Class 22 - Pluto and Charon

Before considering Pluto and Charon, we need to look at Triton - the largest moon of Neptune. Triton is about 78% the size of the Moon and a little larger than Pluto. It is in retrograde orbit around Neptune at 15 Neptune radii away from the planet and in an inclined orbit. The combined effect of the orbital inclination of Triton and Neptune's 26 (or so) degree obliquity means that Triton has very bizarre seasons.

The retrograde orbit almost certainly means that Triton was captured. So, both Pluto and Triton were formed in the outersolar system - one got captured, the other happened upon a safe niche - the 3:2 resonance with Neptune - where it could neither be captured nor flung out of the solar system or inwards to impact the inner solar system bodies. The capture process certainly heated up Triton, causing cryovolcanism - that is, volatile material heated from below and erupting onto the surface. Cryo- means that normally these materials would be frozen.

The text is rather out of date on Pluto. Instead, I refer you to my website on Pluto - particularly the material in the 3 pages towards the bottom. This is also a little out of date and a little low-level for this class - but you should at the very least know this stuff.

Here is the slide show from the class.

Also see Pluto mission page - including movies of the flyby.