NASA’s Europa Clipper spacecraft has successfully captured unprecedented ultraviolet observations of the interstellar comet 3I/ATLAS. This rare glimpse occurred on December 20, 2025, while Earth-based telescopes were unable to view the comet due to its proximity to the Sun. The spacecraft’s unique positioning allowed scientists to analyze the comet’s dust and plasma tails from an unusual angle, revealing critical details about its composition and activity.
The observations were made using the Ultraviolet Spectrograph (UVS), developed by the Southwest Research Institute (SwRI). In July 2025, 3I/ATLAS became the third officially confirmed interstellar object to enter our solar system. Dr. Kurt Retherford, the principal investigator for Europa-UVS, emphasized the significance of this opportunity, stating, “We’re excited that this opportunity to view another target on the way to Jupiter was completely unexpected. Our observations have allowed for a unique and nuanced view of the comet.”
Europa Clipper, launched in 2024, is set to reach the Jovian system in 2030. Upon arrival, it will orbit Jupiter and conduct 49 close flybys of the moon Europa. The UVS instrument collects ultraviolet light to study the atmospheric gases and surface materials on Europa, contributing to a broader understanding of celestial bodies.
NASA’s Jet Propulsion Laboratory (JPL) analysts mapped the path of 3I/ATLAS less than a week after its discovery. They recognized that the Europa Clipper could observe the comet in November 2025, a time when its position near the Sun would obstruct views from Earth and make Mars-based observations challenging. This advantageous timing allowed the spacecraft to bridge critical observation gaps, connecting prior Mars-based data with later Earth-based opportunities.
Unique Perspectives on Cometary Activity
The comet’s trajectory positioned it between Europa Clipper and the Sun, granting the spacecraft a distinctive vantage point. Typically, comets exhibit two primary tails: a dust tail that trails behind and a plasma tail that points away from the Sun. Europa-UVS captured images from a “behind” perspective, allowing scientists to view both tails while simultaneously assessing the comet’s nucleus and surrounding coma.
This analysis is complemented by observations from the SwRI-led UVS instrument aboard the European Space Agency’s Jupiter Icy Moons Explorer (JUICE), which provides an anti-sunward view. Dr. Thomas Greathouse, co-deputy principal investigator of Europa-UVS, expressed optimism that combining these diverse perspectives would enhance understanding of the tails’ geometries.
The Europa-UVS instrument detected signatures of oxygen, hydrogen, and dust, indicating that 3I/ATLAS underwent a phase of intense outgassing shortly after its closest approach to the Sun. Dr. Retherford noted, “Europa-UVS is particularly adept at measuring fundamental transitions from atoms and molecules. We can see gases come off the comet, and water molecules break apart into hydrogen and oxygen atoms.” This capability allows for a detailed examination of the comet’s composition and activities.
Exploring the Origins of Comets
The insights gained from these observations may provide valuable clues about the origins of 3I/ATLAS and similar comets. Dr. Tracy Becker, co-deputy principal investigator of Europa-UVS, stated, “Understanding the composition of the comet and how readily these gases are emitted can give us a clearer view of the comet’s origin and how it may have evolved during transit from elsewhere in the galaxy to our solar system.”
Questions surrounding the comet’s chemical processes and whether they mirror those believed to have occurred during the formation of our solar system are paramount. The mission, managed by JPL for NASA’s Science Mission Directorate in Washington, D.C., was developed in collaboration with the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.
The ongoing research surrounding 3I/ATLAS, bolstered by the unique capabilities of the Europa Clipper, is set to advance our understanding of not only this comet but also the broader mechanisms at play in the formation of celestial bodies throughout the universe.
