Estimates of Proton and Electron Heating Rates Extended to the Near-Sun Environment

TL;DR

This study uses Parker Solar Probe data to extend estimates of proton and electron heating rates in the solar wind down to 0.063 au, revealing a dominant proton heating closer to the Sun and differences from previous models.

Contribution

It provides new empirical measurements of proton and electron heating rates in the near-Sun environment, improving understanding of solar wind heating mechanisms.

Findings

Proton heating becomes more dominant closer to the Sun.

Electron heat conduction flux behavior differs from previous predictions.

Protons receive about 80% of total plasma heating at 13 solar radii.

Abstract

A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first ten encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons in to a distance of 0.063 au (13.5 solar radii), in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ~ 13 solar radii, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.