The planet Mercury does not have any known moons (natural satellites) as of 2014. There has been one known artificial satellite orbiting Mercury, known as Messenger.
Messenger’s mission to Mercury was launched on August 3, 2004 and began an orbit of Mercury in March 2011. In the 1970s, astronomers believed Mercury might have a moon based on large amounts of ultraviolet radiation detected by a National Aeronautics and Space Administration (NASA) spacecraft. It was later determined that the radiation was coming from a distant star, rather than a moon. As of 2014, no moons, rings or signs of life have been seen on Mercury, according to NASA.