NASA Probes Will Measure Makeup of the Moon

Twin spacecraft will measure the moon's gravitational field, and how it formed

A NASA rocket blasted off for the moon on Friday. Once there, the unmanned vehicle will release a pair of satellite probes aimed at learning more about the moon's gravitational field and, eventually, what it's made of.

(Cheese? It's cheese, right?)

The Gravity Recovery and Interior Laboratory (GRAIL) mission was developed with scientists at the Massachusetts Institute of Technology. The mission's "primary science objectives will be to determine the structure of the lunar interior, from crust to core and to advance understanding of the thermal evolution of the Moon," NASA explains. "As a secondary objective, GRAIL will extend knowledge gained from the Moon to the other terrestrial planets."

The satellite probes were launched on the second try, after an initial launch date was scratched because of high winds, Reuters reports. The probes will shoot out more than 930,000 miles into space, to the point where the gravitational pull from the earth and the sun become equal, then slowly drift toward the moon by the very end of the year.

More from Reuters on how the measurement will actually work:

Linked by radio waves, the spacecraft will be able to detect changes in the tug of lunar gravity as small as one micron -- about the width of a red blood cell.

Pockets of terrain with more mass will cause first one and then the second satellite to speed up slightly as they fly over, changing the distance between the two probes in minute, but measurable amounts. Less dense regions will cause the probes to slow slightly.

The measurements are so precise that scientists have to factor out a myriad of other forces, including the pressure of sunlight and the gravitational influences of all other planets in the solar system, even the dwarf planet Pluto, currently about 2.9 billion miles (4.7 billion km) away.

The resulting map will presumably look something like this.