NASA scientists, in a study published in the journal Nature, have discovered the existence of a faint planetary electric field that envelops the Earth between the altitudes of 250 and 768 km from the surface. Our planet, therefore, is not only equipped with a gravitational field and of a magnetic field, but also of a third electric field that covers a fundamental role in planetary dynamics and evolutionThe Earth’s electric field is called “ambipolar” fieldsince it generates a movement in opposite directions of both electrons and positive ions. It plays a key role in the mechanisms of escape of charged particles from the atmosphere at the North and South poles and edit Also the shape of the atmosphere terrestrial itself, in particular by increasing its scale height.
Theorized since the 60s, this electric field has always been difficult to detect, and only thanks to a specific NASA mission, the Endurance mission, it has finally been measured: just think that its voltage is only 0.5 Voltsmore or less corresponding to that of a common watch batterybut enough to overcome the gravitational force and generate a flow of charged particles that escape from the Earth’s atmosphere.
How the Existence of the Earth’s Electric Field Was Theorized
Scientists suspected the existence of a planetary electric field since the time of the first space missions in the 60s. In fact, some satellites launched in that period, while flying over the polar regions of our planet, had measured a flow of charged particles that was moving from our atmosphere into outer space, called “polar wind”. This flow had been measured in particular at high altitudes, in the ionospherethe region where ionized gases (atoms or molecules with electrons removed) from solar radiation are present.
Initially, scientists had hypothesized a mechanism whereby solar radiation heated the particles, providing enough energy to overcome the gravitational attraction and escape the Earth’s atmosphere, however it was realized that this was not the right process, since the particles were fast, but cold, that is, with little thermal energy, so there had to be another mechanism that pushed them to the escape velocities necessary to disperse into space. The most likely suspect was a some kind of planetary electric fieldhowever the instruments of the time were not sensitive enough to measure it.
How the Earth’s Electric Field Was Measured
And this is where the mission Endurance from NASA. Conceived in 2016, the mission consisted of launching a sub-orbital flight near the North Pole, so as to fly with specific instruments through this polar wind of particles. The rocket took off onMay 11, 2022 from the planet’s northernmost space launch base, in Svalbard Islands, reaching a maximum height of 768 kilometers and following, in the 19 minutes of the mission, a long sub-orbital trajectory 518 kilometers.
During the flight, the on-board instruments finally managed to prove the existence of the Earth’s electric fieldmeasuring a potential difference of only 0.55 Voltspractically the voltage of a watch battery, between the quotas of 250 and 768 km from the Earth’s surface. Although small, this value was exactly what was needed to explain the escape of particles from the atmosphere.
How the ambipolar electric field works
The Earth’s weak electric field It starts around the 250 km altitudeat the base of the ionosphere terrestrial where solar radiation strips electrons from the atoms that make up atmospheric gases generating a set of negatively charged electrons and positively charged ions.
Electrons and ions have very different masses, with the electrons so light that a small push (energy) is enough to make them escape from the Earth’s gravitational pull. On the contrary, if we consider the hydrogen ionmade from a single proton, it is 1836 times heavier than an electronso the Earth’s gravitational field, attracting heavier objects with greater force, tends to make the ions fall towards the ground, creating a separation between ions and electrons. However, being oppositely charged particles, This separation generates an electric field which partially counterbalances the effect of gravity.
This electric field is ““ambipolar” or bidirectional, that is, it causes both electrons and positive ions to move in opposite directions. The ions tend to drag the electrons along with them as they sink into the atmosphere due to gravitational force, while, conversely, the electrons attract the ions, lifting them higher into the atmosphere as they attempt to escape into space.
THE’net effect of this “ambipolar” magnetic field is that of extend the height of the ionosphere by as much as 271%lifting some ions (mainly hydrogen and oxygen) to a height such that escape into space through the polar wind. Hydrogen ions, for example, experience an outward force that is about 11 times stronger than Earth’s gravityenough to launch them into space at supersonic speeds.
