The small planet has a complex collection of satellites: Expert team

US astronomers using the Hubble Space Telescope have discovered a fifth and the tiniest moon yet, orbiting the icy dwarf planet Pluto.

The mini-moon is estimated to be irregular in shape and between 10 km and 25 km across. It is visible as a speck of light in Hubble images, NASA said. The newly discovered moon could help reveal more on how the Pluto system came into existence and evolved ever since.

It was detected in nine separate sets of images taken by Hubble’s Wide Field Camera 3 taken during June and July. The Pluto team is intrigued that such a small planet can have such a complex collection of satellites.

“The moons form a series of neatly nested orbits, a bit like Russian dolls,” said Mark Showalter from the Seti Institute, the leader of the team that discovered the new moon.

Pluto’s largest moon, Charon, which is about 1,000 kilometres across, was discovered in 1978.

“The inventory of the Pluto system we’re taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft,” added Alan Stern of the Southwest Research Institute, the mission’s principal investigator.

A NASA spacecraft named New Horizons is currently en-route to Pluto and will arrive there in 2015. New Horizons will return the first ever detailed images of the Pluto system, which is so small and distant that even Hubble can barely see the largest features on its surface.

Pluto was discovered by American Scientist Clyde Tombaugh in 1930. It was regarded as the ninth full-fledged planet in the Solar System but astronomers have since demoted it to a dwarf planet in 2006.

Pluto was declassified as a planet due to a recognition that it is one of several large, icy objects that reside in the Kuiper Belt, a region just beyond the orbit of Neptune.

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