Faced with a fuel shortage, two NASA space probes that have been orbiting the moon for almost a year will purposely crash into a lunar mountain range at nearly 4,000 miles per hour. The gravity recovery and interior laboratory probes, known as Ebb and Flow, were deployed to map the satellite’s gravitational pull.

From the Guardian’s report, it’s unclear whether NASA sent the probes on a kind of kamikaze mission, knowing they’d run out of fuel eventually, or if they were intended to return to Earth. Either way, the idea of two spaceships slamming into the moon at such high speed is both sad and a little thrilling.

Their final mission won’t be in vain. Each probe will thrust its engines until it’s completely out of gas to determine exactly how much fuel it had left–this way, NASA can determine how much fuel will be needed for future expeditions.

“It is going to be difficult to say goodbye,” said Maria Zuber of MIT, who’s been involved with the Grail probes. “Our little robotic twins have been exemplary members of the Grail family and planetary science has advanced in a major way because of their contributions.”

(Photo: Guru Sno Studios/Flickr)