Scientists reported the first successful measurement of Earth’s ambipolar electric field, a planet-wide force proposed more than 60 years earlier. Results from NASA’s suborbital Endurance mission confirmed the field’s existence, measured its strength and helped explain how cold particles escape the atmosphere above the poles. The research was published in Nature.
Spacecraft had detected the so-called polar wind since the late 1960s: a stream of charged particles moving from the atmosphere into space over the North and South Poles. Solar heating could account for some atmospheric loss, but many particles in the polar wind showed no evidence of being heated even though they traveled at supersonic speed. Researchers therefore suspected that another force was lifting them.
The ambipolar field arises where atmospheric atoms separate into negatively charged electrons and positively charged ions, beginning at an altitude of roughly 250 kilometers. Electrons are far lighter and more inclined to escape, while the heavier ions tend to fall under gravity. Their opposing charges produce an electric field that prevents the two populations from separating. The electrons pull ions upward as the ions pull electrons downward, extending the atmosphere and raising some ions high enough to join the polar wind.
The effect is extremely weak at any single point, which made direct detection technically difficult for decades. Glyn Collinson of NASA’s Goddard Space Flight Center and colleagues began developing a suitable instrument in 2016. They chose a suborbital flight from Svalbard, the Norwegian archipelago near the North Pole, because the rocket could pass through the polar wind while collecting the required measurements.
Endurance launched on May 11, 2022, reached 768.03 kilometers and splashed down in the Greenland Sea 19 minutes later. Across a 322-mile vertical range, its instruments detected a change in electric potential of just 0.55 volts, comparable to the voltage of a watch battery. Although small, the measured value was sufficient to account for the observed outflow.
The finding places the ambipolar field alongside gravity and magnetism as a fundamental influence on Earth’s atmosphere. It also gives researchers a firmer basis for examining how the ionosphere is shaped and how atmospheres evolve over long periods. Because atmospheric retention and loss affect planetary conditions, the measurement may also help scientists compare Earth with other worlds and assess which environments could be hospitable to life. The result also demonstrates how a force too faint for earlier instruments can produce large atmospheric effects when acting continuously across hundreds of miles above the planet. over time.
