Interstellar Comet 3I/ATLAS: ESA Releases Data Collected by the JUICE Space Probe
Recently, ALMA data have shown that the interstellar comet 3I/ATLAS contains molecules such as methanol and hydrogen cyanide as it has just passed the orbit of Jupiter and is heading outward from the Solar System, never to return. One of the novelties concerns the information collected by the European space probe JUICE (Jupiter Icy Moons Explorer) of the ESA, which collected data back in November of last year.
As explained by the space agency, due to the distance from Earth and its position relative to our planet, the data regarding the interstellar comet 3I/ATLAS was only recently downloaded for analysis by scientists. Therefore, this information does not reflect the current state of the object but rather that of a few months ago. Nonetheless, this data is essential because the more information we have at our disposal, the better we can understand the history and evolution of interstellar objects, which we still know little about.
ESA JUICE and the Data from the Interstellar Comet 3I/ATLAS
According to reports, the ESA JUICE probe used five of its instruments (which were not specifically designed for this purpose) to gather data on the comet as it was moving away from the Sun. The information is still preliminary, and scientists continue to study the data.
Using the MAJIS instrument (Juice’s Moons And Jupiter Imaging Spectrometer), it was possible to determine that the comet was losing about 2 tons of water vapor every second. Sublimation is a known phenomenon for comets, which are largely composed of frozen water along with many other molecules. The water loss from the interstellar comet 3I/ATLAS is not extreme; in fact, comet 67P/Churyumov-Gerasimenko loses about 300 kg per second, while Halley reaches up to 20 tons per second.
The team handling MAJIS still needs to analyze the data from the second half of November 2025, but those from November 12 indicate that (despite the comet moving away from the Sun) the amount of water vapor released had not significantly decreased.
SWI Instrument Analysis
The SWI (Submillimeter Wave Instrument) of ESA JUICE showed that the water loss from interstellar comet 3I/ATLAS occurred on the side facing the Sun. Interestingly, this loss was not from the comet's nucleus but rather from its coma, which contains frozen dust grains.
Another ongoing analysis aims to understand how much light water and how much semi-heavy water (where a deuterium atom replaces a hydrogen atom) was released at the time, to compare it with data collected by ALMA and JWST. The idea is that this comet formed a long time ago in a particularly cold location with significant ultraviolet radiation from young stars. However, new data are essential for a clearer picture.
The UVS (Ultraviolet Imaging Spectrograph) was used to analyze the emission of oxygen, hydrogen, and carbon atoms in the comet's tail region. These elements were found as much as 5 million km from the comet's nucleus, even though there have been comets with tails up to twice as long as 3I/ATLAS.
The use of the high-resolution scientific camera JANUS (Jovis Amorum ac Natorum Undique Scrutator) was also notable. Despite being over 60 million km from the target, JANUS detected the coma and two tails, along with the nucleus. Again, the data are still under review, but ESA notes that "overall, JANUS shows that, despite its interstellar origin, comet 3I/ATLAS behaved like a typical Solar System comet during its approach to the Sun."
The NavCam of the space probe enabled precise calculations of the trajectory of the interstellar comet, not only through the Solar System but also from outside. These data suggest that the object may originate from the direction of the Milky Way's galactic disk and could therefore have formed over 10 billion years ago (making it older than the Solar System itself).
In the coming months, several scientific papers will be published on 3I/ATLAS based on the data collected by ESA JUICE, allowing for a clearer understanding of the discoveries related to these kinds of space objects, which remain a mystery to scientists.