Parker Solar Probe makes closest pass to the sun yet

The Parker Space Probe (PSP), launched in 2018, was designed to take measurements at the closest distance to the sun ever attempted. With each orbit of the sun, the probe uses the gravity of Venus to slingshot closer to the surface. On December 24, 2024, PSP made its seventh and final assist, achieving the closest approach yet to sun. (3.8 million miles or ~8.86 solar radii above the Sun’s surface.) At least two more encounters at this distance are scheduled and there is the possibility of many more. After each perihelion (close approach to the Sun), the team has waited for news that the spacecraft has phoned home, and, even more eagerly, awaited the transmission of scientific data to what new phenomena occur closer to the Sun  within the solar corona.

Our Sun is the only star that we can study with in-situ instruments. The School of Physics and Astronomy has been a key player, involved since the planning stages of the PSP mission. Measurements of the electric and magnetic fields, and plasma and radio waves are made by the PSP FIELDS instrument, whose PI, Stuart Bale, received his B.A. and Ph.D. in Physics from the School. The School designed and built instrumentation for inclusion on the PSP mission.  Keith Goetz, who leads the SPA effort, made significant contributions to the radio and plasma wave instrument, including high frequency waveform captures. Professor Emeritus John Wygant was also involved in testing and early planning for integration of the instrument and spacecraft; study of Poynting flux. Professor Emeritus Cynthia Cattell is PI for the study of coupling of solar oscillations with small scale electron acceleration generating radio waves; lead for studies of the role of intermediate frequency waves in solar wind evolution. Professor Lindsay Glesener is involved in the study of x-rays associated with small scale electron acceleration and analysis of the EUV emissions for periodicities similar to solar oscillations-(a study which uses PSP data for comparison). Reed Masek, grad student, and the following undergraduates are involved in research studies around PSP data: Ben Leiran, Theo Mahaffey, Yuni Kim, Merlin Phillips, Tien Vo, Jack Redepenning, Alexander Skogsberg, Logan Macgowan, Luke Kathmann, Corie Guggemos, Petra Bibeau, Daniel Tereshko). Lily Hanson and Sadie Elliott are Research staff for the SPA group. 

The SPA group has found that the radio waves generated by electrons accelerated in very small solar flares sometimes occur for many hours with the same ~5-minute period as solar oscillations. Initial studies suggest these events may be an important clue for explaining why the Sun’s atmosphere (the solar corona) is so hot, a key goal for the mission.  As PSP obtained data closer to the Sun, they found that an electromagnetic plasma wave known as whistler waves are no longer observed.  These waves are thought to regulate heat flux in the solar wind and in other astrophysical settings like other stellar winds, the interstellar medium, and accretion disks. Since things seem to work differently close to the Sun, research is ongoing to determine which other waves can perform this function by interacting strongly with electrons in the Sun’s corona. PSP has provided data for five astrophysics senior theses, and involved more than twelve SPA undergrads in the excitement of discoveries in space plasma physics.