Using data from NASA’s Parker Solar Probe, a team of solar physicists calculated the distribution of electrons within the electric field of the Sun; from the electrons’ distribution, the researchers were able to discern the size, breadth, and scope of the solar electric field more clearly than had been done before.
The electric field of the Sun arises from the interaction of protons and electrons generated when hydrogen atoms are stripped apart in the intense heat generated by fusion deep within the star.
In this environment, electrons, with masses 1,800 times less than that of protons, are blown outward, less constrained by gravity than their weightier proton siblings.
But the protons, with their positive charge, exert some control, reining in some electrons due to the familiar attraction forces of oppositely charged particles.
“Electrons are trying to escape, but protons are trying to pull them back. And that is the electric field,” said Dr. Jasper Halekas, a researcher in the Department of Physics and Astronomy at the University of Iowa and a co-investigator for the Solar Wind Electrons, Alphas, and Protons (SWEAP) instrument aboard the Parker Solar Probe.
“If there were no electric field, all the electrons would rush away and be gone. But the electric field keeps it all together as one homogenous flow.”
“Now, imagine the Sun’s electric field as an immense bowl and the electrons as marbles rolling up the sides at differing speeds.”
“Some of the electrons, or marbles in this metaphor, are zippy enough to cross over the lip of the bowl, while others don’t accelerate enough and eventually roll back toward the bowl’s base.”
“We are measuring the ones that come back and not the ones that don’t come back.”
“There’s basically a boundary in energy there between the ones that escape the bowl and the ones that don’t, which can be measured.”
“Since we’re close enough to the Sun, we can make accurate measurements of electrons’ distribution before collisions occur further out that distort the boundary and obscure the imprint of the electric field.”
From those measurements, the physicists can learn more about the solar wind, the million-mile-per-hour jet of plasma from the Sun that washes over the Earth and other planets in the Solar System.
What they found is the Sun’s electric field exerts some influence over the solar wind, but less than had been thought.
“We can now put a number on how much of the acceleration is provided by the Sun’s electric field,” Dr. Halekas said.
“It looks like it’s a small part of the total. It’s not the main thing that gives the solar wind its kick. That then points to other mechanisms that might be giving the solar wind most of its kick.”
The results were published in the Astrophysical Journal.
Jasper Halekas et al. 2021. The sunward electron deficit: A telltale sign of the Sun’s electric potential. ApJ, in press;
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