P5

P5 is a moon of Pluto, which is a dwarf planet. It was discovered in July 2012 by astronomers using the Space Hubble Telescope.

P5, also called S2012 (134340) 1, is the fifth of Pluto’s moons to be discovered. Astronomers used the Wide Field Camera 3 that is fitted to the Hubble Space Telescope to obtain nine sets of images of the satellite. Its brightness is only about half that of P4, which until the P5 discovery was the dimmest of Pluto’s moons. P5 has just one hundred thousandth of Pluto’s brightness.

NASA’s New Horizons space probe, launched in January 2006, is expected to provide more information about Pluto and its satellites – Charon, Nix, Hydra, P4 and P5 – when it flies by the dwarf planet in July 2015. As of August 2012, New Horizons was about halfway between Earth and Pluto, at a distance of about 10 astronomical Units (AU), or 1.5 billion kilometres, from the two planets.

But the discovery of new moons around Pluto may pose some problems for New Horizons as a debris field around it and other Pluto moons may affect the spacecraft. As with Pluto’s other moons, P5’s gravitational field may be too weak to consolidate any debris around it. These tiny bodies, which may not be detectable from Earth, may be the greatest navigational hazard for the spacecraft. The probe is travelling at 13 km per second, the fastest speed achieved so far by a spacecraft launched from Earth. NASA scientists warn that they may have to alter the spacecraft’s course if such debris is identified early enough.

Astronomers believe that P5 has an irregular shape and was formed from a collision of space debris. Such a collision could have occurred billions of years ago. On impact, the satellite would have lost most of its volatile ice, such as that of nitrogen and methane. The remaining body could just consist of water ice. Its orbit around Pluto is located between the orbits of Nix and Charon at about 42,000 kilometres from the barycentre, or centre of mass, of the Pluto-Charon dual system.

P5’s orbit is believed to lie in the same plane as the orbits of Pluto’s other moons. These moons form nested orbits around Pluto and Mark Showalter of the SETI Institute has described them as resembling Russian dolls.