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Friday, August 19, 2011

Pluto’s four moons

For an object that is no longer classified as a planet, Pluto has been accumulating moons of its own.  I thought Pluto only had one moon, Charon, which incidentally is almost half the size of Pluto.  Apparently, I missed the news about moons two and three, Nix and Hydra.  Now astronomers using the Hubble telescope have identified a fourth moon, name to be determined.

At around 20 kilometers across, the new moon, temporarily designated P4, is tiny.  Nix and Hydra are each closer to 70 kilometers in diameter, which is still small enough to walk across in a few days.  In comparison, Charon is about 1000 kilometers across and Pluto itself has a diameter of about 2300 kilometers.

These two images, taken about a week apart by NASA's Hubble Space Telescope, show four moons orbiting the distant, icy dwarf planet Pluto. The green circle in both snapshots marks the newly discovered moon, temporarily dubbed P4, found by Hubble in June.
Credit: NASA, ESA, and M. Showalter (SETI Institute).

BTW, Nix and Hydra were also discovered using the Hubble back in 2005.