A team of astronomers has used NASA's Hubble Space Telescope to obtain the clearest image yet of interstellar comet 3I/ATLAS, enabling the most precise size estimates so far. The icy nucleus may measure up to 3.5 miles (5.6 kilometers) in diameter, but could be as small as 1,000 feet (320 meters). Even Hubble cannot directly see the nucleus, but its observations provide tighter constraints than by Clarence Oxford
Los Angeles CA (SPX) Aug 08, 2025
A team of astronomers has used NASA's Hubble Space Telescope to obtain the clearest image yet of interstellar comet 3I/ATLAS, enabling the most precise size estimates so far. The icy nucleus may measure up to 3.5 miles (5.6 kilometers) in diameter, but could be as small as 1,000 feet (320 meters). Even Hubble cannot directly see the nucleus, but its observations provide tighter constraints than previous ground-based measurements.
Multiple NASA missions, including the James Webb Space Telescope, TESS, the Neil Gehrels Swift Observatory, and a partnership with the W.M. Keck Observatory, will further investigate the comet's composition and refine its size and physical properties.
Hubble imagery also revealed a dust plume emitted from the Sun-warmed side and a faint dust tail trailing the nucleus. The comet's dust-loss rate matches that of solar system comets first detected about 300 million miles from the Sun, though 3I/ATLAS originated in another star system.
Traveling at 130,000 miles (209,000 kilometers) per hour, 3I/ATLAS is the fastest recorded object to enter our solar system. Astronomers believe gravitational encounters with stars and nebulae over billions of years gradually accelerated its speed. Its origin point remains unknown. "It's like glimpsing a rifle bullet for a thousandth of a second," said David Jewitt of the University of California, Los Angeles, who leads the Hubble science team.
Jewitt described the comet as part of an emerging population of interstellar objects detectable thanks to advanced sky surveys such as the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS), which discovered the comet on July 1, 2025, at 420 million miles from the Sun.
3I/ATLAS will stay visible to ground-based telescopes until September before passing too close to the Sun, and should reappear in early December. Continued observations aim to expand understanding of these rare visitors from beyond our solar system.
Research Report:Hubble Space Telescope Observations of the Interstellar Interloper 3I/ATLAS
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