News from the Kuiper Belt News from the Kuiper Belt Hermann Boehnhardt Max-Planck Institute for Solar System Research (Katlenburg-Lindau/Germany)

2 Gloves & Moonboots On Program of the Talk Program of the Talk –Intro: Kuiper Belt dynamics –Physical Properties of TNOs (size & albedo & surface structure, chemistry: colours, spectra) –Kuiper Belt Evolution –Binaries & Large KBOs –Lessons from Pluto Notation: TNO = Transneptunian Object (Europe) KBO = Kuiper Belt Object (USA) for the talk: TNO = KBO H. Boehnhardt:

3 Important Notes (not further explained) Kuiper Belt = remnant bodies from formation period of solar system orbit dynamics controlled by Neptune KBO population is large in number, but small in total mass

4 Neptune Uranus PlutinosCubiwanos Scattered Centaurs ShortP. Comets Kuiper Belt: Escaped from Kuiper Belt: Outer Solar System: Current Situation

5 Example from ESO TNO Survey: 1999 HU11 Global Structure of the Kuiper-Belt KB: d ~ 30 – 55 AU Orbit: a = 30 – 48 AU (… 80 …>100) Incl.: Ecliptic oriented Peculiarities: Sharp outer edge (~50 AU) High inclination population

6 Plutinos, CDOs/Cubewanos, SDOs Plutinos, CDOs/Cubewanos, SDOs The KBO Zoo The KBO Zoo –Resonant Population Plutinos Plutinos: a ~ 39 AU e ~  2:3 Neptune resonance –Classical Disk (CDOs) or Cubewanos Cubewanos: a ~ AU e < 0.1  outside of resonance –Scattered Disk (SDOs): a > 50 AU q ~ 32 AU H. Boehnhardt:  main populations in Kuiper Belt

7 The Extremists: Centaurs & Detached Objects The Extremists: Centaurs & Detached Objects –Centaurs –Centaurs: a ~ AU  inward scattered KBOs, gravitationally cascading orbits in giant planet region Jupiter = great selector (either Jupiter family comet or outward scattering) orbit lifetime ~ few million years JFCs = only comet family in solar system –Detached Objects: –Detached Objects: a > 50 AU & q > 32 AU original SDOs got “detached” from Kuiper Belt by gravitational interaction with passing object (star, planetary embryo)  larger (in number and in size) population expected H. Boehnhardt:

8 Who Has Stolen The Ice Cream? “Missing” Mass & Extension of EKB strawman model: SS mass density distribution scaled with  Pic disk  KB is (too) light/small (0.2 Earth masses, but 40 needed for Pluto formation) H. Boehnhardt: Scenarios: KB beyond 50 AU  ‘wall’ of KBOs  ‘wall’ of KBOs  truncated disk  ‘cold’ disk  The important message: (a)solar system formation disk < 50 AU (b)change in physical properties > 50AU Deep surveys: no classical disk objects (Cubewano) beyond 50 AU (>30mag)

9 Size & Albedo: Simple Principles reflected sunlight F TNO = F o π R 2 a p(φ) / (r 2 Δ 2 ) thermal flux Fo π R 2 (1-a) / Δ 2 = σ T 4 4(2) π R 2 F TNO = flux of TNO Fo = solar flux R = radius T = temperature a = albedo p(φ) = phase function r = heliocentric distance Δ = distance to Earth 4(2) = fast(slow) rotator  F TNO ~ a R 2 /r 4 steep r dependence  T ~ (1-a) 1/4 r -1/2 weak a dependence independent of R

10 Observing TNOs Distance: > 32AU (Neptune) Size: < 1000km Temperature: K  thermal: far IR & submm Brightness: > 20mag & < 3”/h  reflected light: faint & slow ISO, Spitzer, Herschel, ALMA Searches&orbits: 2-4m Physical studies: 8-10m+HST

11 Like Dark Satellites Like Dark Satellites Sizes & Albedo Sizes & Albedo –HST direct imaging Pluto & Charon, Sedna –Visible & thermal-IR/submm fluxes (see above)  “normal” TNOs ~ dark planetesimals (not quite as dark as comets)  “big ones” ~ very high reflectivity (ice surface)  no clear trends found so far H. Boehnhardt:

12 - spectral slope change towards red end of visible spectrum - bi-modality in B-V vs V-R (Tegler&Romanishin 1997): no BVRI Colour-Colour Plots Reddening [%/100nm]

13 Between Blue And Red Visible Wavelength Visible Wavelength –diversity by dynamical type –Cubewanos: red population with blue tail –Plutinos&SDOs: moderately red (comparable to comets) –Centaurs: 2 colour groups H. Boehnhardt:

14 What makes red cheeks and gray faces? Red: high-energy radiation time scales: ~ y complications for high doses Gray: impact resurfacing time scales: ~ y ejecta coma: d (escape, impact) Gray: intrinsic activity & recondensation on surface H. Boehnhardt:

15 Visible & Near-IR Spectroscopy - spectra confirm photometric gradient determinations

16 Looking for Ice Cream H. Boehnhardt: Surface Chemistry –featureless vis. spectra  reddening = wide absorpt. - Tholins & amorphous carbons for continuum –H 2 O absorptions in IR  few % in ~ ¼ of all objects –heterogeneous surface - big TNOs: CH 4, N 2, SO 2 ices Oct, 2001 Sept, 2001

17 Hot/Cold Cubewanos: Compositional & Size Diversity 5°5° Different at 99% Hot Cold B-R vs. v rms : 3.3  600 Km 400 Km 200 Km Sun SPC D-type Asteroids Pholus best explanation: population shift by planet migration (not so good: scattering by proto-planet embryos / passing stars) cold hot

18 Liquid Water in the Kuiper Belt? The Unexpected Surprise The Unexpected Surprise –most KBOs with featureless vis. spectra H. Boehnhardt: 2000 EB nm740 nm - liquid/gaseous water in KBOs? - 26 AL radioactivity from SN explosion close to formation disk? - dust mixing in protoplanet. nebula (Boehnhardt & de Bergh et al.) –3 Plutinos with weak dips in red part of vis. spectrum  wide absorption similar to C asteroids?  water alteration of silicates!

19 The Kuiper Belt Evolution The Kuiper Belt Evolution - Sharp Edge at 50 AU: - Sharp Edge at 50 AU: remnant from formation  no stellar encounter < 100 AU since end of migration -Evolution modeling: Properties to be explained: -dynamical families -dyn. populations of CDOs (hot & cold) incl. orbital parameter distribution -outer edge of the Kuiper Belt at 50AU -mass deficit of the Kuiper Belt (40 m Earth  0.2 m Earth ) -correlation of dynamical and physical properties (colors, sizes) -possible consequences for the inner solar system (late heavy bombardment) H. Boehnhardt:

20 Disk Clean-Up & Heavy Bombardment early bombardment late bombardment (KBOs?) giant planet disk  Oort Cloud inner disk  craters on moon

21 The Nice Model – planet migration due to scattering of remnant disk bodies  Jupiter inward  others outward - resonance and hot population forms - cold population remains untouched - stop of migration when edge of remnant disk is reached 32 AU) - Jupiter/Saturn 2:1 resonance may have produced late heavy bombardment

22 early period today early period: hot Cubewanos (& Plutinos?) migrated to Kuiper Belt  cold Cubewanos = original population until today: hot & cold Cubewanos & Plutinos scattered inward  two Centaurs color populations The New Kuiper Belt Paradigm

23 The TNO Binaries From the observations: From the observations: –More than 50 double TNOs (2 multiple systems included) 13 with orbits measured –Bound orbits within several 1000km distance (0.1-2” separation, most close) –Similar brightness (sizes) of components –Origin: formation (unlikely) capture (favoured) impact (likely for small satellites of large TNOs) H. Boehnhardt:

24 The TNO Binaries First trends: -Small objects “over- abundant” -cold CDOs have more binaries –large bodies seem to have more binaries (?) –similar colors  similar composition?? H. Boehnhardt: higher than exponential growth cold CDOs hot CDOs

25 The TNO Binaries Physical properties: mass determination through Kepler’s law M sys = 4π 2 a 3 /γT 2 M sys with known albedo/size  bulk density of objects or system -dense & light objects ?? (low statistics!)  evolutionary effect ?? H. Boehnhardt:

26 The Large TNOs - detachment processes: - star encounter - planet embryo - large TNOs in all dynamical classes except in cold CDOs  cold CDOs and other TNOs must have formed in different environment - large TNO ~ 1000km diam. (Pluto, Sedna et al.) - Sedna outside of Neptune grav. influence  larger (detached) population still awaiting discovery

27 cumulative number The Large TNOs – CH4, N2, CO dominated spectra  resurfacing due to recondensation of (less organic) volatiles from temporary atmosphere (gravity/temperature balance)  higher albedo (observed)  deviation from expecting power law - large TNO = high bulk density (!?)

28 The Degraded Planet - And The Early Example The Degraded Planet - And The Early Example Pluto (since 1930) & Pluto (since 1930) & Charon (since 1978) & Satellites (since 2005) –Orbit: Plutino-like –Size: large TNO –Type: multiple system –Density: ~1.9 g/cm 3 (not only ices) –Albedo: 0.5/0,3 very high (resurfacing) H. Boehnhardt:

29 The Degraded Planet - And The Early Example The Degraded Planet - And The Early Example - Surface: non-uniform –Chemistry: Pluto: N 2 ice Charon: H 2 O ice –Environment: temp.atmosphere produced by intrinsic activity H. Boehnhardt:

30 New Horizons