Pluto may not be a full-fledged planet anymore, but it's got its share of moons. Including a tiny moon just recently spotted by astronomers. The new addition, which isn't yet named, brings the dwarf planet's number of known satellites to four. That's more than Mercury, Venus, Earth and Mars have combined.

Based on Hubble Space Telescope photographs of Pluto's newfound companion, astronomers estimate the moon to be just a few dozen kilometers in diameter. Hubble also spotted Nix and Hydra, two larger moons of Pluto, in 2005. Its largest moon, Charon, has been known since the 1970s. Pluto's entire system of moons may have emerged from a protoplanetary smashup billions of years ago.

The new moon turned up during a Hubble search for a dust ring around Pluto. Such a ring could pose a hazard to NASA's New Horizons probe, now on its way to Pluto for a flyby in 2015. So far, the search for any rings has come up empty. That's good news for fans of Pluto, who are looking forward to our first close up view. And now New Horizons will have a bit more to check out once it reaches Pluto's neighborhood.

—John Matson

[The above text is a transcript of this podcast.]