Mysterious Areas Above the North Pole
NASA Rockets to Study Mysterious Areas Above the North Pole
POLAR CUSP:
Strange things happen in Earth’s atmosphere at high latitudes. Around local noon, when the Sun is at its highest point, a funnel-shaped gap in our planet’s magnetic field passes overhead. Earth’s magnetic field shields us from the solar wind, the stream of charged particles spewing off the Sun. The gap in that field, called the polar cusp, allows the solar wind a direct line of access to Earth’s atmosphere.
Radio and GPS signals behave strangely when they travel through this part of the sky. In the last 20 years, scientists and spacecraft operators noticed something else unusual as spacecraft pass through this region: They slow down.
“At around 250 miles above Earth, spacecraft feel more drag, sort of like they’ve hit a speed bump,” said Mark Conde, a physicist at the University of Alaska Fairbanks. That’s because the air in the cusp is noticeably denser than air elsewhere in the spacecrafts’ orbits around Earth. But no one knows why, or how. By understanding the forces at play in the cusp, scientists hope to better anticipate changes in spacecraft trajectories.
NASA planned to send a rocket into that region in 2019, but although all systems were ready for launch, the mission never got off the ground. There was little solar activity at the time, and as a result, space weather conditions weren’t right for the mission during the initial launch window. The pandemic further postponed its flight. Now, after a nearly two-year delay, the rocket was able in December 2021 to fly in hopes of answering questions about the cusp. The team is optimistic; the Sun is in a more active stage of its natural cycle this time around, increasing the chances that space weather conditions will be favorable for their mission to study an unusually dense region of the atmosphere.
While the density of Earth’s atmosphere decreases rapidly with height, it stays consistent horizontally. That is, at any given altitude, the atmosphere is roughly the same density around globe.
Except in the cusp, where 250 miles overhead, there’s a pocket of air roughly one and a half times denser than other air at that altitude. “You can’t just increase the mass in a region by a factor of 1.5 and do nothing else, or the sky will fall,” Conde said. Something invisible supports that extra mass, and the mission aims to figure out exactly what it is.
The mission is designed to measure the numerous factors that could potentially explain how the cusp’s dense air stays suspended. Then, Conde said, scientists can “try and sort out which one is doing the work.”
One possibility involves electric and magnetic effects in the ionosphere, the layer of Earth’s upper atmosphere that is ionized by the Sun, meaning it contains electrically charged particles. Electrodynamics could support the denser air indirectly, or it may cause heating that generates vertical winds to keep the dense air aloft. The rocket has an array of instruments designed to measure these effects.
Another explanation might be that air in the entire vertical column of the cusp is denser than its surroundings. Stacked atop heavier air, the dense air 250 miles high would remain buoyant. But having a column of heavier air should also produce horizontal or even vortex-like winds, which the rocket is designed to look for.
And it will do so in style. The rocket will eject 20 soda can-sized canisters, each with its own small rocket motor, in four directions. The canisters are timed to rupture at different altitudes. When they burst, they’ll release vapor tracers — particles often found in firework displays which glow by scattering sunlight or upon exposure to oxygen — in a three-dimensional grid in the sky. The wind will paint the sky with these glowing clouds, revealing how air moves in this unusual section of the atmosphere.
PULSATING AURORA:
A new NASA rocket mission will soon take to the Alaskan skies. The mission will fly above an often-overlooked kind of northern lights to test a theory on what causes them.
The aurora borealis, or northern lights, is a familiar treat to those who call northern latitudes home. Auroras come in different shapes and colors, waving their ribbons of vibrant green, red and purple across the sky. But one variety of aurora displays a peculiar behavior: it pulsates.
“It’s sort of hypnotic, pulsating every few seconds,” said Dr. Alexa Halford, space scientist at NASA and director of the mission. “The blobs and colors remind me of a lava lamp, where you can just sit and stare at it for hours.”
Like all aurora, pulsating aurora are set alight by electrons (and occasionally protons) from near-Earth space. These electrons plunge into our atmosphere and collide with atoms and molecules, causing them to glow in their distinctive colors – red and green by oxygen, blue by nitrogen – as they release their excess energy.
But what sets those electrons into motion in the first place? For pulsating aurora, the going theory points to chorus waves, so named because they were first detected as audio signals in radio receivers during World War I.
But chorus waves are not sound waves – instead, they move through plasma, the electrified gas that makes up over 99% of the observable matter in space. They ripple through the particles trapped within Earth’s magnetic environment, shaking some loose to fall into our atmosphere.
“Chorus waves occur at exactly the right frequency to ‘resonate’ with the electrons that create pulsating aurora, similar to how you pump your feet at just the right time to get a swing to go higher and higher,” said Dr. Allison Jaynes co-investigator for the mission. Eventually, some of these electrons “jump off” the swing – and shoot into our atmosphere.
Chorus waves can launch both low and high-energy electrons, which may explain some puzzling coincidences. Pulsating aurora are caused by fairly low-energy electrons, but they’re often observed alongside flashes of X-ray light known as microbursts, which come from higher-energy electrons.
“Pulsating aurora and microbursts seem to happen at similar times, even though they’re different energy ranges,” Halford said. “So, the big question is, are they the same events? Are they being driven by the same processes in the magnetosphere?”
You can hear the “sound” of Chorus HERE