angular momentum in the kuiper belt
DESCRIPTION
Angular Momentum in the Kuiper Belt. Scott S. Sheppard Carnegie Institution of Washington Department of Terrestrial Magnetism. Main Asteroid Belt 24 > 200 km. Trojan Asteroids 2 ~ 200 km. Kuiper Belt 10,000 > 200 km. Size Comparison of Rocky/Icy Bodies in the Solar System. - PowerPoint PPT PresentationTRANSCRIPT
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Angular Momentum in the Angular Momentum in the Kuiper BeltKuiper Belt
Scott S. Sheppard
Carnegie Institution of WashingtonDepartment of Terrestrial Magnetism
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Main Asteroid Belt24 > 200 km
Trojan Asteroids2 ~ 200 km
Kuiper Belt10,000 > 200 km
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Gravitational Self Compression > Material Strength
Primordial Distribution of Angular Momentum
For Diameters > 200 km:
- Early Collisional environment
Size Comparison of Rocky/Icy Bodies in the Solar System
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Dynamical Classes in the Outer Solar System
Dynamically Disturbed and Collisionally Processed.
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Sedna
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Plan View of the Kuiper Belt
Brightest KBO is19th magnitude
Diameter > 200 kmMag < 22.5
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Overview of DataSample of over 40 large KBOs
1) Light curves
2) Phase curves
UH 2.2m
-> Shapes-> Surface Characteristics-> Densities-> Binaries-> Angular Momenta-> Outgassing
du Pont 2.5m
Short and Long Term Variations
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Short-term Variability
2000 GN171
1. Albedo2. Elongation3. Binary
2000 GN171 period = 7.9 hours
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29% > 0.15 mags18% > 0.40 mags12% > 0.60 mags
KBOs (40 in sample)
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1. Albedo effects are usually only 10 to 20% (Degewij et al. 1979)
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2. Elongation
Rotational Triaxial Ellipsoids (Jacobi Ellipsoids)
Fast Rotations < 7 hours
For large objects (> 200 km)
Spherical Gravitational Compression > Material Strength
Triaxial elongation from rotational angular momentum
(Leone et al. 1984)
P = (3 Pi / G rho)1/2
crit
Centripetal acceleration = gravitational acceleration
As angular momentum increases an object will go frombeing a sphere to biaxial to
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a/b = 100.4 x delta mag
Axis Ratio from rotationallight curve:
Period and amplitude can be related to an objects density
Varuna
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Jewitt and Sheppard 2002
Varuna Density ~ 1100 kg/m 3
Assume Rotationally distortedStrengthless Rubble Pile
Cosmochemically PlausibleRock Fraction ~ 0.5
Porosity ~ 10 to 20%
Chandrasekhar 1987Leone et al. 1984
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1999 TC36
3. Eclipsing Binaries
-Probability of eclipse events to our line of sight decreases as the separation increases
-Tidal interactions distort close components
Photometric Range Max ~ 0.75 mags
Photometric Range Max ~ 1.2 mags(Leone et al. 1984)
(Trujillo and Brown 2002)
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2001 QG298 Period = 13.7744 hoursRange = 1.1 mags
Diameter ~ 250 km
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2001 QG298 HektorKleopatra
2001 QG298 is only the 3rd known minor planet with diameter > 50 km and a photometric range > 1 magnitude
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Trojan Asteroid 624 Hektor
Main Belt Asteroid 216 Kleopatra
KBO 2001 QG298
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Merline, Dumas and Menard 1999
CFHT Adaptive Optics images of Kleopatra
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Sheppard and Jewitt 2004
Comparison of Large Main Belt Asteroids and Kuiper Belt Objects
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Margot 2002
Comparison of typical binary systems within the Solar System.
100 km
100 km
1 km
20,000 km
1000 km
2.5 km
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Funato et al. 2004
KBO Binary Formation Mechanisms:
TidalDisruption
DirectCollisions
Three BodyInteractions
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Known Binaries of Large Minor Planets in the Solar System
Does a largeangular momentumof the primarycorrespond tosatellite formation?
Current angularMomentum ofLarge objects hintsAt an earlier denserKuiper Belt.
Maybe 100 times more dense.
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Noll et al. (2002) found about 4% of KBOs were binary with separations > 0.15”
We find 5 of 34 KBOs are in the close, similar component, eclipsing binary region (15%)
Consistent with Goldreich et al. (2002) model of binary formation but not with the Weidenschilling model (2002)
Collisionless interactionsIn a denser Kuiper BeltDuring the formation epoch.
- Dynamical Friction would create more close in binaries
(Because of projection effects, the fraction may be much larger)
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Conclusions- Many Kuiper Belt Objects have large amplitude light curves
- Some may be rotationally deformed rubble piles- Many are probably contact or nearly contact binaries
- Kuiper Belt must have been about 100 times more dense in the distant past to explain current amount of angular momentum we see.
- Binary formation is still unclear, but direct collisions may have be an important factor.
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Short and Long Term Variability
Consecutive Nights
Multiple Months
Absolute Photometry
Mag = Msun – 2.5 log(albedo x radius x phase / heliocentric x geocentric )2 2 2
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Period = 8.08 hours
Period = 4.04 hours
1995 SM55
V-R=0.38
Single-peak
Double-peak
Binary or Cometary orComplex Rotation?
t = u Q / p K r w
Damping time scale
2 3
u is rigidityQ is ratio energy in oscillation to that lost p is the densityK is irregularity of bodyr is the radiusw is angular frequency
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1. Nonuniform Surface Markings
Iapetus
Photometric Range ~ 0.3 mags
Photometric Range ~ 2 mags
B – V ~ 0.1 mags (Millis 1977)
-synchronous rotation
-atmosphere
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20000 Varuna Rotational Lightcurve (diameter ~ 900 km)
Period = 6.3442 hours
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20000 Varuna: Found No Color Variation with Rotation
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Asteroid and KBO Limiting Densities
Sheppard and Jewitt 2002
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5 KBOs can not be easily explained from albedo or rotational elongation