Completing the Inventory of the Outer Solar System

1. Completing the Inventory of the Outer Solar System Scott S. Sheppard Carnegie Institution of Washington Department of Terrestrial Magnetism

2. Why Observe Asteroids? The Dynamical and Physical Propertiesof asteroids offer one of the few constraints on the origin and migration of the planets. The effects of nebular gas drag, collisions, planetary migration, overlapping resonances, and mass growth of the planets all potentially influence the asteroids formation and evolution. In particular, the currently Stable Reservoirs in our Solar System have a “fossilized” imprint from the evolution of the Solar System.

3. ObservedStableReservoirs Main Asteroid Belt 25 > 200 km Trojans 5 ~ 200 km Irregular Satellites 5 ~ 200 km Kuiper Belt 10,000 > 200 km

4. Wide-Field CCDs on Small/Medium/Large Telescopes Power of a Survey A x Omega A = Area of Telescope Omega = Solid Angle Observed CFHT 3.6m/MegaCam Palomar 1.2m/Quest Subaru 8.3m/SuprimeCam Magellan 6.5m/IMACS

5. 2 Albedo x radius Flux ~ 4 Helio distance Minor Planet Brightness

6. Parallax of Asteroids and Satellites Asteroid Asteroid Jupiter Satellite

7. Trans-Neptunian Objects Dynamically Disturbed and Collisionally Processed

8. The Largest Minor Planets Orcus 1400 km 2003 EL61 1600 km 2005 FY9 1800 km

9. Planets?

10. 2003UB313 2003 EL61 2005 FY9 Pluto

11. Sedna

12. How did the extremly red object Sedna come to be in its currently highly eccentric distant orbit? • If formed in current location must have initially • been on circular orbit (Stern 2005). • If interacted with currently known giant planets • its perihelion must have been raised some how.

13. Theories on Sedna’s History 1. Scattering by Unseen Planet in the Solar System -Neptune only to ~36 AU (Gladman et al. 2002) -Including complicated planet migration ~50 AU (Gomes 2003) 2. Single Stellar Encounter -Galactic tides too weak (only good for Oort cloud ~10,000 AU) -Needs to be very close encounter for Sedna to be excited (~500 AU) -May hint that our Sun formed in a very dense stellar environment. -May cause edge in Kuiper Belt -Too early and Sedna not formed in outer KB, too late disrupts Oort Cloud 3. Highly Eccentric Neptune 4. Massive Scattered Planetary Embryos 5. Massive Trans-Neptunian Disk 6. Capture of Extrasolar Planetesimals

14. Neptune Trojans The first Neptune Trojan was serendipitously discovered in 2001 by Chiang et al. (2003). Our ongoing Neptune Trojan survey has quadrupled the known population. Neptune Trojans (1:1) are distinctly different from other known Neptune resonance populations. -Kuiper Belt resonances may be from sweeping resonance capture of the migrating planets (Hahn and Malhotra 2005). -Trojans would not be captured and are severely depleted during any migration (Gomes 1998; Kortenkamp et al. 2004).

15. Trojan asteroids share a planet’s semi-major axis but lead (L4) or follow (L5) the planet by about 60 degrees near the two triangular Lagrangian points of equilibruim Like the irregular satellites the Trojans of the giant planets lie between the rocky main belt asteroids and volatile-rich Kuiper Belt. No primordial Saturn or Uranus Trojans known or expected (Nesvorny et al. 002). The four known Neptune Trojans appear stable over the age of the solar system (Sheppard and Trujillo 2006).

16. Neptune Trojan Formation Scenarios Neptune can not currently efficiently capture Trojans. Capture or Formation of the Neptune Trojans likely occurred during or just after the planet formation epoch. Gas Drag not efficient at Neptune. No rapid mass growth of the planet. Freeze-in capture: Giant planets migrate across a mutual 2:1 resonance. Their orbits become marginally unstable perturbing many minor planets. Once the planets stabilize any objects in the Lagrangian regions will also become stable and thus trapped (Morbidelli et al. 2005). Collisional interactions within the Lagrangian region (Chiang et al. 2005). In-situ accretion from a subdisk of debris formed from post-migration collisions (Chiang et al. 2005).

17. Neptune Trojan Inclinations Can test formation theories on the inclination distribution of Neptune Trojans.

18. +10 +75 50 :12 -7 -35 +240 375 -180 Magellan-Baade 6.5 meter With the 0.2 square degree IMACS imager. High i : Low i Sheppard and Trujillo 2006 Assuming low albedos the known Neptune Trojans are between 40 to 70 km. with radii > 40 km Maybe 3 to 20 times larger than the Jupiter Trojans and Main belt asteroid populations

19. Freeze-In Capture Tsigais et al. 2005 Gomes et al. 2005

20. Comparison of Colors of Outer Solar System Objects No ultra red material as seen In the Classical Kuiper Belt. Sheppard and Trujillo 2006

21. The Dispersed Populations Classical KBOs MBAs

22. Kuiper Belt Formation

23. The End

24. 1/5 3 2 m / M r a = (2 J ) a p p 2 sun crit p Regular Satellites • 1. “e” is small • 2. “i” is small • 3. “a” is small • Prograde only • -> Formed by Circumplanetary • accretion Satellites Other Irregular Mercury = 0 Venus = 0 Earth = 1 Mars = 2 Jupiter > 8 Saturn > 21 Uranus > 18 Neptune > 7 Pluto = 1 0 0 0 0 55 26 9 6 0 Irregular “outer” Satellites 1. “e” is big 2. “i” is big 3. “a” is big 4. Prograde or Retrograde -> Captured from heliocentric orbits (Burns 1986)

25. Capture? Reversibility of Newton’s Equations Energy dissipation Needed for Permanent capture -Collide with planet -Ejected from system Comet Shoemaker-Levy 9

26. Capture Mechanisms Hartman (During the Planet Formation Epoch) Hartman • Gas Drag (Pollack et al. 1979; Cuk and Burns 2004) • - Extended atmosphere or circumplanetary disk of gas and dust • surrounding the planet (is dependent on satellite size). • Hill Sphere Englargement (Heppenheimer and Porco 1977) • - Mass growth of the planet • Collisional or collisionless interactions (Colombo and Franklin 1971; • Tsui 2000; Funato et al. 2004; Agnor and Hamilton 2004) • - More probable during the heavy bombardment epoch. • Irregular Satellites provide a unique window on processes operating in the young Solar System

27. Jupiter Uranus All giant planets have similar outer satellite systems! Stable over age of the Solar System. Henon 1970 Carruba et al. 2002 Nesvorny et al. 2003 Kozai Effect Carruba et al. 2002 Nesvorny et al. 2003 Neptune Saturn Retrograde vs Prograde Henon 1970 Hamilton & Krivov 1997 Sheppard et al. 2005 Resonances Saha & Tremaine 2003 Whipple & Shelus 1993 Nesvorny et al. 2003 Cuk & Burns 2004 Dynamical Families -> Collisions with Comets or Defunct Gladman et al. 2001 SatellitesAfter capture Sheppard and Jewitt 2003 Nesvorny et al. 2004

28. Collisionless Three Body Interactions as a Capture Mechanism -> Recently described by Agnor and Hamilton 2004 Preferred Because Less Dependent on planet Formation scenario. Each giant Planet may have Had a similar number of Small body encounters. -Less objects further out But bigger Hill spheres KBO 1999 TC36 Viewed by Hubble Captured just after the Planet formation epoch. Funato et al. 2004

29. Where Did Triton Come From?

30. Physical Properties of the Irregular Satellites and Trojans -Currently the space between the giant planets is devoid of small stable objects. -Irregular satellites and Trojans were likely asteroids in heliocentric orbits which did not get ejected into the Oort cloud or incorporated in the planets. -> The irregular satellites and Trojans may be the key needed to showing us the complex transition between rocky objects which formed in the Main asteroid belt and the volatile rich objects which formed in the Kuiper Belt. Brown 2000

31. Volatiles Observed on Phoebe No Volatiles On Jupiter’s Outer Satellites! Produced by NASA/JPL/University Arizona/LPL From Cassini imager and VIMS data. Porco et al. 2005; Clark et al. 2005