The comet 3I/Atlas reached its perihelion on Thursday, October 30, 2025, at 1.36 astronomical units from the Sun, equivalent to about 203 million kilometers. This point marks the closest approach to the central star of the Solar System for the third confirmed interstellar object by science. Astronomers from NASA and the European Space Agency coordinate efforts to track the visitor, which follows a hyperbolic orbit and travels at over 210 thousand kilometers per hour.
Detection occurred on July 1, 2025, by the ATLAS telescope in Chile, and generated initial debates about its nature. Preliminary observations confirmed cometary activity, with release of gases and dust, differentiating it from asteroids. The object, originating from another stellar system, provides data on distant chemical compositions.
During perihelion, the comet was hidden by solar brightness, interrupting terrestrial views. From October 31, space probes resume monitoring, with expectation of Earth visibility from November 3, before dawn, at 9 degrees above the eastern horizon.
Chemical composition reveals distant origins
Spectral analyses from the James Webb Space Telescope detected a coma rich in carbon dioxide, with a proportion eight times greater than water, an unprecedented pattern in local comets. This concentration suggests formation in a cold environment rich in organic compounds, possibly more than seven billion years ago.
The nucleus measures between 320 meters and 5.6 kilometers in diameter, with hydroxyl emission observed at distances greater than three astronomical units from the Sun. Comparative studies with Oumuamua and 2I/Borisov highlight variations in elements such as nickel and cyanide, expanding understanding of stellar processes.
- Carbon dioxide dominates dust ejection, indicating unique formation conditions.
- Relative absence of water points to origins in a dense protoplanetary disk.
- Traces of carbon monoxide and cyanide differentiate the comet from solar objects.
Space observations capture crucial details
The ESA’s ExoMars Trace Gas Orbiter recorded images on October 3, 2025, near Mars, at 30 million kilometers away. The captures show a diffuse point with an elongated coma, without a visible tail at that phase.
NASA’s SPHEREx mission measured the release of two million tons of material between August and September. These data, combined with spectrometers, reveal accelerated sublimation processes due to solar heat.
Ground-based telescopes such as Keck in Hawaii confirmed a rare anticoma, an optical illusion caused by orbital perspective. This elongated structure points toward the Sun, resulting from dust blown by solar wind.
The GOES-19 satellite captured the comet on October 18 via coronagraph, obscured by stellar brightness. Future observations from the Juice probe in November will prioritize the tail in high post-perihelion activity.
Hyperbolic trajectory defines unique journey
The comet crossed Mars’ orbit on October 3, 2025, maintaining a safe distance. Its speed of 68 kilometers per second prevents gravitational capture by the Sun, confirming permanent exit from the Solar System.
On December 19, 2025, the closest approach to Earth will occur, at 1.8 astronomical units, or 269 million kilometers. This configuration allows prolonged observations until March 2026, with estimated brightness in magnitude 12 to 14.
The retrograde orbit, with 175-degree inclination, suggests ejection from another stellar system millions of years ago. Computational models indicate age between 7.6 billion and 14 billion years, older than the Solar System.
Terrestrial visibility requires specialized equipment
From November 3, the comet appears in the morning sky, in the constellation Virgo, near the star Spica. Telescopes with a minimum aperture of 20 centimeters facilitate detection in dark skies, away from light pollution.
The faint brightness requires astronomical binoculars or powerful equipment, without naked-eye visibility. Ideal conditions include clear dawns, with increasing solar elongation for better contrast.
Amateur observers participate in campaigns by the International Asteroid Warning Network, training astrometric measurements. Registrations for workshops occur until November 7, requiring MPC code for observatories.
Encounter with probe opens scientific window
NASA’s Europa Clipper probe may cross debris from the comet’s tail in the coming days, en route to Jupiter. This crossing represents a chance for in-situ analysis of interstellar particles, differentiating them from solar wind by composition.
Probe instruments detect heavy elements such as water and carbon dioxide, absent in solar plasma dominated by hydrogen. Success depends on solar wind direction, with Tailcatcher software predicting trajectories.
Solar Orbiter observations in 2020 validated the method by confirming crossing with another comet. Data from 3I/Atlas will contribute to models of cometary dynamics and planetary formation.
Speculative theories circulate on networks
Astronomers debunk hypotheses of artificial origin, based on initial size estimated at 12 kilometers, adjusted after coma detection. Dust jets toward the Sun result from nuclear rotation and ice distribution, a common phenomenon.
The IAWN uses the comet in annual observation exercises, without activating planetary defense protocols. Minimum distance to Earth excludes collision risks, with trajectory monitored for decades.
Forum publications associate the object with artifacts, but orbital analyses confirm natural behavior. Experts emphasize that chemical variations derive from interstellar environments, not external intentions.
