Interstellar comet 3I/ATLAS, the third confirmed visitor from beyond our solar system, was tracked by more than 20 spacecraft and ground telescopes after its discovery by the ATLAS survey on July 1. It reached speeds up to about 153,000 mph, made perihelion on Oct. 30 at roughly 130 million miles from the sun, and will pass about 168 million miles from Earth on Dec. 19. Claims that the object is artificial, promoted by Avi Loeb, have been widely rejected by other scientists, who say observed behavior is consistent with natural cometary processes.
Interstellar Comet 3I/ATLAS Sweeps Through the Solar System — Tracked by 20+ Telescopes
Interstellar comet 3I/ATLAS, the third confirmed visitor from beyond our solar system, was tracked by more than 20 spacecraft and ground telescopes after its discovery by the ATLAS survey on July 1. It reached speeds up to about 153,000 mph, made perihelion on Oct. 30 at roughly 130 million miles from the sun, and will pass about 168 million miles from Earth on Dec. 19. Claims that the object is artificial, promoted by Avi Loeb, have been widely rejected by other scientists, who say observed behavior is consistent with natural cometary processes.
04:59 AM, 11/21/2025Science
PUNCH spacecraft imagery captured interstellar comet 3I/ATLAS between Sept. 28 and Oct. 10, 2025, when the object lay roughly 231 million to 235 million miles from Earth. Each daily frame is a stacked image composed of multiple observations; the comet’s motion causes background stars to streak, and the bright object that appears near the comet in some frames is Mars.
Discovered on July 1 by the ATLAS survey telescope at Rio Hurtado, Chile, 3I/ATLAS raced through the inner solar system during a period that coincided with a 43-day U.S. federal shutdown. ATLAS (Asteroid Terrestrial-impact Last Alert System) is part of a four-site network that continuously scans the sky for incoming objects. Orbital calculations show 3I/ATLAS poses no risk to Earth: its closest predicted approach is about 168 million miles on Dec. 19.
The comet reached speeds up to roughly 153,000 miles per hour as it passed near Mars, and it made perihelion on Oct. 30 at about 130 million miles from the sun. Size estimates place its diameter between roughly 1,400 feet and 3.5 miles — larger than Manhattan at its widest point (about 2.3 miles) but far smaller than the impactor believed to have ended the age of dinosaurs (perhaps up to nine miles across).
Unprecedented Observational Coverage
The attention this visitor drew is a testament to global observational reach. More than 20 spacecraft and ground telescopes trained instruments on 3I/ATLAS, producing a rich dataset for study. Imaging came from NASA assets including the James Webb Space Telescope and Hubble, the Lucy and Psyche missions (en route to asteroids), Mars-orbiting platforms such as the Mars Reconnaissance Orbiter and MAVEN, ESA’s ExoMars Trace Gas Orbiter, the Perseverance rover, and several solar-observing probes. Two Jupiter-bound missions — NASA’s Europa Clipper and ESA’s Jupiter Icy Moons Explorer (JUICE) — plan to observe the object again as it departs the inner solar system.
Natural Body, Not a Spacecraft
Public curiosity spawned speculation that 3I/ATLAS might be artificial. Harvard astrophysicist Avi Loeb — who has argued that the 2017 interstellar object ʻOumuamua could be technological — and co-authors posted a paper on arXiv suggesting the astrodynamics of 3I/ATLAS warrant similar scrutiny, even proposing it could be "technological, and possibly hostile."
“[I]n this paper we present additional analysis into the astrodynamics of 3I/ATLAS, and hypothesize that this object could be technological, and possibly hostile.” — Loeb et al., arXiv preprint
Most researchers disagree. NASA scientists, including Nicola Fox, have reported that the body behaves like a comet and that no technosignatures have been detected. University of Oxford astrophysicist Chris Lintott dismissed speculative claims as unfounded. Natural cometary processes — fragmentation, surface renewal exposing reflective ice, and outgassing-driven accelerations (including from light gases such as molecular hydrogen) — offer credible explanations for unusual observations.
Where It Goes From Here
3I/ATLAS will make its nearest approach to Earth on Dec. 19, then continue outward through the outer solar system and return to interstellar space, where it likely originated billions of years ago. Amateur astronomers with modest telescopes may spot it in the pre-dawn sky for a limited period, but for most people the visitor will remain a brief, intriguing event in the night sky.