Hubble Space Telescope discovers fourth moon of Pluto

As the Hubble Space Telescope worked to support NASA’s New Horizons mission to Pluto, it also found a fourth moon for the dwarf planet, scientists announced today.

Scientists using the Hubble Space Telescope have discovered a new moon of the dwarf planet Pluto. NASA made the announcment on July 20, 2011, which coincidentally is the anniversary of the first human steps on Earth’s moon in 1969.

Pluto’s new moon – the fourth known for the planet – is temporarily called P4. It has an estimated diameter of only about 8 to 21 miles (13 to 34 km), making it the smallest Plutonian moon. This brings the total to four known moons orbiting Pluto, which scientists classified as a planet in our solar system until 1996 when it was demoted to dwarf planet status by the International Astronomical Union. Mark Showalter of the SETI Institute in Mountain View, Calif., who led the observing program with Hubble, said:

I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion km).

Computer-generated map of Pluto from Hubble images.

Computer-generated map of Pluto from Hubble images.

This newly discovered, tiny moon of Pluto emerged from recent mapping work done by the Hubble Space Telescope to support NASA’s New Horizons mission to explore Pluto.

In a May 2011 interview with EarthSky, Dr. Alan Stern – principal investigator of the New Horizons mission – described mission goals

We’re going on New Horizons not to rewrite the textbooks, but to write the textbooks for the first time about how dwarf planets work, how they operate, how their geology behaves, how they evolved through time, what their moons are like. It’s really going to be revolutionary.

NASA’s Hubble Space Telescope was used to discover three of the four moons of Pluto – Nix, Hydra, and now P4. Pluto’s largest moon, Charon, was first resolved by Hubble as well. The fourth moon discovered, P4, appeared as a very faint smudge in Hubble images from 2006, but it was ignored because it was drowned out by what’s called a diffraction spike, an error in imaging.

Stay tuned for more discoveries to come from NASA’s New Horizons mission, which will reach Pluto in 2015.

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