Launched two years ago, NASA’s Osiris-Rex spacecraft pulled alongside the asteroid Bennu on Monday. Its mission is to survey the asteroid ahead of retrieving pristine bits of the solar system from the rock’s surface and then bringing them back to Earth in the years ahead.

With a short engine burn, the spacecraft matched the speed and direction of Bennu.

A few minutes after noon, Javier Cerna, a communications systems engineer at Lockheed Martin, which built and operates the spacecraft, announced, “We have arrived.”

What does NASA mean by “arrive?”

Osiris-Rex’s arrival at Bennu was not like the landing of NASA’s InSight spacecraft in one piece on the surface of Mars last Monday. (Happily, it landed flawlessly.)

By contrast, Osiris-Rex pulled in at a modest speed, and the moment of arrival was somewhat arbitrary. The spacecraft started the approach phase of its mission in August when it was 1.2 million miles from Bennu. On Monday, it was just 12 miles away, although still too far away to orbit the asteroid.