Comet 3I/ATLAS, the third interstellar object confirmed to cross Sistema Solar, will reach its closest approach to Terra on December 19, 2025. At Nesse moment, the celestial body will be 270 million kilometers from the planet, equivalent to 1.8 astronomical units. The discovery occurred in July 2025 by the ATLAS telescope on Chile, and the event occurs without any risk of collision.
Astronomers from NASA and Agência Espacial Europeia (ESA) have intensified observations since then. The comet travels at around 210 thousand kilometers per hour and reached perihelion, the closest point to Sol, on October 29, 203 million kilometers from the star.
The hyperbolic trajectory confirms its origin external to Sistema Solar, possibly from the thick disk of Via Láctea. Especialistas estimate that the comet’s nucleus is between 440 meters and 5.6 kilometers in diameter.
Discovery and initial trajectory
The ATLAS telescope detected 3I/ATLAS on July 1, 2025, initially as a magnitude 17 object, visible only with advanced equipment. Preliminary Observações of Telescópio Espacial Hubble on July 21 revealed a faint coma and a broad tail pointing east.
In August, studies indicated cometary activity since May 2025, when the object was 6.4 astronomical units from Sol. The composition includes rock, ice and dust, with reddish tones in the coma due to dust particles.
The initial speed of 61 km/s increased to 68 km/s at perihelion. The comet passed within 28 million kilometers of Marte on October 3, allowing observations by probes such as Mars Express and ExoMars Trace Gas Orbiter.
Recent images of Hubble
Hubble captured the second image of the comet on November 30, 2025, 286 million kilometers from Terra. The Wide Field Camera 3 instrument recorded the nucleus and coma with greater brightness than in July, showing sublimation of gases.
Image processing was carried out by J. DePasquale, from STScI, highlighting the water drop shape of the object. Observadores as D. Jewitt, from UCLA, and M.-T. Hui, from Observatório Astronômico from Xangai, confirmed the elongation of 3 seconds of arc in the tail.
These captures occur as the comet heads to the opposite side of Sol in relation to Terra. Visibility for ground-based telescopes persists until January 2026, with the International Asteroid Warning Network campaign.
The brightness reached magnitude 7-8 in October, seven times greater than expected for similar comets.
Observations from probe Juice
ESA’s Jupiter Icy Moons Explorer probe recorded the comet on November 2, 2025, 66 million kilometers away. The NavCam camera and five scientific instruments captured the coma, plasma tail and dust tail.
Launched in April 2023, Juice uses this data to calibrate equipment before reaching Júpiter in 2031. Full data transmission will occur between February 18 and 20, 2026.
The images show jets spewing from the surface, suggesting cryovolcanism, or active ice volcanoes. Essa activity releases about 40 kilograms of methanol per second, above the average for local comets.
Researchers noticed that the color of the coma evolved to redder tones in July, indicating changes in the surface composition.
The mission contributes to understanding Jovian moons with potential subsurface oceans.
Chemical composition details
Spectroscopic analysis reveals high concentration of CO2 and methanol in 3I/ATLAS. Esses compounds, essential for organic chemical processes, were detected in gaseous emissions during perihelion.
Studies of Toni Santana-Ros indicate that the coma became redder throughout July, reflecting dust and surface evolution. Não there is evidence of brightness outbreaks until August 2025.
- The core contains ice that sublimates under solar heat, forming a coma of gas and dust.
- The plasma tail arises from ions carried by the solar wind.
- Dust particles create the secondary tail, visible in images from Juice.
- Released methanol suggests origins in cold interstellar environments.
These elements reinforce the comet’s value as a cosmic time capsule.
Contributions from other space missions
NASA’s PUNCH mission captured 3I/ATLAS incidentally between September 28 and October 10, 2025, while monitoring another comet. Imagens show the object moving against the stellar background.
The STEREO probe recorded the comet during solar activity studies, confirming its position in October. Observações of James Webb Space Telescope complement data from Hubble.
In Marte, ESA rovers and orbiters collected spectra on October 3, analyzing short-range emissions. IAWN’s global campaign includes telescopes at Chile, Arizona and Havaí.
These multi-part contributions ensure comprehensive data before Sistema Solar outputs.
The comet will pass within 50 million kilometers of Júpiter on March 16, 2026.
Unusual activity phenomena
Recent studies point to brightness pulses every 16 hours in 3I/ATLAS, detected by Catalan astronomers. Esse “pulsing” suggests irregular rotations or periodic ejections of material.
Cryovolcanism explains observed ice jets, releasing gases in bursts. The activity began early, at 6.4 AU from Sol, challenging traditional comet models.
Astronomer Qicheng Zhang, from Observatório Lowell, predicts visible reappearance in December for the northern hemisphere. Telescópios with an opening greater than 30 centimeters will allow amateur detection.
- 16 hour pulses indicate possible elongated nucleus.
- Jets from cryovolcanoes cover parts of the surface.
- Blue glow compared to Sol suggests fine dust.
- Activity persists without explosive outbreaks.
These traits distinguish 3I/ATLAS from previous visitors like 2I/Borisov.
Perspectives for future observation
The comet will remain visible until September 2026 for space missions, but ground-based telescopes lose the signal in January. Simuladores online, like NASA’s Eyes on the Solar System, track position in real time.
The origin in the center of Via Láctea implies an age greater than 7 billion years, older than Sistema Solar. Estudos of Avi Loeb explore hypotheses about composition, but confirm natural nature.
International Asteroid Warning Network coordinates astrometry until January 27, 2026. Entusiastas can observe on the eastern horizon with clear skies using astronomy apps.
Data from Juice in February 2026 will provide final analysis of oceans on moons of Júpiter, indirectly benefiting from the observations.
Expected scientific advances
3I/ATLAS offers insights into the formation of distant star systems. Sua mass, exceeding 33 billion tons, and composition rich in water question models of interstellar ejection.
Observations confirm no threat, with a minimum distance of 269 million kilometers on December 19 at 06:01 UTC. The exit speed will be identical to the entry speed, around 61 km/s.
Astronomers predict that the comet will reach magnitude 12 in November, making tracking easier. Colaborações between NASA, ESA and CNSA accelerate publications in journals such as Nature.
The event reinforces the early detection of interstellar objects via surveys such as ATLAS.