The US space agency NASA has succeeded in sending twin satellites into orbit around the moon.
They are hoping the new spacecrafts – known as grails – will help them to discover more about how the moon was formed by studying it in unprecedented detail.
The two grails were launched from Cape Canaveral in Florida last September and have taken a hundred days to reach their destination.
Scientists have described the mission as a journey to the centre of the moon. The grails will measure minute changes in gravity that reflect the uneven distribution of mass over the surface of the moon.
That is because researchers believe the secrets of the moon’s formation are locked away in its interior.
This first mapping phase is due to last for 82 days.