Pluto has four moons!

Recently I read the announcement that astronomers found a fourth moon orbiting Pluto in Hubble Space Telescope observations. Apparently they were not looking for more moons; instead, they were looking for possible rings around Pluto.

My first thought: Wait, Pluto had three moons before?

I blush to admit that I only knew of Charon, Pluto’s largest moon (1207 km in diameter). I missed the announcement in 2005 of the discovery of two more Pluto moons: Nix (46-137 km) and Hydra (61-167 km). Now’s a good time to catch up! The new moon (temporarily designated P4 as “Pluto’s 4th satellite”) is only 13-34 km in diameter. That’s small, but there is precedent: Phobos and Deimos, the moons of Mars, are only 20 and 15 km in diameter respectively.

Here is a composite of two images that provides the basis of the new moon’s discovery:

The timing of this serendipitous discovery is excellent. The New Horizons mission will fly past Pluto in July of 2015, and perhaps it will have the chance to investigate P4 up close — or even add more moons to Pluto’s tiny family!

1 Comment
1 of 1 people learned something from this entry.

  1. Terran said,

    July 26, 2011 at 3:47 pm

    (Learned something new!)

    I blush to admit that I only knew of Charon…

    Heh. Yeah, Charon is as far as I got as well, though now that you mention it, I have a sort-of fuzzy, vague sense that I had heard something about “Nix” a few years ago as well.

    It continues to astound me that Pluto has any moons, given that it’s only barely a planet itself. Oh, wait, it’s not a planet… ;-)

    Thanks for the planetary update of the day!

Post a Comment

I knew this already. I learned something new!