NASA GRAIL Gravity Mapping Satellites Now in Orbit

Grail(Gravity Recovery and Interior Laboratory) satellites is the first NASA spacecraft that will map the gravity field of the Moon.

GRAIL mission satellites lifted off on 10th September 2011. The satellites entered Moons orbit recently on 31st December 2011. Grail mission is expected to improve knowledge of Moon's gravity by 100-1000 times what was previously known.

Scientists believe that details from it might help us to better understand the nature of the far-side of the Moon.   The first gravity-mapping mission will take 82 days. In early June, the Moon will go into eclipse behind the Earth. If the probes can outlast the darkness on their battery power, scientists will likely send them even closer to the surface later in 2012 to conduct a second study, according to BBC News.

Gravity Measuring Technique:

As the pair travel over the moon's orbit, each one will accelerate or de-accelerate as the lunar gravity affect it, the different in distance between the two satellites will be measured and used to determine the gravity irregularities of the moon.