Comets have long captivated astronomers, yet most remain confined to the Kuiper Belt or Oort Cloud beyond our planetary neighborhood. In June 2024, Comet 12P/Pons‑Brooks—colloquially dubbed the "devil comet"—brushed closest to Earth. But a new discovery challenges this paradigm.
Officially designated 3I/ATLAS, the interstellar visitor was first identified by the Asteroid Terrestrial‑impact Last Alert System (ATLAS) survey telescope in Rio Hurtado, Chile, on 1 July 2025. Subsequent pre‑discovery images from three other ATLAS sites and the Zwicky Transient Facility at Caltech’s Palomar Observatory provided the data needed to confirm its extragalactic origin.
Analysis of the trajectory shows the object approached from the direction of the Sagittarius constellation, already residing within Jupiter’s orbit when detected and approximately 410 million miles from the Sun. With a hyperbolic velocity of roughly 137,000 mph, 3I/ATLAS is racing through the inner Solar System and will reach its closest approach to Earth around October, remaining about 150 million miles away—well beyond any threat to our planet. It will, however, come close enough to Mars that the Mars Reconnaissance Orbiter may be able to observe it.
International observations suggest 3I/ATLAS could span up to 12.4 miles across. Its trajectory and speed unequivocally demonstrate that it is not bound by solar gravity, confirming its interstellar provenance. The Minor Planet Center’s analysis of a faint tail—indicative of dust and gas outflow—distinguishes it as a comet rather than an asteroid.
Beyond its exotic origin, 3I/ATLAS is only the third known interstellar object to traverse our Solar System. The first, 1I/'Oumuamua, entered in 2017, followed by 2I/Borisov in 2019, set the precedent. 3I/ATLAS is moving faster than either of its predecessors and is likely a much older remnant of a distant planetary system. University of Canterbury astronomer Michele Bannister expressed her excitement in a Nature interview: "Working on 1I and 2I were transformational opportunities."
As with NASA’s monitoring of the rare exoplanet Enaiposha, the global astronomical community is collaborating to track 3I/ATLAS. Ground‑based telescopes are expected to observe the comet through September, after which it will pass too close to the Sun for optical detection. By early December, however, the object should re‑emerge, allowing continued study of its composition and behavior before it departs the inner Solar System.
Image credit: Nazarii Neshcherenskyi via Shutterstock.
