For the first time ever, NASA has detected a planet-wide electric field surrounding Earth. This field, known as the ambipolar electric field, was discovered by NASA’s suborbital Endurance rocket over 60 years after it was first hypothesized. It is believed to be as fundamental to our planet as its better-known magnetic and gravitational fields.
The discovery, published in the journal *Nature*, is significant because it provides scientists with a new tool to understand how our planet’s atmosphere evolved and how it behaves today. “Any planet with an atmosphere should have an ambipolar field,” explained Glyn Collinson, the lead author of the study and principal investigator of the Endurance mission at NASA’s Goddard Space Flight Center. “Now that we’ve finally measured it, we can begin learning how it’s shaped our planet as well as others over time.”
The electric field originates in the ionosphere, a layer of Earth’s atmosphere located between 37 to 190 miles (60 to 300 kilometers) above the Earth’s surface. Here, ultraviolet radiation from the sun bombards atoms, stripping them of electrons and transforming them into ions. This process, in theory, should create a slight electric field around our planet, as well as other planets with atmospheres.
Hints of this electric field’s existence were first detected in 1968 by spacecraft flying over Earth’s North and South Poles. These hints came in the form of a “polar wind,” a stream of particles escaping from Earth’s atmosphere into space. While some atmospheric escape is expected, particularly after heating from sunlight, the polar wind was more mysterious. The particles within it were cold, meaning they hadn’t been heated, yet they were still moving at supersonic speeds. This posed a puzzle: what was driving these cold particles out of the atmosphere?
The answer, as the researchers discovered, is the ambipolar electric field. It’s a very weak field, with detectable fluctuations only occurring over distances of hundreds of miles. To investigate the origins of the polar wind, the researchers launched the Endurance rocket from a rocket range in Svalbard near the North Pole, sending it to an altitude of 477.23 miles (768.03 km) above the ground. The rocket collected data over a range of 322 miles (518 km) and detected a miniscule 0.55 volt change, about the strength of a watch battery. Despite its small size, this voltage difference pushes hydrogen ions, the most abundant particles in the solar wind, with a force 10.6 times stronger than gravity.
“That’s more than enough to counter gravity — in fact, it’s enough to launch [atmospheric particles] upwards into space at supersonic speeds,” said Alex Glocer, Endurance project scientist at NASA Goddard. “It’s like this conveyor belt, lifting the atmosphere up into space,” added Collinson.
This discovery opens up new avenues for understanding how Earth’s atmosphere has changed over time. By studying the ambipolar electric field, scientists hope to learn how it has influenced the evolution of our planet’s atmosphere and how it continues to shape it today. Furthermore, scientists expect to find similar electric fields in the atmospheres of other planets, such as Venus and Mars, providing valuable insights into the atmospheres of other worlds.
