Pluto and Its Moons
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Pluto has been a mysterious object since its discovery in 1930. It is too small to show a disc in all but the largest telescopes. No probe has visited it and, hence, most of what we know about its physical characteristics is from telescopic data. Recent Hubble Space Telescope images show a few crudely resolved surface features on this distant world. Position measurements along with mathematics and gravitational theory have yielded information on Pluto’s orbit. The New Horizons probe launched in 2006 will not reach Pluto until 2015 and, hopefully, we will get our first close-up images of its surface.
Up until 2006, Pluto was classified as a planet. For many years, it was thought to be similar in size to Mars and Mercury. This changed in the late 1970 s when Pluto’s largest moon, Charon, was discovered. Astronomers measured both the orbital period of Charon and its distance from Pluto, and from this, computed the combined mass of Pluto and Charon. They found that the...