Launched as GRAIL A and GRAIL B in September 2011, the probes were renamed Ebb and Flow by schoolchildren in Montana. The probes operated in almost circular orbit near the lunar poles at an altitude of approximately 34 miles, until their mission came to an end in December 2012. The distance between the twin probes altered a bit as they soared over areas of lesser and greater gravity that were caused by visible topological features on the Moon's surface, such as impact craters and mountains--as well as by masses that were secreted beneath the lunar surface.
The tiny moon--which for now has been designated S/2015 (136472) 1, and playfully nicknamed MK 2, for short--is more than 1,300 times dimmer than Makemake itself. MK 2 was first spotted when it was about 13,000 miles from its dwarf planet parent, and its diameter is estimated to be about 100 miles across. Makemake is 870 miles wide, and the dwarf planet, which was discovered over a decade ago, is named for the creation deity of the Rapa Nui people of Easter Island.
Earlier infrared data did not have sufficient resolution to separate MK 2 from Makemake's veiling glare. The astronomers' reanalysis, however, based on the more recent HST observations, indicates that much of the warmer surface spotted earlier in infrared light may simply be the dark surface of the companion MK 2.