The aurora borealis is one of the world’s most beautiful natural phenomena, a glorious convergence of Earth’s magnetosphere with incoming solar wind. As particles in the atmosphere become energetically excited, an iridescent display of color is produced – a well-understood mechanism. However, the aurora is in fact highly complex, and many of its features and characteristics remain somewhat mysterious. In order to shed some additional light on these uncertainties, NASA is going to send two rockets loaded with scientific instruments up into the aurora itself this winter.
Two instrument packages – CAPER (Cusp Alfven and Plasma Electrodynamics Rocket) and RENU 2 (Rocket Experiment for Neutral Upwelling) – will be launched sometime after November 27th, when the wind speed is low. Their target is the cusp aurora, a specific subset of the complete aurora phenomenon. At the cusp, particularly energetic particles are rapidly accelerated downward into the atmosphere directly from the incoming streams of solar material.
Although these aren’t particularly rare, cusps are quite difficult to spot, as they only occur during the day. Fortunately, as the magnetic North Pole is offset from the geographic North Pole, it’s possible to catch a view of the cusp in Northern Europe (in this case, Norway) near the winter solstice when the days are as dark as possible.
CAPER will be attached to the first rocket to be launched. It will be investigating the electromagnetic waves that cause electrons to be accelerated through the atmosphere. The electrons that propagate downwards towards the planet ricochet off other particles in our atmosphere, releasing energy as visible light and initially creating the cusp aurora – the precursor to the main event at magnetic midnight.
CAPER itself will be sent up into the cusp in order to detect these energetic particles and both low- and high-frequency electromagnetic waves; this will give researchers a better understanding of how particle acceleration in the atmosphere occurs during heightened solar wind activity.
The second rocket will contain the RENU 2 instrumentation suite, which is designed to investigate the behavior of these excited particles in the upper atmosphere, along with their associated electric currents and magnetic field lines. In particular, it will probe a region of densely packed, heated neutral atoms within the cusp.
Until recently, scientists thought that densely packed piles of neutral particles, generated by sunlight-driven heating, were only located in a horizontal section of the atmosphere. However, some rockets traveling through the cusp have experienced friction above this point, which suggests there is a small pocket of high-density neutral atoms that has previously gone undetected. RENU 2 will look out for the generation mechanisms responsible for this upper “speed bump.”
“When solar wind electrons collide with atmospheric electrons, they transfer some of their energy, heating the atmospheric electrons,” said Marc Lessard, principal investigator for RENU 2 at the University of New Hampshire in Durham, in a statement. “The higher heat means the electron populations expand upward along the magnetic field lines.”
Despite only being present in the cusp for just a few minutes, both rockets will provide valuable, novel data at a relatively low cost to NASA.