14b. Pluto, Kuiper Belt & Oort Cloud• Pluto

– Basic characteristics– Pluto’s moons

• The Kuiper Belt– Basic characteristics– Resonant Kuiper Belt objects– Classical Kuiper Belt objects

• The Oort Cloud– Basic characteristics

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• Satellites much smaller than parent planets

• 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

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

http://upload.wikimedia.org/wikipedia/commons/thumb/8/81/Outersolarsystem_objectpositions_labels_comp.png/611px-Outersolarsystem_objectpositions_labels_comp.png

KBO’s ScatteredDisc

Objects

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• ~ 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 Estonian1932

• 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 objectsOCO’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

– 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