Astronomers Identify Interstellar Comet 3I/ATLAS, Third of Its Kind

Astronomers have successfully tracked the interstellar comet 3I/ATLAS, marking it as only the third such object ever observed, following the notable interstellar asteroid 1I/ʻOumuamua discovered in 2017 and the interstellar comet 2I/Borisov identified in 2019. This significant astronomical event was reported on July 4, 2025, as 3I/ATLAS currently travels approximately 670 million kilometers (420 million miles) from the Sun, with its closest approach expected in October 2025. During this approach, the comet will pass just inside the orbit of Mars, raising significant interest among the astronomical community.

3I/ATLAS is estimated to have a diameter of up to 20 kilometers (12 miles) and is hurtling through space at a speed of approximately 60 kilometers per second (37 miles per second) relative to the Sun. Notably, it poses no threat to Earth, as it will come no closer than 240 million kilometers (150 million miles) — a distance exceeding 1.5 times that between Earth and the Sun.

The comet is classified as an active comet. As it nears the Sun, it may undergo a process known as sublimation, where frozen gases convert directly into vapor, resulting in the release of dust and ice particles that form a glowing coma and tail. However, astronomers note that by the time the comet reaches its closest position to Earth, it will be obscured by the Sun but is expected to re-emerge by early December 2025, providing further opportunities for observation.

Professor John Tonry, an astronomer at the University of Hawai’i and a key figure in the discovery, stated, "Spotting a possible interstellar object is incredibly rare, and it’s exciting that our Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope caught it. These interstellar visitors provide an extremely interesting glimpse of things from solar systems other than our own." His statement underscores the rarity of such discoveries, as many interstellar objects traverse the inner Solar System each year; however, 3I/ATLAS is distinguished as the largest thus far.

The likelihood of an interstellar object impacting Earth is exceedingly low, with estimates suggesting a less than 1 in 10 million chance each year. Nevertheless, the ATLAS system remains vigilant in its mission to monitor the sky for any potential threats.

As astronomers utilize telescopes in locations such as Hawai’i and Chile to monitor the comet’s trajectory and behavior, they are particularly interested in its composition. An official statement from the European Space Agency (ESA) remarked, "What makes interstellar objects like 3I/ATLAS so extraordinary is their absolutely foreign nature. While every planet, moon, asteroid, comet, and lifeform that formed in our Solar System shares a common origin, a common heritage, interstellar visitors are true outsiders. They are remnants of other planetary systems, carrying with them clues about the formation of worlds far beyond our own."

The implications of studying interstellar comets like 3I/ATLAS extend beyond mere observation; they represent a tangible connection to the broader galaxy and the materials formed in environments entirely different from our own. As noted by ESA astronomers, "To visit one would be to connect humankind with the Universe on a far greater scale."

Overall, the discovery of 3I/ATLAS adds to humanity's understanding of interstellar phenomena and the dynamics of our Solar System. As scientists prepare for further observations in late 2025, the potential for new insights into the origins of our universe remains a compelling prospect, inviting both scientific inquiry and public intrigue regarding these cosmic wanderers.