Comet 3I/Atlas, the third interstellar object detected by science, reappears in the sky from the end of November 2025. Astronomers in Santa Catarina plan detailed observations of the visitor, who travels at 210 thousand kilometers per hour.
Discovered in July by the ATLAS telescope in Chile, the comet follows a hyperbolic trajectory and does not orbit the Sun. Experts from the Federal University of Santa Catarina confirm that it approaches 270 million kilometers from Earth, without risk of collision.
The object is intriguing due to its composition rich in carbon dioxide, eight times higher than that of local comets. James Webb Space Telescope observations reveal CO2-dominated coma released early during solar approach.
Discovery and trajectory of the 3I/Atlas
Astronomers identified the comet on July 1, 2025, near the constellation Sagittarius. Initially classified as an asteroid, subsequent analyzes confirmed cometary activity with a tail and coma.
The hyperbolic orbit, with an eccentricity greater than 6, indicates origins outside the Solar System. The comet reached perihelion on October 29, 203 million kilometers from the Sun, within the orbit of Mars.
Studies estimate its age at 7 billion years, possibly older than the Sun. NASA data indicate a diameter between 5.6 and 30 kilometers, with a speed of 61 km/s.
Surprising chemical composition
The nucleus releases gas and dust at greater distances than expected. Proportion of CO2 in relation to water differs from solar comets, suggesting formation in a distant stellar environment.
ESA observations detect jets directed towards the Sun, influenced by the object’s rotation. All identified compounds occur in local comets, but in altered proportions.
Analysis by the National Observatory in Brazil validates that the comet does not alter trajectories in an anomalous way.
Preparations for observation in SC
In Santa Catarina, professor Daniel Ruschel Dutra, from UFSC, coordinates morning searches. Medium-sized telescopes will capture the comet in the constellation Virgo between November 3 and 17.
Equipment such as astronomical binoculars or amateur telescopes will be essential, as the brightness reaches magnitude 11. The best period begins on November 27th, during the IAWN global campaign.
Places such as the Joinville Astronomical Observatory already schedule public sessions. Clear weather conditions favor visibility on the coast and plateau.
Global monitoring campaign
The International Asteroid Warning Network organizes exercises from November 27, 2025 toJanuary 27, 2026. Astronomers improve orbital measurements with data from global telescopes.
Space missions contribute: ESA’s Juice will observe the comet near Venus in November. NASA’s Europa Clipper crosses the object’s possible tail earlier this month.
- Participants need MPC code for observatories.
- Focus on comet astrometry, more complex due to tails.
- Online workshop opens registration until November 7th.
Passages near planets
The comet passed 30 million kilometers from Mars on October 3. Images from ESA’s Trace Gas Orbiter recorded details of the coma.
On November 3, it approaches Venus at 97 million kilometers. The Juice probe will capture data during the gravitational maneuver.
In March 2026, it will pass Jupiter at 54 million kilometers. Juno will provide additional observations before exit from the Solar System.
The trajectory allows comparisons with Oumuamua and Borisov, the two previous interstellars.
Visibility and practical tips
The comet appears before sunrise, around 4:30 am in SC. Angular elongation increases in December, improving conditions.
Astronomers recommend apps like TheSkyLive for tracking. Avoid light pollution in urban areas.
- Use equatorial-mount telescopes for scanning.
- Record images on CCD for later analysis.
- Share data with networks like IAWN for collective science.
Brightness may vary with ice sublimation, but projections indicate visibility until December.
Unique scientific opportunities
3I/Atlas offers window into interstellar chemistry. Studies compare reactions to the solar wind with local comets.
Preliminary data suggests primitive material from the early Universe. Earth-based observations complement space missions. The early detection, at 4.5 AU from the Sun, highlights advances in surveys such as ATLAS.