The US space agency (Nasa) has succeeded in placing two new satellites in orbit around the Moon.
Both spacecraft were put in elliptical paths around the lunar body over the weekend after performing braking manoeuvres following their more than 100-day journey from Earth.
The identical Grail Twins are to map gravity variations across the lunar body in unprecedented detail.
This will help scientists refine our theories for how the Moon Formed.
It will also enable them to test new ideas, such as the provocative suggestion made earlier this year that there were probably two moons in the sky above Earth billions of years ago.
Lead scientist Dr Maria Zuber is certainly hoping for some dramatic discoveries.
“Grail is a journey to the centre of the Moon and it will use exceedingly precise measurements of gravity to reveal what the inside of the Moon is like,” the Massachusetts Institute of Technology (MIT) researcher said.
“This information will be combined with the plethora of remarkable observations of the Moon that have been taken by other satellites before, and together they will enable us to reconstruct the Moon’s early evolution.”
The 300kg Grail spacecraft were launched from Cape Canaveral, Florida, last September, and took a long spiral out to their destination.
This weekend, they approached the Moon over the south pole, 25 hours apart. Each satellite in turn fired its main engine to slow it and put it in an elliptical orbit around the lunar sphere.
This orbit has a period of 11.5 hours and must now gradually be reduced in size and circularised before any science can begin.
A series of further burns on each spacecraft should achieve this goal by March.
The twins will then map the small variations in gravity across the lunar surface from an altitude of 55km.
These gravity differences are the result of an uneven distribution of mass. Obvious examples at the Moon’s surface include big mountain ranges or deep impact basins, but even inside the lunar body the rock will be arranged in an irregular fashion, with some regions being denser than others.
All this will have a subtle influence on the pull of gravity sensed by the over-flying spacecraft.
The Grail twins will make their measurements by carrying out a carefully calibrated pursuit of each other.
(source: BBC)
