Mythical names of Kerberos and Styx have been given to two recently discovered moons of Pluto, but people's choice Vulcan was not allowed.
The names were chosen after a public vote in which around half a million people voted. Kerberos and Styx were the second and third choices.
But the most popular name Vulcan - the planet Spock is from in the Star Trek movies - was not allowed.
The International Astronomical Union, who are in charge of naming the moons, say they must derive from mythology and the name Vulcan was not appropriate.
Pluto was a planet for 76 years, but in 2006 it lost its planet status and is now a dwarf planet.
Astronomers have so far spotted five moons travelling around it.
Kerberos and Styx were first seen in 2011 and 2012 by astronomers in America, but were known as P4 and P5 - not as catchy as the new names!