Hubble Reveals Stunning Details of Interstellar Comet 3I/ATLAS
The Hubble Space Telescope has provided the most detailed images of the interstellar comet 3I/ATLAS, allowing astronomers to confirm its identity as a comet. The latest observations reveal a coma filled with dust particles and early signs of a tail, indicating typical cometary behavior. Discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS), this comet is unique due to its extraordinary speed, traveling at an astonishing 130,000 mph (209,000 kph). It is moving so rapidly that it will escape the sun’s gravitational pull.
The origin of 3I/ATLAS remains a mystery. According to David Jewitt, a professor at the University of California, Los Angeles and the science lead on the Hubble observations, “No one knows where the comet came from… It’s like glimpsing a rifle bullet for a thousandth of a second.” This enigmatic object has journeyed through interstellar space for eons, gaining speed through gravitational slingshots with stars along the way.
As comets approach the sun, they warm up, leading to outgassing that produces a coma and tails. The Hubble observations indicate that 3I/ATLAS has a coma created from dust particles lifted from its surface. The nucleus, obscured by this coma, is estimated to be between 1,000 feet (320 meters) and 3.5 miles (5.6 kilometers) in diameter, showcasing significant variability in its size.
Astronomers have also detected a dust plume emanating from the comet’s sun-facing side, contributing to the coma, and observed the initial formation of a dust tail. These features suggest that 3I/ATLAS behaves similarly to comets originating from within the solar system, despite its unique speed and trajectory.
Although discovered by a network designed to identify hazardous asteroids, 3I/ATLAS poses no threat to Earth. The closest approach will be at a distance of 1.8 AU (167 million miles or 270 million kilometers), significantly farther than Mars. On October 29, 2025, during perihelion, the comet will be mostly obscured by the sun’s glare from Earth, yet it will remain visible to Mars and its orbiting spacecraft.
Astronomers are keen to monitor 3I/ATLAS as it nears the sun, anticipating an increase in activity due to sublimation of ices. They hope to conduct spectroscopic observations to uncover its composition, enabling comparisons with native solar system comets. Notably, a previous interstellar object, 2I/Borisov, exhibited a higher abundance of carbon monoxide than typical solar system comets.
This discovery highlights that 3I/ATLAS is the third known interstellar object, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. Estimates suggest that there could be as many as 10,000 such objects of various sizes passing through the solar system at any given time. However, the uncertainty surrounding the size of 3I/ATLAS complicates efforts to gauge the population of interstellar objects accurately.
The results from the Hubble observations have been accepted for publication in The Astrophysical Journal Letters, with a pre-print study currently available. As the Vera C. Rubin Observatory in Chile becomes fully operational, astronomers expect to discover at least one interstellar visitor per year on average, further expanding our understanding of these cosmic wanderers.
“This latest interstellar tourist is one of a previously undetected population of objects bursting onto the scene,” said Jewitt. “We’ve crossed a threshold.” The ongoing study of 3I/ATLAS promises to shed light on the origins and characteristics of comets, bringing us closer to understanding the interstellar phenomena that traverse our solar system.
