The Hubble Space Telescope recently uncovered a tiny addition to icy Pluto’s system: a new moon, for the time being named P4.
Pluto, which was reclassified as a dwarf planet in 2006, already has three other satellites: Charon, Nix, and Hydra. The latest addition is Pluto’s smallest companion with a diameter between eight and 21 miles.
Charon was Pluto’s first moon, discovered in 1978, while Nix and Hydra were found in 2005.
P4 has the third outermost orbit around Pluto, located between the orbits of Nix and Hydra.
Hubble first saw this fourth moon on June 28, and the observation was confirmed when new pictures were taken early in July.
P4 had been overlooked until now because earlier pictures of Pluto had short exposures. Longer exposures finally revealed that P4 was more than just a smudge.
Amazingly, the Hubble Telescope was located three billion miles away from Pluto when it took pictures of the satellite system.
The discovery was made as Hubble helps prepare the New Horizons spacecraft for its visit to Pluto in 2015. The goal of New Horizons, launched in 2006, is to travel closer to Pluto than any other spacecraft and learn more about the outer edges of our solar system.
Hubble had previously proved “invaluable to planning for New Horizons’ close encounter,” according to a NASA news release, when it mapped the surface of Pluto.
Now, as if NASA was not already looking forward to a closer look at Pluto, this new moon presents yet another mystery about the icy planet that warrants further investigation.
Below are Hubble's pictures confirming the existence of Pluto's new moon, P4.
