In a groundbreaking discovery, an international team of scientists has confirmed the existence of a global electric field on Earth, known as the ambipolar electric field.
Hypothesized over 60 years ago, this field is as fundamental to our planet as gravity and the magnetic field, influencing critical atmospheric processes.
Using data from NASA’s Endurance mission, which launched a suborbital rocket from the Arctic, researchers were able to detect and measure this elusive field, revealing its significant impact on Earth’s ionosphere and atmospheric escape.
The role of the ambipolar electric field in Earth's atmosphere
The ambipolar electric field plays a crucial role in the behavior of charged particles in Earth's upper atmosphere, particularly in the ionosphere—a region where solar radiation ionizes gases, creating a mix of free electrons and ions. This field is generated as a result of the interactions between these positively charged ions and negatively charged electrons. The ambipolar field acts in both directions: it pulls electrons downward while lifting ions upward, preventing the separation of charges and maintaining the integrity of the ionosphere.
This electric field is not just a static feature; it actively contributes to the phenomenon known as the polar wind—a steady outflow of charged particles from Earth’s atmosphere into space, particularly over the polar regions. Since the late 1960s, spacecraft flying over the poles have detected this outflow, which theorists had linked to an unseen electric field. However, due to its weak nature, measuring this field directly had long been beyond the capabilities of existing technology. The polar wind itself is a fascinating process: particles that are relatively cold and unheated somehow achieve supersonic speeds as they escape Earth’s gravitational pull. The discovery and measurement of the ambipolar electric field provide the missing piece in understanding how these particles are accelerated to such high velocities.
Measuring the ambipolar field: the Endurance mission
The Endurance mission was specifically designed to detect the ambipolar electric field and quantify its effects. On May 11, 2022, a suborbital rocket carrying highly sensitive instruments was launched from Svalbard, a Norwegian archipelago located close to the North Pole. The location was chosen for its proximity to the polar wind region, where the field’s effects are most pronounced. The rocket’s instruments were tailored to detect minute changes in electric potential across a range of altitudes, from 150 miles (250 kilometers) to 477 miles (768 kilometers) above Earth.
During its 19-minute flight, the rocket gathered data that revealed a change in electric potential of only 0.55 volts—a value that might seem insignificant, but is actually crucial in explaining the dynamics of the polar wind. Glyn Collinson, the lead researcher from NASA’s Goddard Space Flight Center, explained that this seemingly tiny amount of voltage is “about as strong as a watch battery,” yet it is sufficient to generate the forces necessary to lift charged particles, such as hydrogen ions, out of the atmosphere and into space.
The data collected also showed that the ambipolar field has a significant impact on the ionosphere’s structure. For instance, hydrogen ions, which are the most abundant particles in the polar wind, experience a force from this field that is more than ten times stronger than gravity, propelling them into space at supersonic speeds. The field also affects heavier particles like oxygen ions, effectively reducing their weight and allowing them to reach higher altitudes than they would under the influence of gravity alone. This upward lift increases the “scale height” of the ionosphere by 271%, meaning that the ionosphere remains denser at greater heights than previously understood.
Implications for Earth’s atmospheric evolution and planetary science
The discovery of the ambipolar electric field has profound implications for our understanding of Earth’s atmospheric processes and its evolution over time. This field, now confirmed as a fundamental aspect of Earth’s environment, likely plays a crucial role in shaping the long-term behavior of the atmosphere. By influencing the rate at which particles escape into space, the ambipolar field may have contributed to the gradual loss of atmospheric components over geological timescales, affecting everything from climate to the sustainability of life.
Furthermore, this discovery is not just significant for Earth; it opens new avenues for studying other planets with atmospheres. Similar electric fields are expected to exist on planets like Venus and Mars, where atmospheric escape also occurs. By understanding how the ambipolar field operates on Earth, scientists can develop better models to predict and study atmospheric behavior on other planets. This knowledge is particularly important in the search for habitable environments beyond Earth, as the presence and strength of such fields could influence a planet’s ability to retain an atmosphere capable of supporting life.
Collinson emphasized the broader impact of this discovery by stating, “Any planet with an atmosphere should have an ambipolar field. Now that we’ve finally measured it, we can begin learning how it’s shaped our planet as well as others over time.” This insight could help researchers understand why planets like Mars have lost much of their atmosphere, while Earth has retained a thick, life-sustaining envelope of gases.