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
• Orbit:
5.9 . 109 km
39.53
• Day:
6d.09h 17m 51s 0.27
• Year:
248.6 years
248.6
.
Earth
AU
.
Earth
.
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
– A “rocky” core
(~25% of Pluto’s mass)
(~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
• 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
1978
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
• Quaoar measured
June 2002
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
• Quaoar measured
• Quaoar announced
4 June 2002
September 2002
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 membersPluto 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
Pluto's moons
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
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
• Two categories
– Dynamically cold population
• Orbital eccentricity < 0.1
• Orbital inclination < 10°
– Dynamically hot population
• Orbital eccentricity > 0.1
• Orbital inclination > 10° & < 30°
“Q-B-1-os”
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
Eris
Dysnomia
http://upload.wikimedia.org/wikipedia/commons/5/5b/Eris_and_dysnomia2.jpg
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
– Only 4 candidates have been identified
•
•
•
•
2000 CR105
2003 Sedna
2006 SQ372
2008 KV42
OCO’s
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