It has been hurtling through the interstellar medium of the Milky Way galaxy for billions of years, Darryl Z. Seligman, assistant professor of physics and astronomy at Michigan State University, said. This long journey passed a major milestone on December 19, 2025, when comet 3I/ATLAS, which is identical to only the third interstellar object ever discovered, passed by at its closest approach to the planet, 168 million miles (270 million kilometers) above us.
The Asteroid Terrestrial-impact Last Alert System telescope that was located in Chile found the 3I/ATLAS comet on the 1st of July, 2025, and is thus the third confirmed visitor that originated from outside the solar system, after the 1st visitor, 1I/‘Oumuamua, was spotted in 2017, followed by the 2nd visitor, 2I/Borisov, that was discovered in 2019. The type of this visitor’s orbit is classified under that of a hyperbola, with this visitor observed to be moving with a speed of above 144,000 mph or 231,900 km/h, meaning that this visitor is not bound to the sun gravitationally.
The perceived orbit of this visitor that originated from outside the solar system could be that of the thin disk that is found within our Milky Way galaxy, having been kicked-out from the primordial disk of planetesimals millions of years back, that is between 7 billion years.
The closeness of the comet made it possible for scientists to analyze the composition of another star system. The comet showed greenish brightness in the last week of November because of the gas diatomic carbon (C₂) vaporized by the warming radiation of sunlight. Some gas and dust jets were found on the surface of the comet. The wobbling jet was calculated using the Two-Meter Twin Telescope installed at the Teide Observatory on the Canary Island of Tenerife, indicating that the rotational period of this comet is between 14 and 17 hours. The X-ray halo with a diameter of 250,000 miles (400,000 kilometers) was revealed using XMM-Newton and also XRISM observatory.
“We’re excited that this opportunity to view another target on the way to Jupiter was completely unexpected,” said Kurt Retherford, the principal investigator on the Europa-UVS mission from the Southwest Research Institute. This information on the comet, utilizing technology that will be applied to analyze the ocean on the Moon in the coming times ahead, will come into good use in identifying the chemicals composed in the comet based on its oxygen and hydrogen emission in the ultra-violet range. The ultraviolet image of comet 3I/ATLAS was recorded by the Jupiter moon-bound spacecraft Europa Clipper on the 6th of November. The image was taken from 102 million miles (164 million kilometers); this is approximately 164 million kilometers.
The double-tailed coma and feature of comet 3I/ATLAS were detected through the Ultraviolet Spectrograph (UVS). The oxygen and hydrogen spectral lines were detected. The brightness level of this comet was magnitude 11. The comet’s brightness level made it invisible to the naked eye to people on our world’s surface. The application of a medium to large-sized telescope Aperture capability of 12 inches would assist in pointing out the comet as the green streak close to the star Regulus in the constellations of Leo. The comet applications such as Seestar S50, Unistellar eVscope 2 would assist in observing comet 3I/ATLAS through its applications alone.
The applications of Stellarium, SkySafari Pro would assist in pointing out the comet through the application of its coordinates. The applications of NASA’s Eyes on the Solar System would assist in viewing the comet’s orbit through three dimensions. The path that comet 3I/ATLAS will follow when exiting our heliosphere in early 2026 when moving to Intergalactic Space on route to Jupiter will assist. The Virtual Telescope Project in Manciano, Italy, advertised that there will be a FREE live webcast of the event on their YouTube channel and that it would be live from 11 p.m. EST on the 18th. The live webcast of the other events that were not in the United States has had an event delay. The weather conditions are responsible for this delay.
Despite that, the re-broadcasting of live webcast shall remain as the remembered occurrence of the actual encounter itself. The encounter in the case of the 3I/ATLAS spacecraft flyby highlights the significance of the quick detection and tracking of Interstellar Objects. Future surveys like that of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) Survey are expected to reveal dozens of Interstellar Objects annually. Until that time, the optical, UV, and X-ray observation phenomena introduced in this passage will premise the improvement of contemporary understanding on the physics of comets as the Interstellar World waits to be dispersed within the entire galaxy.
