On September 5, 2022, NASA's Parker Solar Probe gracefully flew by one of the most powerful coronal mass ejections (CMEs) on record - not only an impressive feat of engineering, but also a major advance for the scientific community.
Recently, NASA's Parker Solar Probe passed through the most powerful collection of particles on record, providing key insights into 20-year-old theories about how particles interact with interplanetary dust. This interaction affects space weather forecasts and is critical to technology here on Earth. Image source: NASAGSFC/CIL/BrianMonroe
Parker's journey through a coronal mass ejection helped prove a 20-year-old theory that the interaction of coronal mass ejections with interplanetary dust has important implications for space weather forecasts. The results were recently published in The Astrophysical Journal.
A 2003 paper speculated that CMEs could interact with interplanetary dust orbiting the star and even pull the dust out of orbit. Collections of radioactive particles, giant eruptions of the sun's outer atmosphere, or corona, help drive the formation of space weather that can endanger satellites, interfere with communications and navigation technology, and even paralyze Earth's power grid. Understanding more about how these events interact with interplanetary dust can help scientists better predict how quickly CMEs travel from the sun to Earth and predict when Earth will be affected by CMEs.
Parker has now observed this phenomenon for the first time.
"Interactions between CMEs and dust have been theorized for two decades, but were not observed until the Parker Solar Probe observed CMEs acting like vacuum cleaners clearing dust in their path," said lead author Guillermo Stenborg, an astrophysicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, which built and operates the spacecraft.
Interplanetary dust consists of tiny particles from asteroids, comets and even planets, and is found throughout the solar system. One manifestation of interplanetary dust clouds is a faint glow called a zodiac that can sometimes be seen before sunrise or after sunset.
The CME moved this dust about 6 million miles from the Sun - about one-sixth the distance between the Sun and Mercury - but it was almost immediately replenished by interplanetary dust floating around the solar system.
Parker's in situ observations were critical to the discovery because observing the dynamics of dust after a CME from a distance is challenging. According to the researchers, Parker's observations can also provide insights into phenomena related to the lower levels of the corona, such as coronal dimming caused by low-density regions in the corona, a phenomenon that often occurs after CME outbreaks.
On September 5, 2022, Parker Solar Probe's Wide Field Solar Probe (WISPR) camera observed the spacecraft passing through a giant coronal mass ejection. Coronal mass ejections are giant eruptions of plasma and energy from the solar corona that are the driving force of space weather. Source: NASA/Johns Hopkins APL/Naval Research Laboratory
The scientists observed that the interaction between CMEs and dust showed up as a decrease in brightness in images taken by Parker's Wide Field Imager for Solar Probe (WISPR) camera. This is because interplanetary dust reflects light, amplifying the brightness wherever the dust is present.
To find this decrease in brightness, the team had to calculate the average background brightness of the WISPR images over several similar orbits -- sifting out normal brightness variations due to solar streamlines and other changes in the corona.
"Parker has orbited the Sun four times at the same distance, which allows us to nicely compare data from one time to the next," Sternberg said. "By removing changes in brightness caused by coronal movement and other phenomena, we were able to isolate changes caused by dust depletion."
Because scientists only observed this effect during the September 5 event, Stenborg and the team reasoned that dust depletion might only occur in the most powerful CMEs.
However, studying the physics behind this interaction could have implications for space weather forecasts. Scientists are just beginning to understand how interplanetary dust affects the shape and speed of CMEs. However, more research is needed to better understand these interactions.
Parker has completed its sixth flyby of Venus, and during its next five close approaches, it will use Venus's gravity to bring itself closer to the sun. This occurs as the Sun itself approaches solar maximum, the period of most sunspot and solar activity in the Sun's 11-year cycle. As solar activity increases, scientists hope to have the opportunity to see more of these rare phenomena and explore how they may affect our Earth environment and the interplanetary medium.