3I/ATLAS is only the third object of its kind ever observed, following the interstellar asteroid 1I/ʻOumuamua in 2017 and the interstellar comet 2I/Borisov in 2019.
The discovery image of 3I/ATLAS from the ATLAS telescope. Image credit: University of Hawai’i.
3I/ATLAS is currently around 670 million km (420 million miles) from the Sun and will make its closest approach in October 2025, passing just inside the orbit of Mars.
It is thought to be up to 20 km (12 miles) in diameter and is traveling roughly 60 km per second (37 miles per second) relative to the Sun.
It poses no danger to Earth, coming no closer than 240 million km (150 million miles) — over 1.5 times the distance between Earth and the Sun.
3I/ATLAS is an active comet; if it heats up sufficiently as it nears the Sun, it could begin to sublimate — a process in which frozen gases transform directly into vapor, carrying dust and ice particles into space to form a glowing coma and tail.
However, by the time the comet reaches its closest point to Earth, it will be hidden behind the Sun. It is expected to reappear by early December 2025, offering astronomers another window for study.
“Spotting a possible interstellar object is incredibly rare, and it’s exciting that our Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope caught it,” said Professor John Tonry, an astronomer at the University of Hawai’i.
“These interstellar visitors provide an extremely interesting glimpse of things from solar systems other than our own.”
“Quite a few come through our inner Solar System each year, although 3I/ATLAS is by far the biggest to date.”
“The chances of one actually hitting the Earth are infinitesimal, less than 1 in 10 million each year, but ATLAS is continually searching the sky for any object that might pose a problem.”
Astronomers are using telescopes in Hawai’i, Chile, and other countries to monitor the comet’s progress.
They are interested in learning more about this interstellar visitor’s composition and behavior.
“What makes interstellar objects like 3I/ATLAS so extraordinary is their absolutely foreign nature,” ESA astronomers said in a statement.
“While every planet, moon, asteroid, comet and lifeform that formed in our Solar System shares a common origin, a common heritage, interstellar visitors are true outsiders.”
“They are remnants of other planetary systems, carrying with them clues about the formation of worlds far beyond our own.”
“It may be thousands of years until humans visit a planet in another solar system and interstellar comets offer the tantalizing opportunity for us to touch something truly otherworldly.”
“These icy wanderers offer a rare, tangible connection to the broader galaxy — to materials formed in environments entirely unlike our own.”
“To visit one would be to connect humankind with the Universe on a far greater scale.”