The Fifth Moon of Pluto

In the past decade alone, four out of Pluto’s five moons known thus far have been discovered. The latest addition, provisionally titled S/2012 (134340) 1 or P5, is only between 6 and 15 miles (10 to 24 kilometers) in diameter, orbiting a mere 29,000 miles (47,000 km) away from Pluto and posses an irregular shape. S/2012 P 1 (also known as S/2012 (134340) 1 or P5) is a small natural satellite of Pluto whose existence was announced on July 11, 2012. P5 is believed to have formed, like the rest of Pluto’s moons, after a large body in the Kuiper belt collided with the dwarf planet. Because of its tiny size, the moon retained an irregular shape, since its gravity was too small to shape it into a sphere.

Pluto’s other satellites are Charon, discovered in 1978, Nix and Hydra discovered in 2005, and P4 first sighted in 2011. Charon was first imaged by the United States Naval Observatory Flagstaff Station in Arizona, while the rest, including P5, were observed by the ever-resourceful Hubble Space Telescope.

Pluto has five known moons. The largest, Charon, is proportionally larger, compared to its primary, than any known satellite of a planetary-mass object. The other moons, Nix,Hydra, S/2011 P 1 ("P4") and S/2012 P 1 ("P5") are much smaller.The team that discovered S/2011 P 1 also found possible evidence of a couple of even fainter moons, but this needs more study to be confirmed.

The moon was discovered using nine sets of images taken between June 26 and July 9, 2012 by the Wide Field Camera 3 fitted to theHubble Space Telescope. The survey work leading to the moon's discovery was in preparation for the arrival of the New Horizons space probe, currently en route to the Pluto system. The discovery of a new, small moon led to concerns that the region of space may harbor many more bodies that are too small to be detected, raising fears that the probe may be damaged by an uncharted body as it passes through the system. It is speculated that the unexpectedly complex moon system around Pluto is the result of a collision between Pluto and another Kuiper belt object in the distant past. The detection of P5, coupled with that of P4 last year, makes the surrounding area a lot more crowded than initially thought and warrants a re-trajectory if an unfortunate collision is to be 100% averted. The team is using Hubble's powerful vision to scour the Pluto system to uncover potential hazards to the New Horizons spacecraft. Moving past the dwarf planet at a speed of 30,000 miles per hour, New Horizons could be destroyed in a collision with even a BB-shot-size piece of orbital debris.

“We’re finding more and more, so our concern about hazards is going up,” New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colo.

At this rate, there’s no telling how many more moons will be discovered in the future; people need to keep in mind that the Solar System is extremely vast. If the solar system were to be a truck, the sun, which is ~110 times the diameter of Earth across and can fit 1.3 million Earths in its volume, would represent a tiny dot on its surface. There’s still much to be discovered; much more.

The moon is estimated to have a diameter of between 10 and 25 kilometers (6 and 16 mi). These figures are inferred from theapparent magnitude of the moon and by using an estimated albedoof 0.35 and 0.04 for the lower and upper bounds respectively.

S/2012 P 1's orbital period is estimated to be 20.2 +/- 0.1 days, putting it about 5.4% from a 1:3 resonance with the Charon-Pluto orbital period. With Pluto's other moons Nix, S/2011 P 1 and Hydra, it forms part of a 1:3:4:5:6 sequence of near resonances.

The innermost moon, Charon, was discovered by James Christy on June 22, 1978, nearly half a century after Pluto. Two outer moons were imaged by the Hubble Space Telescope Pluto Companion Search Team in May 2005, and precovered from Hubble images taken in June 2002. With the orbits confirmed, the moons have been given definitive names: Hydra (Pluto III, formerly S/2005 P 1) and Nix (Pluto II, formerly S/2005 P 2). The names were chosen in part because the initials (NH) allude to theNew Horizons mission. Further Hubble observations were made in February and March 2006. The possibility of rings created by impacts on the smaller moons will be investigated by the New Horizons probe. The fourth moon was announced in July 2011,and the fifth in July 2012.

The International Astronomical Union, which oversees the naming of celestial bodies, stipulates that objects in Pluto’s vicinity must be named according to underworld mythology. Hence Pluto, Charon, Nix and Hydra. P4 and P5 have yet to be named.

In the years following the New Horizons Pluto flyby, astronomers plan to use the infrared vision of Hubble's planned successor, NASA's James Webb Space Telescope, for follow-up observations. The Webb telescope will be able to measure the surface chemistry of Pluto, its moons, and many other bodies that lie in the distant Kuiper Belt along with Pluto.