The Interstellar Enigma: Unraveling 3I/ATLAS – Facts, Observations, and Hypotheses

As of October 28, 2025, the interstellar object known as 3I/ATLAS continues to captivate astronomers, scientists, and the public alike. Discovered earlier this year, this visitor from beyond our solar system is the third confirmed interstellar comet, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. With its perihelion – the closest approach to the Sun – imminent on October 29, 2025, at approximately 11:47 Universal Time (UT), 3I/ATLAS represents a unique opportunity to study material from another star system. However, its unusual characteristics have sparked debates, ranging from it being a pristine ancient comet to speculative theories of artificial origin. This article reviews the latest data from NASA, ESA, and observatories worldwide.

Discovery and Initial Confirmation

3I/ATLAS, formally designated C/2025 N1 (ATLAS) and previously labeled A11pl3Z, was first detected on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) at its Río Hurtado station in Chile. At the time, it appeared as a faint object with an apparent magnitude of 18, located about 4.51 AU (astronomical units, or Earth-Sun distances) from the Sun and 3.50 AU from Earth, near the constellations Serpens Cauda and Sagittarius. Initial submissions to the Minor Planet Center (MPC) suggested a highly eccentric orbit, prompting its temporary listing as a potential near-Earth object. Follow-up observations from observatories like the Zwicky Transient Facility (ZTF), ATLAS itself, and NASA’s Transiting Exoplanet Survey Satellite (TESS) extended the observation arc back to May 7, 2025, confirming its hyperbolic trajectory and interstellar origin.

By July 2, 2025, marginal cometary activity – a faint coma and tail-like elongation – was detected by telescopes including the Deep Random Survey, Lowell Discovery Telescope, and Canada-France-Hawaii Telescope, solidifying its classification as a comet. The MPC officially named it 3I/ATLAS, marking it as the third interstellar object (hence “3I”). Its delayed discovery was attributed to its path through dense star fields near the Galactic Center, which obscured it in earlier surveys. Recent analyses suggest that improved detection algorithms could have spotted it earlier, highlighting advancements in asteroid tracking technology.

Orbital Trajectory and Close Approaches

3I/ATLAS travels on a hyperbolic orbit with an eccentricity of approximately 6.137 – the highest among known interstellar objects – indicating it is unbound to the Sun’s gravity and will exit the solar system after its visit. Its inbound velocity relative to the Sun is about 58 km/s, faster than ’Oumuamua (26 km/s) or Borisov (32 km/s), and it reaches a maximum speed of 68.3 km/s at perihelion. The orbit is retrograde (inclination ~175°), nearly aligned with the ecliptic plane (within 5°), and originates from the southern celestial hemisphere, contrary to expectations of more northern arrivals based on solar motion. This unusual direction may imply origins from a specific stellar population or gravitational perturbations in the galaxy.

Key milestones include:

• Closest approach to Mars: October 3, 2025, at 0.1935 AU.
• Perihelion: October 29, 2025, at 1.356 AU from the Sun (approximately 130 million miles or 210 million kilometers), on the far side from Earth.
• Closest to Venus: November 3, 2025, at 0.649 AU.
• Closest to Earth: December 19, 2025, at 1.797 AU (no collision risk, about 270 million kilometers).
• Closest to Jupiter: March 16, 2026, at 0.359 AU.

This trajectory allows for potential gravitational assists, and its alignment with planetary orbits has raised questions about whether it’s coincidental or engineered. As of today, October 28, 2025, the comet is nearing perihelion but has been spied by amateur astronomers and spacecraft like NOAA’s GOES-19 and NASA’s PUNCH mission, appearing as a faint +11th magnitude object despite expectations of solar obscuration. NASA confirms it will pass just inside the orbit of Mars during perihelion, posing no threat to Earth.

Physical Characteristics and Composition

Estimates of the nucleus size vary, with Hubble Space Telescope data suggesting an upper limit of 5.6 km and a lower limit of 0.44 km, though early brightness implied up to 20 km (later revised due to coma contribution). Some descriptions liken its size to that of Manhattan, emphasizing its substantial scale for an interstellar visitor. The absolute magnitude is greater than 15.4, and its rotation period is around 16-17 hours, with decreasing brightness variations as the coma grows.

The comet is reddish (B-V = 0.98), suggesting large dust grains and organic tholins, similar to D-type asteroids and other interstellar comets. Its coma is elliptical, up to 26,400 km across, with a CO2 gas extension of at least 348,000 km. Dust ejection rates are modest (~6-60 kg/s), and it shows a Sun-facing plume from uneven sublimation. Recent images from October 23, 2025, reveal a giant ‘jet’ shooting toward the Sun, likely a result of intensified volatile sublimation as it approaches perihelion. Composition highlights include:

• High CO2-to-H2O ratio (8:1), one of the highest known.
• Water vapor (6.6 kg/s), CO (14 kg/s), cyanide (CN), and atomic nickel (without iron, unusual).
• No C2, C3, NH2, or O I detected, indicating carbon-chain depletion.

Activity began at ~6.4 AU, driven by volatiles like CO2 and CO rather than water, and it has developed an anti-solar tail up to 100,000 km long by mid-September. This early activity suggests a highly volatile-rich surface, possibly preserved from its long interstellar journey.

Observations and Anomalies

Observations span ground-based telescopes (e.g., VLT, Gemini South, Nordic Optical Telescope) and space assets like Hubble, JWST, SPHEREx, ExoMars, and Mars Express. JWST’s August 6, 2025, data revealed extended CO2 and water emissions, while SPHEREx detected strong water ice and CO2 coma. Between October 1 and 7, 2025, ESA’s ExoMars Trace Gas Orbiter (TGO) and Mars Express spacecraft captured detailed images and data during the comet’s close approach to Mars, providing insights into its coma and potential atmospheric interactions. NASA’s Perseverance rover also spotted a faint glow from the comet during this period. Recent amateur images show a green hue from cyanogen gas and a condensed coma offset sunward.

Anomalies include:

• High eccentricity and velocity.
• Unusual CO2 dominance and lack of iron with nickel.
• Sun-facing plume and asymmetric CN coma, now including the observed giant jet.
• High negative polarization, like trans-Neptunian objects.
• Activity onset far from the Sun, without outbursts or fragmentation so far.

Recent reports suggest it has “slowed down” or appeared visible away from expected positions, but these may stem from observational challenges or misinterpretations amid hype. The giant jet, extending significantly toward the Sun, adds to the intrigue, potentially indicating internal structural changes or uneven heating.

Hypotheses: Natural Comet or Something More?

Natural Origin

The consensus among most astronomers is that 3I/ATLAS is a natural interstellar comet, likely ejected from a distant star system’s protoplanetary disk billions of years ago. Its age could exceed the solar system’s 4.6 billion years by up to 14 billion, making it potentially the oldest comet observed. Formed beyond the CO2 frost line around a low-metallicity star, its composition reflects primordial conditions, with high CO2 from radiation exposure or an insulating crust. Ejection likely occurred via gravitational interactions with a giant planet. This view is supported by JWST and SPHEREx data showing typical cometary volatiles. Its study could improve asteroid detection and planetary defense, as campaigns are now underway to refine orbit predictions for future interstellar objects, potentially aiding in averting Earth impacts from similar visitors.

Artificial or Technological Hypotheses

Harvard’s Avi Loeb posits that anomalies – like its large implied size, ecliptic alignment, hidden perihelion, and nickel-rich composition – suggest it could be an extraterrestrial probe or “Trojan Horse.” He estimates a 40% chance it is alien technology, based on its unusual trajectory and composition. Loeb invokes the “Dark Forest” hypothesis from Liu Cixin’s Three-Body Problem, where interstellar visitors might be hostile, hiding intentions. Perihelion serves as an “acid test”: a natural comet might fragment under solar heat, while an artificial one could maneuver, emit signals, or deploy probes. Loeb suggests it targets Mars for reconnaissance, possibly linked to ancient nuclear events there.

Current Status and Future Prospects

As of October 28, 2025, 3I/ATLAS is at approximately +11th magnitude, visible to amateurs despite nearing solar conjunction. No major disruptions like fragmentation have been reported, though solar heating could intensify activity tomorrow during its precise perihelion passage. Upcoming observations include Hubble’s ultraviolet spectroscopy in November and JWST in December to monitor outbound changes. ESA’s JUICE may capture data near Venus, and NASA’s Juno near Jupiter in 2026. Spacecraft flybys are infeasible now, but future missions could target similar objects. The comet’s passage is also being used to test new planetary defense strategies, emphasizing its role in preparing for potential hazardous interstellar intruders.

Whether a cosmic relic or something engineered, 3I/ATLAS challenges our understanding of the universe. As perihelion unfolds, the “acid test” may resolve lingering mysteries – or ignite new ones.

References

• Spying Interstellar Comet 3I/ATLAS Near Perihelion by David Dickinson
• Interstellar comet 3I/ATLAS could help protect Earth from dangerous asteroids. Here’s how by Elizabeth Howell
• How Manhattan-size comet 31/ATLAS could help save the world by Ben Cost
• ESA’s ExoMars and Mars Express observe comet 3I/ATLAS by ESA Staff
• Comet 3I/ATLAS by NASA Science Team
• New images of interstellar object 3I/ATLAS show giant ‘jet’ shooting toward the sun by Brandon Specktor
• 3I/Atlas on its way to Sun: Should we be worried as Harvard astronomer says 40% chance interstellar comet is alien technology? by Global Desk
• An interstellar comet will reach its closest point to the sun this week. Don’t worry, it won’t even come close to Earth by Yahoo News Staff
• Interstellar object 3I/ATLAS is about to get very active – Space photo of the week by Brandon Specktor
• 3I/ATLAS: An Interstellar Enigma – Natural Comet or Engineered Probe? by Spectroscopy Online Staff
• Is the Interstellar Object 3I/ATLAS Alien Technology? by Adam Hibberd, Adam Crowl, and Abraham Loeb