A team of astronomers has captured the sharpest image ever of the unexpected interstellar comet 3I/ATLAS, using NASA’s Hubble Space Telescope’s sharp vision.
Hubble is one of many missions across NASA’s fleet of space telescopes scheduled to observe this comet, together providing more information about its size and physical properties.
Although the comet poses no threat to Earth, NASA’s space telescope helps support the agency’s ongoing mission to discover, track and better understand near-Earth objects.
Hubble’s observations allowed astronomers to more accurately estimate the size of the comet’s solid ice core. The upper limit of core diameter is 3.5 miles (5.6 kilometers), although they can be as small as 1,000 feet (320 meters), the researchers report.
Although the Hubble image provides tighter constraints on the size of the core compared to previous ground-based estimates. The comet’s solid nucleus cannot currently be seen directly, even by Hubble.
Observations from other NASA missions including the James Webb Space Telescope, TESS (Transiting Exoplanet Survey Satellite), and the Neil Gehrels Swift Observatory, as well as NASA’s partnership with the WM Keck Observatory, will help further refine our knowledge of comets, including their chemical makeup.
Hubble also captured plumes of dust ejected from the comet’s sun-warmed side. A slight tail trail of dust flows away from the comet’s nucleus.
The Hubble data yield dust loss rates consistent with a comet first detected about 300 million miles from the Sun. This behavior is very similar to the characteristics of comets previously seen heading towards the Sun and originating from within our solar system.
The big difference is that these interstellar visitors come from other solar systems elsewhere in our Milky Way galaxy.
Comet 3I/ATLAS sped through our solar system at an incredible speed of 130,000 miles (209,000 kilometers) per hour, the highest speed ever recorded for a visitor to the solar system. This astonishing speed is proof that the comet has been drifting in interstellar space for billions of years.
The gravitational ejection effect of the countless stars and nebulae that the comet passes through adds momentum, increasing its speed. The longer 3I/ATLAS is in space, the higher its speed.
No one knows where the comet came from. It’s like looking at a rifle bullet for a thousandth of a second. “You can’t project it back accurately to know where it started its journey,” said David Jewitt of the University of California, Los Angeles, science team leader for the Hubble observations.
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“This latest interstellar tourist is one of a population of previously undetected objects that have suddenly appeared and will be gradually revealed,” Jewitt said. “This is now possible because we have advanced sky survey capabilities that we didn’t have before. We have passed a critical point.”
This comet was discovered by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) on July 1, 2025, at a distance of 420 million miles from the Sun. ATLAS is an asteroid impact early warning system developed by the University of Hawai’i.
Meanwhile, other NASA missions will provide new insights into this third interstellar intruder, helping to refine our understanding of these objects for the benefit of all.
3I/ATLAS is expected to remain visible to ground-based telescopes until September, after which it will pass too close to the Sun to be observed, and is expected to reappear on the other side of the Sun in early December. (Science Daily/Z-2)
