NASA's THEMIS Mission Provides First Strong Evidence Explaining Mysteries of Auroras

The beautiful polar lights predominantly seen in the high-latitude regions of the planet are called the aurora. The northern lights are called aurora borealis, while the southern lights are called aurora australis.

But aside from those two polar lights, scientists also found that there are also auroral beads that show up just before a large auroral display. They are caused by electrical storms that happen in space known as substorms.

The auroral bead is a special type of aurora seen in the night sky that looked like a glowing necklace. Before, scientists were unsure if these auroral beads are somewhat linked with the auroral displays that happen before the substorms or if they are produced by disturbances close to the Earth's atmosphere.

But NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission and the powerful computer models have provided the first evidence of events that happens in space that causes the appearance of the auroral beads. They also demonstrated the role these beads play in Earth's near-space environment.

Vassilis Angelopoulos, the principal investigator of THEMIS, said that auroral beads are caused by the turbulence in the plasma that surrounds the Earth. They published their findings in the Journal of Geophysical Research: Space Physics and also in Geophysical Research Letters and Journal of Geophysical Research: Space Physics.

Uncovering the Mysteries of Auroral Beads

When the charged particles are trapped in Earth's magnetosphere and are directed to the planet's atmosphere, they collide with nitrogen, hydrogen, and oxygen atoms, causing them to glow. This phenomenon is known as auroras.

The interaction between the plasma belched by the Sun and the Earth's magnetic field creates floating bubbles plasma behind Earth and imbalances in it creates 2,500-mile wide fingers of plasma stretch towards the Earth. This forms the distinct auroral bead shape in the sky.

Therefore, auroral beads come first before substorms happen. Scientists want to know how, why, and when these beads might trigger a large auroral display. Theoretically speaking, the beads might tangle magnetic field lines, causing a magnetic reconnection, which ends up creating full-scale substorms and auroras in the night sky.

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New Computer Models Explain Events Where THEMIS Passes

THEMIS has been taking a thorough observation and measurement of the magnetosphere since 2007 to understand what causes the substorms that create auroras. So far, it has found that magnetic reconnection is the main driver of substorms.

NASA's Center for Geospace Storms scientist Slava Merkin said that to understand the features of the aurora, it is important to resolve the global and smaller, local scales which makes it challenging for now. It needs to have very refined algorithms and supercomputers.

That is why new computer simulations are used in explaining small-scale structures to help interpret what happens in the space where the three THEMIS pass. This new computer simulations almost perfectly match THEMIS and ground observations.

Using these new computer models, it opens a lot of new doors in understanding the auroras and sees them in a larger picture.