Earth has been found to have an ambipolar electric field

Using observations from a NASA suborbital rocket, an international team of scientists has successfully measured for the first time a planet-wide electric field that is thought to be as fundamental to Earth as its gravitational and magnetic fields. The existence of this field, called the “ambipolar electric field,” was first hypothesized more than 60 years ago. According to that hypothesis, the ambipolar electric field makes a crucial contribution to the escape of atmospheric mass from our planet above the North and South Poles.

Measurements by NASA’s Endurance rocket and subsequent in-depth analysis have confirmed the existence of the ambipolar field and quantified its strength, revealing its role in atmospheric escape and in shaping the ionosphere, a layer of the upper atmosphere.

The study was carried out by a team led by Glyn A. Collinson of NASA’s Goddard Space Flight Center in the United States.

Knowing the complex motions and evolution of our planet’s atmosphere well enough can provide clues not only about Earth’s atmospheric history, but also about the atmospheric history of other planets. In the case of planets outside our solar system, this knowledge can be crucial in determining which of these worlds might be habitable.

Since the late 1960s, spacecraft flying over the Earth’s poles have detected a stream of particles flowing from the atmosphere into space. Scientists predicted this flow, which they dubbed the “polar wind,” and spurred research into its causes.

Some amount of flux from our atmosphere was to be expected. Intense, unfiltered sunlight should cause some atmospheric gas particles to escape into space, like steam evaporating from a pot of hot water. But the observed polar wind was more mysterious. Many of its particles were cold, with no signs of having been heated, and yet they were traveling at supersonic speeds.

Something had to be pulling these particles out of the atmosphere. Many scientists suspected that an as-yet-undiscovered electric field might be at work.

The hypothetical electric field, generated at the subatomic scale, was expected to be extremely weak, with its effects felt only up to a distance of several hundred kilometres. For decades, detecting such an electric field was beyond the reach of existing technology. In 2016, Collinson and his colleagues began developing a new instrument that, if all went well, would be able to measure Earth’s ambipolar field.

That kind of measurement and mission profile were a perfect fit for a suborbital rocket flight launched from the Arctic, specifically from Svalbard, a Norwegian archipelago located just a few hundred kilometers from the North Pole and home to the world’s northernmost rocket launch base.

“Svalbard is the only rocket launch site in the world from which you can fly through the polar wind and make the measurements we needed,” explains Suzie Imber of the University of Leicester in the UK and co-author of the new study.

On May 11, 2022, the Endurance mission rocket lifted off and reached an altitude of 768 kilometers, splashing down 19 minutes later in the Greenland Sea. Throughout the space in which it collected data, the Endurance rocket measured a change in electrical potential of just 0.55 volts.

Half a volt is almost nothing: it’s about the same as a watch battery. But it’s just the right amount of voltage to explain the polar wind, Collinson says.

Hydrogen ions, the most abundant type of particle in the polar wind, experience a force that tends to push them upward toward the outside of the polar wind. This force is 10.6 times stronger than that of gravity. That’s more than enough to counteract gravity — enough, in fact, to propel them into space at supersonic speeds, says NASA co-author Alex Glocer.

Heavier particles also get an upward boost. Oxygen ions at that same altitude, immersed in this half-volt field, weigh half as much. The team found that overall, the ambipolar field increases what’s known as the “scale height” of the ionosphere by 271 percent, meaning the ionosphere is denser at higher altitudes than it would be without it. It’s like a conveyor belt that lifts part of the atmosphere up into space.

The discovered electric field is bidirectional, or ambipolar, because it works in both directions. Ions, as they sink into the atmosphere under the effect of gravity, tend to drag electrons along with them. At the same time, electrons tend to lift ions to higher altitudes when they are propelled upward. The net effect of the ambipolar field is to increase the height of the atmosphere, as well as lift some ions high enough to escape into space with the polar wind. (Image: NASA/Conceptual Image Lab/Wes Buchanan/Krystofer Kim)

The discovery made after carefully analyzing data collected by the Endurance mission has opened up many new avenues of research. The ambipolar field, as fundamental energy field on our planet as are the gravitational and magnetic fields, may have continually influenced the evolution of our atmosphere in ways that we are only now beginning to explore. Because it is created by the internal dynamics of an atmosphere, it is thought that similar electric fields must exist on other planets, including Venus and Mars.

“Any planet with an atmosphere should have an ambipolar field,” Collinson says. “Now that we have finally measured Earth’s, we can start to learn how it has shaped our planet over time.”

The study is titled “Earth’s ambipolar electrostatic field and its role in ion escape to space.” It has been published in the academic journal Nature. (Source: NCYT by Amazings)