According to Sky & Telescope, P5 was announced by the IAU's Central Bureau for Astronomical Telegrams last night and it's a dinky moon, potentially smaller than P4, which was discovered a year ago in July 2011.
P4 is thought to have a diameter of between 8 to 21 miles (13 to 34 kilometers), whereas Pluto's largest moon Charon measures 648 miles (1,043 kilometers). Nix and Hydra have diameters of 20 to 70 miles (32 to 113 kilometers).
P5 is orbiting Pluto at a distance of around 26,000 miles (42,000 kilometers) in the same plane as Pluto's other moons, indicating that Pluto may have been hit in the solar system's history, spewing debris that accumulated in orbit, creating the system of satellites we see today.
The continuing discoveries of small moons around Pluto is causing some concern for scientists with NASA's New Horizons mission that, in 2015, will make a flyby of the little world.
As cautioned by New Horizons lead scientist Alan Stern last year, it's not so much that Pluto plays host to more small moons, the growing concern is for the potential clouds of dust and other small debris that the increasingly populated satellite system may generate.
"Even more worrisome than the possibility of many small moons themselves is the concern that these moons will generate debris rings, or even 3-D debris clouds around Pluto that could pose an impact hazard to New Horizons as it flies through the system at high speed," Stern said in a November 2011 mission update.
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As we spot more moons surrounding Pluto, the hazard becomes more acute, but the New Horizons team have a few tricks up their sleeve.
As discussed during a February Space Hangout with Alan Stern (video below), we were able to discuss some of the contingency plans, including aiming the New Horizons probe at Charon's orbit. The rationale is that Charon's gravity should clear a doughnut-shaped region around Pluto that will be relatively clear of dust and other debris, reducing the risk of a hyper-velocity impact with a hypothetical debris cloud.
Watch the space hangout (the Pluto debris discussion starts at around 33 minutes):
Image: The Pluto system, including the location of P5. Credit: NASA, ESA, and M. Showalter (SETI Institute)