April 14, 2021

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Nasa unlocks mysteries of the phenomenon of ‘space auroras’

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A Nasa mission has unlocked the mysteries of the phenomenon of space auroras and how they form across the galaxy.

A special type of aurora, draped east to west across the night sky like a glowing pearl necklace, is helping researchers better understand the science of auroras and their powerful drivers out in space.

Known as auroral beads, these lights often show up just before large auroral displays, which are caused by electrical storms in space called substorms.

They are atmospheric phenomenons made up of bands of light caused by charged solar particles following the Earth’s magnetic lines of force.

If a planet has an atmosphere and magnetic field there is usually an aurora.

Previously, scientists were not sure if auroral beads are somehow connected to other auroral displays as a phenomenon in space that precedes substorms, or if they are caused by disturbances closer to Earth’s atmosphere.

Aural beads as seen from space (Credits: NASA/SWNS)

But powerful new computer models combined with observations from 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 demonstrated the important role they play in the space environment around Earth.

By providing a broader picture than can be seen with the three THEMIS spacecraft or ground observations alone, the new models have shown that auroral beads are caused by turbulence in the plasma – a fourth state of matter, made up of gaseous and highly conductive charged particles – surrounding Earth.

The results will ultimately help scientists better understand the full range of swirling structures seen in the auroras, the researchers said.

Professor Vassilis Angelopoulos, principal investigator of THEMIS at the University of California, Los Angeles, said: ‘Now we know for certain that the formation of these beads is part of a process that precedes the triggering of a substorm in space.

‘This is an important new piece of the puzzle.’

Auroras are created when charged particles from the Sun are trapped in Earth’s magnetic environment – the magnetosphere – and are funnelled into Earth’s upper atmosphere, where collisions cause hydrogen, oxygen, and nitrogen atoms and molecules to glow.

Aurora borealis. Lofoten islands, Norway. Aurora. Green northern lights. Starry sky with polar lights. Night winter landscape with aurora, sea with sky reflection and snowy mountains.

Auroras as we know them are created by charged particles from the sun getting trapped in Earth’s magnetosphere (Credits: Getty Images)

By modelling the near-Earth environment on scales from tens of miles to 1.2 million miles, the THEMIS scientists were able to show the details of how auroral beads form.

Dr Evgeny Panov, lead author on one of the new papers and THEMIS scientist at the Space Research Institute of the Austrian Academy of Sciences, said: ‘THEMIS observations have now revealed turbulences in space that cause flows seen lighting up the sky as of single pearls in the glowing auroral necklace.

‘These turbulences in space are initially caused by lighter and more agile electrons, moving with the weight of particles 2000 times heavier, and which theoretically may develop to full-scale auroral substorms.’

As streaming clouds of plasma belched by the Sun pass Earth, their interaction with the Earth’s magnetic field creates buoyant bubbles of plasma behind Earth.

Like a lava lamp, imbalances in the buoyancy between the bubbles and heavier plasma in the magnetosphere creates fingers of plasma 2,500 miles wide that stretch down towards Earth, scientists said.

Signatures of these fingers create the distinct bead-shaped structure in the aurora, experts say.

Dr David Sibeck, THEMIS project scientist at Nasa’s Goddard Space Flight Center in Greenbelt, Maryland, said: ‘There’s been a realisation that, all summed up, these relatively little transient events that happen around the magnetosphere are somehow important.

‘We have only recently gotten to the point where computing power is good enough to capture the basic physics in these systems.’

Now that scientists understand the auroral beads precede substorms, they want to figure out how, why and when the beads might trigger full-blown substorm, the researchers said.

At least in theory, the fingers may tangle magnetic field lines and cause an explosive event known as magnetic reconnection, which is well known to create full-scale substorms and auroras that fill the nightside sky, experts said.

Since its launch in 2007, THEMIS has been taking detailed measurements as it passes through the magnetosphere in order to understand the causes of the substorms that lead to auroras.

Nasa's THEMIS spacecraft has been watching auroras since 2007 (Nasa/JPL)

Nasa’s THEMIS spacecraft has been watching auroras since 2007 (Nasa/JPL)

In its prime mission, THEMIS was able to show that magnetic reconnection is a primary driver of substorms.

The new results highlight the importance of structures and phenomenon on smaller scales – those hundreds and thousands of miles across as compared to ones spanning millions of miles.

Dr Slava Merkin, co-author on one of the new papers and scientist at Nasa’s Center for Geospace Storms headquartered at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said: ‘In order to understand these features in the aurora, you really need to resolve both global and smaller, local scales. That’s why it was so challenging up to now.

‘It requires very sophisticated algorithms and very big supercomputers.’

The new computer simulations almost perfectly match THEMIS and ground observations, according to the authors of the study.

After the initial success of the new computer models, THEMIS scientists are eager to apply them to other unexplained auroral phenomena, they added.

Particularly in explaining small-scale structures, computer models are essential as they can help interpret what happens in between the spaces where the three THEMIS spacecraft pass, experts said.

Dr 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, said: ‘There’s lots of very dynamic, very small-scale structures that people see in the auroras which are hard to connect to the larger picture in space since they happen very quickly and on very small scales..

‘Now that we can use global models to characterise and investigate them, that opens up a lot of new doors.’

The findings of the missions were published in the journals Geophysical Research Letters and Journal of Geophysical Research: Space Physics.

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