Moon and Mars 
Two NASA spacecraft are entering their final month of work — mapping the gravitational field of the Moon in exquisite detail. Their efforts will help scientists understand the way the Moon is put together, from its blotchy skin to its heavy core.
The probes form a mission known as GRAIL. And they’re not alone in their lunar studies — three other craft are also orbiting the Moon. One is taking the sharpest pictures of the lunar surface ever snapped from orbit. The others are studying the Moon’s composition and its interaction with the solar wind.
Having five working spacecraft in lunar orbit is a record. Even during the busy days in the run-up to the Apollo missions, NASA never had more than two fully operational craft at the Moon at one time.
GRAIL began its science mission in early March. The two craft follow the same orbital path, with one craft trailing the other. Instruments aboard the craft measure their distance from each other to less than a thousandth of an inch. Such tiny changes in distance reveal variations in the Moon’s pull, yielding detailed maps of its gravitational field.
The mission will end around the end of May, though, because the two craft will no longer be able to track each other — turning the quintet of active lunar explorers into a trio.
Look for the Moon in the south at nightfall. Another world that’s getting a detailed look stands above it: the planet Mars. It looks like a fairly bright yellow-orange star.
Script by Damond Benningfield, Copyright 2012