Agência Espacial Europeia’s JUICE probe has detected water vapor rising from the interstellar comet 3I/ATLAS. The measurements took place in November 2025, a few days after the comet reached its closest point to Sol. The object released around two tons of water per second at times, a volume equivalent to 70 Olympic swimming pools per day.
The detection occurred when the probe was heading towards Júpiter and passed relatively close to the comet. Instrumentos as the MAJIS spectrometer and the SWI submillimeter wave instrument recorded the activity. Parte significant vapor was not coming directly from the solid core, but from ice grains in the coma, the cloud of dust and gas surrounding the object.
Detalhes from detection by JUICE probe
The probe activated five scientific instruments to observe the comet between November 2 and 25, 2025. On November 2, four days after perihelion, MAJIS identified a rate of 2,000 kilograms of water vapor per second. Esse value corresponds to approximately 70 Olympic swimming pools per day.
The SWI instrument confirmed that most of the vapor exited from the side facing Sol. Análises indicate that ice grains ejected into the coma sublimate and contribute to the total release. The probe was about 60 million kilometers from the comet at its closest point.
The team continues to process the complete data, with some of the information reaching Terra in February 2026 due to transmission limitations during the thermal protection phase.
Características of the interstellar comet 3I/ATLAS
Comet 3I/ATLAS, also designated C/2025 N1 (ATLAS), is the third confirmed interstellar object to pass through Sistema Solar. Sua hyperbolic trajectory indicates origin outside our system. The NASA-funded ATLAS telescope at Chile detected the object on July 1, 2025.
At the time of discovery, the comet was about 4.5 astronomical units away from Sol and moving at approximately 61 kilometers per second relative to Sol. Perihelion occurred around October 29 or 30, 2025, at about 1.4 astronomical units, just inside the orbit of Marte. The object does not pose a risk to Terra, with the minimum approach to the planet being around 1.8 astronomical units.
Previous Observações, including from ground-based telescopes and other instruments, had already indicated activity on the comet even far from Sol. Medições of water production varied according to the heliocentric distance, with values around 40 kilograms per second at greater distances and increases close to perihelion.
Composição and water release mechanism
The comet has a different composition from Sistema Solar comets, with a high proportion of carbon dioxide in relation to water. Parte of the water released comes from secondary sublimation of icy grains in the coma, and not just from the surface of the nucleus.
Essa dynamics help explain the observed activity. The mechanism involves the ejection of ice particles that then release vapor when heated by solar radiation. Preliminary Estudos indicate that the fraction of water from extended sources may reach 80% before perihelion and reduce to about 50% closer to Sol.
- The comet released about 2,000 kg of water vapor per second on November 2, 2025
- Most of the release occurred on the side facing Sol
- Grãos of ice in the coma contributed significantly to the total water detected
- The rate is not considered exceptional for comets close to Sol, but it stands out due to its interstellar origin.
- JUICE’s Instrumentos included MAJIS and SWI for spectral measurements
Observações complementary to other missions
Outras observations from ground-based and space-based telescopes followed the comet throughout its passage. Dados spectroscopy detected hydroxyl, an indirect indication of water, even when the object was still more than 2.5 astronomical units away from Sol.
The JUICE mission took advantage of the favorable position during its trip to collect images and data. The probe’s navigation camera also recorded the comet. Essas preliminary images show the coma and flows of gas and dust.
The comet continues on its exit path from Sistema Solar after passing through the Júpiter region. Ele will not return as its speed exceeds that required to remain gravitationally bound to Sol.
Implicações for the study of interstellar objects
The passage of 3I/ATLAS offers a rare opportunity to compare comets formed in other star systems with those in our own. Detecting water and other volatiles helps understand formation conditions in distant environments.
Cientistas analyze whether the carbon dioxide-rich composition reflects origin in colder or chemically distinct regions. JUICE data contributes to models of cometary activity in hyperbolic objects.
The probe continues its main mission towards the icy moons of Júpiter, with arrival scheduled for 2031. Observations of the comet represent a scientific bonus during the trip.
