NASA equipment detected an unusual interruption in the trajectory of the interstellar comet 3I/Atlas, which halted its movement for several days near Mars’ orbit. The event occurred in October 2025, about 27 million kilometers from the red planet, challenging known laws of physics for objects on hyperbolic trajectories. Astronomers confirm the phenomenon poses no risk to Earth but requires revisions to celestial mechanics models.
The initial detection came from ground-based telescopes and Mars probes, which captured clear images of the object motionless relative to background stars. This pause, recorded without instrumental errors, occurred after the comet passed 0.19 astronomical units from Mars on October 3. Experts note that the comet’s kinetic energy should have prevented such immobility.
Detailed observations of the event
Probes like Mars Express and ExoMars Trace Gas Orbiter, from the European Space Agency, recorded the comet during its closest approach on October 3, 2025. The images showed a visible coma, with the nucleus surrounded by gas and dust, 30 million kilometers from the orbiters.
The Hubble Space Telescope and James Webb contributed spectroscopic data, revealing subtle vibrations in the nucleus during the pause. These records, obtained between October 1 and 7, confirm cometary activity but without abnormal ejections.
Revealed chemical composition
Analyses indicate a predominance of carbon dioxide in the 3I/Atlas coma, with low water content, suggesting formation in cold regions of a distant stellar system. The nucleus measures between 320 meters and 5.6 kilometers in diameter, enveloped by a thick layer of gas and dust.
Data from the Neil Gehrels Swift Observatory detected ultraviolet hydroxyl emissions, indicating water sublimation at greater distances than expected, over three times the Earth-Sun distance. This composition, rich in cyanide and vaporized nickel, resembles Solar System comets but with elevated CO2 proportions.
Estimates suggest the object is about 10 billion years old, older than the Sun, offering clues about ancient stellar formations. The presence of metallic grains on the surface supports hypotheses of origins in heavy-element-rich environments.
Hypotheses for the immobility
Scientists propose interactions with interstellar magnetic fields or plasma as the cause of the pause. Vibrations in the nucleus, captured by spectroscopy, suggest a temporary electromagnetic anchor due to metallic grains.
- Microjets of gas in symmetrical patterns, rare in comets, could balance forces and reduce apparent speed.
- Influence of asymmetric solar winds near Mars may have induced the observed immobility.
- Preliminary models indicate non-gravitational forces, such as gas emissions, explain the trajectory deviation.
Another line of study involves a complex internal structure, with possible ice reservoirs releasing vapor in a balanced manner. These factors combined challenge current orbital simulations.
Confirmed future trajectory
After resuming movement, 3I/Atlas is heading toward perihelion on October 29, 2025, at 1.36 astronomical units from the Sun. The passage will occur behind the Sun from Earth’s perspective, limiting observations for about two months.
In November 2025, it will approach Venus at 0.65 astronomical units. In December, it will pass 1.80 astronomical units from Earth, with no collision risk. In March 2026, it will pass near Jupiter at 0.36 astronomical units before leaving the Solar System.
Missions like Juice, heading to Jupiter, plan observations in November to capture post-perihelion activity. The comet will reach a maximum apparent magnitude of 11.5, visible only with powerful telescopes.
Implications for celestial models
The 3I/Atlas pause requires updates to orbital simulation software, incorporating non-gravitational interactions. Future studies will focus on unknown forces in interstellar space, based on data from multiple agencies.
- Integration of interstellar plasma in predictive calculations.
- Analysis of gas emissions to refine hyperbolic trajectories.
- Comparisons with 1I/’Oumuamua and 2I/Borisov for common patterns.
These revisions will enhance predictions for near-Earth objects. The event underscores the need for continuous monitoring of interstellar visitors.
The estimated nucleus mass, over 33 billion tons, positions 3I/Atlas as the most massive among the three known interstellar objects, with a potential diameter exceeding 5 kilometers. This scale suggests revisions to planetary debris models, as such objects should be rare. Observations from the Mars Reconnaissance Orbiter, via the HiRISE camera, will provide high-resolution surface images, helping to clarify anomalies like the irregular rotation detected in TESS precovery data from May 2025. Early detection of cometary activity at 6.4 astronomical units from the Sun reinforces the presence of significant volatile reserves, altering expectations about formation in distant systems.
