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

The Dynamical and Physical Properties of 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. Why Observe Asteroids?

Main Asteroid Belt 25 > 200 km Trojans 5 ~ 200 km Kuiper Belt 10,000 > 200 km Irregular Satellites 5 ~ 200 km Observed Stable Reservoirs

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 Magellan 6.5m/IMACS Subaru 8.3m/SuprimeCam Palomar 1.2m/Quest

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

Parallax of Asteroids and Satellites Jupiter Satellite Asteroid

Dynamically Disturbed and Collisionally Processed Trans-Neptunian Objects

The Largest Minor Planets Orcus 1400 km 2003 EL km 2005 FY km

Planets?

2003UB EL FY9 Pluto

Sedna

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.

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

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).

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).

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). Neptune Trojan Formation Scenarios

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

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

Gomes et al Tsigais et al Freeze-In Capture

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

The Dispersed Populations Classical KBOs MBAs

Kuiper Belt Formation

The End

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

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

1.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). 2.Hill Sphere Englargement (Heppenheimer and Porco 1977) - Mass growth of the planet 3.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. (During the Planet Formation Epoch)  Irregular Satellites provide a unique window on processes operating in the young Solar System Hartman Capture Mechanisms

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

Collisionless Three Body Interactions as a Capture Mechanism KBO 1999 TC36 Viewed by Hubble Funato et al > 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 Captured just after the Planet formation epoch.

Where Did Triton Come From?

-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 Physical Properties of the Irregular Satellites and Trojans

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