Pluto Pluto is still included in your book
Pluto? • Pluto is still included in your book as a planet, but has recently been demoted to a dwarf planet • We will discuss some of the characteristics of Pluto today and compare them to the other planets • With your current knowledge of the planets, you can also judge whether Pluto is 'worthy' of planetary status
Properties of Pluto Semimajor Axis 39. 5 A. U. Orbital Eccentricity 0. 249 Orbital Period 248 years Rotational Period -6. 4 days Mass 1. 27 x 1022 kg 0. 0021 x Earth Radius 1137 km 0. 18 x Earth Average Density 2. 06 g/cm 3 0. 374 x Earth Surface Gravity 0. 66 m/s 2 0. 067 x Earth Surface Temperature 40 - 60 K ~300 K for Earth Atmosphere Methane?
Discovery of Pluto • As was the case with Neptune, it was believed that an unseen planet was still tugging on the others • The lead searcher for this undiscovered planet was Percival Lowell, who spent over a decade looking • _ • Surprisingly, Pluto is too small to have any gravitational effects on Uranus or Neptune, and was found essentially by chance
Pluto's Orbit • _ • At perihelion, Pluto is only 29. 66 A. U. from the Sun, while at aphelion, Pluto is 49. 31 A. U. away • This orbit actually brings Pluto inside of Neptune's orbit for a period of time • The two will never collide, however, because the planets share a 3: 2 resonance Pluto orbits the Sun 3 times in the time it take for 2 revolutions of Neptune
Observations of Pluto Ground-based image • Pluto's huge distance from the Sun and its very small size make it hard to observe • _ • Ground-based measurements of the Pluto-Charon system require the best telescopes on Earth • Hubble Space Telescope has provided the most detailed images of Pluto and Charon to date HST
Pluto and Charon • Pluto and Charon are very similar in size – Pluto diameter ~ 2270 km – Charon diameter ~ 1300 km • The two bodies are tidally locked, so that the same side constantly faces the other body • _ • Recently, Pluto and Charon's orbit was aligned with Earth so that many eclipses between the two were visible
More Moons for Pluto • In 2005, astronomers using the Hubble Space Telescope discovered two more moons in orbit around Pluto • The two small bodies are named Nix and Hydra • _
Pluto's Surface • Direct measurements of Pluto's surface have not been made, but it assumed to be an ice/rock mixture • Spectroscopic studies have revealed the presence of methane • _ • • The 'image' at right is an HST model based on multiple observations
Visiting Pluto • The first probe to visit Pluto and Charon will be the New Horizons spacecraft • New Horizons was launched in January of this year • _ • This craft will provide the first real images of Pluto and Charon's surface
What is Pluto? • Pluto is far from the Sun, has a very odd orbit, and exhibits characteristic more like a moon than a planet • A combination of factors has led astronomers to believe that Pluto may be a member of the Kuiper belt • No matter what Pluto actually is, its title as a planet has been stripped by the International Astronomical Union ?
What Defines a Planet? • _
The Troublemakers Note: All images are artist conceptions
The IAU Definition The definition of a planet as of August 2006 is: 1. _ 2. _ 3. _ A dwarf planet fulfills conditions 1&2. All other objects are small Solar System bodies.
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