Two Rockets Launched From Alaska To Unravel The Mystery Of The “black Aurora”

The Northern Lights are one of the most striking visual and physical phenomena that it is given to a human being to admire. When the skies are dressed in these green or purple draperies that dance in the polar sky, it is because of the energetic particles ejected by the Sun which collide with the gases of the upper atmosphere.

However, it sometimes happens that this usual mechanism reverses, revealing areas of total darkness called ” black aurora » in the middle of this ballet of light. A phenomenon known since the 1970s, which we understood quite poorly then. To lift the veil on these anomalies, NASA launched two suborbital missions last week: BADASS (we laugh at NASA!) and GNEISS. Sounding rockets that perform short parabolic flights, plunging their instruments directly into the plasma of the ionosphere (upper layer of the atmosphere between 80 and 1,000 km altitude). This is the only way to get measurements on site of the dynamics of electric currents where the aurora shines and where these famous holes appear.

BADASS : measure dark auroras in real time

On February 9, the BADASS mission rocket (Black and Diffuse Auroral Science Surveyor) reached an apogee of 360 kilometers. At this altitude, the craft was able to cross the shadow zones of the aurora in order to confirm aa theory that has kept astrophysicists in suspense for more than twenty-five years. We have to go back to 1996 to understand where this hypothesis about dark auroras comes from, the date of the launch of the European Cluster mission and, later, by NASA’s FAST satellite.

At the time, these missions made it possible to understand that these pockets of darkness were a physical phenomenon distinct from the aurora itselfwhich could be described as “ anti-aurorae ».

When an aurora occurs, our atmosphere is bombarded with electrons, which collide with the oxygen and nitrogen atoms that compose it; this is what produces these sublime light patterns. But in the case of the dark dawn, the reverse process takes place : a powerful electric field sucks electrons out of the ionosphere and into space. This ascending current empties the area of its energetic particles, creating by contrast these “ holes » dark in the middle of light rays.

For Marilia Samara, head of the mission BADASSthe results lived up to what was hoped for: the instruments worked exactly as expected, delivering the measurements necessary to identify the causes of this inversion. These measurements will now be analyzed by NASA, which has for the first time physical surveys captured at the heart of these magnetic anomalies.

GNEISS : the 3D scanner of the ionosphere

On February 10, the GNEISS mission (Geophysical Non-Equilibrium Ionospheric System Science) took over to map the variations in plasma density within the auroral zone. Thanks to two rockets propelled to an altitude of 319 kilometers, NASA was able to multiply the points of view. By crossing the data from these two machines with those from a network of ground receivers, researchers obtained a three-dimensional view of the auroras.

The interest is to understand how these gray areas impact the waves which cross the ionosphere. Until now, the surveys were limited to the trajectory traveled by the rocket, which did not make it possible to measure the real extent of the auroral disturbance. The ionosphere acting as a conductor for GPS signals and high frequency radio communications, when a dark aurora locally empties this layer of its electrons, it forms an area where signals can no longer circulate normally.

Thanks to the measurements collected by GNEISS et BADASSNASA will be able to better predict the energy transfers that occur between the magnetosphere and the ionosphere. It may seem slightly esoteric expressed this way, but this data will be a gold mine for many areas sensitive to magnetic variations. Security of satellite megaconstellations, reliability of radio links (airliners or offshore oil stations, for example), continuity of satellite telephone services in the Far North, positioning precision for autonomous ships crossing Arctic routes, etc. The list of beneficiaries is as long as an arm and without this better understanding of atmospheric plasma dynamics, our knowledge of space weather would still remain too incomplete. This is why dark auroras are just as important to understand as auroras: they are also parasites for our most advanced technologies.