Interstellar Comet 3I/Atlas: Fastest and Largest Discovery Yet

Astronomers have made a significant discovery with the confirmation of the interstellar comet 3I/Atlas, noted for its exceptional size and speed. Officially recognized by the International Astronomical Union’s Minor Planet Center (MPC) this week, 3I/Atlas is traveling on a hyperbolic trajectory through the solar system, which will ultimately lead it back to interstellar space after a brief visit. This remarkable comet, which is estimated to have a nucleus spanning between six and twelve miles (10 to 20 kilometers), is racing through space at a staggering velocity of over 60 kilometers per second (approximately 135,000 miles per hour). Such speed indicates that it cannot be captured by the Sun’s gravitational pull, confirming its extrasolar origin.

The announcement of this discovery was made on July 9, 2025, following initial observations by a telescope in Chile as part of the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) survey. According to Peter Veres, an astronomer at the MPC who played a pivotal role in confirming the comet's status, early images revealed a characteristic hazy glow typical of comets, suggesting that gas and dust are being released as sunlight warms its surface. “It looks kind of fuzzy,” Veres remarked, indicating the presence of a short tail as well.

Richard Moissl, head of planetary defense at the European Space Agency, has reassured that 3I/Atlas poses no threat to Earth or Mars during its passage. “It will fly deep through the solar system, passing just inside the orbit of Mars,” he stated, noting that its closest approach to the Sun, or perihelion, is scheduled for October 29, 2025. After this point, the comet is expected to fade as it speeds away into the depths of space.

Interstellar comets, such as 3I/Atlas, differ significantly from those bound to the solar system. Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, explained the formation process of these icy bodies, which likely originate around distant stars. “We think that these little ice balls get formed associated with star systems and then are freed as another star passes by, causing them to wander through the galaxy,” he elaborated. 3I/Atlas now joins the ranks of other notable interstellar visitors, following the detection of 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.

The MPC initially designated the object as A11pl3Z, but the “3I” prefix signifies its confirmed interstellar status. As astronomers gather more data, they hope to refine their understanding of the comet's orbit, rotation rate, and composition. Observing the chemical makeup of 3I/Atlas could provide insights into the conditions under which it formed, which may differ from solar system comets. Mark Norris, an astronomer at the University of Central Lancashire, highlighted the potential for discovering many more interstellar objects, suggesting that models indicate up to 10,000 such bodies might be drifting within the solar system at any given time, most of which remain undetected due to their small size and faintness.

The upcoming Vera C. Rubin Observatory in Chile is scheduled to facilitate a wide-field survey, promising to uncover further interstellar objects. Each discovery enhances the scientific understanding of planetary system formation and offers unique insights into the chemistry of distant celestial bodies. While scientists acknowledge that intercepting 3I/Atlas with a spacecraft is not feasible due to the object’s rapid speed, ground-based and space-based telescopes will capture high-resolution images and spectra during its brief appearance in the solar system.

The study of interstellar comets not only contributes to astronomical knowledge but also enhances planetary defense capabilities by improving the identification and orbit assessment of such objects. The rapid detection and analysis of 3I/Atlas exemplify the ongoing evolution in planetary defense methodologies, as researchers prepare for future encounters with similar cosmic phenomena. As 3I/Atlas continues its celestial journey, astronomers remain eager to unveil the mysteries of this icy wanderer from beyond the stars.