New moons for Neptune?

Astronomers say they have discovered three additional moons circling Neptune. If confirmed, the findings would bring to 11 the planet’s retinue and would be the first Neptunian moons found since Voyager 2 flew past the planet in 1989 and the first discovered with ground-based telescopes since 1949.

Only 30 to 40 kilometers in diameter, the newly discovered bodies are too dim by a factor of 100 million to be discerned by the naked eye. Also complicating their observation is their great distance from Neptune–roughly 60 times as far as Triton, the planet’s largest moon. A team led by Matthew J. Holman of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and J.J. Kavelaars of the National Research Council of Canada in Ottawa reported the findings in a Jan. 13 circular of the International Astronomical Union.

Each of the bodies orbits in a plane different from that of most of the solar system’s planets. According to the astronomers, one of the objects orbits Neptune in the direction opposite to the planet’s rotation. Their findings suggest the purported moons arose from collisions or were captured by the planet shortly after the solar system formed.

But planetary scientist Brian G. Marsden of Harvard-Smithsonian cautions that it’s not certain that the objects are in fact satellites of Neptune. New observations, based on the predicted positions of these objects a few months from now, should determine whether these denizens of the solar system belong to Neptune, he notes.

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