Wednesday, July 20, 2011

Pluto Has A Fourth Moon!

Once again, the planet that was originally discovered through a fortunate series of circumstances and subsequently recognized as a new prototype for a third class of bodies orbiting our Sun (and likely other stars as well) has surprised us. Astronomers using the Hubble Space Telescope to search for rings around Pluto found something else, something unexpected: Pluto has a fourth moon!

The tiny moon is the smallest of the Pluto system, estimated to be 8-21 miles in diameter, and is located between two of Pluto's other small moons, Nix and Hydra. Interestingly, Pluto's moons, including its large moon Charon, which is big enough to be in hydrsostatic equilibrium, are believed to have formed via an impact between another celestial body and Pluto. If that sounds familiar, it should. The only other moon in our solar system known to have formed like this is Earth's moon.

Observation of this tiny new moon will be added to the agenda of New Horizons, for its flyby of Pluto four years from now.

Dr. Mark Showalter of the SETI Institute in Mountain View, California, marveled at Hubble's ability to see such a tiny object more than three billion miles from Earth. This finding highlights the importance of space telescopes and serves as a reminder that the James Webb Space Telescope, which is in danger of losing its funding, is a crucial need for our continuing to make pioneering discoveries in astronomy.

The notion that Pluto may have more than the three moons we know of has long been discussed, but answers were not expected until the New Horizons flyby. This discovery emphasizes yet again how premature any "reclassification" of Pluto is. It strongly suggests there is much more about the Pluto system we have yet to learn. How can we classify or reclassify something about which we know so little?

The Pluto system is the only one in our solar system in which a small, non-gas giant has multiple moons, which formed in a collision similar to the one that created Earth's moon. We are only beginning to understand this little planet that is truly a "strange, new world."

For more on the discovery, visit .

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