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Transcript
Trans-Neptunian Objects and Pluto Astronomy 311 Professor Lee Carkner Lecture 21 Trans-Neptunian Region Beyond Neptune is the region of small, icy, Trans-Neptunian Objects The region is populated by icy planetesimals that either formed at the edge of the solar system or were ejected out by the planets Pluto -- God of the Underworld Pluto is the God of the Dead in Roman mythology The Discovery of Pluto In the late 1800’s it was believed that Neptune’s orbit was being perturbed by a 9th planet In 1930 a young astronomer named Clyde Tombaugh found a very faint planet near Lowell’s predicted position The Discovery of Pluto Observing Pluto Through most telescopes Pluto simply appears as a faint star Pluto Facts Size: 2300 km Orbit: 39.5 AU Description: Pluto’s Orbit Pluto’s orbit is much more eccentric and much more inclined than any planet Pluto’s orbit carries it inside the orbit of Neptune Pluto is tipped on its side like Uranus Composition of Pluto Pluto has a density of 2000 kg/m3 Pluto is probably composed of ice and rock Spectra of Pluto reveal the presence of methane, nitrogen and carbon monoxide HST Images Pluto Features of Pluto The other bright regions may be areas where impacts have gouged out fresh ice Pluto and Charon Charon Pluto’s moon Charon was discovered as a small bulge in a high resolution image (1978) Pluto and Charon are in a close, tidally locked orbit Where Do Comets Come From? Comets are small (few km) icy bodies that sometimes come in to the inner solar system on highly elliptical orbits Short period comets Long period comets The Kuiper Belt Around 1950 Kuiper and Edgeworth proposed a belt of comets out beyond Neptune In 1992 the first (besides Pluto) Kuiper belt object was discovered (QB1) The Kuiper Belt Discovering Kuiper Belt Objects The Known Kuiper Belt There are now hundreds of known Kuiper Belt Objects (KBOs) Total population of large KBO’s may be 70000 (larger than 100 km) Kuiper belt seems to end at about 50 AU Larger and larger KBO’s being detected Eris The largest KBO currently known is called Eris Larger than Pluto Semi-major axis of 68 AU, but is currently at 97 AU due to high eccentricity Has a small moon, Dysnomia Large KBO Size Comparisons Is Pluto a Planet? Pro Con What Makes Something a Planet? Planets used to be obvious Needed new definition when rest of solar system was discovered with telescopes The International Astronomical Union (which has authority over these things) removed Pluto from the list of planets in 2006 The Oort Cloud In 1950 Dutch astronomer Jan Oort postulated a spherical shell of comets surrounding the solar system at about 50,000 AU Population of the Oort Cloud The Oort cloud is the source of the long period comets They are too far away to see, so we only have indirect methods of studying them Diagram of the Oort Cloud Summary Past the orbit of Neptune the solar system is made up of many small icy bodies Kuiper Belt extends from 30-500 AU formed from left over planetesimals at the edge of the solar system Oort Cloud extends from 1000-100,000 AU formed from ejected icy planetesimals Summary: Pluto Description: small, cold , distant Pluto resembles a large Kuiper belt object more than a planet Has a closely orbiting large moon Charon Properties Thin atmosphere Very cold (~50 K) Bright surface features possibly composed of fresher ice
