Asteroid exploration has been all the rage lately, and the European Space Agency (ESA) isn’t missing out on the fun.

On February 4, ESA released new details about its upcoming Hera mission — the first spacecraft to explore a binary asteroid. The mission will launch to asteroid 65803 Didymos, a binary pair made up of one large body and a smaller object that orbits around it, in 2023. Aptly nicknamed Didymoon, the smaller of the two stretches just 525 feet (160 meters) in diameter — making it the tiniest asteroid ever targeted for exploration.

Sizing up Didymos

When it comes to the asteroids we’ve visited, Didymos is definitely on the smaller side. Its larger half is just 2,600 feet (780 meters) in diameter, which pales in comparison to asteroids like 253 Mathilde, which is over 30 miles (50 kilometers) wide and was visited by NASA’s Near Earth Asteroid Rendezvous (NEAR) mission in 1997.

In fact, only two of the asteroids we’ve probed are smaller than Didymos. Asteroid Bennu, which is currently being studied by NASA’s OSIRIS-REx spacecraft, measures just 1,600 feet (500 meters) across. And Itokawa, investigated by JAXA’s Hayabusa mission in 2005, stretches only 1,150 feet (350 meters). With Didymoon spanning less than half of that, it will by far be the smallest asteroid ever explored.