The instruments on the twin GRAIL spacecraft lunar orbiters are so precise they can detect a change in the distance between them the size of a red blood cell.
The sun produced a fourth solar flare this week, two X-class flares, the strongest kind. Expect possible auroras, especially on the morning of September 11.
New images released today by NASA show tracks from Apollo 17's lunar rover - and the last footprints left on the moon by astronauts - from the year 1972.