What can comets tell us about solar activity and space weather?

In early October 2024, comet C/2023 A3 – better known as Tsuchinshan-ATLAS – made an unforgettable appearance as it passed between the Earth and the Sun, offering scientists a rare and spectacular view. 

This comet, which was discovered in 2023, was captured by the U.S. Naval Research Laboratory’s (NRL) Large Angle and Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO). 

For several days, LASCO tracked the comet, producing breathtaking images of its journey, especially its massive dust trail, which remained visible even after the nucleus had moved away.

Comet flyby and solar space weather

LASCO principal investigator Karl Battams described the event as “one of the most spectacular that we have seen,” with the dense dust trail coalescing in a unique formation that spanned the entire field of view. 

This rare view occurred because the SOHO spacecraft crossed the comet’s orbital plane, allowing it to observe the dust trail edge-on. This phenomenon has never been seen in such detail.

While Tsuchinshan-ATLAS didn’t surpass the brilliance of Comet McNaught from 2007, it still earned the distinction of being the second brightest comet observed by LASCO, reaching a visual magnitude of -4.0. 

The comet’s passage also presented a scientific opportunity, as its dust and gas tails likely interacted with solar outflows, potentially offering new insights into the near-Sun environment and solar space weather.

Solar ejections and stunning halos

Around the same time, NRL’s Compact Coronagraph (CCOR) instrument also achieved significant milestones by collecting its first images of coronal mass ejections (CMEs). 

Launched aboard NOAA’s GOES-19 spacecraft in June 2024, CCOR is designed to observe the outer atmosphere of the Sun – known as the solar corona – by creating an artificial eclipse using an occulter to block the Sun’s glare.

One of the most striking observations occurred on October 3, when CCOR captured a halo CME, a type of solar ejection that appears as a near-circular shape around the Sun. 

This particular CME resulted in visible northern lights across much of the northern United States, a stunning reminder of the Sun’s powerful influence on Earth. 

Monitoring space weather in real time

Another halo CME followed on October 10, linked to an active region on the Sun’s surface, further showcasing CCOR’s capability to monitor space weather in real-time.

“By creating an artificial eclipse, the CCOR allows scientists to study the Sun’s corona, which can produce powerful solar storms that can disrupt Earth-based technologies,” said Arnaud Thernisien, a research physicist at NRL. 

These observations are critical as they provide early warnings for solar storms that have the potential to interfere with satellites, communications, and even power grids on Earth.

Understanding comets and solar activity 

The recent data collected from Tsuchinshan-ATLAS and CMEs illustrate the vital role of NRL’s instruments in advancing our understanding of both comets and solar activity. 

The LASCO instrument, which has been operational for nearly 30 years, continues to be instrumental in studying the Sun and its surroundings. It also contributes to the Sungrazer Project, a citizen science initiative responsible for discovering over half of all documented comets.

Meanwhile, CCOR-1, the first operational coronagraph in the United States, represents a breakthrough in solar observation. It provides near real-time data crucial for space weather forecasting, allowing scientists to predict and mitigate the effects of solar storms. 

This success is only the beginning, with CCOR-2 slated for launch in 2025 and a compact coronagraph planned for the European Space Agency’s Vigil mission in 2031.

The future of space observation

As these cutting-edge instruments continue to push the boundaries of space observation, researchers are already looking to the future. 

With CCOR’s successful observations of CMEs and LASCO’s continued monitoring of celestial objects like Tsuchinshan-ATLAS, scientists are gaining unprecedented insights into the interactions between comets, solar activity, and space weather.

“NRL’s instruments are providing a wealth of information that helps us understand the dynamics of space weather and the broader solar environment,” said Thernisien. 

The collaboration between NASA, NOAA, and international partners promises to enhance our ability to predict solar storms and understand the fundamental processes shaping our solar system.

As comet Tsuchinshan-ATLAS continues its journey back to the Oort Cloud and beyond, and as CCOR-1 and LASCO maintain their vigilant watch on the Sun, the data gathered will be invaluable for future missions and discoveries in the ever-evolving field of space science.

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