NASA’s Parker Solar Probe spent five hours in the sun’s extended solar environment, also known as the corona. This spacecraft is the first ever to reach the sun’s outer limits.
Justin C. Kasper, the first writer, is Deputy Chief Technology Officer at BWX and a professor at Michigan. Johns Hopkins University Applied Physics Laboratory is leading the mission.
The probe was able to make the first direct observations of the sun’s atmosphere. This allowed for the measurement of phenomena that were previously only approximated.
The Alfven critical area is the point at which the sun’s outer edges begin. This is the point below where the sun, its gravitational forces, and magnetic forces control the solar wind. This area is believed to be the source of sudden changes in the sun’s magnetic fields, known as switchbacks.
Kasper stated that NASA was not the first to think of the idea of sending a spacecraft into the magnetic atmosphere of the sun.
NASA launched Parker Solar Probe in 2018 intending to finally reach the sun’s corona and make humanity’s first trip to a star.
The probe spent five hours in April below the Alfven critical area, where it was in direct contact with the sun’s plasma. Below the surface, the magnetic field’s pressure and energy were greater than the pressures and energies of the particles. The spacecraft passed over and under the surface three times during its encounter. This was the first time that a spacecraft has touched the atmosphere of the sun and entered the solar corona.
Surprisingly the researchers found that the critical surface of Alfven is wrinkled. Data suggest that the Alfven critical surface’s largest and farthest wrinkle was caused by a pseudostreamer, a large magnetic structure measuring more than 40 degrees in diameter. It is located back on the innermost visible side of the sun. It is unknown why a pseudostreamer would move the Alfven critical area away from the sun.
Researchers found that switchbacks were less common below the Alfven critical area than they were above it. This could indicate that coronal switchbacks are not formed within it. Low rates of magnetic reconnection at the sun’s surface may have resulted in less wind stream mass, which could have led to fewer switchbacks.
The probe also found evidence of a possible power boost inside the corona. This could be a result of unknown physics that affect heating and dissipation.
“We have been studying the sun’s corona for many decades and know that there is fascinating physics to heat and accelerate solar wind plasma. Nour E. Raouafi (JHU/APL Parker Solar Probe Project Scientist) said that we still don’t know what this physics is.
These observations were made during Parker Solar Probe’s eighth encounter with sunlight. All data are available publicly in the NASA PSP archive. Numerous studies have predicted that the probe will first pass within the sun’s borders in 2021.
Parker Solar Probe is the fastest-known object to be built by humans. It has made many discoveries since its launch. These include explosions that create space weather and the dangers of superspeedy dust.
These new observations suggest that spacecraft direct observations have much to offer about the physics behind solar wind formation and coronal heating. Parker Solar Probe has reached its goal of touching the sun. Now, it will descend further into the atmosphere of the sun and stay there for longer periods.
Gary Zank, coinvestigator of the probe’s Solar Wind Electrons Alphas and Protons instrument and a member of the National Academy of Sciences, said that “it is difficult to overstate both the significance of the event and the observations made with Parker Solar Probe.” Since the dawn of the space age, the heliospheric world has struggled for over 50 years with the question of how the solar corona heats to generate the solar wind. The sub-Alfvenic measurement of the solar wind could be the biggest step in understanding the physics that drives the solar wind’s acceleration since Parker’s original model.
“This is the event that many heliophysics dreamed of for their entire careers!” Zank agreed.
The results were published in Physical Review Letters. They were announced at a press conference held at the American Geophysical Union Fall Meeting 2020 on December 14.
