NASA confirms "ambipolar" electric field in the Earth's atmosphere
The suborbital rocket mission "Endurance" has detected an electric field that drives the polar wind and raises the ionosphere by 271 percent.
Image of the Earth as seen from the apex of the "Endurance" mission
(Image: NASA)
In the 1960s, satellites discovered a constant stream of charged particles flowing into space above the polar regions. In these areas of space, the Earth's magnetic field lines are open and extend into space. Charged particles from the upper atmosphere (electrons and ions) can escape along these lines and form the polar wind. What drives this polar wind has long been a mystery. Researchers at NASA have now demonstrated a weak global electric field that catapults the particles into space by taking measurements on the suborbital rocket mission "Endurance". The field is created at an altitude of around 250 kilometers in the ionosphere, where atoms decay into electrons and positively charged ions. It forms because the electrons in the ionosphere want to escape into space due to their thermal energy. However, the positively charged ions hold them back. This charging effect leads to a weak electrostatic field that works in both directions and is therefore referred to as an "ambipolar field". Although it is weak, it has a major influence on the movement of the charged particles.
Suborbital rocket mission "Endurance"
To detect the electric field, Glyn Collinson, lead Endurance researcher at NASA's Goddard Space Flight Center and lead author of the study published in Nature, and his team developed a new instrument to detect weak electric fields. During the Endurance mission, which launched from Svalbard, Norway, on May 11, 2022, the rocket flew through the polar wind region to an altitude of 768 kilometers and landed 19 minutes later in the Greenland Sea. The mission collected data over an altitude range of 518 kilometers (between 250 km and 718 km) in the "polar wind". From the data, the researchers determined a potential difference of just 0.55 volts. However, this is "exactly the right amount to explain the polar wind", according to the publication. This is because the ambipolar field increases the outward force on protons by more than ten times the gravitational force and hurls the particles into space at supersonic speed.
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Influence on the ionosphere
The team discovered that the ambipolar field has a significant influence on the structure and density of the ionosphere. They found that the field raises the ionosphere in the polar regions by 271 percent, from 77 to almost 209 kilometers high. This happens because the outward-striving electrons cannot transport the heavier positive ions directly into space, but their attraction creates a buoyancy effect – like a dog on a leash pulling its much larger master or mistress behind it, according to Collinson.
Furthermore, the ambipolar field considerably increases the plasma density in the ionosphere. At the boundary of the magnetosphere at an altitude of around 768 kilometers, the density is more than 3800 percent higher than it would be without the electrostatic field, according to the publication. "It’s like this conveyor belt, lifting the atmosphere up into space", says Collinson in a NASA statement. As a result, the layer of the ionosphere with a high concentration of ions and electrons extends further upwards than previously assumed.
The scientists hope that the discovery will open up new opportunities to investigate how this fundamental energy field, together with gravity and magnetism, has influenced the development of the Earth's atmosphere over time. The team assumes that other planets with atmospheres – such as Mars or Venus – also have similar electric fields. In fact, they even suspect that "every planet with an atmosphere [...] may have such an ambipolar field".
(vza)
