Dwarf planet Makemake has a moon
NASA/ESA/Southwest Research Institute (A. Parker)

Dwarf planet Makemake has a moon

Astronomers have spotted a small, faint moon orbiting the dwarf planet Makemake. One of our solar system’s five dwarf planets, Makemake—an icy, 1400-kilometer-wide orb that circles the sun far beyond Pluto—was discovered in 2005. The first images of its newly described companion, a moon nicknamed MK 2 (at lower right in the artist’s representation, above), were taken by the Hubble Space Telescope in April 2015, researchers reported today. The belated discovery likely stems from several factors, the researchers say: The moon is only about 160 kilometers across, as dark as charcoal, and its orbit is edge-on as seen from Earth, so the satellite (which is an estimated 1300 times fainter than Makemake itself) spends much of its time lost in the bright glare of its parent world. The shape of MK 2’s orbit isn’t yet clear, but it apparently circles Makemake at a distance of at least 21,000 kilometers. If the satellite’s path is circular, the moon takes at least 12 days to loop around the dwarf planet, data suggest. Future analyses of the orbit will help astronomers determine the mass of the Makemake/MK 2 system, thus adding insight into the materials of which the objects are made, the researchers say. They might also provide better understanding into the history of the pair: If the orbit is dramatically elongated, that might suggest MK 2 was gravitationally captured by Makemake long after the two formed in separate regions of space, whereas a circular orbit could bolster the notion that the pair formed together.