphere.

Jupiter’s magnetic field is extremely strong – about 20,000 times as strong as Earth’s – and therefore its magnetosphere, the area controlled by this magnetic field, is extremely large. If it was visible in the night sky, it would cover a region several times the size of our moon.

The work was supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the UK’s Science and Technology Facilities Council (STFC), Royal Society, and Natural Environment Research Council, as well as ESA and NASA.

* Jupiter’s X-ray aurora alone releases about a gigawatt, equivalent to what one power station might produce over a period of days.

Jupiter with false colour X-ray aurora overlaid


Binzheng Zhang, Peter A. Delamere, Zhonghua Yao, Bertrand Bonfond, D. Lin, Kareem A. Sorathia, Oliver J. Brambles, William Lotko, Jeff S. Garretson, Viacheslav G. Merkin, Denis Grodent, William R. Dunn, John G. Lyon, “How Jupiter’s unusual magnetospheric topology structures its aurora”, Science Advances  09 Apr 2021: Vol. 7, no. 15, eabd1204 DOI: https://doi.org/10.1126/sciadv.abd1204


  • Credit: ESA/NASA/Yao/Dunn. Bottom image: Overlaid image of Jupiter’s north pole from NASA’s satellite Juno and NASA’s Chandra X-ray telescope. The X-ray aurora (purple) is overlaid on a visible Junocam image.

Provided by UCL

Physicists Determine How Auroras Are Created (Planetary Science)

The aurora borealis, or northern lights, that fill the sky in high-latitude regions have fascinated people for thousands of years. But how they’re created, while theorized, had not been conclusively proven.

In a new study, a team of physicists led by University of Iowa reports definitive evidence that the most brilliant auroras are produced by powerful electromagnetic waves during geomagnetic storms. The phenomena, known as Alfven waves, accelerate electrons toward Earth, causing the particles to produce the familiar atmospheric light show.

The study, published online June 7 in the journal Nature Communications, concludes a decades-long quest to demonstrate experimentally the physical mechanisms for the acceleration of electrons by Alfven waves under conditions corresponding to Earth’s auroral magnetosphere.

“Measurements revealed this small population of electrons undergoes ‘resonant acceleration’ by the Alfven wave’s electric field, similar to a surfer catching a wave and being continually accelerated as the surfer moves along with the wave,” says Greg Howes, associate professor in the Department of Physics and Astronomy at Iowa and study co-author.

Scientists have known that energized particles that emanate from the sun—such as electrons racing at approximately 45 million miles per hour—precipitate along the Earth’s magnetic field lines into the upper atmosphere, where they collide with oxygen and nitrogen molecules, kicking them into an excited state. These excited molecules relax by emitting light, producing the colorful hues of the aurora.

The theory was supported by spacecraft missions that frequently found Alfven waves traveling Earthward above auroras, presumably accelerating electrons along the way. Although space-based measurements had supported the theory, limitations inherent to spacecraft and rocket measurements had prevented a definitive test.

a graphic illustrating how auroras are created
Physicists led by the University of Iowa report definitive evidence of how auroras are created. In experiments, the physicists demonstrated the physical mechanisms for the acceleration of electrons by Alfven waves under conditions corresponding to Earth’s auroral magnetosphere. Illustration by Austin Montelius.

The physicists were able to find confirmatory evidence in a series of experiments conducted at the Large Plasma Device (LPD) in UCLA’s Basic Plasma Science Facility, a national collaborative research facility supported jointly by the U.S. Department of Energy and National Science Foundation.

“The idea that these waves can energize the electrons that create the aurora goes back more than four decades, but this is the first time we’ve been able to confirm definitively that it works,” says Craig Kletzing, professor in the Department of Physics and Astronomy at Iowa and a study co-author. “These experiments let us make the key measurements that show that the space measurements and theory do, indeed, explain a major way in which the aurora are created.”

The phenomenon of electrons “surfing” on the electric field of a wave is a theoretical process known as Landau damping, first proposed by Russian physicist Lev Landau in 1946. Through numerical simulations and mathematical modeling, the researchers demonstrated that the results of their experiment agreed with the predicted signature for Landau damping.

The agreement of experiment, simulation, and modeling provides the first direct evidence that Alfven waves can produce accelerated electrons, causing the aurora, says Troy Carter, professor of physics at UCLA and director of the UCLA Plasma Science and Technology Institute.

“This challenging experiment required a measurement of the very small population of electrons moving down the LPD chamber at nearly the same speed as the Alfven waves, numbering less than one in a thousand of the electrons in the plasma,” Carter says.

James Schroeder, assistant professor of physics at Wheaton College and the study’s corresponding author, earned a doctorate at Iowa. Frederick Skiff, professor in the UI Department of Physics and Astronomy, is a study co-author. Stephen Vincena, a research physicist at UCLA, and Seth Dorfman, with the Space Science Institute and a visiting researcher at UCLA, are contributing authors.

More detailed information is available at homepage.physics.uiowa.edu/~ghowes/research/aurora.html.

The U.S. National Science Foundation, the U.S. Department of Energy, and NASA funded the research.

Featured image: Physicists led by the University of Iowa report definitive evidence of how auroras are created. In experiments, the physicists demonstrated the physical mechanisms for the acceleration of electrons by Alfven waves under conditions corresponding to Earth’s auroral magnetosphere. Photo courtesy of NASA.

Provided by University of Iowa

Physicists Describe New Type of Aurora (Planetary Science)

Discovery comes from reanalysis of two-decade-old video

For millennia, humans in the high latitudes have been enthralled by auroras—the northern and southern lights. Yet even after all that time, it appears the ethereal, dancing ribbons of light above Earth still hold some secrets.

In a new study, physicists led by the University of Iowa report a new feature to Earth’s atmospheric light show. Examining video taken nearly two decades ago, the researchers describe multiple instances where a section of the diffuse aurora—the faint, background-like glow accompanying the more vivid light commonly associated with auroras—goes dark, as if scrubbed by a giant blotter. Then, after a short period of time, the blacked-out section suddenly reappears.

The researchers say the behavior, which they call “diffuse auroral erasers,” has never been mentioned in the scientific literature. The findings appear in the Journal of Geophysical Research Space Physics.

Auroras occur when charged particles flowing from the sun—called the solar wind—interact with Earth’s protective magnetic bubble. Some of those particles escape and fall toward our planet, and the energy released during their collisions with gases in Earth’s atmosphere generate the light associated with auroras.

“The biggest thing about these erasers that we didn’t know before but know now is that they exist,” says Allison Jaynes, assistant professor in the Department of Physics and Astronomy at Iowa and study co-author. “It raises the question: Are these a common phenomenon that has been overlooked, or are they rare?

“Knowing they exist means there is a process that is creating them,” Jaynes continues, “and it may be a process that we haven’t started to look at yet because we never knew they were happening until now.”

It was on March 15, 2002, that David Knudsen, a physicist at the University of Calgary, set up a video camera in Churchill, a town along Hudson Bay in Canada, to film auroras. Knudsen’s group was a little disheartened; the forecast called for clear, dark skies—normally perfect conditions for viewing auroras—but no dazzling illumination was happening. Still, the team was using a camera specially designed to capture low-level light, much like night-vision goggles.

Though the scientists saw only mostly darkness as they gazed upward with their own eyes, the camera was picking up all sorts of auroral activity, including an unusual sequence where areas of the diffuse aurora disappeared, then came back.

Knudsen, looking at the video as it was being recorded, scribbled in his notebook, “pulsating ‘black out’ diffuse glow, which then fills in over several seconds.”

“What surprised me, and what made me write it in the notebook, is when a patch brightened and turned off, the background diffuse aurora was erased. It went away,” says Knudsen, a Fort Dodge, Iowa, native who has studied aurora for more than 35 years and is a co-author on the study. “There was a hole in the diffuse aurora. And then that hole would fill back in after a half-minute or so. I had never seen something like that before.”

The note lay dormant, and the video unstudied, until Iowa’s Jaynes handed it to graduate student Riley Troyer to investigate. Jaynes learned about Knudsen’s recording at a scientific meeting in 2010and referenced the eraser note in her doctoral thesis on diffuse aurora a few years later. Now on the faculty at Iowa, she wanted to learn more about the phenomenon.

“I knew there was something there. I knew it was different and unique,” says Jaynes, assistant professor in the Department of Physics and Astronomy. “l had some ideas how it could be analyzed, but I hadn’t done that yet. I handed it to Riley, and he went much further with it by figuring out his own way to analyze the data and produce some significant conclusions.”

Knudsen research notes
Notes written by David Knudsen, a physicist at the University of Calgary, in 2002 make mention of a “pulsating ‘black out’ diffuse glow, which then fills in over several seconds.” © IOWA

Troyer, from Fairbanks, Alaska, took up the assignment with gusto.

“I’ve seen hundreds of auroras growing up,” says Troyer, who is in his third year of doctoral studies at Iowa. “They’re part of my heritage, something I can study while keeping ties to where I’m from.”

Troyer created a software program to key in on frames in the video when the faint erasers were visible. In all, he cataloged 22 eraser events in the two-hour recording.

“The most valuable thing we found is showing the time that it takes for the aurora to go from an eraser event (when the diffuse aurora is blotted out) to be filled or colored again,” says Troyer, who is the paper’s corresponding author, “and how long it takes to go from that erased state back to being diffuse aurora. Having a value on that will help with future modeling of magnetic fields.”

Jaynes says learning about diffuse auroral erasers is akin to studying DNA to understand the entire human body.

“Particles that fall into our atmosphere from space can affect our atmospheric layers and our climate,” Jaynes says. “While particles with diffuse aurora may not be the main cause, they are smaller building blocks that can help us understand the aurora system as a whole, and may broaden our understanding how auroras happen on other planets in our solar system.”

Study co-authors are Sarah Jones, from NASA Goddard Space Flight Center and who was part of Knudsen’s team in Churchill, and Trond Trondsen, with Keo Scientific Ltd., who built the camera that filmed the diffuse aurora.

Reference: Troyer, R. N., Jaynes, A. N., Jones, S. L., Knudsen, D. J., & Trondsen, T. S. (2021). The diffuse auroral eraser. Journal of Geophysical Research: Space Physics, 126, e2020JA028805. https://doi.org/10.1029/2020JA028805

Provided by University of Iowa

Confirmation Of An Auroral Phenomenon Discovered by Finns (Planetary Science)

A new auroral phenomenon discovered by Finnish researchers a year ago is probably caused by areas of increased oxygen atom density occurring in an atmospheric wave channel. The speculative explanation offered by the researchers gained support from a new study.

Observations made by University of Helsinki researchers increased the validity of a speculative mechanism according to which a type of aurora borealis named ‘dunes’ is born. In the new study, photographs of the phenomenon taken by an international group of hobbyists in Finland, Norway and Scotland were compared to concurrent satellite data. 

Video: A time lapse video recorded by a Scottish aurora borealis hobbyist Grame Whipps was used to determine the speed of the phenomenon at over 200 m/s.

The rare type of aurora borealis was seen in the sky on 20 January 2016 and recorded in photos taken by several hobbyists.

“The dunes were seen for almost four hours in a very extensive area, with the pattern extending roughly 1,500 kilometres from east to west and some 400 kilometres from north to south,” says Postdoctoral Researcher Maxime Grandin from the Centre of Excellence in Research of Sustainable Space coordinated by the University of Helsinki.

Useful photographic and video material was collected in close cooperation with Finnish aurora borealis hobbyists, utilising both the internet and social media. Among other things, a time lapse video shot on the night in question by a Scottish hobbyist was found. The video was used to estimate the dunes’ propagation speed at over 200 m/s.

The study was published in the esteemed AGU Advances journal.

Valid­ity of the wave guide the­ory con­firmed

Northern Lights are born when charged particles ejected by the Sun, such as electrons, collide with oxygen atoms and nitrogen molecules in Earth’s atmosphere. The collision momentarily excites the atmospheric species, and this excitation is released in the form of light.

New types of aurora borealis are rarely discovered. The identification of this new auroral form last year was the result of an exceptional collaboration between hobbyists who provided observations and researchers who started looking into the matter.

The new auroral form named dunes is relatively rare, and its presumed origin is peculiar.

“The differences in brightness within the dune waves appear to be caused by the increased density of atmospheric oxygen atoms,” says Professor Minna Palmroth.

A year ago, researchers at the Centre of Excellence in Research of Sustainable Space concluded that the dune-like shape of the new auroral emission type could be caused by concentrations of atmospheric oxygen. This increased density of oxygen atoms is assumed to be brought about by an atmospheric wave known as a mesospheric bore travelling horizontally within a wave guide established in the upper atmosphere.

Places and photographers associated with the images: (a) Aura, Finland, Jukka Hilska; (b) Engerdal, Norway, Knut Holmseth; (c) Karmøy, Norway, Kjetil Vinorum; (d) Isle of Mull, Scotland, Barry Whenman; (e) Lendalfoot, Scotland, Mark Ferrier, and (f) Rattray, Scotland, Graeme Whipps. The bottom row shows the same pictures with annotations indicating the cardinal directions and the most prominent dune elements. (figure reproduced from Grandin et al., 2021) © Grandin et al., 2021

This rare wave guide is created in between the boundary of the atmospheric layer known as the mesosphere, which is called the mesopause, and an inversion layer that is intermittently formed below the mesopause. This enables waves of a certain wavelength to travel long distances through the channel without subsiding.

The electron precipitation and temperature observations made in the recently published study supported the interpretations of the dunes’ origins made a year earlier. An independent observation was made of the wave channel appearing in the area of the dunes, but there are no observation data for the mesospheric bore itself yet.

“Next, we will be looking for observations of the mesospheric bore in the wave guide,” Maxime Grandin says.

According to the observation data, electron precipitation occurred in the area where the dunes appeared on 20 January 2016. Therefore, it is highly likely that electrons having the appropriate energy to bring about auroral emissions at an altitude of roughly 100 kilometres were involved. The observations were collected by the SSUSI instrument carried by a DMSP satellite, which measures, among other things, electron precipitation.

On the night in question, there was an exceptionally strong temperature inversion layer in the mesosphere, or a barrier generated by layers of air with different temperatures. The inversion layer associated with the origins of the wave channel was measured with the SABER instrument carried by the TIMED satellite. The observation supports the hypothesis according to which the auroral form originates in areas of increased oxygen density occurring in the upper atmosphere wave guide.

The photographic and video material was acquired from aurora borealis hobbyists in three countries: Graeme Whipps (Scotland), Mark Ferrier (Scotland), Jukka Hilska (Finland), Kjetil Vinorum (Norway), Knut Holmseth (Norway) and Barry Whenman (Scotland).

Featured image: A green-tinged steady wave pattern can be seen in the dune-like aurora borealis event. The recently completed study supported an interpretation according to which the auroral form originates in the increased density of oxygen atoms in the wave guide. © Graeme Whipps

Grandin, M., Palmroth, M., Whipps, G., Kalliokoski, M., Ferrier, M., Paxton, L. J., Mlynczak, M. G., Hilska, J., Holmseth, K., Vinorum, K., and Whenman, B. (2021). Large-scale dune aurora event investigation combining Citizen Scientists’ photographs and spacecraft observations. AGU Advances, 2, e2020AV000338, https://doi.org/10.1029/2020AV000338

Provided by University of Helsinki

New Research Reveals Secret To Jupiter’s Curious Aurora Activity (Planetary Science)

Auroral displays continue to intrigue scientists, whether the bright lights shine over Earth or over another planet. The lights hold clues to the makeup of a planet’s magnetic field and how that field operates.

New research about Jupiter proves that point — and adds to the intrigue.

Peter Delamere, a professor of space physics at the University of Alaska Fairbanks Geophysical Institute, is among an international team of 13 researchers who have made a key discovery related to the aurora of our solar system’s largest planet.

The team’s work was published April 9, 2021, in the journal Science Advances. The research paper, titled “How Jupiter’s unusual magnetospheric topology structures its aurora,” was written by Binzheng Zhang of the Department of Earth Sciences at the University of Hong Kong; Delamere is the primary co-author.

NASA’s Hubble Space Telescope made this close up view of an electric-blue aurora that is eerily glowing one half million miles away on the faint planet Jupiter in 2010. © UAF

Research done with a newly developed global magnetohydrodynamic model of Jupiter’s magnetosphere provides evidence in support of a previously controversial and criticized idea that Delamere and researcher Fran Bagenal of the University of Colorado at Boulder put forward in a 2010 paper — that Jupiter’s polar cap is threaded in part with closed magnetic field lines rather than entirely with open magnetic field lines, as is the case with most other planets in our solar system.

“We as a community tend to polarize — either open or closed — and couldn’t imagine a solution where it was a little of both,” said Delamere, who has been studying Jupiter since 2000. “Yet in hindsight, that is exactly what the aurora was revealing to us.”

Open lines are those that emanate from a planet but trail off into space away from the sun instead of reconnecting with a corresponding location in the opposite hemisphere.

Peter Delamere © UAF

On Earth, for example, the aurora appears on closed field lines around an area referred to as the auroral oval. It’s the high latitude ring near — but not at — each end of Earth’s magnetic axis.

Within that ring on Earth, however, and as with some other planets in our solar system, is an empty spot referred to as the polar cap. It’s a place where magnetic field lines stream out unconnected — and where the aurorae rarely appear because of it. Think of it like an incomplete electrical circuit in your home: No complete circuit, no lights.

Jupiter, however, has a polar cap in which the aurora dazzles. That puzzled scientists.

The problem, Delamere said, is that researchers were so Earth-centric in their thinking about Jupiter because of what they had learned about Earth’s own magnetic fields.

The arrival at Jupiter of NASA’s Juno spacecraft in July 2016 provided images of the polar cap and aurora. But those images, along with some captured by the Hubble Space Telescope, couldn’t resolve the disagreement among scientists about open lines versus closed lines. 

So Delamere and the rest of the research team used computer modeling for help. Their research revealed a largely closed polar region with a small crescent-shaped area of open flux, accounting for only about 9 percent of the polar cap region. The rest was active with aurora, signifying closed magnetic field lines.

Jupiter, it turns out, possesses a mix of open and closed lines in its polar caps.

“There was no model or no understanding to explain how you could have a crescent of open flux like this simulation is producing,” he said. “It just never even entered my mind. I don’t think anybody in the community could have imagined this solution. Yet this simulation has produced it.”

“To me, this is a major paradigm shift for the way that we understand magnetospheres.”

What else does this reveal? More work for researchers.

“It raises many questions about how the solar wind interacts with Jupiter’s magnetosphere and influences the dynamics,” Delamere said.

Jupiter’s aurorally active polar cap could, for example, be due to the rapidity of the planet’s rotation — once every 10 hours compared to Earth’s once every 24 hours — and the enormity of its magnetosphere. Both reduce the impact of the solar wind, meaning the polar cap magnetic field lines are less likely to be torn apart to become open lines.

And to what extent does Jupiter’s moon Io affect the magnetic lines within Jupiter’s polar cap? Io is electrodynamically linked to Jupiter, something unique in our solar system, and as such is constantly stripped of heavy ions by its parent planet.

As the paper notes, “The jury is still out on the magnetic structure of Jupiter’s magnetosphere and what exactly its aurora is telling us about its topology.”

NOTE TO EDITORS: The paper is available at https://advances.sciencemag.org/content/7/15/eabd1204

Featured image: This 2016 image is a composite of two different Hubble observations. The Auroras were photographed during a series of Hubble Space Telescope imaging spectrograph far-ultraviolet-light observations taking place as NASA’s JUNO spacecraft approaches and enters into orbit around Jupiter © NASA

Reference: Binzheng Zhang, Peter A. Delamere, Zhonghua Yao, Bertrand Bonfond, D. Lin, Kareem A. Sorathia, Oliver J. Brambles, William Lotko, Jeff S. Garretson, Viacheslav G. Merkin, Denis Grodent, William R. Dunn, John G. Lyon, “How Jupiter’s unusual magnetospheric topology structures its aurora”, Science Advances  09 Apr 2021: Vol. 7, no. 15, eabd1204 DOI: 10.1126/sciadv.abd1204

Provided by University of Alaska Fairbanks

SwRI Scientists Discover A New Auroral Feature on Jupiter (Planetary Science)

The SwRI-led Ultraviolet Spectrograph (UVS) orbiting Jupiter aboard NASA’s Juno spacecraft has detected new faint aurora features, characterized by ring-like emissions, which expand rapidly over time. SwRI scientists determined that charged particles coming from the edge of Jupiter’s massive magnetosphere triggered these auroral emissions.

“We think these newly discovered faint ultraviolet features originate millions of miles away from Jupiter, near the Jovian magnetosphere’s boundary with the solar wind,” said Dr. Vincent Hue, lead author of a paper accepted by the Journal of Geophysical Research: Space Physics. “The solar wind is a supersonic stream of charged particles emitted by the Sun. When they reach Jupiter, they interact with its magnetosphere in a way that is still not well understood.”

Both Jupiter and Earth have magnetic fields that provide protection from the solar wind. The stronger the magnetic field, the larger the magnetosphere. Jupiter’s magnetic field is 20,000 times stronger than Earth’s and creates a magnetosphere so large it begins to deflect the solar wind 2–4 million miles before it reaches Jupiter.

“Despite decades of observations from Earth combined with numerous in-situ spacecraft measurements, scientists still do not fully understand the role the solar wind plays in moderating Jupiter’s auroral emissions,” said SwRI’s Dr. Thomas Greathouse, a co-author on this study. “Jupiter’s magnetospheric dynamics, the motion of charged particles within its magnetosphere, is largely controlled by Jupiter’s 10-hour rotation, the fastest in the solar system. The solar wind’s role is still debated.”

The SwRI-led Ultraviolet Spectrograph (UVS) orbiting Jupiter aboard NASA’s Juno spacecraft allowed scientists to discover faint ring-like aurora features, shown here in false color expanding rapidly over time. Courtesy of NASA/SWRI/JPL-Caltech/SwRI/V. Hue/G. R. Gladstone

One of the goals of the Juno mission, recently approved by NASA for an extension until 2025, is to explore Jupiter’s magnetosphere by measuring its auroras with the UVS instrument. Previous observations with the Hubble Space Telescope and Juno have allowed scientists to determine that most of Jupiter’s powerful auroras are generated by internal processes, that is the motion of charged particles within the magnetosphere. However, on numerous occasions, UVS has detected a faint type of aurora, characterized by rings of emissions expanding rapidly with time.

“The high-latitude location of the rings indicates that the particles causing the emissions are coming from the distant Jovian magnetosphere, near its boundary with the solar wind,” said Bertrand Bonfond, a co-author on this study from Belgium’s Liège University. In this region, plasma from the solar wind often interacts with the Jovian plasma in a way that is thought to form “Kelvin-Helmholtz” instabilities. These phenomena occur when there are shear velocities, such as at the interface between two fluids moving at different speeds. Another potential candidate to produce the rings are dayside magnetic reconnection events, where oppositely directed Jovian and interplanetary magnetic fields converge, rearrange and reconnect.

Both of these processes are thought to generate particle beams that could travel along the Jovian magnetic field lines, to eventually precipitate and trigger the ring auroras on Jupiter.

“Although this study does not conclude what processes produce these features, the Juno extended mission will allow us to capture and study more of these faint transient events,” Hue said.

The Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Dr. Scott J. Bolton, of SwRI. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.

For more information, read the paper at https://doi.org/10.1029/2020JA028971, visit Planetary Science or contact Deb Schmid at +1 210 522 2254 Communications Department, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.

Featured image: SwRI-led Ultraviolet Spectrograph (UVS) orbiting Jupiter aboard NASA’s Juno spacecraft allowed scientists to discover faint aurora features likely triggered by charged particles coming from the edge of Jupiter’s massive magnetosphere. This occurrence, shown in the false color series of images recorded 30 seconds apart (red panels), displays the characteristically ring-like emissions, expanding rapidly over time. Courtesy of NASA/SWRI/JPL-Caltech/SwRI/V. Hue/G. R. Gladstone/B. Bonfond

Reference: Hue, V., Greathouse, T. K., Gladstone, G. R., Bonfond, B., Gérard, J.‐C., Vogt, M. F., et al. (2021). Detection and characterization of circular expanding UV‐emissions observed in Jupiter’s polar auroral regions. Journal of Geophysical Research: Space Physics, 126, e2020JA028971. https://doi.org/10.1029/2020JA028971

Provided by Southwest Research Institute

The Aurora’s Very High Altitude Booster (Planetary Science)

A critical ingredient for auroras exists much higher in space than previously thought, according to new research in the journal Scientific Reports. The dazzling light displays in the polar night skies require an electric accelerator to propel charged particles down through the atmosphere. Scientists at Nagoya University and colleagues in Japan, Taiwan and the US have found that it exists beyond 30,000 kilometres above the Earth’s surface – offering insight not just about Earth, but other planets as well.

The story of aurora formation begins with supersonic plasma propelled from the Sun into space as high-speed, charged particles. When these charged particles get close to Earth, they are deflected and funnelled in streams along the planet’s magnetic field lines, eventually flowing towards the poles.

“Most electrons in the magnetosphere don’t reach the part of the upper atmosphere called the ionosphere, because they are repelled by the Earth’s magnetic field,” explains Shun Imajo of Nagoya University’s Institute for Space-Earth Environmental Research, the study’s first author.

But some particles receive a boost of energy, accelerating them into Earth’s upper atmosphere where they collide with and excite oxygen and nitrogen atoms at an altitude of about 100 kilometres. When these atoms relax from their state of excitation, they emit the auroral lights. Still, many details about this process remain a mystery.

“We don’t know all the details of how the electric field that accelerates electrons into the ionosphere is generated or even how high above Earth it is,” Imajo says.

Scientists had assumed electron acceleration happened at altitudes between 1,000 and 20,000 kilometres above Earth. This new research revealed the acceleration region extends beyond 30,000 kilometres.

“Our study shows that the electric field that accelerates auroral particles can exist at any height along a magnetic field line and is not limited to the transition region between the ionosphere and magnetosphere at several thousand kilometres,” says Imajo. “This suggests that unknown magnetospheric mechanisms are at play.”

The team reached this finding by examining data from ground-based imagers in the US and Canada and from the electron detector on Arase, a Japanese satellite studying a radiation belt in Earth’s inner magnetosphere. The data was taken from 15 September 2017 when Arase was at about 30,000 kilometres altitude and located within a thin active auroral arc for several minutes. The team was able to measure upward and downward movements of electrons and protons, ultimately finding the acceleration region of electrons began above the satellite and extended below it.

To further investigate this so-called very high-altitude acceleration region, the team next aims to analyse data from multiple aurora events, compare high-altitude and low-altitude observations, and conduct numerical simulations of electric potential.

“Understanding how this electric field forms will fill in gaps for understanding aurora emission and electron transport on Earth and other planets, including Jupiter and Saturn,” Imajo says.

The paper, “Active auroral arc powered by accelerated electrons from very high altitudes,” was published online in Scientific Reports on January 18, 2021 at DOI: 10.1038/s41598-020-79665-5.

Featured image: The Arase satellite captured data about electrons accelerated from very high altitudes. © ERG science center

Provided by Nagoya University

Killer Electrons in Strumming Sky Lights (Planetary Science)

Computer simulations explain how electrons with wide-ranging energies rain into Earth’s upper and middle atmosphere during a phenomenon known as the pulsating aurora. The findings, published in the journal Geophysical Research Letters, suggest that the higher-energy electrons resulting from this process could cause destruction of the part of the ozone in the mesosphere, about 60 kilometres above Earth’s surface. The study was a collaboration between scientists in Japan, including at Nagoya University, and colleagues in the US, including from NASA.

Low-energy (blue) and high-energy (yellow) electrons form during the process that generates the pulsating aurora. The high-energy ‘relativistic’ electrons could cause localized destruction of the ozone. ©PsA project

The northern and southern lights that people are typically aware of, called the aurora borealis and australis, look like coloured curtains of reds, greens, and purples spreading across the night skies. But there is another kind of aurora that is less frequently seen. The pulsating aurora looks more like indistinct wisps of cloud strumming across the sky.

Scientists have only recently developed the technologies enabling them to understand how the pulsating aurora forms. Now, an international research team, led by Yoshizumi Miyoshi of Nagoya University’s Institute for Space-Earth Environmental Research, has developed a theory to explain the wide-energy electron precipitations of pulsating auroras and conducted computer simulations that validate their theory.

Their findings suggest that both low- and high-energy electrons originate simultaneously from interactions between chorus waves and electrons in the Earth’s magnetosphere.

Chorus waves are plasma waves generated near the magnetic equator. Once formed, they travel northwards and southwards, interacting with electrons in Earth’s magnetosphere. This interaction energizes the electrons, scattering them down into the upper atmosphere, where they release the light energy that appears as a pulsating aurora.

The electrons that result from these interactions range from lower-energy ones, of only a few hundred kiloelectron volts, to very high-energy ones, of several thousand kiloelectron volts, or ‘megaelectron’ volts.

Miyoshi and his team suggest that the high-energy electrons of pulsating auroras are ‘relativistic’ electrons, otherwise known as killer electrons, because of the damage they can cause when they penetrate satellites.

“Our theory indicates that so-called killer electrons that precipitate into the middle atmosphere are associated with the pulsating aurora, and could be involved in ozone destruction,” says Miyoshi.

The team next plans to test their theory by studying measurements taken during a space rocket mission called ‘loss through auroral microburst pulsations’ (LAMP), which is due to launch in December 2021. LAMP is a collaboration between NASA, the Japan Aerospace Exploration Agency (JAXA), Nagoya University, and other institutions. LAMP experiments will be able to observe the killer electrons associated with the pulsating aurora.

References: Miyoshi, Y., Saito, S., Kurita, S., Asamura, K., Hosokawa, K., Sakanoi, T., et al. (2020). Relativistic electron microbursts as high‐energy tail of pulsating aurora electrons. Geophysical Research Letters, 47, e2020GL090360. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL090360 https://doi.org/10.1029/2020GL090360

Provided by Nagoya University

Aurora-chasing citizen scientists help discover a new feature of STEVE

In 2018, a new aurora-like discovery struck the world. From 2015 to 2016, citizen scientists reported 30 instances of a purple ribbon in the sky, with a green picket fence structure underneath. Now named STEVE, or Strong Thermal Emission Velocity Enhancement, this phenomenon is still new to scientists, who are working to understand all its details. What they do know is that STEVE is not a normal aurora – some think maybe it’s not an aurora at all – and a new finding about the formation of streaks within the structure brings scientists one step closer to solving the mystery.

Taken July 17, 2018, at Little Kenosee Lake, Saskatchewan, Canada, this photo shows the tiny green streaks below STEVE. Neil Zeller, photographer and co-author on the paper, commented “STEVE was bright and powerful for a full hour that night.” ©Copyright Neil Zeller

“Often in physics, we build our understanding then test the extreme cases or test the cases in a different environment,” Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, explains. “STEVE is different than the usual aurora, but it is made of light and it is driven by the auroral system. In finding these tiny little streaks, we may be learning something fundamentally new in how green auroral light can be produced.”

These “tiny little streaks” are extraordinarily small point-like features within the green picket fence of STEVE. In a new paper for AGU Advances, researchers share their latest findings on these points. They suggest the streaks could be moving points of light – elongated in the images due to blur from the cameras. The tip of the streak in one image will line up with the end of the tail in the next image, contributing to this speculation from the scientists. However, there are still a lot of questions to be answered – determining whether the green light is a point or indeed a line, is one extra clue to help scientists figure out what causes green light.

“I’m not entirely sure about anything with respect to this phenomenon just yet,” Joshua Semeter, a professor at Boston University and first author on the paper, said. “You have other sequences where it looks like there is a tube-shaped structure that persists from image to image and doesn’t seem to conform to a moving point source, so we’re not really sure about that yet.”

STEVE as a whole is something that scientists are still working to label. Scientists tend to classify optical features in the sky into two categories: airglow and aurora. When airglow occurs at night, atoms in the atmosphere recombine and release some of their stored energy in the form of light, creating bright swaths of color. By studying the patterns in airglow, scientists can learn more about that area of the atmosphere, the ionosphere. To be classified as an aurora, on the other hand, that release of light must be caused by electron bombardment. These features are formed differently but also look different – airglow can occur across Earth, while auroras form in a broad ring around Earth’s magnetic poles.

Two different angles of distinctive green streaks below a STEVE event on Aug. 31, 2016, near Carstairs, Alberta, Canada. Recent research about the formation of these streaks is allowing scientists to learn more about this aurora-like phenomenon. View animated GIF: https://www.nasa.gov/sites/default/files/thumbnails/image/stevemay.gif ©Copyright Neil Zeller.

“STEVE in general appears to not conform well to either one of those categories,” Semeter said. “The emissions are coming from mechanisms that we don’t fully understand just yet.”

STEVE’s purple emissions are likely a result of ions moving at a supersonic speed. The green emissions seem to be related to eddies, like the ones you might see forming in a river, moving more slowly than the other water around it. The green features are also moving more slowly than the structures in the purple emissions, and scientists speculate they could be caused by turbulence in the space particles – a brew of charged particles and magnetic field, called plasma – at these altitudes.

“We know this kind of turbulence occurs. There are people who base their entire careers on studying turbulence in the ionospheric plasma formed by very rapid flows.” Semeter said. “The evidence generally comes from radar measurements. We don’t ever have an optical signature.” Semeter suggests that when it comes to the appearance of STEVE, the flows in these instances are so extreme, that we can actually see them in the atmosphere.

“This paper is the tip of the iceberg in this new area of these tiny little pieces of the picket fence. Something we do in physics is try to chip away to increase our understanding,” MacDonald said. “This paper establishes the altitude range and some of the techniques we can use to identify these features, then they can be better resolved in other observations.”

To establish the altitude range and identify these features, the scientists extensively used photos and videos captured by citizen scientists.

“Citizen scientists are the ones who brought the STEVE phenomenon to the scientists’ attention. Their photos are typically longer time lapse than our traditional scientific observations,” MacDonald said. “Citizen scientists don’t get into the patterns that scientists get into. They do things differently. They are free to move the camera around and take whatever exposure they want.” However, to make this new discovery of the points within STEVE, photographers actually took shorter exposure photographs to capture this movement.

To get those photographs, citizen scientists spend hours in the freezing cold, late at night, waiting for an aurora – or hopefully STEVE – to appear. While data can indicate if an aurora will show up, indicators for STEVE haven’t been identified yet. However, the aurora chasers show up and take pictures anyway.

Neil Zeller, a photographer and co-author on the paper, says he didn’t originally plan to be a citizen scientist. “It was just for the beauty of it,” Zeller explained. Zeller has been involved with the discovery of STEVE from the start. He showed a picture he took of STEVE to MacDonald years ago, sparking the first research into the phenomena. Now he’s a co-author on this paper.

“It’s an honor, it really is,” Zeller said about contributing to this research. “I tend to take a step back from the scientists doing the work. I’m out there for the beauty of it and to capture these phenomena in the sky.”

This paper also made use of another valuable citizen scientist contribution – a volunteer database of STEVE observations. Michael Hunnekuhl, another author on the paper, maintains this database and has contributed to STEVE findings in the past. Hunnekuhl noticed the streaks in the photographs independently of the scientists on the paper, and his detailed record and triangulation techniques were pivotal in this research.

Zeller and other citizen scientists plan to keep taking and examining those pictures, capturing the beauty of Earth’s atmosphere, and MacDonald, Semeter, and other scientists will keep studying them, uncovering more about this new phenomenon.

Provided by NASA Goddard