Astronomers using the Hubble Space Telescope (HST) have found a fourth moon orbiting Pluto, the icy dwarf planet that is 3 billion miles from Earth.
The unexpected and amazing discovery was made when the space telescope was searching for potential rings around the distant planet.
The tiny sphere of ice and rock smaller than Earth's moon, temporarily named P4, now joins the three previously known moons of Pluto: Charon, Hydra, and Nix.
The new moon has been temporarily named P4 until the International Astronomical Union (IAU) approve of a suitably mythical name.
Alan Stern, New Horizons’ principal investigator of the Southwest Research Institute stated, "Pluto's satellite system is truly knocking our socks off with surprises — it's magnificently complex, and getting more crowded all the time. I can't wait till we get there to see what other surprises this planet and its moons have in store for us!"
"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than three billion miles.”-- Mark Showalter of the SETI Institute in Mountain View, California
Pluto’s 4 moons
The entire moon system of Pluto is believed to have been formed due to collision between the dwarf planet and another planetary body in the early history of our solar system. Material was flung out due to the impact which united to form the four moons.
P4 was first detected by the HST Wide Field Camera 3 on June 28, 2011 and confirmed in follow-up images captured on 3 and 18 July.
The biggest, Charon, was discovered in 1978 at the US Naval Observatory and confirmed using Hubble in 1990, while Nix and Hydra were discovered by Hubble in 2005.
Mark Showalter of the SETI Institute in Mountain View, Calif., who led this observing program with Hubble, stated, "I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than three billion miles.”
The 4th moon
According to the US space agency, P4 is the smallest of the four moons and is located between the orbits of Nix and Hydra. It has an estimated diameter of only eight to 21 miles.
In contrast, Charon, the planet’s largest moon is 648 miles across, almost 80 times bigger while the diameter of the other two moons, Nix and Hydra, are in the range of 20 to 70 miles.
The new moon is about 10 percent as bright as Nix which was Pluto’s smallest moon.
Showalter stated, “The reason there’s such a big uncertainty [about] its size is that it all kind of depends on how bright the surface is.
"If it’s a fairly bright surface, then it would be a smaller object. If it’s a fairly dark body, like some of the distant outer solar objects are very, very dark, then it would have to be the larger size. If you consider those are still remarkably small objects when you consider we are seeing it from three billion miles [4.8 Billion kilometers] away.”
The discovery of the new moon paves the way for NASA’s New Horizons mission which is scheduled to fly through the Pluto system in 2015.