美国航天局将发射月球探测器

The U.S. space agency is preparing for Thursday's launch of two unmanned spacecraft to the moon, nearly forty years after man last walked on the moon.
 
NASA's Gravity Recovery and Interior Laboratory, or GRAIL, mission spacecraft will orbit the moon before landing on the lunar surface.
 
The mission will map the moon from its core to its surface, including the far side of the moon which humans have never explored.
 
Tuesday, NASA released high resolution photographs showing the remnants of the space agency's previous lunar visits. The photos show tire tracks from the Apollo 17 lunar rover.
 
In November, NASA will launch a spacecraft bound for Mars. The flight to Mars is expected to last two years.