Discovered on July 1, 2025, 3I/ATLAS is the third confirmed interstellar object we have observed. It has a hyperbolic orbit, is not gravitationally bound to the Sun and will pass through our solar system. The first two interstellar objects that Earth has observed were 1I/’Oumuamua in 2017 and 2I/Borisov in 2019.

Why have we included it as an Enigma? This object has captured the nation's attention due to its fascinating and highly anomalous characteristics:

• Orbit : 3I/ATLAS follows a highly hyperbolic trajectory with an eccentricity of about 6.1 — far higher than typical long-period comets, which usually have eccentricities only slightly above 1.
• Speed : Inbound excess velocity ~58 km/s, nearly twice the speed of prior interstellar objects.
• Highly active : Significant gas and dust outgassing was detected when 3I/ATLAS was still far from the Sun, where many Solar-System comets are only just waking up.
• Size : Current estimates suggest it has a nucleus several miles across. Early Hubble observations placed an upper limit of roughly 3–4 miles. Recent Rubin Observatory measurements suggest it could be closer to ~7 miles in diameter. If the Rubin estimate holds, 3I/ATLAS would be roughly 10–25× larger than 2I/Borisov by diameter, and around 20–30× longer than ʻOumuamua.
• Surface : Polarimetric observations from several telescopes show that it exhibits unusually strong negative polarization, placing it among the more extreme light-scattering behaviors measured in any comet.
• Gas plume : Its gas coma is unusually CO₂-rich, with a measured CO₂/H₂O ratio of about 8:1—much higher than in typical comets, which are usually water-dominated.
• Sunward jets : Observations confirm that 3I/ATLAS displays both sunward and anti-solar jet structures. Their detailed physical interpretation — including their size, required surface area, or long-range orientation — is still uncertain and not yet established
• Coma : CO₂/H₂O ratio of 8:1 is the highest ever measured in a comet
• Nickel : Spectroscopic observations detected strong atomic nickel emission from 3I/ATLAS even when it was still far from the Sun — at distances where temperatures are typically too low to release metals in comets. In Solar-System comets, nickel and iron vapor usually appear in similar amounts, but in 3I/ATLAS, nickel was detected without a comparable detection of iron. This unusual Ni/Fe ratio is not yet understood and remains one of the most puzzling characteristics.

Harvard astrophysicist Avi Loeb argues in this paper that these anomalies suggest the object could be advanced extraterrestrial technology. Most scientists believe 3I/ATLAS is a highly unusual comet like nothing we have ever seen before. They suggest that its strange behavior and chemistry are because it's an ancient comet, that it originates from a metal-poor star parent system, and that perhaps it was bombarded with radiation.

As of December 2025, 3I/ATLAS remains an unidentified, anomalous (interstellar) mystery. Below you’ll find a timeline of key scientific discoveries and imagery from observers around the world. It reached its closest approach to the Sun (perihelion) on October 30, 2025, and its closest approach to Earth will be December 19, 2025 (~269 million km away). For skywatchers, 3I/ATLAS won’t be visible to the naked eye, but it can be observed and recorded with medium to large telescopes under dark and clear skies. If you capture any quality media of the object and want to be included in this Collection, send your media to [email protected] – include the date of the observation, your equipment info, the name of the observer to be credited. Happy sky and spacewatching.