What is 3I/ATLAS?: New interstellar object spotted hurtling through solar system, can we see it from Earth

The object, now officially named 3I/ATLAS (previously labelled A11pl3Z), was detected on Tuesday (July 1), by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile. Travelling at over 60 kilometres per second, it is believed to have originated from a distant star system.

Rough estimates suggest 3I/ATLAS is between 10 and 20 kilometres wide, though it could be smaller if composed largely of reflective ice. For context, that would make it comparable in size to Manhattan.

Despite its high speed and unusual origin, scientists say 3I/ATLAS poses no threat to Earth. However, its arrival has prompted renewed interest in interstellar phenomena and preparations for future encounters.

The European Space Agency (ESA) has confirmed that work is ongoing on its Comet Interceptor spacecraft, a mission designed to meet just such a cosmic traveller.

"To this end, ESA is preparing the Comet Interceptor mission," the agency said in a statement on Thursday. "The spacecraft will be launched in 2029 into a parking orbit at the Sun–Earth Lagrange Point 2 (L2), lying in wait for a suitable target – a pristine comet from the distant Oort Cloud that surrounds our Solar System, or, unlikely but highly appealing, an interstellar object."

While it is improbable that Comet Interceptor will reach 3I/ATLAS, ESA said the spacecraft will be a "first demonstration of a rapid-response mission that waits in space for its target."

"It will be a pathfinder for possible future missions to intercept these mysterious visitors," ESA explained.

The mission, which passed its Critical Design Review in December 2024, is set to launch in 2029 alongside ESA’s ARIEL spacecraft. From its position at L2, a stable orbital point behind Earth, it will be ready to intercept any suitable object that crosses its path.

This latest discovery follows 1I/‘Oumuamua, first detected in 2017, and 2I/Borisov, discovered in 2019. 'Oumuamua’s strange shape and acceleration pattern sparked speculation it could be an artificial object, though no evidence has confirmed such claims. Borisov, by contrast, was confirmed to be an active interstellar comet.

3I/ATLAS joins this rare category of celestial visitors not bound by our Sun's gravity.

“Whether it’s 1I/‘Oumuamua, 2I/Borisov, 3I/ATLAS or the future target of an interceptor mission, each new interstellar visitor reminds us that we are part of a vast and dynamic galaxy – and that sometimes, the Universe comes to us,” ESA said.

Due to its size and distance, 3I/ATLAS is not visible to the naked eye and would require professional-grade telescopes to observe.