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Solar System Science David Jewitt, UCLA Tuesday, October 25, 14:00 -14:40 Topics: • Structure of solar system (Oort cloud, Kuiper belt, comets) • Processes (impact, rotational disruption, capture, debris production, binary formation, crystallization, endogenic activity) Background movie by Alex Parker Background Three Domains of the Solar System: • Terrestrial planets: Mercury - Mars (asteroids) • Giant planets: Jupiter - Neptune • Comets: Oort Cloud, Kuiper belt Comets Mass-Loss Lifetime << Age of Solar System Long Period vs Short Period Oort cloud vs Kuiper belt 100 AU Oort Cloud Oort Cloud • No strong hyperbolics • Width of peak < ∆EJ • Comets in the peak are first arrivals • Too many first arrivals relative to Nth arrivals. Why? Oort Cloud • Dynamics alone cannot explain the distribution of orbital energies. • Oort introduced a “fading parameter” to reduce the number of returning comets relative to 1st arrivals. Dones et al. (2004) Oort Cloud r ~ 50,000 AU VK ~ 100 m s-1 12 • JWST canNassess ~ 1011the- 10 composition of longperiod comet from M nuclei ~ 1 - 10 MEnIR ? spectroscopy Isotropized ~ 1 Gyr • Perhaps find evidence for “interstellar frosting” Hot Topics • Determine nucleus size distribution from thermal IR photometry of pre-active LPCs • Two-step formation (emplacement efficiency =1-10%) • Comet-sharing between stars in birth cluster? • Existence/population of inner Oort Cloud? • Nature of the fading parameter? (is it real?) • Can OC be directly observed? How? Kuiper Belt Kuiper Belt in Perspective Jewitt & Haghighipour (2008) Centaurs N Scattered Resonant 1:1 3:2 2:1 Detached Classical N Edge Jewitt & Luu (2002) Kuiper Belt • r ~ 30 to >2000 AU • VK ≤ 5 km s-1 • N (a > 1km) ~ 109 - 1010 • M ~ 0.1 ME (now, 10 - 50 originally) • Dynamical fossil • Resonant objects indicate planetary migration. • Migration offers novel possibilities for solar system re-arrangement & a plaything for dynamicists Gomes et al. 2005 Attributes of the Nice Model • Explains lunar Late-Heavy Bombardment @800 Myr post-formation • Flexible model can fit many disparate solar system properties • Might supply “niche” populations (Trojans, irregular satellites) Problems with the Nice Model • Model struggles to make any observationally testable predictions (too flexible) • Original Nice model expelled the Earth • Requires 30 M Kuiper belt to survive ~800 Myr without agglomeration (to provide dynamical friction damping). How? • The best data provide no evidence for the LHB: the model beautifully Earth explains something that did not happen V = 27 25 23 V = 27 -> Radius ~ 10 or 15 km Surface density ~ 100 deg-2 • KBO albedo & size determinations • nIR spectroscopy for compositional studies • Identify eclipsing/contact binary population V = 27 25 23 r > 30 km - Primordial r < 30 km - Collisionally modified <--JFCs Gould (2012) Schlichting et al. (2013) Large KBO Pluto Hydrocarbon haze Snakeskin terrain Convective nitrogen sea 8:1 Binary Planet Nine? Trujillo & Sheppard (2014) Nature, 507, 471 • Orbital and real-space alignment, if real, could be produced by an external planet. • If it exists, emplacement by planet-planet scattering seems likely, but requires additional perturbation (by another unseen planet?) to raise the perihelion. • Strong scattering seems strange in the context of the dynamically cold system of known planets (e ~ 0, i ~ 0). • No direct evidence exists. Indirect evidence seems to be weakening (as of Oct 2016). Comets 67P from Rosetta 1 km Planetesimal or collision fragment? Sublimation: Water ice sublimation drops precipitously with increasing distance. It is incapable of launching dust particles beyond about 5 AU. But…the ice might be amorphous Amorphous vs Crystalline Ice 8.5 AU 11.8 AU 7.9 AU 5.3 AU 5.5 AU 5.8 AU 17P/Holmes Outburst 3x105 kg/s, E/m ~ 105 J kg-1 Likely crystallization runaway Li et al. (2011) Hot Topics • Is the ice amorphous? • If so, why do KBOs appear crystalline? • What is the nature of cometary organics & what is their role in the origin of life? JWST nIR spectroscopy will help decide Transients Impact Ice Sublimation Radiation torques - YORP Crystallization energy Endogenic activity The Active Asteroids Already have examples of… • Hypervelocity impacts • Sublimation • Thermal and desiccation fracture • YORP torque spin-up • More? 2010 December Asteroid Impact Asteroid Ice (596) Scheila 133P/Elst-Pizarro 30 m projectile 110 km target ∆v ~ 5 km/s E ~ 1/4 Megatonne Periodic emission of dust near perihelion dm/dt ≤ 1 kg/s Thermal trigger likely = sublimation No gas yet detected 2010 December Jewitt et al. (2011) Hsieh & Jewitt (2006) P/2013 R3 - YORP Disruption a = 3.003, e = 0.273, i = 0.90, TJ = 3.18 Shedding & Satellite Formation by YORP spin-up Kevin Walsh and Patrik Michel Observatoire de la Cote d'Azur (OCDA) Hirabayashi et al (2014) YORP Disruptions Observed R3 Jewitt et al. (2014) P5 Jewitt et al. (2013) 3 2 Predicted Number of Events Per Year 1 Rotational Disruption 0 -1 • Same may apply for debris production around other stars -2 -3 • Radiation torques may dominate collisional destruction in the asteroid belt (for sub-km asteroids) Impact Disruption -4 -5 0.1 1.0 Diameter [km] Marzari et al. (2011), Veras et al. (2014) Endogenic activity Active Objects Enceladus D ~ 500 km Enceladus production ~few x 100 kg/s 0.06" Enceladus • Planetary volcanology • Activity vs. time - tidal trigger? • Secular evolution JWST can provide longterm, remote monitoring of activity (Enceladus, Europa, Io) T ~ 100 K -> BB peak @30 µm Summary Expect science impacts in • Nature of primitive bodies (Kuiper belt, Oort Cloud, Centaurs, Trojans, comets) • Compositional studies of primitive bodies • Active Objects (hypervelocity impact clouds, rotational instabilities, weird volcanism) BUT the most exciting science will come not from detailed observing plans, but from observational surprises END