The two twin spacecraft that make up the GRAIL (Gravity Recovery and Interior Laboratory) mission took off on a Delta II launch vehicle. The lift off was originally scheduled for Thursday but strong winds and a review of some systems determined the delay. The spacefract’s journey will follow a trajectory that will bring them to the Moon at low speed: in this way they’ll take three to four months to reach their destination but they’ll require a limited amount of fuel, there will be no danger to their instruments and they’ll reach at low speed the expected very low lunar orbit, about 50 km (a little more than 30 miles) above the Moon.

Working in pairs for 82 days, the two spacecraft will collect data on the changes in the lunar gravity using a microwave system that will provide a very precise measure of the distance between them.

The GRAIL mission aims to map the structure of the lunar crust and lithosphere to understand how it evolved. The Moon has an asymmetrical structure with the side facing the Earth which has vast seas of solidified lava while in the hidden side there are highlands.

The data received will be analyzed for about a year and will be combined with those already available to scientists. Valuable data were obtained thanks to the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater Observation and Sensing in Satellite (LCROSS), two spacecraft launched just over two years ago. The LRO was to map the lunar topography, also in view of possible future human exploration. The LCROSS instead had the specific purpose of looking for water in the form of ice on the Moon.

Understanding the Moon’s evolution will help to understand the Earth’s. According to today’s most accepted theory, which has been the subject of very sophisticated simulations for several years, about four billion years ago the early Earth was hit by a Mars-sized planet, almost causing its destruction and throwing huge amounts of material in its orbit.

For years, the proponents of this theory claimed that the debris left by the impact had coalesced to form the Moon. Recently however a variant of this theory has been proposed that suggests the formation of two separate moons that over time got closer and closer until they collided. According to this theory their collision occurred at low speed and this is the reason why on the Moon there’s no crater to identify it but there are highlands.

The Earth is tied to the Moon as for example their combined motion causes tides and over time increases the duration of the day. Consequently, in addition to increasing our scientific knowledge, GRAIL mission will allow us to better understand the conditions under which life evolved on Earth. We’ll have to wait to have some results but it’s worth it.