A strange electric field around the Earth, long suspected to exist, has been detected for the very first time, and it is believed to cause a polar wind which launches particles into space at supersonic speeds.
This “ambipolar electric field” is a weak electrical field covering the entire planet, and was first theorized to exist over 60 years ago, but has finally been detected thanks to observations from NASA’s Endurance rocket, according to a new paper in the journal Nature.
The ambipolar electric field is thought to be a major driver of charged particles flowing into space above the poles—known as the “polar wind”—and may have influenced our planet’s atmosphere in several other ways.
NASA’s Goddard Space Flight Center / Andøya Space/Leif Jonny Eilertsen
The Earth’s ambipolar electric field is a phenomenon that occurs in the ionosphere, the upper part of the Earth’s atmosphere, where ions and electrons are present in significant quantities. In the Earth’s ionosphere, electrons and ions may drift apart, so in order to keep the densities of positive and negative charges nearly equal, an electric field develops—this is the ambipolar electric field.
This electrical field was suggested to exist in the 1960s to explain why particles had suddenly been detected flowing from the atmosphere into space over the poles, a phenomenon dubbed the polar wind.
Hydrogen ions in particular were seen to be pushed outward with a force 10.6 times as strong as the force of gravity pulling them back down.
“That’s more than enough to counter gravity—in fact, it’s enough to launch them upward into space at supersonic speeds,” study co-author Alex Glocer, an Endurance project scientist at NASA Goddard, said in a statement.
This polar wind mystified scientists, as the particles didn’t seem like they had been heated, and yet were traveling faster than the speed of sound.
“Something had to be drawing these particles out of the atmosphere,” study lead author Glyn Collinson, principal investigator of Endurance at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in the statement. “It’s like this conveyor belt, lifting the atmosphere up into space.”
A weak electrical field generated on the subatomic scale was hypothesized to be the driver, named the ambipolar electric field. This was unproven to exist, until now.
The NASA Endurance rocket mission was launched from the island of Svalbard in Norway, just a few hundred miles from the north pole, in May 2022, flying to a height of around 480 miles and measuring the change in voltage of the atmosphere.
“Svalbard is the only rocket range in the world where you can fly through the polar wind and make the measurements we needed,” study co-author Suzie Imber, a space physicist at the University of Leicester, said in the statement.
The rocket only measures a change of 0.55 volts across an altitude range of 322 miles.
“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.”
This confirmation of the ambipolar field around our planet has major implications for the evolution of Earth’s atmosphere, as well as those of Venus and Mars.
“Any planet with an atmosphere should have an ambipolar field,” Collinson said. “Now that we’ve finally measured it, we can begin learning how it’s shaped our planet as well as others over time.”
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References
Collinson, G. A., Glocer, A., Pfaff, R., Barjatya, A., Conway, R., Breneman, A., Clemmons, J., Eparvier, F., Michell, R., Mitchell, D., Imber, S., Akbari, H., Davis, L., Kavanagh, A., Robertson, E., Swanson, D., Xu, S., Miller, J., Cameron, T., . . . Ghalib, A. (2024). Earth’s ambipolar electrostatic field and its role in ion escape to space. Nature.
