The comet, first discovered in 2023, was observed by NRL's Large Angle and Spectrometric Coronagraph (LASCO) aboard the joint NASA and European Space Agency (ESA) Solar and Heliospheric Observatory (SOHO) spacecraft from Oct. 7-11. Although the comet's nucleus moved out of view, its expansive dust trail remained visible for several days.
SOHO, positioned at the Lagrange (L1) point, observed the comet's passage from a unique angle, which caused its brightness to dramatically increase as sunlight illuminated the comet's surrounding dust from behind. While LASCO has recorded thousands of comets in its nearly three decades of operation, the passage of comet Tsuchinshan-ATLAS showcased a never-before-seen phenomenon.
On Oct. 14, the comet's dusty trail briefly condensed into a narrow, dense band that spanned the entire field of view. This event occurred when the SOHO spacecraft crossed the comet's orbital plane, providing a rare edge-on perspective of the comet's dust sheet. The dust plane eventually shifted into the lower part of LASCO's data, illuminating half of the field of view.
"LASCO has seen many beautiful comet transits during its decades of operations, but seeing a side-on view of a comet's dust plane absolutely ranks as one of the most spectacular that we have seen," said Dr. Karl Battams, NRL scientist and LASCO Principal Investigator.
Although some scientists speculated that this might be the brightest comet LASCO had ever observed - possibly outshining the record-holding Comet McNaught of 2007 - Tsuchinshan-ATLAS did not reach that peak but did achieve a visual magnitude brighter than -4.0, making it the second brightest comet LASCO has observed.
"We knew this comet was going to be bright, but the extremely fortuitous viewing geometry here has led to a truly spectacular sequence of images," added Battams.
In addition to LASCO's observations, NRL's HI-1 heliospheric imager on NASA's Solar Terrestrial Relations Observatory-A (STEREO-A) spacecraft, operational since 2006, and the Compact Coronagraph (CCOR-1) on NOAA's GOES-19 satellite also recorded the comet from Oct. 4-9.
Tsuchinshan-ATLAS is currently visible to observers in the northern hemisphere during the early evening, shortly after sunset. As it climbs higher into the night sky, the comet will gradually fade, though it will remain a binocular object for several weeks. Eventually, the comet will retreat into the Oort Cloud - a distant region of the solar system - and may even be ejected from the solar system altogether.
NRL's LASCO instrument also plays a crucial role in the NASA-funded Sungrazer Project, a citizen science initiative launched in 2003. This project encourages amateur astronomers to discover previously unknown comets using LASCO and STEREO-A data. To date, the project has been responsible for discovering more than half of all officially documented comets.
Related Links
Naval Research Laboratory
Asteroid and Comet Mission News, Science and Technology
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