Interstellar Comet 3I/ATLAS Discovered Passing Through Solar System
Astronomers have identified 3I/ATLAS, the third known interstellar object, currently traversing our solar system without posing any threat to Earth.
On July 1, 2025, the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Rio Hurtado, Chile, detected a new interstellar comet, now designated 3I/ATLAS. This marks the third known interstellar object to pass through our solar system, following 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.
3I/ATLAS is currently approximately 420 million miles (670 million kilometers) from the Sun, traveling at a speed of 137,000 miles per hour (61 kilometers per second). It is projected to reach its closest point to the Sun on October 30, 2025, at a distance of about 1.4 astronomical units (130 million miles, or 210 million kilometers), just inside the orbit of Mars. The comet will not come closer than 1.8 astronomical units (170 million miles, or 270 million kilometers) to Earth, posing no threat to our planet.
Observations indicate that 3I/ATLAS is an active comet with an icy nucleus and a surrounding coma—a cloud of gas and dust. Its nucleus is estimated to be between 0.32 to 5.6 kilometers in diameter. The comet's origin is traced to the Milky Way's thick disk, a region populated by older stars, suggesting that 3I/ATLAS could be between 7.6 and 14 billion years old, potentially making it the oldest comet observed to date.
Astronomers are actively studying 3I/ATLAS to gain insights into the composition and behavior of interstellar objects. The comet is expected to remain visible to ground-based telescopes through September 2025, after which it will pass too close to the Sun to observe. It will reappear on the other side of the Sun by early December 2025, allowing for renewed observations.