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NASA Discovers a Long-Sought Global Electric Field on Earth

A snow-covered view of the polar cap from space. The curvature of the Earth is visible along the horizon against a dark background.
The geographic North Pole seen from the Endurance rocket ship at 477 miles (768 kilometers) altitude above the Arctic. The faint red and green streaks at the top of the image are artifacts of lens flare.
Credits: NASA
The headshot image of Miles Hatfield

Miles Hatfield

The headshot image of Rachel Lense

Rachel Lense

Aug 28, 2024
Article

Contents

Key Points

  • A rocket team reports the first successful detection of Earth’s ambipolar electric field: a weak, planet-wide electric field as fundamental as Earth’s gravity and magnetic fields.
  • First hypothesized more than 60 years ago, the ambipolar electric field is a key driver of the “polar wind,” a steady outflow of charged particles into space that occurs above Earth’s poles.
  • This electric field lifts charged particles in our upper atmosphere to greater heights than they would otherwise reach and may have shaped our planet’s evolution in ways yet to be explored.

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 the rocket, NASA’s Endurance mission, 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.

Understanding the complex movements and evolution of our planet’s atmosphere provides clues not only to the history of Earth but also gives us insight into the mysteries of other planets and determining which ones might be hospitable to life. The paper was published Wednesday, Aug. 28, 2024, in the journal Nature.

Credit: NASA's Goddard Space Flight Center/Lacey Young
Download this video and related animations from NASA's Scientific Visualization Studio.

An Electric Field Drawing Particles Out to Space

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 they had been heated — yet they were traveling 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 got to work inventing a new instrument they thought was up to the task of measuring Earth’s ambipolar field.

How the Ambipolar Field Works

  • 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 given their opposite electric charges, an electric field forms to tether them together, preventing any separation of charges and counteracting some of the effects of gravity.

    This animated image shows a photon from the Sun collides with an oxygen atom, knocking an electron loose. As the atoms and molecules lose electrons, they become positively charged, making them ions. This process is known as ionization.
    An artist’s concept of ionization occurring in the upper atmosphere when fast-moving photons knock electrons from elements and molecules.

  • 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.

    Animation credits: NASA/Conceptual Image Lab/Wes Buchanan/Krystofer Kim

    This animation shows a collection of particles feeling the pull of gravity competing with the tug of energized electrons. Large, white ions swing downward as smaller, purple electrons tug upward. The bidirectional nature of this connection gives the field its name: the ambipolar electric field. Ambi- is a prefix borrowed from Latin to mean “both” and the field’s effects are felt most strongly at the poles.

Launching a Rocket from the Arctic

The team’s instruments and ideas were best suited for a suborbital rocket flight launched from the Arctic. In a nod to the ship that carried Ernest Shackleton on his famous 1914 voyage to Antarctica, the team named their mission Endurance. The scientists set a course for Svalbard, a Norwegian archipelago just a few hundred miles from the North Pole and home to the northernmost rocket range in the world.

“Svalbard is the only rocket range in the world where you can fly through the polar wind and make the measurements we needed,” said Suzie Imber, a space physicist at the University of Leicester, UK, and co-author of the paper.

On May 11, 2022, Endurance launched and reached an altitude of 477.23 miles (768.03 kilometers), splashing down 19 minutes later in the Greenland Sea. Across the 322-mile altitude range where it collected data, Endurance measured a change in electric potential of only 0.55 volts.

“A half a volt is almost nothing — it’s only about as strong as a watch battery,” Collinson said. “But that’s just the right amount to explain the polar wind.”