ACES II Mission Will Investigate Earth’s Auroral Current

By Michael Horton •  Updated: 11/16/22 •  5 min read

The NASA-funded Aurora Current and Electrodynamics Structures II, or ACES II, instrument will launch from the Andya Space launch site in Andenes, Norway, for its second trip into orbit. The launch is scheduled for November 16, 2022.

Electrons from space are streaming into our atmosphere from high above. As they shoot down Earth’s magnetic field lines, they interact with gases in our atmosphere, causing them to glow. From the ground, observers see effervescent ribbons of ruby and emerald: the aurora borealis and australis, or northern and southern lights.

Earth’s Auroral Current

The auroral current carried charged particles (electrons and ions) from space into our atmosphere and back out to space. Credit: NASA

However, auroras are only one component of a much larger system. They are powered by a larger electrical circuit that connects our planet to near-Earth space, much like a lightbulb plugged into an outlet.

“It’s these incoming high-energy electrons that produce the auroral display we’re familiar with, but there’s also part of the system that is unseen,”

said University of Iowa physicist Scott Bounds, principal investigator for the ACES II mission.

The Auroral Current

Just as charged particles enter our atmosphere, a stream of charged particles exits into space. This inflow and outflow together form a global electrical circuit known as the auroral current.

What happens at the “turnaround point,” where the inflow ends and the outflow begins, is one of the biggest mysteries about the auroral current. The turnaround point is in the ionosphere, a region of our atmosphere that extends into space and begins about 40 miles overhead. Here, neutral gases and charged particles coexist and interact.

Border Town Bustle

The ionosphere is comparable to a bustling border town where foreigners unfamiliar with each other’s customs meet and exchange goods. The particles from space arriving from above are electrically charged.

Because they are accustomed to the vastness of space, they rarely collide with each other. Their electric charge keeps them attached to Earth’s magnetic field lines, which they spiral around as they plunge into our atmosphere or into space.

Incoming lower-altitude particles are neutral gases from our atmosphere. They bounce back and forth through dense crowds hundreds of times per second. They move freely across magnetic field lines as they are carried about by the wind because they lack an electric charge.

These two populations merge in the ionosphere, colliding, combining, separating, and interacting in complex ways. It’s a tumultuous scene. Nonetheless, the auroral current is kept churning by turbulent mixing in the ionosphere.


Most auroral current studies to date have only measured inflow and outflow from high above the ionosphere, making simplified assumptions about what’s going on below. ACES II was created to address this issue by taking a “snapshot” of the entire auroral current at one point in time.

The plan is to launch two rockets: a “high-flyer” that will measure particles flowing into and out of our atmosphere, and a “low-flyer” that will observe the dynamic exchange in the ionosphere that keeps everything moving.

Every night, the auroral oval — the magnetic “ring” encircling Earth’s northern magnetic pole within which auroras form — passes overhead at the Andya Space Center in Andenes, Norway. Bounds and his team will wait until the auroral oval, which indicates that the auroral current is flowing above them, is overhead.

High Flyer And Low Flyer Rockets

Credit: NASA

The high-flyer will then be launched by the crew, with a target peak altitude of about 255 miles (410 km). The instrument’s objective is to observe the streams of particles entering and leaving our atmosphere.

They will launch the low-flyer about two minutes later. It will ascend through the lower ionosphere, peaking at about 99 miles (159 km). Its objective is to record the energy exchange that takes place at the point where inflow and outflow switch places.

In order to ensure that they are measuring different components of the same current, the two rockets’ trajectories are aligned in space and time. Both the high- and low-flyer, like all sounding rockets, will take their measurements and return to Earth a short while later.

Aurora Current and Electrodynamics Structures

In 2009, the Poker Flat Research Range in Fairbanks, Alaska, served as the launch site for the first mission of the Aurora Current and Electrodynamics Structures instrument. It passed through an active, erratic aurora there. It was similar to taking a weather reading on a particularly squally day.

“We got great results, but what we want to understand for this flight is the ‘average case,'”

Bounds said. Because Andya is much nearer to the magnetic north pole of the planet, it is easier to observe milder, more common auroras that don’t extend as far south.

If everything goes according to plan, ACES II will aid in the modelling of the auroral current as a whole, including its most challenging component: our ionosphere.

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