Part II: Lessons from Pluto on the Origin of the Solar System

1. Comets, Kuiper Belt and Solar System Dynamics Part II: Lessons from Pluto on the Origin of the Solar System Silvia Protopapa & Elias Roussos Lectures on “Origins of Solar Systems” February 13-15, 2006

2. Pluto and Charon Radius Mass Surface composition Atmospheric composition Albedo

3. Pluto’s heliocentric motion “The origin of Pluto’s unusual orbit-the most eccentric and inclined of all the planets-remains a mystery.” “The orbits of Pluto and Neptune overlap, but close approaches of these two planets are prevented by the existence of a resonance condition: Pluto’s orbital period is exactly 3/2 that of Neptune.” [Malhotra, 1993]

4. Trans –Neptunian Populations Plutinos × scattered disk bodies ● classical bodies Outer Solar system: Current Situation resonant bodies hot classical KBOs Kuiper belt Scattered disk Kuiper Belt: Classical KBOs resonant population classical belt Plutinos cold classical KBOs Escaped from Kuiper Belt: ShorP. Comets dynamically cold population hot population Centaurus Scatterd [Morbidelli and Brown, 2003]

5. Long-term stability of orbits in the Kuiper Belt i=1◦ [Duncan, Levison, Budd, 1995]

6. Long-term stability of orbits in the Kuiper Belt 0 [Duncan, Levison, Budd, 1995]

7. Origin of the resonant populations 3:4 2:3 3:5 1:2 ● surviving particles removed particles . Final distribution of the Kuiper belt bodies according to the sweeping resonances scenario. [Malhotra,1993] • Explains: • existence of MMRs with Neptune • large eccentricities of MMRs with Neptune

8. Origin of the hot populations Gomes scenario Red dots represent the local population, originally in the 40-50 AU zone Green dots represent the population coming from Neptune’s region • Explains: • Bimodal inclination distribution of the classical KBOs • Colour distribution

9. Binary systems in the Kuiper Belt Formation of Binaries: CFHT 1. Two large bodies penetrate one another’s Hill sphere. The loss of energy needed to stabilize the binary orbit can then occur either through dynamical friction from surrounding small bodies, or through the gravitational scattering of a third large body. [Goldreich, 2002] • A dozen binary KBOs are known • Bound orbits within several 1000km distance (0.1-2” separation) • Components with similar brightnesses, widely separeted and comparably sized • Components orbit one other with eccentricities of order unity 2. Collision of two planetesimals within the sphere of influence of a third body during low-velocity accretion in the solar nebula. [Weidenschilling, 2002] HST 3. Exchange reaction in which a binary whose primary component is much more massive than the secondary interacts with a third body, whose mass is comparable to that of the primary. The low-mass secondary component is ejected and replaced by the third body in a wide but eccentric orbit.[Funato, 2004]

10. What we can learn from Pluto’s size?

11. Accretion in the early outer solar system OBSERVATIONAL CONSTRAINTS: RESULTS: • ONE BODY WITH RADIUS OF ~1000Km (PLUTO) • ~105 KBOs WITH RADII >50Km BETWEEN 30-50AU • TIMESCALES COMPARABLE TO THE FORMATION TIMESCALE FOR NEPTUNE <108 yr MORE PLUTOS KBOs [Kenyon and Luu, 1999]

12. Lessons from Pluto Orbit unusual More of this kind? Yes, KBOs Pluto & KBOs Origin of these objects Multiplity of Pluto 12 TNB Formation mechanisms Pluto’s size needed for formation of Puto More Plutos

13. Thank you!

14. Mean motion resonance collision protection mechanism 2:3 MMR Neptune corotating frame

15. Hill sphere • If the mass of the smaller body is m, and it orbits a heavier body of mass M at a distancea, the radius r of the Hill sphere of the smaller body is • For example, the Earth (5.97×1024 kg) orbits the Sun (1.99×1030 kg) at a distance of 149.6 Gm. The Hill sphere for Earth thus extends out to about 1.5 Gm (0.01 AU). The Moon's orbit, at a distance of 0.370 Gm from Earth, is comfortably within the gravitational sphere of influence of Earth and is therefore not at risk of being pulled into an independent orbit around the Sun.