At high latitudes, strange things happen in the Earth’s atmosphere. A funnel-shaped breach in our planet’s magnetic field passes overhead at local noon when the Sun is at its highest point.
The magnetic field of the Earth protects us from the solar wind, which is a stream of charged particles ejected from the Sun.
The polar cusp, a gap in that field, offers the solar wind direct access to the Earth’s atmosphere.
When radio and GPS signals pass over this area of the sky, they behave strangely. Scientists and satellite operators have discovered something else strange about spacecraft passing through this region in the last 20 years: they slow down.
“At around 250 miles above Earth, spacecraft feel more drag, sort of like they’ve hit a speed bump,” says Mark Conde, a physicist at the University of Alaska Fairbanks and the principal investigator for NASA’s Cusp Region Experiment-2, or CREX-2, sounding rocket mission.
“That’s because the air in the cusp is noticeably denser than air elsewhere in the spacecrafts’ orbits around Earth.”
According to NASA, no one has an explanation for why these strange phenomena happen.
To understand this strange phenomenon, At 3:25 a.m. EST, the CREX-2 payload was successfully launched from Norway’s Andya Space Center on December 1.
CREX-2 was programmed to learn more about the dynamics of the cusp as part of the Grand Challenge Initiative – CUSP in 2019, but despite having all of the systems in place, the mission was never launched.
As a result of the lack of solar activity at the time, space weather conditions were unsuitable for the mission during the initial launch window.
The COVID-19 outbreak delayed its departure even more. CREX-2 is set to fly again after an almost two-year hiatus in the hopes of solving questions regarding the cusp. The crew is upbeat because the Sun is in a more active phase of its natural cycle this time, increasing the likelihood that space weather conditions would be good for their mission to examine an extremely dense part of the atmosphere.
While the density of the Earth’s atmosphere reduces significantly as one rises in altitude, it remains constant horizontally. That is, the atmosphere is nearly the same density around the world at any given altitude.
Except at the cusp, where a pocket of air nearly one and a half times denser than other air at that altitude exists 250 miles overhead.
“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,” said Conde.
That extra mass is supported by something unseen, and the CREX-2 mission is tasked with figuring out what it is.
The mission’s goal is to collect data on a variety of elements that could explain why the cusp’s dense air remains suspended.
Electric and magnetic effects in the ionosphere, the layer of Earth’s upper atmosphere that is ionized by the Sun and hence contains electrically charged particles, are one possibility. The denser air may be supported indirectly by electrodynamics, or it could be heated, causing vertical winds to hold the dense air aloft. CREX-2 features a number of equipment for measuring these impacts.
Another possibility is that the air in the cusp’s vertical column is denser than the air around it. The dense air 250 miles high would remain buoyant if stacked atop heavier air. A column of heavier air, on the other hand, should produce horizontal or even vortex-like winds, which CREX-2 is programmed to detect.
It will do so in style, too. The rocket will fire 20 soda can-sized canisters in four directions, each with its own miniature rocket motor. At various altitudes, the canisters are timed to rupture. When they explode, vapor tracers — particles that glow by scattering sunlight or when exposed to oxygen, as seen in fireworks displays — will be released in a three-dimensional grid in the sky. The wind will blow these light clouds across the sky, illustrating how air travels in this particular part of the environment.
This part of the endeavor demands a lot of planning. “It’s quite a big chess game,” Conde explained. To gain a complete picture of the wind patterns, the crew needs to examine the tracers from a variety of angles. Over the span of 20-30 minutes, scientists, some of whom are graduate students, will be stationed throughout Scandinavia to photograph the tracers. One student will photograph them from a plane flying from Iceland’s Reykjavik, while others will photograph them from two locations on the Norwegian island of Svalbard.
There are a few “Goldilocks” requirements for launch. The cusp is only visible around local noon, and the sky must be dark to see the tracers’ glow. CREX-2 will launch in the middle of the winter, when there is very little sunlight at these far northern latitudes.
“We’re threading a needle,” Conde said. “We get about an hour or two each day when conditions are suitable to do the experiment.” And, at least two of the stations need a clear view of the tracers for sufficient data collection. The 2019 launch window was open for 17 days, not one of which was suitable for CREX-2 to fly.
“The rocket business is a high-stakes game,” Conde said. “You’ll spend two or three years developing a payload, but ultimately, it all comes down to choosing when to press the button to capture the science you want.”
That moment does not always arrive. Conde and the CREX-2 crew are looking forward to another launch opportunity.
“Honestly, it feels amazing,” Conde said. “To finally be trying again — I’m not quite sure I have the words for it.”
Source: NASA
Image Credit: NASA
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