NASA conducts 1st successful measurement of Earth’s ambipolar electric field

Using observations from a NASA suborbital rocket, an international team of scientists has, for the first time, successfully measured a planet-wide electric field thought to be as fundamental to Earth as its gravity and magnetic fields.

Known as the ambipolar electric field, scientists first hypothesized over 60 years ago that it drove how our planet’s atmosphere can escape above Earth’s North and South Poles.

Measurements from NASA’s Endurance mission rocket have confirmed the existence of the ambipolar field and quantified its strength, revealing its role in driving atmospheric escape and shaping our ionosphere—a layer of the upper atmosphere—more broadly.

Long-sought discovery

Since the late 1960s, spacecraft flying over Earth’s poles have detected a stream of particles flowing from our atmosphere into space.

Theorists predicted this outflow, which they dubbed the “polar wind,” spurring research to understand its causes.

Some amount of outflow from our atmosphere was expected. Intense, unfiltered sunlight should cause some particles from our air to escape into space, like steam evaporating from a pot of water.

But the observed polar wind was more mysterious. Many particles within it were cold, with no signs of heating, yet they traveled at supersonic speeds.

“Something had to be drawing these particles out of the atmosphere,” said Glyn Collinson, principal investigator of Endurance at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the paper. Scientists suspected a yet-to-be-discovered electric field could be at work.

The hypothesized electric field, generated at the subatomic scale, was expected to be incredibly weak, with its effects felt only over hundreds of miles.

For decades, detecting it was beyond the limits of existing technology. In 2016, Collinson and his team invented a new instrument they thought was up to measuring Earth’s ambipolar field.

Ambipolar Field

A weak electric field in the upper atmosphere may loft charged particles into space.

Scientists theorized this electric field should begin at around 150 miles (250 kilometers) altitude, where atoms in our atmosphere break apart into negatively charged electrons and positively charged ions.

Electrons are incredibly light — the slightest kick of energy could send them shooting out to space. Ions are at least 1,836 times heavier and tend to sink toward the ground.

If gravity alone were in play, the two populations, once separated, would drift apart over time. But they were given their opposite electric charges, and an electric field formed to tether them together, preventing any charges’ separation and counteracting gravity’s effects.

This electric field is bidirectional, or “ambipolar,” because it works in both directions. Ions pull the electrons down with them as they sink with gravity.

At the same time, electrons lift ions to greater heights as they attempt to escape to space, like a tiny dog tugging on its sluggish owner’s leash.

The net effect of the ambipolar field is to extend the height of the atmosphere, lifting some ions high enough to escape with the polar wind.

Endurance’s discovery has opened many new paths for exploration.

The ambipolar field, alongside gravity and magnetism, is a fundamental energy field of our planet. It may have continuously shaped the evolution of our atmosphere in ways we can now begin to explore.

Because the internal dynamics of an atmosphere create it, similar electric fields may exist on other planets, including Venus and Mars.