In preparation for the New Horizons mission's flyby in 2015, Hubble has scanned the Pluto system several times to identify any potential hazards to the spacecraft's passage.
In May 2005, Hubble first spotted two new moons around Pluto and Charon. These moons were later given the names Nix and Hydra, which come from Greek mythology concerning Pluto, the god of the underworld. Nix is the Greek goddess of the night, and mother of Charon. The mythological Hydra is a nine-headed serpent with its den at the entrance to Hades. Note that it is absolutely no coincidence whatsoever that the letters "N" and "H" also happen to be the initial letters in "New Horizons."
Hubble made two more discoveries in 2011 and 2012. These new moons, even smaller than Nix and Hydra, were given temporary designations P4 and P5. During February 2013, a non-binding internet vote was held to see what the public thought should be the names for the new moons. Over 450,000 votes were cast, with Vulcan, the name of the home planet of the Star Trek character Mr. Spock, getting the most votes.
On July 2, 2013, the naming decision was announced. The official name for P4 is now Kerberos, and for P5 it is now Styx. Kerberos is a three-headed dog in Greek mythology (like Fluffy in the first Harry Potter book). Styx is the river one must cross to get to the underworld. These names were second and third place in the voting. The first-place Vulcan was not selected because it has already been used in astronomy.
In 1846, French mathematician Urbain Le Verrier gained fame for predicting the existence of the planet Neptune based on deviations in the orbit of Uranus. Le Verrier had been studying Mercury's orbit as well, and found its motion also did not follow predictions. In 1859, he proposed the existence of a planet between Mercury and the Sun, and called it Vulcan after the Roman god of fire. Astronomers made significant searches for Vulcan, but the hypothetical planet does not exist. Instead, the deviations of Mercury were explained by Albert Einstein's general theory of relativity, published in 1915. Hence, Vulcan has its astronomical legacy, as a planet destroyed not by the Romulan Nero, but by Einstein's equations.
The new moons Kerberos and Styx join a fascinating system in our solar system's Kuiper Belt. Pluto and Charon form a double object, with each orbiting the center of mass in between them. Add four small to tiny moons around that, and New Horizons has much to study in its relatively quick flyby at 30,000 miles per hour. Even at such tremendous speed, the spacecraft team recently concluded that the flight plan had less than a 0.3 percent chance of a critical hazard. Hubble's deep observations were crucial to that evaluation, and provided the bonus of four new moons. However, Vulcan is not one of them, and, alas, Spock will have to look elsewhere to re-establish his homeworld.