Maps of Moon's far side give new clues to its origin

Maps of Moon's far side give new clues to its origin :
BRISBANE: Astronomers have gained new insight into how the Moon formed by combining a new topographical map with knowledge about the Moon's gravity.

The map is the first to cover the Moon from pole to pole and shows craters never before seen, researchers report today in a trio of papers in the U.S. journal Science.

The experts also reveal the first direct observations of gravitational anomalies on the satellite's far side, which, combined with the topographic data, suggest that the Moon has very little water – a key clue to understanding its origin and evolution.

Two-faced Moon
"The surface can tell us a lot about what's happening inside the Moon, but until now mapping has been very limited," said C.K Shum an earth scientist at Ohio State University in the U.S. and co-author of one of the studies. "With this new high-resolution map, we can confirm that there is very little water on the Moon today, even deep in the interior. And we can use that information to think about water on other planets, including Mars."
The data was collected by SELENE, a Japanese satellite that has subsidiary satellites that relay information from the main craft back to Earth, while it is out of sight on the far side of the Moon. That allows the researchers to track the satellite's movements accurately and be certain of the quality of the data, said study co-author Noriyuki Namiki, of Kyushu University in Fukuoka, Japan.
Using a laser altimeter, SELENE has mapped the Moon's entire surface to a resolution of 15 km (meaning that objects as small as 15-km-wide can be seen). This is up from the previous resolution of 20 to 60 km provided by NASA's 1994 Clementine mission, which only mapped part of the surface.

Rigid crust
From Earth we always see the same side of the Moon (the near side) as its rotation is tidally locked with ours.
The new map shows the substantial differences between the Moon's near and far sides. The side of the Moon that faces Earth is covered with low-lying, smooth, dark volcanic rock, while the on the far side there are older, heavily cratered highlands.
The map also gives hints about the Moon's interior, because it doesn't show the surface crust bending over areas of unusually high gravity on the far side. The rigidity of the crust suggests that there is very little water even deep inside the Moon, the researchers said, because water would make the Moon's crust more flexible.

"The abundance of water is a key parameter to understanding the formation and evolution of the Moon," said co-author of one study Araki Hiroshi, an astronomer at the National Astronomical Observatory of Japan in Tokyo.
The lack of water suggested by SELENE supports the theory that the Moon was formed in a giant collision between a still-molten Earth and a wandering proto-planet. Astronomers believe that such an impact would have heated the debris that became the Moon, evaporating off its water and explaining why the Moon is dry even though it is close to a watery Earth.
Astrophysicist Sarah Maddison, of Swinburne University in Melbourne, Australia, said that getting a good map of the whole Moon was an important step, because knowing the exact shape of the Moon gave researchers better information about its gravity.