14b. Pluto, Kuiper Belt & Oort Cloud Basic characteristics Pluto’s moons The Kuiper Belt Resonant Kuiper Belt objects Classical Kuiper Belt objects The Oort Cloud

Pluto Data: Numbers Diameter: 2,290.km 0.18 . Earth Mass: 1.0 . 1022 kg 0.002 . Earth Density: 2.0 . water 0.36 . Earth Orbit: 5.9 . 109 km 39.53 AU Day: 6d.09h 17m 51s 0.27 . Earth Year: 248.6 years 248.6 . Earth

Pluto Data: Special Features Pluto is the farthest planet from the Sun Pluto is the smallest planet Pluto has a very thin atmosphere Pluto is much smaller than the Moon Pluto has only ~0.18 . the mass of the Moon Pluto has only ~0.66 . diameter of the Moon Pluto’s interior likely consists of two layers An “icy” mantle (~25% of Pluto’s mass) A “rocky” core (~75% of Pluto’s mass) Pluto is extremely difficult to observe from Earth Pluto is extremely small & far from the Sun Pluto’s moon Charon has ~0.08 . Pluto’s mass

Pluto Data (Table 14-5)

Pluto’s Amazing Discovery The reason for a search Apparent discrepancies in Neptune’s predicted orbit Actually no unaccounted perturbations of Neptune The actual search Percival Lowell Urged construction of a wide-field astronomical camera Camera was completed in 1929 Clyde Tombaugh worked at Lowell Observatory Discovered Planet X on 18 February 1930 Announced discovery on 13 March 1930 Some obvious problems Much more dim & small than expected More highly elliptical orbit than any other planet More steeply inclined orbit than any other planet

Pluto & Charon Are Unique Objects Planetary patterns Terrestrial planets H2 & He poor planets with solid surfaces Satellites much smaller than parent planets Jovian planets H2 & He rich planets with no solid surfaces Pluto’s patterns Composition Mixture of ices & rock with a solid surface Satellite Closest in mass & diameter of all Solar System pairs

The Discovery of Charon U.S. Naval Observatory James W. Christy 1978 Examined existing photographs of Pluto Noted a bulge on one side Examination of other photos confirmed a moon Fundamental characteristics Orbital period of ~ 6.4 days < 5 % the Earth-Moon distance Mutual synchronous axial rotation One side of Charon always faces Pluto One side of Pluto always faces Charon

Determining Surface Characteristics An extremely rare alignment Charon’s line of nodes points directly toward Earth Throughout the years 1985 to 1990 Mutual eclipses of Pluto & Charon Determined most accurate sizes of Pluto & Charon Determined generalized brightness patterns of Pluto & Charon The Hubble Space Telescope Also helpful in determining surface brightness

Kuiper Belt Objects (KBO’s) Hypothesized Gerard Kuiper 1951 Proposed a source region for some comets Discovered David Jewitt & Jane Luu 1992 Found 1992 QB1 ~ 42 AU from the Sun Spectrally very similar to Pluto & Charon More than 1,000 KBO’s have been discovered Quaoar discovered June 2002 Quaoar measured September 2002 ~ 1,300 km in diameter & in a nearly circular orbit Implications Pluto & Charon may be the closest & largest KBO’s Should we still consider Pluto a planet ? ? ?

Computer-Derived Views of Pluto

Kuiper Belt Objects (KBO’s) Hypothesized Gerard Kuiper 1951 Proposed as a source region for short-period comets Discovered David Jewitt & Jane Luu 1992 Found 1992 QB1 ~ 42 AU from the Sun Spectrally very similar to Pluto & Charon 1,352 known KBO’s as of early 2008 Quaoar discovered 4 June 2002 Quaoar measured September 2002 Quaoar announced 7 October 2002 ~ 1,300 km in diameter & in a nearly circular orbit Implications Pluto & Charon may be the closest large KBOs I.A.U. no longer considers Pluto a [major] planet ! ! !

Resonant Kuiper Belt Objects 1:2 resonance Twotinos 14 confirmed members 2:3 resonance Plutinos 92 confirmed members Pluto is the naming member 104 possible members 2:5 resonance 6 confirmed members 3:5 resonance 10 confirmed members 4:7 resonance 5 confirmed members Additional resonances are known 6 confirmed members in 6 resonances

Resonant TNO Orbits http://en.wikipedia.org/wiki/Image:TheKuiperBelt_classes-en.svg

Pluto In Color Pluto rotating http://upload.wikimedia.org/wikipedia/en/3/30/Pluto.jpg Pluto rotating

The Discovery of Hydra & Nix http://upload.wikimedia.org/wikipedia/commons/3/31/Pluto_system_2005_discovery_images.jpg Pluto's moons

The Largest Plutinos http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/ ThePlutinos_Size_Albedo_Color2.svg/250px-ThePlutinos_Size_Albedo_Color2.svg.png

Trans-Neptunian Objects (TNO’s) http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/ TheTransneptunians_73AU.svg/800px-TheTransneptunians_73AU.svg.png

8 Largest Trans-Neptunian Objects http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/EightTNOs.png/800px-EightTNOs.png

Still More Trans-Neptunian Objects http://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/ TheTransneptunians_Size_Albedo_Color.svg/600px-TheTransneptunians_Size_Albedo_Color.svg.png

The Outer Solar System KBO’s Scattered Disc Objects http://upload.wikimedia.org/wikipedia/commons/thumb/8/81/Outersolarsystem_objectpositions_labels_comp.png/ 611px-Outersolarsystem_objectpositions_labels_comp.png

Classical Kuiper Belt Objects Neptune’s influence negligible from 42 to 48 AU Small-object orbits are essentially undisturbed About two-thirds of all known KBO’s are here Possible observational bias ⇒ Close enough to be seen First discovered KBO was labeled QB1 Classical KBO’s are known as cubewanos “Q-B-1-os” Two categories Dynamically cold population Orbital eccentricity < 0.1 Orbital inclination < 10° Dynamically hot population Orbital eccentricity > 0.1 Orbital inclination > 10° & < 30°

Eris Basic facts Largest known KBO One moon named Dysnomia ~ 1,300 + 200 km in diameter Highly uncertain Ninth largest known object in orbit around the Sun One moon named Dysnomia http://upload.wikimedia.org/wikipedia/commons/5/5b/Eris_and_dysnomia2.jpg Dysnomia Eris

The Orbit of Eris http://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Eris_Orbit.svg/644px-Eris_Orbit.svg.png

The Öpik-Oort Cloud Hypothesized by two astronomers Ernst Öpik Estonian 1932 Comets originate in a distant spherical cloud Jan Hendrik Oort Dutch 1950 Comets completely sublimate after a few orbits Comets have survived to the present time Basic characteristics Spherical cloud of dormant long-period comets ~ 50 to 50,000 AU from the Sun ~ 1 light year ~ 25% the distance to Alpha Centauri, the nearest star

Features of the Öpik-Oort Cloud Two segments Inner cloud Torus distribution 50 to 20,000 AU from the Sun Source of Halley-type comets Outer cloud Spherical distribution 20,000 to 50,000 AU from the Sun Source of long-period comets Oort Cloud objects OCO’s Only 4 candidates have been identified 2000 CR105 2003 Sedna 2006 SQ372 2008 KV42

The Kuiper Belt & Oort Cloud http://upload.wikimedia.org/wikipedia/commons/0/03/Kuiper_oort.jpg

Sedna Named after the Inuit goddess of the sea Orbital parameters Discovered in 2003 Farthest presently known natural Solar System object Maximum possible diameter is ~ 75% that of Pluto Orbital parameters 76.361 AU Perihelion Visible only when it is closest to the Sun 937 AU Aphelion

Sedna’s Orbit & the Oort Cloud http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/ Oort_cloud_Sedna_orbit.svg/600px-Oort_cloud_Sedna_orbit.svg.png