We describe the discovery of a satellite in orbit about the dwarf planet ( 136472 ) Makemake .
This satellite , provisionally designated S/2015 ( 136472 ) 1 , was detected in imaging data collected with the Hubble Space Telescope ’ s Wide Field Camera 3 on UTC April 27 , 2015 at 7.80 \pm 0.04 magnitudes fainter than Makemake .
It likely evaded detection in previous satellite searches due to a nearly edge-on orbital configuration , placing it deep within the glare of Makemake during a substantial fraction of its orbital period .
This configuration would place Makemake and its satellite near a mutual event season .
Insufficient orbital motion was detected to make a detailed characterization of its orbital properties , prohibiting a measurement of the system mass with the discovery data alone .
Preliminary analysis indicates that if the orbit is circular , its orbital period must be longer than 12.4 days , and must have a semi-major axis \gtrsim 21,000 km .
We find that the properties of Makemake ’ s moon suggest that the majority of the dark material detected in the system by thermal observations may not reside on the surface of Makemake , but may instead be attributable to S/2015 ( 136472 ) 1 having a uniform dark surface .
This “ dark moon hypothesis ” can be directly tested with future JWST observations .
We discuss the implications of this discovery for the spin state , figure , and thermal properties of Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites .