New moons for Neptune

Neptune is a gas giant planet

By Dr David Whitehouse BBC News Online science editor

Astronomers have found three new moons orbiting the distant gas-giant planet Neptune.

The discovery boosts the number of known satellites of the gas giant to 11.

They are the first moons to be discovered orbiting Neptune since the Voyager II flyby in 1989, and the first discovered from a ground-based telescope since 1949.

The researchers were led by JJ Kavelaars of the National Research Council of Canada and Matthew Holman of the Harvard-Smithsonian Center for Astrophysics.

Researchers believe that the giant planet's compliment of irregular satellites is the result of an ancient collision between a former moon and a passing comet or asteroid.

"Such collisions result in the ejection of parts of the original parent moon and the production of families of satellites," Dr Kavelaars told BBC News Online.

"Those families are exactly what we're finding."

Points of light

Prior to this find, Neptune was known to have two irregularly-shaped satellites and six regular satellites.

The new ones were undetected during the Voyager II 1989 encounter because they are faint and at a great distance from Neptune.

The object (circled) was spotted by US and Canadian scientists

According to Holman, "The discovery of these moons has opened a window through which we can observe the conditions in the solar system at the time the planets were forming."

To find the new moons, Holman and Kavelaars employed a new technique.

Using the four-metre Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile, and the 3.6-meter Canada-France-Hawaii Telescope in Hawaii, they took multiple exposures of the sky surrounding the planet Neptune.

The images were digitally combined after correcting for the Neptune's motion across the sky. This way, stars showed up in the final combined image as streaks of light, while the tiny moons appeared as points of light.

The new satellites are only about 35 kilometres in size. Their small size and distance from the Sun means they are 100 million times fainter than can be seen with the unaided eye.

"These discoveries required painstakingly careful observations, and will figure prominently when astronomy textbooks are revised," says Arthur Carty, president of the National Research Council of Canada.