Comet – Photo: Nazarii Neshcherenskyi/istock
NASA equipment detected that the interstellar comet 3I/Atlas halted its movement for days near Mars’ orbit, approximately 27 million kilometers from the planet, in October 2025. The phenomenon occurred during the passage of the third confirmed interstellar object in the Solar System, first identified in July 2025 by the Atlas telescope in Chile. Astronomers state that the pause defies known laws of physics, as hyperbolic trajectories like that of 3I/Atlas should not allow sudden stops due to the involved kinetic energy.
The U.S. space agency confirmed no instrumental errors in the records, reinforcing the event’s validity. The comet, traveling at an average speed of 210,000 km/h, remained nearly motionless relative to background stars, necessitating updates to orbital simulation software.
- Telescopic observations captured clear images of the comet’s nucleus and coma.
- Martian probes recorded gas emissions during the close approach.
- The composition shows a high concentration of carbon dioxide, unusual for local comets.
Initial detection and confirmation
The 3I/Atlas comet was first spotted on July 1, 2025, with a trajectory indicating an origin outside the Solar System. On July 2, observatories in Chile, Arizona, and Hawaii confirmed a marginal coma and a three-arcsecond tail-like elongation, classifying it as a comet. The 3I designation marks it as the third interstellar visitor, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019.
The pause occurred near its perihelion, projected for October 29, 2025, at 203 million kilometers from the Sun, between Earth and Mars’ orbits. Telescopes like Hubble recorded the object at 570 million kilometers in July, revealing a teardrop-shaped icy nucleus enveloped in dust.
Spectroscopic data showed subtle vibrations in the nucleus during the standstill, suggesting interactions with interstellar plasma or magnetic fields. NASA ruled out measurement errors after multiple analyses.
Chemical composition and origins
Analysis of the 3I/Atlas coma revealed a predominance of carbon dioxide with low water content, indicating formation in cold regions of a distant stellar system. The nucleus, measuring between 320 meters and 5.6 kilometers in diameter, is covered by a thick gas and dust layer, with an estimated age of 10 billion years, older than the Sun.
Metallic grains on the surface support theories of temporary electromagnetic anchoring. Symmetric microjets of gas, rare in comets, suggest a complex internal structure, with cyanide and nickel vapor emissions similar to Solar System comets.
James Webb Space Telescope data from August 2025 confirmed a CO2-to-water ratio of 1.4, consistent with local objects, but excess CO2 suggests limited water ice sublimation. These chemical traits provide insights into ancient stellar system formation.
Theories behind the pause
Scientists propose solar magnetic field interactions as a cause, creating a temporary anchor counteracting the comet’s velocity. ESA’s Mars Express and ExoMars probes, capturing data from October 1 to 7, recorded the object at 30 million kilometers during its closest Mars approach on October 3.
Another hypothesis involves symmetric gas ejections neutralizing momentum, detected by Martian orbiter spectrometers. The lack of a prominent tail in early images supports low activity before solar heating.
Very Large Telescope observations revealed high nickel concentrations without corresponding iron emissions, diverging from typical cometary patterns. These findings require incorporating non-gravitational forces into predictive models.
The proximity to Mars enabled detailed records, making the event a natural laboratory for studying gas emissions and brightness.
Future trajectory and monitoring
After resuming movement, 3I/Atlas heads toward perihelion on October 29, 2025, passing Venus at 97 million kilometers on November 3 and Jupiter at 54 million kilometers on March 16, 2026. A solar conjunction on October 21 will obscure it from Earth’s view until December, but ESA’s Juice mission will monitor it in November.
NASA’s Perseverance, Curiosity, and Mars Reconnaissance Orbiter collected data during the Mars flyby, focusing on extreme negative polarization and ecliptic alignment. The comet poses no risk to Earth, maintaining a minimum distance of 269 million kilometers on December 19, 2025.
Estimated at 33 billion tons, three to five orders of magnitude larger than prior interstellar objects, it shows measurable non-gravitational acceleration. Orbital simulations will integrate these interactions for accurate predictions.
Significance for interstellar research
The event underscores the diversity of interstellar visitors, with 3I/Atlas displaying eight documented anomalies, including an anti-solar tail and nickel enrichment. Observations from the Spitzer Space Telescope and TESS satellite indicate cometary activity since May 2025, at 6.4 astronomical units from the Sun.
The Hera probe is expected to traverse the ionic tail between October 25 and November 1, measuring magnetic draping. An estimated age of 7.6 to 14 billion years suggests an origin in the Milky Way’s thick disk, with low heavy element levels.
These findings enhance understanding of planetary formation in distant stellar environments, with no evidence of threats or artificial origins.
