Aurora mysteries unlocked with NASA’s THEMIS mission

A special kind of aurora, spinning east-west across the night sky like a glowing pearl necklace, helps scientists better understand the science of auroras and their powerful drivers in space. Known as auroral beads, these lights often appear just in front of large auroral displays, which are caused by electrical storms in space called substorms. Previously, scientists were not sure if auroral beads are somehow connected to other auroral displays as a phenomenon in space that precedes preforms, or if they are caused by disturbances closer to the Earth’s atmosphere.

But powerful new computer models combined with observations of NASA’s Time History of Events and Macroscale Interactions During Substorms – THEMIS – mission have provided the first strong evidence of the events in space that lead to the appearance of these beads, and demonstrate the important role they play in our nearby space environment.

“Now we know for sure that the formation of these beads is part of a process that precedes the triggering of a substorm in space,” said Vassilis Angelopoulos, principal investigator of THEMIS at the University of California, Los Angeles. “This is an important new piece of the puzzle.”

By providing a broader image than just using the three THEMIS spacecraft as ground observations, the new models have shown that auroral beads are caused by turbulence in the plasma – a fourth state of matter, consisting of gaseous and highly conductive charged particles – surrounding earth. The results, recently published in the journals Geophysical research letters en Journal of Geophysical Research: Space Physics, will eventually help scientists to see the full range of healing structures in the auroras.

“THEMIS observations have now revealed turbulences in space that cause currents that illuminate the sky as if from some pearls in the glowing auroral chain,” said Evgeny Panov, lead author on one of the new papers and THEMIS scientist at the Space Research Institute of the Austrian Academy of Sciences. “These turbulences in space are initially caused by lighter and rougher electrons, moving with the weight of particles 2000 times heavier, and which could theoretically develop into fully auroral substorms.”

Mysteries of Auroral Beads Formation

Auroras are formed when charged particles of the sun are in the earth’s magnetic environment – the magnetosphere – and are found in the earth’s upper atmosphere, where collisions of hydrogen, oxygen, and nitrogen atoms and molecules glow. . By modeling the near-Earth environment at scales of tens of miles to 1.2 million miles, THEMIS scientists were able to show the details of how auroral beads form.

As flowing clouds of plasma passing through the Sun pass the Earth, its interaction with the Earth’s magnetic field creates floating bubbles of plasma behind Earth. Like a lava lamp, an imbalance occurs in the drift between the bubbles and heavier plasma in the magnetosphere fingers of plasma 2,500 miles wide extending to Earth. Signatures of these fingers create the distinct bead-shaped structure in the aurora.

“There has been a realization that, all in all, these relatively small transient events that occur around the magnetosphere are somehow important,” said David Sibeck, THEMIS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We have only recently come to the point that computing power is good enough to capture the basic physics in these systems.”

Now that scientists understand the auroral beads for subforms, they want to figure out how, why, and when the beads can trigger sustained substorm. At least in theory, the fingers can wave magnetic field lines and cause an explosive event, known as magnetic connection, which is known to create full-scale substorms and aurorae that fill the night sky.

New models open new doors

Since its launch in 2007, THEMIS has taken detailed measurements as it travels through the magnetosphere to understand the causes of the sub-storms that lead to auroras. In its main mission, THEMIS was able to demonstrate that magnetic reconnection is a primary driver of substorms. The new results highlight the importance of structures and phenomena on smaller scales – those hundreds and thousands of miles across compared to those that span millions of miles.

“To understand these features in the aurora, you really need to solve both global and smaller, local scales. That’s why it was so challenging so far,” said Slava Merkin, co-author of one of the new papers and scientist at NASA. Center for Geospace Storms headquartered at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “It requires very sophisticated algorithms and very large supercomputers.”

The new computer simulations correspond almost perfectly with THEMIS and observations of ground. Following the initial success of the new computer models, THEMIS scientists know how to increase them to apply them to other unexplined aural phenomena. Especially when explaining small-scale structures, computer models are essential because they can help interpret what is happening between the spaces where the three THEMIS spaceships pass.

“There are a lot of very dynamic, very small-scale structures that people see in the auroras that are difficult to connect to the larger image in space, because they happen very quickly and on very small scales. , “said Kareem Sorathia, lead author on one of the new papers and scientist at NASA’s Center for Geospace Storms headquartered at Johns Hopkins Applied Physics Laboratory. “Now that we can use global models to characterize and research them, that opens up a lot of new doors.”