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Dwarf Planets and Kuiper Belt Objects • Dwarf planets • Pluto Properties The Discovery of Planet X A Discovered Feb 8, 1930 by then 24-year old Clyde Tombaugh Its existence was predicted by Percival Lowell using the same techniques that Leverrier used to find Neptune Moons---Charon, Nix and Hydra Ceres, Pluto, Eris, Haumea, and Makemake B Kuiper Belt Objects Resonant objects, Classical, Scatered Objects Orbit: Pluto Period 248 years Semi-major axis 39.5 AU e= 0.25 inclination of 17o to ecliptic Physical Properties Neptune Period=164.88 years Distance= 30.1 AU Locked in 3:2 resonance with Neptune 248/164.88 = 3/2 Mass=0.002 x Earth's mass Radius 0.2 x Earth's radius Density 1.84 g/cc Rotation -6.4 days Tilt 122o Temp -223 C (solid methane) Surface suggests solid ice covers the planet (N2, CH4, CO). This ice probably sublimates into a thin atmosphere during the day and falls a snow at night. Pluto-Charon System 6.4 days Discovered in 1978 Charon 6.4 days Pluto 19,700 km ! ~ 35 % ice and 65 % rock. ! orbital period of 6.4 days ---identical to the rotation period of Pluto! !Charon rotates once for each revolution just as the Earth's Moon does the same side of Charon always faces Pluto Pluto’s two other Moons: Nix and Hydra Nix and Hydra have circular orbits in the same plane as Charon, but are more distant from the planet. a series of eclipses (1985-1991) occurred provided detailed information on the properties of size Charon Radius Mass= (1/2 Pluto) 11.6% of Pluto Kuiper Belt Objects Nix •The Kuiper belt contains objects with an average distance to the sun of 30 to about 55 AU, usually having closeto-circular orbits with a small inclination from the ecliptic. Nix Hydra Hydra Charon Orbit Period Charon 6.4 days Nix 25 days Hydra 38 days Origin for all three satellites---a giant impact led to the formation of Charon, Nix and Hydra A vast number of frozen bodies beyond the orbit of Neptune, known as "The Kuiper Belt." These Kuiper Belt Objects number in the millions, many are the size of mountains to the size of Pluto. A dwarf planet is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite More explicitly, it has to have sufficient mass to overcome its compressive strengthand achieve hydrostatic equilibrium Five dwarf planets: Eris (.0028), Pluto (.0022), Haumea (.00067), Makemake (.00067), and Ceres (.00015) ------- Mass(Earth Masses) Kuiper belt objects are further classified into the following groups: Resonant objects---- are locked in an orbital resonance with Neptune. Objects with a 1:2 resonance are also called twotinos, and objects with a 2:3 resonance are called plutinos, after their most prominent member, Pluto. Classical Kuiper belt objects (also called cubewanos) have no such resonance, moving on almost circular orbits, unperturbed by Neptune. Examples are Quaoar and Makemake. The scattered disk contains objects further from the Sun, usually with very irregular orbits. A typical example is Eris. (MAH-kay ) It is suspected 2000 dwarf planets may be found when the entire region is explored. Plutinos Orbital resonances These resonances occur when Neptune's orbital period is a precise fraction of that of the object, such as 1:2, or 3:4. New Horizons Mission to Pluto Plutinos 2:3 resonance most heavily populated with over 200 known objects is the 2:3 resonance. Objects in this resonance complete 2 orbits for every 3 of Neptune, and are known as plutinos---Pluto is among them. The 3:4, 3:5, 4:7 and 2:5 resonances are less populated New Horizons Launch 2006, arrive at Pluto by 2015. After Pluto, the spaceship will visit one or more Kuiper Belt Objects End of Chapter 13b Uranus, Neptune, & Pluto Go to Chapter 14a