By Mara Johnson-Groh NASA’s Goddard Space Flight Center
Late on August 16, 2020, the Sun released a burst of light and energy known as a solar flare. This B1-class solar flare – the second smallest class of flare – peaked at 1:26p.m. EDT.
NASA’s Solar Dynamics Observatory observes the Aug. 16, 2020, B-class flare at 131, 171, and 193 angstroms. Credit: NASA/SDO
Solar flares, which are abrupt outbursts of energy and light on the solar surface, are often accompanied by CMEs. B-class flares – or “background” flares – were originally the lowest class of flare before lower level A-class flares were observed. B-class flares are relatively common; there have been at least three B-class flares in the last week.
The recent activity occurred in an otherwise quiet area of the Sun, providing an example of activity that did not originate from a sunspot – the darkened, magnetically active patches on the solar surface that often spawn flares and CMEs.
Three months later, the science team convened at NASA’s Goddard Space Flight Center on the outskirts of Washington, D.C. Button-up shirts replaced down coats, their hair not ruffled from beanies and headlamps. But the mood, an eagerness to proceed, remained. Even Zaccarine — back at school and unable to make the meeting — had spent the past months helping with designs for a new instrument. It would fly on the next mission, VISIONS-3.
The next two days were filled with discussion. Each team member presented their preliminary findings, sharing open questions with the group. Each of the 11 instruments onboard captured a different part of the picture; the findings of one could often explain anomalies in the other. But telling the whole story would require many more meetings like this one.
Pfaff was the last to present, sharing the results from his electric fields experiment before departing for another meeting. The remaining members gathered around a table in Rowland’s new office, to which he had just moved after returning from Ny-Ålesund. By his estimates, Rowland would spend the next year or two here, in front of a computer screen under fluorescent lighting, analyzing data from that 15-minute rocket flight. Around him were mostly the familiar knick-knacks of his old office — books about physics, family pictures, academic regalia. Just to the right of his desk, second shelf from the bottom, was a new trinket. It was a small triangle, outlined in red, framing the silhouette of a polar bear.♦
On the snow-covered balcony, the science team huddled together in t-shirts and indoor slippers, too rushed to don their coats. Everyone was there except Rowland.
The first rocket was already in the air, but many on the team — glued to their computers until the last moments — had missed it. The flight of the second rocket would be their first chance to see the launch.
“Thirty seconds,” an unidentified voice called from inside.
The hall door opened. With only a few moments left, Rowland made his way into the huddle. The crowd lifted their phones to capture the event, but all eyes were off in the distance, staring toward the launchpad. Suddenly, all faces were illuminated. A collective sigh rose up as an intensely bright flash illuminated the terrain. Ny-Ålesund was surrounded by mountains — for the first time, they could see them.
The bright orb lifted quickly into the sky, followed a few moments later by a thunderous rumble. The trail of light continued on its arc as heads craned out over the balcony. The light began to dim, then suddenly brightened again. “Second stage!” Pfaff called out, to hollers of approval. Then the rocket passed out of view.
Without a word, the entire crowd rushed for the door, running back to their computers to watch the data stream in. As they took their places, Rowland hovered among them like a conductor surveying his orchestra.
“First images!” he called out, pointing at a screen at the first station. It was the CCD imager, nitrogen-cooled, that was now flashing images in four square boxes, arranged two-by-two on the screen. At first, they each flickered rapidly, unsynchronized. Then suddenly, a semicircle of bright light appeared in all of them. “We’ve got the limb of the Earth!” he cried — the horizon was in view. The rocket was in space, looking back down at them.
Rowland continued down the line. Next up was a particle counter, measuring the oxygen ions escaping the atmosphere as the rocket flew through them. “We got the counts?” he called. Zaccarine, still glued to her screen, raised a thumbs-up.
Rowland scanned the room. Scientists watched their data roll in, narrating each dip and turn to one another like sports announcers. Radio chatter crackled in the background. At just under four minutes into the flight, all of the instruments were on, and no problems had been reported. Rowland stood, hands on the back of an empty seat, as his eyes welled with tears. A team member reached for a handshake but Rowland went for a hug.
Moen and Pfaff, the two veterans, met him in the middle of the room for congratulations. “Everything seems to be working,” Rowland said. He smiled and looked at Pfaff. “Looks like you might make your conference after all.”
Pfaff paced in front of the Wall of Science, stroking his chin, weighing the signs that launchable conditions were approaching. He had spent earlier hours on the phone, rapidly rebooking flights to make his science conference on time. But that was earlier, when conditions weren’t good. Now, everyone was at full attention.
In the background, the tinny sound of voices over a video chat trickled in. Moen, the professor from Oslo, was speaking with colleagues 50 miles south in Longyearbyen. One voice belonged to Fred Sigernes, Chief of the Kjell Henriksen Observatory, who was running the all-sky imager, the instrument that detected the cusp on the Wall of Science. The other voice belonged to Kjellmar Oksavik, a professor at the University of Bergen and at UNIS in Svalbard. He was running the EISCAT radar, scanning the sky for atmospheric heating. They kept the line open as they worked, ready to discuss every bit of new data as it appeared, in real time.
At 11 a.m. — with one hour left in the day’s launch window — the solar wind’s magnetic field started to point south.
Rowland, sensing the opportunity to launch may be drawing close, OK’d the launch team to arm the rocket. “Let’s run the clock down to three minutes,” he said. It was as close to zero as they could get. Below that, the rocket was switched to internal battery power and the engineers completed their final checks.
Fifteen minutes passed and the solar wind’s magnetic field was still pointing south, but always zig-zagging, threatening to head north at any moment. The red blob marking the cusp remained too far north above Ny-Ålesund to launch through. A call came in over a walkie-talkie, and Rowland picked it up.
“We have some concern about surface winds.” It was Range Control. “It is not really stable enough just yet, and they are quite high. If you see something you want to start the count for, we will have to assess the winds at that point to make a decision if we can go or not.”
Rowland paused, working through his options. The cusp was still too far north at the moment, but given the steady stream of southward-pointing solar wind hitting Earth, it was due to move any moment. Once it moved into the rocket’s trajectory, they needed it to heat the atmosphere before they’d be ready to launch. “We’ll let it cook for a few minutes,” Rowland responded, “and then we’ll pick up the count.”
Before Rowland finished his sentence, Pfaff was already gesturing to him. “It’s slowly moving south,” he said. They rushed out to the Wall of Science, and Pfaff pointed to the red blob marking the cusp. “This used to be up here, now it’s right on top of us.”
By 11:50 a.m., with just ten minutes left in the launch window, the atmosphere was starting to heat up. The EISCAT radar’s measurements, once cool blues and greens, were turning orange and yellow. Now, time was of the essence.
“It’s three minutes to get in the air, and another couple to get to apogee — we’re five minutes from measuring anything,” said Rowland. It wasn’t the data now, but five minutes into the future, that they depended on. Rowland turned to Moen, who spoke to his colleagues over the video chat. “Should we go?” Moen asked.
Rowland looked around to the surrounding science team. The stakes were high enough to demand a unanimous decision. If they launched toward a transient, momentary fluke of heating that disappeared before they reached it, three years of work on the mission would be wasted. But waiting too long could lead to a similar fate if they missed their only chance. “Any dissenters?” he asked.
A hushed discussion ensued over the video chat as Rowland, out of earshot, studied the Wall of Science. Pfaff leaned in to the computer to listen closely. “They’re saying go!” Pfaff yelled. Everyone turned to Rowland. That was all the resolution he needed.
Rowland notified Range Control of their decision to launch and rushed back to the Wall of Science. At the bottom left display, the clock, long frozen at three minutes, began to count down.
Each day, the science team prepared just the same. At 3 a.m., Rowland opened the giant doors of the Telemetry Readout building, where they were stationed. Over the next five hours, they stepped through instrument preparations, tests, and practice countdowns. It had now reached 8 a.m. on the fourth day of the launch window. Practice was over — it was time to try, once more, for the real thing.
Rowland sat in the front room of the building, hunched over his laptop. Two long tables stretched out to either side of him, stacked with computer monitors of different shapes and sizes. Streams of data danced across their screen, one for each of the 11 instruments on the rocket. These were the rocket’s vital signs, so they watched them meticulously, beginning long before launch. Beside Rowland, Zaccarine, the youngest member of the science team, stared at the temperature readouts from one of the instruments that she’d watched for three days now.
Across the room, Pfaff inspected long sheets of paper showing data from several instruments. Pfaff was familiar with the challenges of launching from Ny-Ålesund, and could advise Rowland on what to look for. But he couldn’t stay long. He was scheduled to deliver two lectures at a science conference back in Washington, D.C., and had almost left that morning. At the last minute, he delayed his flight: The weather seemed promising today.
The rest of the team gathered in the adjacent main hall. Jøran Moen and Andres Spicher from the University of Oslo, a professor and postdoc respectively, sat at a small table, sipping coffee from skinny white mugs. Moen was in charge of one of the instruments, but he also knew the cusp region well. He was one of the chief architects of the Grand Challenge Initiative – Cusp, the international sounding rocket campaign to explore the cusp, of which Rowland’s mission was one part.
Across the room, Matt Zettergren, a professor from Embry-Riddle, was fiddling with cables dangling from his laptop. One clicked into place, and a large screen in the middle of the room came alive. Four scientists gazed up at it, their faces illuminated by the blue-white glow.
This was the Wall of Science, as they playfully called it. Its geometric arrangement of windows resembled farmland seen from a plane. The separate plots of data were beamed back from satellites in space and ground-based instruments. They blinked, shifted, and refreshed each at their own cadence. But each parcel had its own significance, requiring the right attention and know-how to read it. The Wall of Science contained all the information they had to decide whether, and when, to launch.
“This is our upstream space weather buoy,” said Rowland, pointing to a window in the upper right-hand corner of the screen. It was one of three windows that, together, told the story of atmospheric escape, following a gust of solar wind as it approached Earth, flowed through cusp, and triggered the aurora and fountains of escaping oxygen.
The first window showed a red squiggly line stretching across the plot. The data came from NASA’s Advanced Composition Explorer, or ACE satellite, perched one million miles closer to the Sun than we are. The science team looked to this data to see what the solar wind was blowing their way, some 45 minutes to an hour before it hit Earth.
This red squiggly line measured the solar wind’s magnetic field. Like Earth itself, the solar wind is magnetic, with its own north and south pole. But while north, on Earth, points in one steady direction, the solar wind is far less stable. A compass placed inside it would spin from moment to moment, depending on the changing activity on the Sun.
The scientists were waiting for the solar wind to point south, and to stay that way for a while. When a southward-pointed solar wind collided with Earth’s northward-pointed magnetic field, the two would fuse. It was the first step toward the ideal cusp aurora.
The effects of this collision could be seen on Earth, and were displayed in the next window. In two wavelengths of red light emitted by the aurora, it showed the location of the cusp over Svalbard.
At the moment, the cusp was positioned to the northeast of the island, out of range of the rockets’ trajectory. But the arrival of a southward-pointing gust of solar wind would intensify the aurora, dragging the cusp southward, towards the rocket’s planned trajectory.
Once the cusp started shifting south, launchable conditions were closing in. But to fire the rockets, the science team looked to the final window, placed on the far left of the screen. It told them when the aurora had reached its boiling point, and the oxygen was starting to escape. The data were from the EISCAT radar, short for European Incoherent Scatter Scientific Association. The two EISCAT antennas measured the density and temperature of the atmosphere over Ny-Ålesund, and at the peak of the rocket’s trajectory. When oxygen in the air started to boil, they would see it here. It would be time to start the countdown.
There was one more window squeezed into the bottom left corner, the only one that the team itself controlled. It was a simple digital clock. When it struck zero, rockets would fly.
At the entrance to the mess hall, Ny-Ålesund residents abandon snow-covered shoes for cozy slippers or socks. Inside, the warm air washes over wind-whipped faces, carrying the smell of rich soups, tea, and bread. “The chef is the most important person here,” Rowland quipped.
Residents make the pilgrimage to the mess hall three times a day: first for breakfast, beginning at 7:30 a.m. sharp, then for lunch, which runs from 12:20 to 1, and finally dinner from 4:50 to 5:30. Meals are not served outside of those hours, so the mess hall’s schedule is the town’s heartbeat. It also makes for a reliable meeting ground — a place hungry colleagues gather to discuss the day’s events.
The science team sat together at a table for lunch. The launch window on the second day had just closed — another scrub — but this time it wasn’t the wind. Instead, the aurora had eluded them.
In broad strokes, all types of aurora have a similar origin story. They form when negatively charged electrons crash into the gases in our atmosphere, jarring those gases into high-energy states. As they relax back to normal they give off their excess energy in the form of light: the ruby reds and emerald greens that illuminate the northern and southern skies.
Most of these auroras are formed by the same population of electrons. These electrons come from inside Earth’s magnetic field.
But the cusp auroras — the kind that form above Ny-Ålesund for just a few hours a day — are from a different stock of electrons. When they set the sky alight, they are at the end of a 93-million-mile journey, direct from the Sun.
Most particles that flow off the Sun — collectively known as the solar wind — don’t have that fate. By and large, they are deflected around Earth’s magnetic field, sent skimming off into space. But near the north and south poles, there are two funnels where solar particles can slip inside.
These holes in our protective shield are known as the polar cusps. They’re the only places on Earth where the oncoming solar wind directly collides with our atmosphere. The polar cusps are anchored to the Sun-facing side of Earth; as the planet rotates, they remain in perpetual daylight, piping electrons from the Sun into the polar atmosphere. And between the hours of 10 a.m. and noon, the town of Ny-Ålesund passes right beneath one of them.
The cusp aurora hold secrets that extend far beyond Ny-Ålesund, both in space and time. Some 4.2 billion years ago, Mars had a hearty atmosphere along with liquid water on its surface. In its prime, scientists estimate, it might have been suitable for life. But through the millennia, the solar wind stripped Mars’s atmosphere to produce the exposed, barren landscape we see today. Partly, this is due to Mars’s weak magnetic field, which is unable to protect the planet as well as Earth’s can. Yet the story is more complicated than that, for Venus’s magnetic field is also weaker than Earth’s, yet it boasts an atmosphere 90 times thicker.
A planet’s fate lies in a complicated balancing act between countless physical processes, some that drain its atmosphere away and some that grow it. In the cusp aurora, some of these processes can be spied up close.
But Rowland is also looking to the future. Today, with just over 4,000 confirmed exoplanets, or planets orbiting stars elsewhere in the universe, the race is on to determine which of them are potentially habitable. But the dynamics of their atmospheres — which make or break their suitability for life — remain poorly understood. At present, we can do no more than make intelligent guesses, based on scientific models, about what their atmospheres might be like. To check the accuracy of these models, we test them with data collected on Earth. Data just like what Rowland’s team were here to get.
But there were no guarantees that the cusp auroras would cross their path. When the Sun’s activity is low, the cusp passes just north of Ny-Ålesund, outside of their approved launch trajectory. But a healthy gust of solar wind, they knew, could push it south, right into their path. So they waited, readying their rockets to ambush the aurora at the perfect moment.
At 3:45 am, the van rumbled over a snow-covered road away from the team’s dormitories. The launchpad was a ten-minute ride outside the town limits. Ny-Ålesund’s boundaries are marked with triangle-shaped signs, outlined in red, encasing the silhouette of a polar bear. “STOP!” they read, “Do not walk beyond this sign without your firearm.”
So far, residents had delivered nothing more than warning shots, but that summer’s 11 polar bear sightings kept them on their guard. Lately, the biggest nuisance had been a large male, nicknamed Whitey, who destroyed several of the vacation cabins used during warmer months. Half-joking “Wanted” posters hanging inside the mess hall show a picture of him, snout protruding through a cabin window. He is on the inside, looking out.
As the van approached the launchpad, tufts of snow skimmed across the ground like tiny clouds on a miniature landscape. The chassis hummed from the wind’s vibration — it was gusting hard today.
Today was the first of 15 opportunities to launch. Day 1 launches do happen occasionally. But for some missions, even two weeks won’t beget the combination of clear weather, pristine aurora, and no engineering issues. It’s not unheard of for entire teams to pack up and try again next year.
Across the snow, two yellow scaffolding towers aimed themselves skyward at a forty-five-degree angle. These were the launchers, and on the underside of each, encased in a Styrofoam shell, was a ready-to-launch rocket. Named by shortening their mission number, the nearest rocket was “39,” and behind it, “40.” Together, they comprised the VISIONS-2 mission.
These were sounding rockets — so-called for the nautical term “to sound,” meaning “to measure.” They vary in size, but can stand up to 65 feet tall and are usually just slim enough for a bear-hug. Sounding rockets fly anywhere from 30 to 800 miles high, carrying scientific instruments into space before falling back to Earth. The two on the launchpad carried 11 instruments between them. One rocket would spin through its flight, gathering data from all viewing angles, while the other would steady itself after launch for those experiments that required a stable view. They would launch two minutes apart along a southward trajectory, peaking around 300 miles high and landing some 15 minutes later in the Greenland Sea.
The rockets and their launchers are controlled from the blockhouse, a modest building 100 yards from the launchpad. Inside, a burly man with a bushy beard stood in the middle of a tiny room, surrounded by eight engineers. Glenn Maxfield, the launcher systems manager, was one of the leaders of the team. He spent much of his time outside, with the rocket. But right now, he and the rest of the team were staring at a temperature gauge. Something was wrong.
The temperature gauge monitored a special camera aboard one of the rockets known as a charge-coupled device, or CCD. The CCD camera would capture imagery of the aurora as the rocket flew through it. But to work properly, it had to be cold — below -31 degrees Fahrenheit. Too warm and it would ruin their view of the aurora, producing “dark noise” that resembles an overexposed photograph.
To keep it cold the team was using a liquid nitrogen cooling system. But nitrogen was now pooling at a U-turn in the plumbing inside the rocket. If it wasn’t fixed, the instruments could cool so quickly they could fracture.
Maxfield was on the phone with Range Control, the team that coordinated launch operations. Range Control, noting increasing winds, wanted to lower the rockets from their ready-to-launch positions.
“Right now, I don’t know how much nitrogen is in there, and if we go down, there’s the potential that it runs into the instruments,” Maxfield said. But the solution was already in the works. Maxfield had opened a valve to allow excess nitrogen to evaporate out from the rocket; he could hear it hiss as it steamed away. Now, they just had to wait. He hung up the phone and headed back out to the rocket.
A few moments later Maxfield returned, looking satisfied. The hiss had stopped. The liquid was gone, and the CCD camera had reached the target temperature. “I think we’re good,” he said.
Sounding rockets “go where you point them,” Rowland said. “Unless it’s windy. Then they go somewhere else.”
The success of a sounding rocket mission depends on fixing just these kinds of problems as they arise. But it’s at least as dependent on the weather, which is much harder to control. Ground winds could endanger a rocket still on the launchpad, but winds higher up were at least as threatening. For all their complicated mechanics, sounding rockets have no rudder, no real-time ability to steer once they’re in flight. Sounding rockets “go where you point them,” Rowland, the mission leader, said. “Unless it’s windy. Then they go somewhere else.”
So the team doesn’t take chances: The launch systems could accommodate winds up to 20 miles per hour, but no more. Gusty conditions could send the team home for the day. A prolonged storm could squander their entire two-week window.
Monitoring those winds was the job of Anders Moen and Tommy Jensen, both employees of the Andøya Space Center, the Norwegian agency responsible for operating the range. Inside the blockhouse, they were tracking a weather balloon. Their screen displayed a simplified map of Svalbard, with Ny-Ålesund at the center. A thin line squiggled across Ny-Ålesund to a point somewhere over the Arctic Ocean, marking the balloon’s current location. It was almost out of range — about time to launch another.
Moen and Jensen got up and continued into the neighboring open hangar. Next to its rolling door was a collection of giant metal gas tanks. Jensen reached for one, turned the dial, and a hollow hissing sound began. He held up a white balloon from his fist, which hung first like an empty bag then righted itself, filling rapidly until reaching a 5-foot diameter. Moen tied it to a GPS device — a small white box about the size of a paperback novel. Jensen pushed a button on the wall and the large rolling door opened.
Outside the hangar, the wind was loud, and snow tussled in front of them like tumbleweed. Jensen raised his arm, waiting for a signal on his walkie-talkie, as Moen carried the white box. A moment’s pause, a walkie-talkie confirmation, and he let it free. With a loud tearing sound, it took off like a dragster as the white box jerked from Moen’s hand, whipping frantically after the balloon. Shooting off at a diagonal, the balloon quickly disappeared into the darkness.
During launches, Moen and Jensen carried out this ritual several times a day. After release, the GPS device would send real-time data showing the balloon’s altitude, speed, and direction that allowed them to monitor high-altitude winds. In a few moments, a new line would trace across Moen and Jensen’s monitor. They turned and walked back into the hangar as the rolling door closed behind them.
Soon after, the signal from the newly launched GPS balloon was coming in, and the news wasn’t good. It was showing gusts at 37 miles per hour, well above their cutoff. Range Control radioed in and recommended “scrubbing,” or ending the launch attempt for the day. Shortly afterward, Rowland made it official.
Chasing the aurora from the world’s northernmost rocket range
In the tiny Arctic town of Ny-Ålesund, where polar bears outnumber people, winter means three months without sunlight. The unending darkness is ideal for those who seek a strange breed of northern lights, normally obscured by daylight. When these unusual auroras shine, Earth’s atmosphere leaks into space.
NASA scientists traveled to Ny-Ålesund to launch rockets through these auroras and witness oxygen particles right in the middle of their escape. Piercing these fleeting auroras, some 300 miles high, would require strategy, patience — and a fair bit of luck. This is their story.
When the bus finally came to a stop, they found themselves inside a glass-walled garage. A man was standing inside.
“Welcome to Ny-Ålesund!” the man cheered. His messily-parted, shoulder-length brown hair would fit in on tour with a heavy metal band. But this was Doug Rowland, NASA rocket scientist, and the team’s leader. He was the one who had called them to meet in this cold, dark, and strangely beautiful place.
The newcomers stepped off the bus and into the garage’s light. Among the first was Sophie Zaccarine, who waved hello to Rowland with both arms overhead. A 21-year-old engineering physics major, Zaccarine would monitor one of the scientific instruments during the flight. Over the past three years, she had worked through summer internships and short visits to NASA to design and build a small electronics enclosure that, very soon, would become her first bit of hardware in space. Robert Pfaff strode in later, nodding at staff as he passed them. Pfaff was a co-investigator, in charge of one of the experiments, and a veteran rocket man. He led the very first NASA launch from this remote arctic town in 1997, and has launched more rockets here than anyone else at the agency.
As Rowland greeted each of the 11 new arrivals, he appeared visibly relieved — his science team was finally here. Rowland had been on the island for a few weeks already, helping to reassemble the two rockets after they had traveled across the Atlantic Ocean in pieces, by cargo ship. Today, after three years of development, they now stood fully-assembled and ready at the launchpad a few miles away. But soon they would be much farther, some 300 miles high, flying through an aurora. If all went as planned.
The science team had landed in Ny-Ålesund, the northernmost civilian settlement in the world. A tiny research town on the Norwegian Archipelago of Svalbard, it is a place where trees do not grow. The only fresh food arrives by cargo ship after a voyage across arctic waters. During winter months, Ny-Ålesund’s resident population drops to 30 for the dark season, which is when the team had arrived. It was December. For the next three months, the Sun wouldn’t rise.
Daytime darkness was important, for only against a dark backdrop could the special aurora borealis they sought be seen with the naked eye. But the main reason for coming to this place was not the dark sky, per se. It was what transpired far above it.
Between the daytime hours of 10 a.m. and noon, a magnetic portal to space passes over Ny-Ålesund. For those two hours, the barrier between sky and space is at its thinnest. Energetic particles normally deterred by Earth’s magnetic field rush into Ny-Ålesund’s air. They strike atmospheric gases, setting the sky alight with auroras that shine during the day. But the strangest thing about these auroras is not visible at all. Inside them, gases are beginning to cook, and some reach their boiling point. Through these auroras, massive amounts of oxygen are boiled away to space.
The process is known as atmospheric escape. It has been happening on Earth for billions of years, and will continue for a billion more — a timescale too long to impact humans. Yet the physical reactions set forth inside these auroras are cogs in the much larger machine of atmospheric change. Over time, they have transformed Earth from a molten ball of magma into the rich, balanced catalyst for life that it is today. To understand atmospheric escape is, in part, to understand how we got here.
So these NASA-funded researchers traveled to Ny-Ålesund to study these auroras and the oxygen they set free. They wanted to understand the precise mechanism of heating, and better quantify exactly how much oxygen is lost this way. In pursuit of these questions, they came armed with the heavy artillery of their trade. They would shoot scientific rockets into the aurora, measuring the oxygen right as it started to escape.
It would take a large team, some sixty-one members in all, each with their own set of skills and responsibilities. Some would monitor the rockets and the precious scientific instruments they carried. Others studied the sky to forecast when to launch. Yet others would coordinate these teams, ensuring each step was taken at the right time and in the proper order. But together, with good timing and a healthy dose of luck, they would attempt to place scientific instruments inside an active aurora. They would watch, up close, how bits of Earth’s atmosphere escape to space.
Tracking Charged Particles into Earth’s Atmosphere with ELFIN
By Mara Johnson-Groh NASA’s Goddard Space Flight Center
On September 2, 2019 — after a year of quiet conditions in space since its September 2018 launch — a NASA CubeSat the size of a large toaster flew straight through a solar storm, when a burst of material ejected by the Sun dramatically increased the number of highly charged particles coursing through Earth’s magnetic environment. These observations from the CubeSat — called ELFIN, short for Electron Losses and Fields Investigation — allowed the scientists to see events that are usually too weak to see under normal conditions.
ELFIN’s job, as it circles through Earth’s polar regions, is to measure super-speedy charged particles falling into Earth’s atmosphere, and for the first time, uncover what pushed them there. The highly energetic electrons and ions measured by ELFIN originate in the Van Allen radiation belts, the concentric rings of charged particles trapped around Earth by the planet’s magnetic field. These charged particles can spark aurora, and if strong enough, disrupt telecommunications, so understanding what sends them hurtling towards Earth is important to protecting our assets in space and on the ground.
Here’s what that ELFIN data looked like in the solar storm.
The graphs show data over a period of just a few minutes on September 2 with each color (right axis) showing how many particles are present at a given energy (left axis). Red represents higher numbers — and the spike in the middle shows that the particle count was in the millions across a wide range of energies. Because ELFIN can also determine the direction in which the particles are traveling relative to the Earth’s magnetic field — a measurement known as pitch angle — they can figure out which of these particles are circling around Earth, trapped by the magnetic fields, versus those that are raining down out of the belts toward our planet. ELFIN is the first satellite to quickly survey the whole latitudinal range of the radiation belts with this capability — taking measurements of pitch angle while simultaneously measuring the particles’ energies at high resolution.
In this case, the particles were falling into Earth’s atmosphere as it flew over Norway and the North Sea. Having seen a precipitation event, the scientists looked to see if they could identify what caused it. Particles typically get dislodged by electromagnetic waves pushing them out of orbit. Different waves dislodge particles with different energies or different travel directions. By looking at the distribution of particles that fell into the atmosphere, the scientists hoped to find out which type of wave was responsible. In particular, ELFIN scientists are looking to see if a type of wave known as an electromagnetic ion cyclotron wave, or EMIC wave, can scatter these particles into Earth’s atmosphere. This type of wave typically knocks down only high-energy particles — those with energies above 900,000 electronvolts.
The measurements, shown in the bottom panel of the graph above, show a spike of precipitating particles at these high energies, suggesting EMIC waves might be involved. But since it did not also measure EMIC waves, which often occur farther out from where the particles precipitate, the case is not yet closed. The mission expects to answer this question as it continues to collect data over the next one and a half years.
Other NASA missions — like the Magnetospheric Multiscale mission and the Time History of Events and Macroscale Interactions during Substorms mission, which orbit farther out — may be able to collaborate with ELFIN by directly measuring the EMIC waves near the equator that launch the particles, which follow along magnetic field lines all the way down to ELFIN. These types of conjunction measurements from different instruments and vantage points will allow scientists to learn more about EMIC waves scattering phenomena than any single-point observation could.
ELFIN was developed at the University of California, Los Angeles, where over 200 students have contributed to the mission. The mission is funded by NASA and the National Science Foundation.
Imagine, if you will, that you are driving to your favorite restaurant. The traffic is bad, so you use your GPS to find the best route. To get your current location, your phone or GPS listens to a satellite in the Earth’s upper atmosphere. This satellite sends the GPS system information that allows it to determine where you are and the quickest way to get to your destination.
But sometimes, the signal gets interrupted, the GPS won’t load, or it points you in the wrong direction. Why does this happen?
Ryan McGranaghan, space scientist at ASTRA, LLC and NASA affiliate, tried to tackle this problem by figuring out when a GPS is right and when it’s likely to be wrong. To achieve this, McGranaghan turned to observations from past disturbances in GPS signals. He explored how to use machine learning to try and figure out what made it go haywire in each case.
The main thing he was trying to predict was a phenomenon called ionospheric scintillation. When the electrically-charged part of our atmosphere, known as the ionosphere, becomes too disturbed, it garbles GPS signals that pass through it.
But predicting when a scintillation event is going to happen is no easy task. The atmosphere is a complicated, constantly-changing mix of physics and chemistry, and we still don’t have the ability to consider all factors for predicting when a scintillation event will occur.
To guess the future, look to the past
To start, McGranaghan looked at past data, where we already knew the outcome, and tried to use his algorithm to “guess,” based on a huge number of input variables, whether a given event would cause GPS disruption or not. It’s a bit like solving math problems and then checking your answers at the back of the book.
The graph below shows data on scintillation in the ionosphere. The vertical axis shows a calculation of how disturbed the ionosphere is over time, using data from multiple sources. The higher up on the axis, the more disturbed the ionosphere was at the time. (Click on the graph to see a larger version.)
The ionosphere is never perfectly undisturbed — the dots are always above zero — so the black dashed line on the graph is determined by scientists to mark when communication begins getting disrupted. As you can see, towards the middle of the graph particles in the ionosphere wiggled past the threshold, enough to disrupt satellite signals.
That is where machine learning comes in. McGranaghan trained a support vector machine, or SVM, to try and guess the recipe for a scintillation event.
A Support Vector Machine isn’t a real machine, made of metal and gears. Rather, it’s an algorithm, a mathematical procedure that is used to separate complicated data into two groups. In this case, the support vector machine tried to guess, while only looking at the ingredients and not the outcome, which were “scintillation events” — dots that landed above the dashed line — and which “non-scintillation events,” landing below.
To do this, you have to first give the SVM some training data for it to practice on, where you show it both the ingredients and the outcomes. From this training data, it tries to “learn” (hence “machine learning”) which ingredients tend to produce which kind of outcomes, and then come up with a general rule.
After a lot of the training data is fed into the algorithm and it has had plenty of time to practice, then you give it new data. Now you’re showing just the ingredients, keeping the outcome hidden, and it tries to guess. Based on its experience with the training data, how well does it guess?
Understanding the Results
In the case of ionospheric scintillation events, there are a few different kinds of guesses.
There are the two ways it can be right: guessing it was a scintillation event, and it really was — we’ll call that a hit — or guessing that it wasn’t a scintillation event, and it wasn’t — we’ll call that a correct rejection. In the graph below, these are color-coded as follows:
Correct responses Hit – Green
Correct Rejection – Blue
There are two ways to be wrong as well: guessing that there wasn’t a scintillation event, and there was — a miss — and guessing that there was a scintillation event and there wasn’t — a false alarm.
Incorrect responses Miss – Red
False Alarm – Yellow
After feeding the data to the algorithm, the SVM made its guesses. We’ll now color-code the same data we saw above, but according to this new color scheme:
As you can see, it looks very similar to the previous graph, now in technicolor. Those colors are the result of the SVM identifying scintillation, and scientists marking how “correct” the SVM was.
The dark blue dots reveal where the SVM correctly identified that it was not a scintillation event. If the SVM had incorrectly identified that there was no scintillation event — a miss — the color would be red.
The green dots are cases where the SVM correctly identified that scintillation is happening. Notice that it correctly identified all the dots that were above the dashed line as scintillation events. But also notice the yellow dots. Those mean the SVM incorrectly identified those data points as scintillation — a little overzealous in identifying an event as scintillation. These false alarms mean the SVM is predicting scintillation when it is not occurring, at least not to a degree that would interrupt signals.
The Future of Scintillation Predictions
This is just the beginning of a potentially powerful tool for predicting ionospheric scintillation. In the future, the SVM algorithm could be taught to be more careful about what it labels as scintillation; or, another machine learning algorithm could be applied to get more accurate results.
Regardless, it would be up to the scientist reading the predictions to make the final decisions: both when the scintillation events could occur, and the best way to manage the loss of communication with the satellite.