Hubble detects new moon around Pluto

The discovery of moons around dwarf planets beyond Neptune, known as trans-Neptunian objects, is causing astronomers to question how they got there in the first place.

The Hubble Space Telescope has discovered a tiny fourth moon orbiting the distant icy dwarf planet Pluto, ABC reports, referring to NASA.

The space telescope was searching for rings around the dwarf planet at the edge of our solar system when it came across P4, the temporary name for the newly discovered moon.

With an estimated diameter of 13 to 34 kilometres, P4 is the smallest of Pluto's four moons.

Pluto's largest moon, Charon, is 1,043 kilometres across, and its other moons, Nix and Hydra, are in the range of 32 to 113 kilometres in diameter.

"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 kilometers)," says Mark Showalter of the SETI Institute in Mountain View, California, who led this observing program with Hubble.

Professor Paul Francis, an astronomer at the Australian National University's Mount Stromlo Observatory agrees.
"You're only seeing it because it's reflecting sunlight. It's a very small thing, a very long way from the Sun so there isn't much sunlight to reflect."

Francis says the discovery of moons around dwarf planets beyond Neptune, known as trans-Neptunian objects, is causing astronomers to question how they got there in the first place.

"We have no idea where they came from," he says. "Some are big like Charon (Pluto's largest moon) and some absolutely tiny like this new one, which is weird because there isn't much gravity to hold the moon in. How they have so many moons when there isn't much gravity to lock them in is a tricky puzzle."

One explanation is that Pluto's moons formed when Pluto and another planet-sized body collided in the early history of our solar system. Earth's Moon may have formed the same way.

P4 is located between the orbits of Nix and Hydra, both of which were discovered by Hubble in 2005. Charon was discovered in 1978 at the US Naval Observatory.