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Pluto & Friends

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Pluto & Friends Pluto & Friends - Outline • Discovery of Pluto • Characteristics of Pluto • Characteristics of Charon • Pluto’s Downfall as a Major Planet • Large Kuiper Objects • The IAU Resolution Discovery of Pluto • Another planet required to account for apparent perturbations in the orbits of Uranus & Neptune • Unsuccessful attempts were made by Percival Lowell to find an additional planet • Finally discovered in 1930 by Clyde Tombaugh using a newly developed wide-field camera at the Lowell Observatory • Pluto was named after the Roman god of the underworld, and Charon (Pluto’s moon) was named after the mythical boatman who carried the dead into the realm of Pluto Discovery Photographs (Note - new techniques & instrumentation drive a lot of ground-breaking science) Clyde Tombaugh. 65% of the sky photographed & thousands of hours logged over a 10-month period leading up to the discovery of Pluto Properties of Pluto • Average Distance from the Sun: 5.5 light hours (39.5 AU) • Rotation Rate: 6.4 Earth days • Orbital Period: 248 Earth years Atmosphere: Nitrogen & • Axis Tilt: 118° other gases that sublimate from the surface • Number of Moons: 3 Pluto’s Orbit • Orbital Inclination = 17° • Orbital Eccentricity = 0.25 For a circular orbit, Eccentricity = 0.0 Mercury’s Eccentricity = 0.21 Aphelion = 49.3 AU; Perihelion = 29.3 AU Effect ! sublimation & refreshing of volatiles on the surface of Pluto • Axis Tilt = 118° Axis Tilt of Uranus = 98° Pluto’s orbit Relative to the Other Planets Map of the Surface of Pluto • Mass = 0.25% Earth’s Mass • Density = 2.1 g cm-3 • Surface: Reflectivity ~ 30-50% Methane Ice ! Bright Spots ?? ! Dark Spots Charon - 1978 discovery • Mass = 10% Pluto’s Mass (Mmoon = 1.25% Mearth) • Density = 1.6 g cm-3 (a bit low) • Surface = water ice • Charon’s orbital period is equal to Pluto’s rotation period • Formation? Similar to the formation of the Moon, which explains densities Charon’s Orbit Standing on the Surface of Pluto • The sky would be black • The sun would be 1600 times fainter than from the Earth • Charon would loom motionless in the sky with an angular diameter 10 times that of the Moon as viewed from the Earth 2005 Announcement of 2 new moons of Pluto • Designated - S/2005 P1 and S/2005 P2 • 5,000 times fainter than Pluto New Horizons. The Mission: • To map the surface composition & temperature of Pluto & Charon • To characterize the geology & morphology of Pluto & Charon • To characterize the neutral atmosphere & escape rate • To search for rings & additional satellites • To conduct similar investigations of one or more KBOs Trajectory & Present Location September 21-24, 2006 - First View of Pluto by New Horizons Pluto & its moon(s) probably resemble - • The nuclei of comets (ala Tempel) • & Neptune’s moon Triton (discussed later) Brief Review - Oort Cloud & Kuiper Belt • Long Period Comets – Random Inclinations (Oort Cloud) • Short Period Comets – Low Inclinations (Kuiper Belt) The First KBO • Discovered in 1992 • D. Jewitt & J. Luu • Large field of view CCD Images Origin of the Kuiper Belt • Planetesimals whose accretion was disrupted by the formation of Neptune • Neptune stirred up the motions of KBO, causing more collisions Formation of KBOs & Comets Kuiper Belt Orbits Pluto’s Downfall as a Major Planet Plutinos Pluto’s Downfall But… Pluto has at least one moon! Pluto & Charon KBO • So do some KBOs. Large KBOs: (1) Varuna • Discovered in 2000 by McMillan (Spacewatch) • Size ~ 1060 km in diameter (I.e., 40% of Pluto’s diameter) • Orbital Period ~ 283 years • Distance ~ 40-45 AU from Sun • Inclination ~ 17 degrees Size of Varuna compared to other solar system objects How are Sizes of these Distant Objects Determined? • Distance to object • Measure of reflected solar light • Measure of albedo based on comparing optical (reflected) & thermal (absorbed & reradiated as heat) submillimeter-wave light • + some other assumptions Albedo vs. Size Pluto Charon Varuna (2) Quaoar • Discovered in 2002 by Trujillo & Brown • Size ~ 1250 km in diameter • Orbital Period ~ 285 years • Orbit has low eccentricity, with an inclination of 8 degrees & a Sun-Quaoar distance of ~ 43.3 AU. Size of Quaoar compared with other solar system objects Orbit of Quaoar (3) Sedna • Discovered in 2004 by Brown, Trujillo, & Rabinowitz • Size < 1800 km in diameter • Orbital Period ~ 10,500 years • Orbit is extremely elliptical, with a closest approach of 76 AU • First Discovered Oort Cloud Object?? Rough Size of Sedna compared to other solar system objects Zooming out to the Orbit of Sedna Video (4) 2003 UB313 - aka The “10th Planet” • Discovered in 2003 by Brown, Trujillo, & Rabinowitz • Size > 2210 km in diameter, I.e., equal to or larger than Pluto in size • Orbital Period ~ 560 years • Perihelion ~ 38 AU, Aphelion ~ 97 AU • Inclination ~ 44 degrees!! How did such a massive object get so far off the plane of the solar system?? Orbit of 2003 UB313 Spectrum of 2003 UB313 - similar to that of Pluto 2003 UB313 appears to have a moon Moons are quite commonplace Large Objects Continue to be Discovered… 75% Pluto size Period ~ 307 yr Distance ~ 39-52 AU from Sun Inclination ~ 29 degrees 75% Pluto size Period ~ 285 yr Distance ~ 35-52 AU from Sun Inclination ~ 28 degrees IAU Resolution on Pluto: The Triggers • The similarities in the properties of Pluto & the KBOs (mainly the Plutinos) • The exhibit at the Hayden Planetarium in 2001 which showed that there are only 8 planets • The discovery of KBOs comparable to Pluto in size This is a messy issue politically • The public has been told for many years Pluto is a planet • Tombaugh’s family clearly does not want Pluto demoted • The UB313 discoverers would like to be credited for discovering the 10th planet • The team involved in the New Horizons mission to Pluto (launched January 2006) do not want Pluto demoted • But there is also a desire (among the public and some scientist) to have an exact definition of a planet. The definition must please the public and the scientific community .
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