On September 5, 2022, NASA’s Parker Solar Probe lifted off gracefully past one of the most powerful coronal mass ejections (CMEs) ever recorded; not only an impressive feat of engineering, but also a huge boon to the scientific community. Parker’s journey through the CME helps confirm a 20-year-old theory about the interaction of CMEs with interplanetary dust, and that theory has implications for space weather forecasts. Results recently published Astrophysical Journal.

A 2003 paper theorized that CMEs could interact with interplanetary dust in orbit around our star and even transport the dust out. CMEs are massive explosions originating from the Sun’s outer atmosphere, or corona, that contribute to changes in space weather that can threaten satellites, disrupt communications and navigation technologies, and even disable power grids on Earth. Learning more about how these events interact with interplanetary dust could help scientists better predict how fast CMEs can travel from the Sun to Earth and predict when the planet might see their effects.

Parker observed this phenomenon for the first time.

“These interactions between CMEs and dust were theorized two decades ago but were not observed until the Parker Solar Probe saw the CME acting like a vacuum cleaner, clearing dust from its path,” said astrophysicist Guillermo Stenborg of Johns Hopkins. Applied Physics Laboratory (APL) in Laurel, Maryland, and lead author of the paper. APL built and operated the spacecraft.

This dust consists of tiny particles from asteroids, comets, and even planets, and is found throughout the solar system. A type of faint glow called zodiacal light, sometimes visible before sunrise or after sunset, is a manifestation of the interplanetary dust cloud.

The CME pushed dust about 6 million miles into the Sun (about one-sixth the distance between the Sun and Mercury), but it was almost immediately populated by interplanetary dust floating through the Solar System.

Because dust dynamics from CMEs are difficult to characterize remotely, Parker’s in situ observations were critical to this discovery. According to the researchers, Parker’s observations may also provide insight into related phenomena in the lower part of the corona, such as coronal darkening caused by low-density regions in the corona that often occur after a CME explosion.

Scientists observed the interaction between CME and dust in the form of dimming in images taken from Parker’s Wide Field Imager for the Solar Probe (WISPR). This is because interplanetary dust reflects light, increasing the brightness where the dust is located.

To identify this dimming event, the team needed to calculate the average background brightness of WISPR images taken from several similar orbits, filtering out normal brightness variations caused by solar radiation and other changes in the solar corona.

“Parker flew around the Sun the same distance four times, which allows us to compare the data very well from one flyby to the next,” Stenborg said. “By eliminating changes in brightness due to coronal shifts and other events, we were able to isolate changes due to dust depletion.”

Because scientists have only observed this effect in conjunction with the September 5 event, Stenborg and his team suggest that dust depletion may occur only in the strongest CMEs. Still, studying the physics behind this interaction could have important implications for space weather predictions. Scientists are just beginning to understand that interplanetary dust affects the shape and speed of CMEs. However, more research is needed to better understand these interactions.

Parker completed his sixth flyby of Venus, using the planet’s gravity to get even closer to the Sun over the next five approaches. This occurs as the Sun approaches solar maximum, the period when sunspots and solar activity are greatest in the Sun’s 11-year cycle. As solar activity increases, scientists hope to be able to see more of these rare events and study how they might affect our Earth and the interplanetary environment.