NASA’s STEREO (Solar-Earth Relations Observatory), the NASA/ESA SOHO (Solar-Heliospheric Observatory), and NASA’s PUNCH (Corona-Heliosphere Integrating Polarimeter) missions had the extraordinary capability to observe sky regions near the Sun, enabling them to monitor 3I/ATLAS as it traversed behind the Sun from Earth’s perspective.
3I/ATLAS moves at an incredible speed of 209,000 km (130,000 miles) per hour, visualized through a series of colorized stacked images captured from September 11 to 25, 2025, using the Heliocentric Imager-1 instrument aboard NASA’s STEREO-A spacecraft. Image credit: NASA / Lowell Observatory / Qicheng Zhang.
STEREO monitored the interstellar comet 3I/ATLAS between September 11 and October 2, 2025.
The mission aims to examine solar activity and its effects on the entire solar system and is part of a collection of NASA spacecraft studying comets, offering insights on their size, physical characteristics, and chemical makeup.
Initially, it was believed that comet 3I/ATLAS would be too dim for STEREO’s instruments, but advanced image processing using the visible-light telescope Heliospheric Imager-1 and the stacking of images revealed 3I/ATLAS effectively.
By overlaying multiple exposures, distinct images were produced, showing the comet slightly brighter at the center.
This image of 3I/ATLAS combines observations from the NASA/ESA SOHO mission between October 15 and 26, 2025. Image credit: NASA / ESA / Lowell Observatory / Qicheng Zhang.
The SOHO spacecraft managed to catch a glimpse of 3I/ATLAS from October 15 to 26, 2025.
During this time frame, the LASCO instrument suite onboard SOHO identified comets crossing its observation area from around 358 million km (222 million miles) away, which is more than twice Earth’s distance from the Sun.
SOHO orbits at Sun-Earth Lagrange Point 1, a gravitational equilibrium point approximately 1.6 million km (1 million miles) closer to the Sun along the Sun-Earth axis.
Members of the SOHO team also utilized stacking techniques to create images of 3I/ATLAS.
In this image, 3I/ATLAS is clearly visible as a bright object in the center, created by consolidating observations from NASA’s PUNCH mission conducted from September 20 to October 3, 2025. Image credit: NASA/Southwest Research Institute.
The PUNCH mission observed 3I/ATLAS from September 20 to October 3, 2025.
These observations indicated that the comet’s tail extended slightly to the lower right.
During this period, the comet was so dim that the PUNCH team was uncertain if the spacecraft would be able to detect it well, given its primary focus on studying the Sun’s atmosphere and solar wind rather than comets.
However, by collecting multiple observations, 3I/ATLAS and its tail became distinctly visible.
“We’re truly pushing the limits of this system,” stated Dr. Kevin Walsh, a planetary scientist at the Southwest Research Institute who led the PUNCH observations of comets.
Source: www.sci.news
