Hubble Telescope Captures Fastest Interstellar Comet 3I/ATLAS in Stunning Close-Up, Shedding Light on Mysterious Visitor from Another Solar System

An unprecedented image, captured by the Hubble Telescope’s Wide Field Camera 3 on July 21, offers the clearest view yet of an interstellar comet designated as 3I/ATLAS. The comet was approximately 277 million miles (445 million kilometers) away from Earth at the time of observation.

The image reveals a teardrop-shaped dust cocoon streaking from the comet’s icy nucleus. A comet’s nucleus comprises ice, dust, and rocks. When comets approach stars like our sun, heat causes them to release gas and dust, forming distinctive tails.

The Hubble Telescope is one of several instruments tracking 3I/ATLAS, first discovered on July 1, as it speeds at an impressive 130,000 miles (209,000 kilometers) per hour through our solar system. This speed makes 3I/ATLAS the fastest interstellar object ever observed within our galaxy to date.

New observations, including those made with Hubble, are helping scientists gain insights into the comet’s size. The nucleus, currently not visible directly, may measure up to 3.5 miles (5.6 kilometers) in diameter or as small as 1,000 feet (305 meters) across according to a paper accepted by The Astrophysical Journal Letters.

Other space-based telescopes such as the James Webb Space Telescope, the Transiting Exoplanet Survey Satellite, and the Neil Gehrels Swift Observatory, together with ground-based observations from the W.M. Keck Observatory in Hawaii, are expected to provide more information about the object’s chemical composition. 3I/ATLAS will remain observable through ground-based telescopes until September before approaching too close to the sun to be seen again until its reappearance on the other side of our star in early December.

Despite these observations, several mysteries surrounding 3I/ATLAS persist, including its origin. In a statement, lead study author David Jewitt, professor of astronomy at the University of California, Los Angeles, likened studying the comet to glimpsing a rifle bullet for a thousandth of a second, making it challenging to determine its point of origin accurately.

Although 3I/ATLAS behaves similarly to comets native to our solar system, its high speed suggests it is an interstellar visitor. Scientists estimate it has been traveling through interstellar space for billions of years. As objects travel through space, they gain momentum due to gravitational interactions with stars and stellar nurseries. Thus, the longer 3I/ATLAS has been in space, the faster it moves.

Since its discovery in 2017, 3I/ATLAS is only the third known interstellar object observed within our solar system after ‘Oumuamua and 2I/Borisov. According to Matthew Hopkins, a recent doctoral student in the department of physics at the University of Oxford who authored a separate study about the object, 3I/ATLAS’ velocity is particularly useful for understanding its properties.

Hopkins found the discovery of 3I/ATLAS remarkably timely, occurring just five days after he completed his doctoral work involving predictions about future interstellar object discoveries. Hopkins will soon begin a postdoctoral research fellowship at the University of Canterbury in New Zealand, where he will continue his research on 3I/ATLAS.

During his doctoral studies, Hopkins and his collaborators in New Zealand developed the Ōtautahi–Oxford model, a combination of data from the Milky Way’s star population and models of how planetary systems form that could help astronomers determine what interstellar object populations should look like. Now, Hopkins is the lead author of a separate preprint study about 3I/ATLAS.

Determining the age of interstellar objects is challenging, but Hopkins and his colleagues believe 3I/ATLAS has around a 67% chance of being more than 7.6 billion years old, while our sun, solar system, and comets are only 4.5 billion years old.

Although the interstellar comet’s entry into our solar system was purely coincidental, Hopkins asserts that such visitors are not entirely rare. We simply do not detect them most of the time due to their small size. Astronomers are eager for the Vera C. Rubin Observatory, which recently released its first images, to scan the skies for interstellar objects. The observatory’s massive primary mirror spanning 28 feet (8.4 meters) across allows it to spot small, faint, and distant objects, making it ideal for detecting rapidly moving interstellar objects.

Hopkins’ coauthors estimate that the Rubin Observatory could identify between five and 50 interstellar objects over the next ten years. Hopkins is optimistic about discovering more interstellar objects, as this could help astronomers better understand their variety or similarities, especially since the first three have been distinctly different from each other.

“This latest interstellar tourist is one of a previously undetected population of objects that will gradually emerge,” Jewitt said. “We’ve crossed a threshold.”