In the Solar System there are six planetary satellite systems containing 175 known natural satellites. Four planetoids are also known to have natural satellites: Pluto, Haumea, Makemake, and Eris. As of October 2016, there are over 300 asteroids known to have moons.
The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System (although there are minor planetary systems with even greater ratios, notably the Pluto–Charon system). At 3,474 km (2,158 miles) across, Earth's Moon is 0.27 times the diameter of Earth. 
- ↑ Sheppard, Scott S.. "The Giant Planet Satellite and Moon Page". Departament of Terrestrial Magnetism at Carniege Institution for science. http://www.dtm.ciw.edu/users/sheppard/satellites/. Retrieved 2012-09-11.
- ↑ "How Many Solar System Bodies". NASA/JPL Solar System Dynamics. http://ssd.jpl.nasa.gov/?body_count. Retrieved 2012-01-26.
- ↑ "Planet and Satellite Names and Discoverers". International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). http://planetarynames.wr.usgs.gov/Page/Planets#DwarfPlanets. Retrieved 2012-01-27.
- ↑ "Asteroids with satellites". http://www.johnstonsarchive.net/astro/asteroidmoons.html.
- ↑ Glenday, Craig (2014). Guinness World Records 2014. pp. 186. ISBN 9781908843159.