Just a few days ago, on December 1, an Oriole IV rocket was launched into space from the Norwegian base of Andøya to release, at several hundred km of altitude, the NASA device CREX-2 (Cusp Region Experiment-2). His goal: to study the strange phenomena that happen in the atmosphere above the North Pole from the earth. There, in effect, when the Sun is at its highest point, a funnel-shaped gap opens up in the Earth’s magnetic field, the natural shield that protects us from charged particles of solar origin and from the harmful cosmic rays that affect us. continuously bombard from space. And through that gap, called ‘polar cusp’ (and which also occurs at the South Pole) radiation penetrates, in a straight line, to the atmosphere.
But that is not all. Also, radio and GPS signals behave strangely when traveling through that part of the sky. And to top it all, for the past 20 years, scientists and spacecraft operators have been noticing something even more unusual: When spacecraft pass through this region, their speed slows down.
“Approximately 400 km above Earth,” explains Mark Conde, a physicist at the University of Alaska Fairbanks and CREX-2 principal investigator. spaceships seem heavier, as if they had reached their speed limit. “The reason is because at the polar cusp the air is noticeably denser than that found by spacecraft on other orbital routes around the Earth. But no one knows why this is the case or how this phenomenon can take place The mission of CREX-2 is precisely to find out.
Two years late
The mission has started two years late. It was initially scheduled for 2019, but although it was completely ready for launch, it did not take off, since at that time there was very little solar activity and the conditions were not suitable to carry out the study. Then, in 2020, the COVID 19 pandemic delayed the flight again. And now, with the Sun in a more active stage and conditions much more favorable to study the cusp, CREX-2 has finally been launched.
A ‘bag’ of heavy air
Although the density of the Earth’s atmosphere decreases rapidly with height, it remains constant horizontally. That is, at any given altitude, the atmosphere has roughly the same density throughout the world.
But that does not happen at the cusp, 400 km above the North Pole, where there is an air pocket about one and a half times denser than is usual at that altitude. According to Conde, “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.” So something invisible is supporting all that extra mass, and CREX-2 aims to find out exactly what.
According to the researchers, a possible explanation would be the presence of electrical and magnetic effects in the ionosphere, the upper layer of the atmosphere, which is ionized by the Sun. That means that this layer contains electrically charged particles, which could help it support the damage. denser air, or also cause a heating that generates vertical winds to keep the bag of dense air up there. In any case, CREX-2 has a series of instruments specially designed to measure these effects.
Another explanation for the phenomenon would be that the air in the entire vertical column of the cusp is denser than that of its surroundings. Thus, stacked on heavier air, the dense air at a height of 400 km would keep floating. But having a heavier column of air should also produce horizontal or even vortex-shaped winds. And CREX-2 is designed to search for those winds.
A task, by the way, not easy. In fact, to achieve this, the rocket will eject 20 cans the size of soda cans, each with its own motor, in four different directions. The containers are programmed to break at different altitudes. And when they explode, they will release vapor tracers – particles often found in fireworks displays that glow by scattering sunlight or being exposed to oxygen – on a three-dimensional grid in the sky. The wind will ‘paint’ the sky with those bright clouds, revealing how air moves in that unusual part of the atmosphere.
A complicated logistics
The logistics to achieve this, however, are complicated. Researchers need to view these tracers from several angles at once to fully understand the wind patterns. So the scientists will be spread out across Scandinavia, taking pictures of the tracers around the same time, all within 20 to 30 minutes. One student will document them from a plane flying from Reykjavik, Iceland, and others will capture the highlights from two different points on the Norwegian island of Svalbard.
The cusp, furthermore, only exists around local noon, but the sky must be dark for the brightness of the tracers to be visible. That is why CREX-2 has been launched in mid-winter, when there is very little sunlight in these extreme northern latitudes.
“It’s like threading a needle,” says Conde. “We have about an hour or two a day in which the conditions are suitable to carry out 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, but none of them were suitable for CREX-2 to fly.
Now, finally, the investigators have gotten the mission started. “The rocket business is a high-risk game,” Conde concludes. “You spend two or three years developing an experiment, but in the end it comes down to choosing when to press the button to capture the science you want.” And sometimes, that moment doesn’t come.