NASA's Europa Clipper spacecraft has obtained ultraviolet observations of the interstellar comet 3I/ATLAS, filling a viewing gap when Earth and Mars telescopes were obstructed. The data reveals hydrogen, oxygen, and signs of intense gas release from the comet. These findings could provide insights into cometary formation around other stars.
In November 2025, NASA's Europa Clipper spacecraft, en route to Jupiter, unexpectedly observed the interstellar comet 3I/ATLAS using its Ultraviolet Spectrograph (UVS) instrument, led by the Southwest Research Institute. This comet, confirmed as the third interstellar object to enter our solar system in July 2025, was difficult to view from Earth due to its proximity to the Sun and suboptimal conditions from Mars.
The spacecraft's position offered a unique perspective, positioned between the comet and the Sun, allowing a view of the dust and plasma tails from behind, toward the nucleus and coma. This complemented earlier Mars observations from late September and anticipated Earth views. "We're excited that this opportunity to view another target on the way to Jupiter was completely unexpected," said Dr. Kurt Retherford, principal investigator for Europa-UVS at SwRI. "Our observations have allowed for a unique and nuanced view of the comet."
The UVS detected oxygen, hydrogen, and dust signatures, indicating high outgassing activity shortly after the comet's closest solar approach. "Europa-UVS is particularly adept at measuring fundamental transitions from atoms and molecules," Retherford explained. "We can see gases come off the comet, and water molecules break apart into hydrogen and oxygen atoms."
Simultaneously, the UVS on ESA's Jupiter Icy Moons Explorer (JUICE) provided an opposing view, aiding a fuller understanding of the tails' structure. "We're hopeful that this new view, along with observations from Earth-based assets and other spacecraft, will help us to piece together a more complete understanding of the tails' geometries," noted Dr. Thomas Greathouse, co-deputy principal investigator.
Such data on the comet's composition and gas emissions may illuminate its origins beyond our solar system. "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," said Dr. Tracy Becker, another co-deputy principal investigator. The Europa Clipper, launched in 2024, will arrive at Jupiter in 2030 for 49 flybys of Europa, studying its atmosphere and surface. The mission is managed by NASA's Jet Propulsion Laboratory in partnership with the Johns Hopkins University Applied Physics Laboratory.
