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
.10
22kg 0.002
.Earth
• Density:
2.0
.water 0.36
.Earth
• Orbit:
5.9
.10
9km 39.53 AU
• Day:
6
d.09
h17
m51
s0.27
.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 Scattered
Disc 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 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 – 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
