Styx (moon)

Styx, also called (134340) Pluto V, is a tiny moon that orbits the dwarf planet Pluto. It was found in 2012 using the Hubble Space Telescope and is the smallest of Pluto's five known moons. Scientists learned about Styx when the New Horizons spacecraft flew by Pluto in 2015, taking pictures of Pluto and its moons, including Styx.

Styx is very small, about 16 kilometers (9.9 miles) across at its widest point. It is the second moon closest to Pluto and takes about 20.1 days to go around Pluto once. Styx was discovered one year after another moon called Kerberos.

Discovery and observations

Styx was discovered by a team led by astronomer Mark R. Showalter using images taken by the Wide Field Camera 3 on the Hubble in June and July 2012. The discovery was announced on 11 July 2012. Styx is much smaller and dimmer than Pluto and even the smallest of Pluto’s other moons.

The discovery happened while preparing for the flight of the uncrewed New Horizons spacecraft, which flew by Pluto on 14 July 2015. Finding another small moon around Pluto raised concerns that more tiny objects might be there, which could have been dangerous for the spacecraft. However, New Horizons safely traveled through the area without finding any extra moons or rings.

Origin

Pluto has a group of moons that might have formed after Pluto crashed into a big object in space long ago. These moons could have come from the pieces left after the crash, just like how Earth’s Moon may have formed from an old crash. The way the moons move around Pluto might have helped collect the pieces from that old crash.

Physical characteristics

Styx was first thought to be between 10 and 25 kilometers wide, but later measurements showed it to be about 16 kilometers long, 9 kilometers wide, and 8 kilometers tall. Scientists believe Styx formed from pieces left over after a collision. This process likely removed some of the more changeable icy materials, leaving mostly water ice.

Orbit

Animation of moons of Pluto around the barycenter of Pluto – Ecliptic plane

Front view

Side view

   Pluto ·    Charon ·    Styx ·    Nix ·    Kerberos ·    Hydra

Styx orbits the Pluto–Charon barycenter at a distance of 42,656 km, sitting between the orbits of Charon and Nix. All of Pluto's moons seem to travel in orbits that are almost circular and lie in the same plane. Styx's discoverer, Mark Showalter, described them as "neatly nested ... a bit like Russian dolls".

Its orbital period is 20.16155 days, which is about 5.0% different from a special pattern related to Charon's orbit around Pluto. Together with the moons Nix, Kerberos, and Hydra, Styx helps create an unusual pattern of orbits. Unlike its orbit, Styx's rotation is unpredictable and changes quickly.

Naming

Before any of Pluto's moons were found, a writer named Edmond Hamilton mentioned three moons of Pluto in his 1940 science fiction book, naming them Charon, Styx, and Cerberus.

When Styx was discovered, it got the minor planet designation S/2012 (134340) 1 because it was the first moon found around Pluto in 2012. It's often called "P5," meaning it was the fifth moon of Pluto to be found.

Names for Pluto's moons are chosen from stories about the god Pluto in old classical mythology. In 2013, people were asked to vote online for names for two of the newly found moons. Actor William Shatner, famous for playing Captain James T. Kirk in Star Trek, suggested the names Vulcan and Romulus. Vulcan won the vote, but it couldn't be used because it wasn't related to Pluto's stories and had already been used for other things. On 2 July 2013, the group that decides on space names officially chose Styx as the name for P5.