NEW YORK: Nasa's twin Grail probes arrived at the moon in early January - and one has just sent back its first video from the 'dark' side of the moon, the one we don't see from Earth.
The video shows a flight from the north pole to the south pole of the moon.
'It's very rugged and covered with impact craters from asteroids that hit the moon's surface,' says Maria Zuber, Nasa's principal investigator on Grail.
In the video, the north pole of the Moon is visible at the top of the screen as the spacecraft flies toward the lunar south pole.
The side explored in the video can never be seen from Earth. The moon is 'tidally locked' to earth, so one side always faces away from us.
It's the first video from the two probes - named 'Ebb' and 'Flow' - but many more will be sent back as American school pupils join in an interactive project to explore the moon's 'other' side.
One of the biggest features seen on the lower third of the Moon in the video is the Mare Orientale, a 560 mile-wide impact basin that straddles both the Moon’s near and far side.
Near the bottom of the screen, the video shows the 93-mile-wide Drygalski crater - recognisable from the distinctive star-shaped formation in the middle. It's a central peak within the crater, created billions of years ago by a comet or asteroid impact.
The footage shows a journey from the north to the south pole of the 'dark side' of the moon, revealing huge craters caused by asteroid and comet impacts billions of years ago.
The two probes will continue to orbit the moon in tight formation to measure its gravity - and map its little-understood interior.
The probes will measure gravity by monitoring its effects on their flight paths as they fly over the moon's surface just 35 miles up.
The $496million mission will also be closely watched by schoolchildren. A project by Sally Ride, the first American woman in space, will allow school pupils to use cameras aboard the probes to zoom in and pick out their favourite lunar spots to photograph.
‘We have had great response from schools around the country, more than 2,500 signed up to participate so far,’ Ride said.
'In mid-March, the first pictures of the Moon will be taken by students. I expect this will excite many students about possible careers in science and engineering.’
The mission could answer questions such as whether there was ever a second moon - and why our moon is such an odd shape.
Nasa's Charles Boulden said. 'The twin GRAIL spacecraft will vastly expand our knowledge of our Moon and the evolution of our own planet.'
Grail is expected to help researchers better understand why the moon is asymmetrical and how it formed by mapping the uneven lunar gravity field.
Nasa describes the mission as a 'journey to the centre of the moon.'
Previous lunar missions have attempted to study the moon's gravity - which is about one-sixth Earth's pull - with mixed results.
Grail is the first mission devoted to this goal.