Interstellar object 3I/ATLAS, also designated comet C/2025 N1 (ATLAS), did not “disappear,” but became difficult to observe for several weeks due to its geometry: after a period of visibility for ground-based telescopes, it passed too close to the Sun in the sky, and then reappeared “on the other side of the Sun,” opening a new window for observation.
As noted by NASA and the European Space Agency (ESA), 3I/ATLAS is the third confirmed interstellar object discovered in the Solar System, after Oumuamua (2017) and 2I/Borisov (2019).
The comet was first recorded on July 1, 2025, by the ATLAS system in Chile.
The closest approach of 3I/ATLAS to Earth is expected on December 19, 2025, at a distance of about 270 million km (approximately 1.8 AU). ESA separately emphasizes that at the moment of maximum approach, the object will be on the other side of the Sun relative to Earth and will not pose a threat to the planet.
The key “latest” scientific highlights are related not so much to the trajectory as to the physics of the comet. According to ESA, James Webb’s observations have already detected a set of components typical for comets in the coma, including water and carbon-containing compounds, and in late November-early December, the XRISM and XMM-Newton X-ray observatories registered diffuse X-ray glow around the nucleus – ESA calls 3I/ATLAS the first interstellar comet observed in the X-ray range.
A separate line of discussion in scientific popularization concerns “anomalies” such as non-gravitational acceleration and the unusual structure of the tail. Some studies interpret this as a normal consequence of gas and dust ejection (outgassing), which creates a small reactive thrust – these effects are characteristic of active comets and are used in models of their motion.
3I/ATLAS is an interstellar active comet discovered on July 1, 2025. According to ESA data, its perihelion (maximum approach to the Sun) occurred on October 29, 2025, and its closest approach to Earth was on December 19, 2025. NASA estimates the upper limit of the nucleus diameter to be 5.6 km, although the actual size may be significantly smaller.
