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In September 2011, for the 11th mission of their Discovery Program, NASA launched the twin spacecraft GRAIL (Gravity Recovery And Interior Laboratory), GRAIL A and GRAIL B, which entered the Moon’s orbit during New Year’s weekend. For the first six months of 2012, the spacecraft will produce the most detailed and accurate map of the Moon’s gravitational field yet.
The Moon, the earth’s natural satellite, has the most unique gravitational field of all the other rocky bodies’ in the inner solar system: it is lumpy, and the lumpiest of them all. The surface, which generally affects gravitational fields, is itself lumpy, having various geological structures, such as craters, smooth plains, flat lava flows, and mountains. The surface came to be as it is today because asteroids and other space junk smashed into the natural satellite when it was still forming.
To measure its gravitational field, GRAIL A and GRAIL B will orbit the Moon at a low altitude. This way, their instruments would be more sensitive and will more likely produce accurate results. Orbiting in tandem, they will measure the changes of the distance between each other caused by the differences in strength of the field.
NASA plans for the mission to end in June, but hopes to keep the twin spacecraft studying the Moon for an additional six months to find out additional information about the natural satellite. Through mapping the gravitational field, GRAIL A and GRAIL B can also study the structure of the lithosphere (the crust) and what the Moon is like below the surface. They may then find out if there is presence of a solid core and discover what the Moon’s thermal evolution was like (i.e. how the natural satellite heated and cooled).
If GRAIL A and GRAIL B successfully determined all of this information, we would be given insight as to how the Moon formed.
“This mission will rewrite the textbooks on the evolution of the Moon,” says Maria Zuber in a NASA press release. Zuber is the GRAIL principal investigator from the Massachusetts Institute of Technology.
In turn, we would discover the planetary evolution process of other rocky bodies in the solar system, particularly Earth’s, since the Moon is essentially an entire geological record of the solar system, which is aged 4.5 billion years.
Charles Bolden, NASA Administrator, adds in another NASA press release, “NASA greets the new year with a new mission of exploration. The twin GRAIL spacecraft will vastly expand our knowledge of our moon and the evolution of our own planet. We begin this year reminding people around the world that NASA does big, bold things in order to reach for new heights and reveal the unknown.”