The Ambipolar Electric Field: Its Existence, Strength, and Mechanisms Confirmed by NASA

 

     The Endurance Rocket Mission launched in the spring of 2022. One aspect of the mission was to confirm the existence, and properties, and to measure the weak “ambipolar” electric field generated by Earth’s ionosphere. The existence of the field was suggested- hypothesized in 1955 and now it has been confirmed and measured. The ambipolar electric field begins about 150 miles above the planet and has been described as a “great invisible force” that lifts up the sky. It also drives the polar winds which in turn drive global weather patterns. 

     A 2022 paper about the mission in Space Science Reviews explains the formation of the Earth’s ambipolar field as follows:

“The ionosphere of any planet consists of ions and electrons in approximately equal numbers. In the absence of electrical forces, electrons, being three to four orders of magnitude lighter than ions, would easily escape the pull of gravity guided along the magnetic field, resulting in a net positive electric charge. However, the Coulomb force restricts electron motion away from the ions. As the electrons pull away, an electric field forms to resist their separation, preventing a net charge from forming and satisfying quasineutrality (see Fig. 2). This field acts equally (but oppositely) on both electrons and ions: restraining and slowing the negatively charged electrons, and pulling and accelerating positively charged ions out of the ionosphere. The associated ambipolar electric potential drop is critical to the formation of Earths “polar wind” which flows outward along open magnetic fields above our polar caps (Banks and Holzer 1968), and helps to transport ions to higher altitudes where other energization mechanisms may be at play (Moore and Khazanov 2010).”

Figure 2 is shown below.

 

     The paper continues its explanation of the ambipolar field:

“While crucial to ion outflow, the ambipolar potential is extremely challenging to measure given its small magnitude. Current theory and simulations predict that it could be as weak as ≈ 0.4 V (calculated from our Polar Wind Outflow model, Glocer et al. 2007, 2009, 2012, 2017) across the exobase transition region (< 780 km). The first successful direct measure[1]ment of an ionospheric ambipolar potential drop was at the planet Venus (Collinson et al. 2016). Surprisingly, Venus’ potential drop was found to be +10 V. Such a strong potential drop is an order of magnitude larger than the 0.9 V predicted by equation (2) (Collinson et al. 2019). This potential drop was found to be stable, persistent, and capable of accelerating oxygen ions directly to escape velocities. This surprising result raises a compelling question: How strong is Earth’s ambipolar potential?”

     The magnitude and the role played by the ambipolar field regarding ion outflow, or the unknown importance of Earth’s ambipolar field in mediating ionospheric escape is what the mission set out to determine. Ionospheric photoelectrons are used to measure electric potential. The figure below shows photoelectron spectra measured for Venus and compares it with expected photoelectron spectra for the Earth to be measured by the Endurance mission (although it is at a different resolution and the graph for Earth is in different units so I am unsure how the end result compared to the prediction)

     Goals of the mission include determining the strength of the electric potential drop across Earth’s exobase transition region, determining the vertical distribution of the electric potential, and de-tangling the competing underlying physical processes that drive the strength and distribution of the electric potential.

What Did They Find?

   According to lead researcher Glyn Collinson of NASA:

“Whenever spacecraft have flown over the poles of the Earth, they have felt this supersonic wind of particles called the polar wind.”

“There must be some invisible force lurking there responsible for this outflow, but we’ve never been able to measure it because we didn’t have the technology.”

“This field is so fundamental to understanding the way the planet works. It’s been here since the beginning alongside gravity and magnetism. It’s been wafting particles to space and stretching up the sky since the beginning”

     The field is difficult to detect because it is so weak, just 0.55 volts, similar to a watch battery. However, this is just the right amount to explain the polar winds. He added:

“Despite being weak it’s incredibly important, it counters gravity and it lifts the skies up. It’s like this conveyor belt, lifting the atmosphere up into space.”

“The team found that hydrogen ions, the most abundant type of particle in the polar wind, experience an outward force from this field, which is 10.6 times stronger than gravity.”

Alex Glocer, the Endurance project scientist at Nasa Goddard and co-author of the paper, said: “That’s more than enough to counter gravity – in fact, it’s enough to launch them upwards into space at supersonic speeds.”

Dr. Collinson added: “What makes Earth the special place that we all call home? One of the reasons may be to do with the energy fields that our planet creates.”

“One of them is gravity. It’s important for life because it’s holding our atmosphere up. The second field is the magnetic field that’s protecting our planet from the stream of particles that comes from the sun.”

“Our rocket has discovered, and finally measured, number three. Now that we’ve finally measured it, we can begin learning how it’s shaped our planet as well as others over time.”

     The mission was launched from Norway, near the North Pole. Results of the mission were published on August 28, 2024, in the journal Nature. The abstract of the paper is given below:

Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected1,2,3. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave–particle interactions4 and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field)5,6. Observations of heated O+ ions in the magnetosphere are consistent with resonant wave–particle interactions7. By contrast, observations of cold supersonic H+ flowing out of the polar ionosphere8,9 (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55 ± 0.09 V electric potential drop between 250 km and 768 km from a planetary electrostatic field (E∥⊕ = 1.09 ± 0.17 μV m−1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer that this increases the supply of cold O+ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave–particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind9,10 and is probably the origin of the cold H+ ion population1 that dominates much of the magnetosphere. 

     

Spectrometer and sensors shown below:

     An article in AS USA sums up the Earth's three fields:

Gravitational field: It is responsible for maintaining our atmosphere and if there were not enough gravity it would go into space.

Magnetic field: The shield that protects planet Earth from the solar wind, the stream of charged particles released by the sun.

Ambipolar field: Counteracts gravity and ejects particles into space. According to scientists, it is as fundamental to the way our planet works as the other two fields.

 

References:

Nasa makes discovery ‘as important as gravity’ about Earth. Sarah Knapton. The Telegraph. August 29, 2024. Nasa makes discovery ‘as important as gravity’ about Earth (msn.com)

The Endurance Rocket Mission. Glyn Collinson, et al. NASA. Space Science Reviews · August 2022. Collinsonetal2022b-TheEnduranceRocketMission.pdf

NASA Unveils An Electric Field Around Earth That’s Just As Vital As Gravity. Damjan. Technology. August 31, 2024. NASA Unveils An Electric Field Around Earth That’s Just As Vital As Gravity (dailysquared.com)

Earth’s ambipolar electrostatic field and its role in ion escape to space. Glyn A. Collinson et al. Nature volume 632, pages1021–1025. August 28, 2024. Earth’s ambipolar electrostatic field and its role in ion escape to space | Nature

Ambipolar electric field. Wikipedia. Ambipolar electric field - Simple English Wikipedia, the free encyclopedia

The Earth and the incredible discovery of the third energy field that surrounds it and changes how we understand it. Alberto Zaragoza Lerma and Greg Heilman. AS USA. September 8, 2024. The Earth and the incredible discovery of the third energy field that surrounds it and changes how we understand it (msn.com)