Angular Momentum in the Angular Momentum in the Kuiper BeltKuiper Belt
Scott S. Sheppard
Carnegie Institution of WashingtonDepartment of Terrestrial Magnetism
Main Asteroid Belt24 > 200 km
Trojan Asteroids2 ~ 200 km
Kuiper Belt10,000 > 200 km
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
Dynamical Classes in the Outer Solar System
Dynamically Disturbed and Collisionally Processed.
Sedna
Plan View of the Kuiper Belt
Brightest KBO is19th magnitude
Diameter > 200 kmMag < 22.5
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
Short-term Variability
2000 GN171
1. Albedo2. Elongation3. Binary
2000 GN171 period = 7.9 hours
29% > 0.15 mags18% > 0.40 mags12% > 0.60 mags
KBOs (40 in sample)
1. Albedo effects are usually only 10 to 20% (Degewij et al. 1979)
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
a/b = 100.4 x delta mag
Axis Ratio from rotationallight curve:
Period and amplitude can be related to an objects density
Varuna
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
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)
2001 QG298 Period = 13.7744 hoursRange = 1.1 mags
Diameter ~ 250 km
2001 QG298 HektorKleopatra
2001 QG298 is only the 3rd known minor planet with diameter > 50 km and a photometric range > 1 magnitude
Trojan Asteroid 624 Hektor
Main Belt Asteroid 216 Kleopatra
KBO 2001 QG298
Merline, Dumas and Menard 1999
CFHT Adaptive Optics images of Kleopatra
Sheppard and Jewitt 2004
Comparison of Large Main Belt Asteroids and Kuiper Belt Objects
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
Funato et al. 2004
KBO Binary Formation Mechanisms:
TidalDisruption
DirectCollisions
Three BodyInteractions
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.
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)
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.
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
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
1. Nonuniform Surface Markings
Iapetus
Photometric Range ~ 0.3 mags
Photometric Range ~ 2 mags
B – V ~ 0.1 mags (Millis 1977)
-synchronous rotation
-atmosphere
20000 Varuna Rotational Lightcurve (diameter ~ 900 km)
Period = 6.3442 hours
20000 Varuna: Found No Color Variation with Rotation
Asteroid and KBO Limiting Densities
Sheppard and Jewitt 2002
5 KBOs can not be easily explained from albedo or rotational elongation