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

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 simply be closest & largest KBO’s The I.A.U. no longer considers Pluto a [major] planet ! ! !

Resonant Kuiper Belt Objects Three orbital resonances with Neptune 2:3 resonance Plutinos 92 confirmed members Pluto is the naming member 104 possible members 1:2 resonance 14 confirmed members 2:5 resonance 6 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 http://upload.wikimedia.org/wikipedia/en/3/30/Pluto.jpg

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

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

Eight 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 May be 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 independently 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 long-period comets ~ 50 to 50,000 AU from the Sun ~ 1 light year ~ 25% the distance to Alpha Centauri, the nearest star

Some 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 two candidates have been identified Sedna 2000 CR105

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

Candidate Oort Cloud Objects (OCO’s)

Sedna Named after Sedna Inuit goddess of the sea Orbital parameters Discovered in 2003 At the time, the farthest known natural Solar System object Maximum possible diameter is ~ 75% that of Pluto Orbital parameters 76.16 AU Perihelion Visible only when it is closest to the Sun 975 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