On September 5, 2022, NASA’s Parker Solar Probe executed a graceful maneuver through one of the most potent coronal mass ejections (CMEs) ever observed. This event showcased not only the probe’s remarkable engineering but also delivered a significant contribution to the scientific community. Parker’s traversal through the CME offered compelling evidence in support of a two-decade-old hypothesis regarding the interaction between CMEs and interplanetary dust, which carries profound implications for space weather predictions. The findings stemming from this mission were recently detailed in The Astrophysical Journal.
In 2003, a paper postulated that CMEs might engage with and transport interplanetary dust particles orbiting our sun. These CMEs, colossal eruptions from the sun’s outer layer or corona, play a pivotal role in shaping space weather. This phenomenon, in turn, has far-reaching implications, as it can jeopardize satellites, disrupt communication and navigation systems, and even disrupt terrestrial power grids. Unraveling the intricacies of these interactions between CMEs and interplanetary dust holds the potential to enhance our ability to predict the speed at which CMEs can travel from the sun to Earth, ultimately facilitating forecasts of their potential impact on our planet.
Parker Solar Probe has now borne witness to this phenomenon for the very first time. As Guillermo Stenborg, an astrophysicist at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, and the lead author of the paper, elucidated, “These interactions between CMEs and dust were theorized two decades ago, but had not been observed until Parker Solar Probe viewed a CME act like a vacuum cleaner, clearing the dust out of its path.” It’s noteworthy that APL was responsible for both constructing and operating the spacecraft.
The interplanetary dust involved in this interaction consists of minuscule particles originating from asteroids, comets, and even planets, and it permeates the entirety of our solar system. A faint glow known as zodiacal light, occasionally visible before sunrise or after sunset, serves as one manifestation of this interplanetary dust cloud.
Remarkably, the CME displaced this dust to a distance of approximately 6 million miles from the sun, equivalent to about one-sixth of the distance between the sun and Mercury. However, the dust was swiftly replenished by interplanetary particles scattered throughout the solar system.
Parker’s in-situ observations were indispensable in making this groundbreaking discovery, as assessing dust dynamics in the aftermath of CMEs is an arduous task from a remote vantage point. Furthermore, these observations could offer valuable insights into related phenomena occurring lower in the corona, such as coronal dimming triggered by low-density regions that often follow CME eruptions.
The interaction between the CME and dust was discerned through a reduction in brightness in images captured by Parker’s Wide-field Imager for Solar Probe (WISPR) camera. This dimming effect occurred because interplanetary dust particles reflect light, augmenting brightness where they are present.
To pinpoint these instances of diminished brightness, the research team had to compute the average background brightness across multiple orbits, thereby filtering out normal brightness fluctuations stemming from solar streamers and other changes in the solar corona. As Stenborg explained, “Parker has orbited the sun four times at the same distance, allowing us to compare data from one pass to the next very well. By removing brightness variations due to coronal shifts and other phenomena, we were able to isolate the variations caused by dust depletion.”
It is worth noting that, as of now, scientists have exclusively observed this phenomenon in connection with the September 5 event. Therefore, Stenborg and his team posit that dust depletion may only manifest in the presence of the most powerful CMEs.
Nonetheless, delving deeper into the physics governing this interaction holds significant promise for advancing space weather prediction. Researchers are only beginning to comprehend how interplanetary dust influences the trajectory and speed of a CME. Consequently, further investigations are warranted to gain a more comprehensive understanding of these intricate interactions.
Parker Solar Probe has now completed its sixth Venus flyby, utilizing the planet’s gravity to position itself even closer to the sun for its subsequent five close approaches. This endeavor coincides with the sun’s approach to solar maximum, a phase in the sun’s 11-year cycle marked by heightened sunspot and solar activity. As solar activity escalates, scientists eagerly anticipate the opportunity to observe more of these rare phenomena and explore their potential implications for both our Earth’s environment and the interplanetary medium.