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News from the Kuiper Belt

News from the Kuiper Belt. Hermann Boehnhardt Max-Planck Institute for Solar System Research (Katlenburg-Lindau/Germany). Program of the Talk Intro: Kuiper Belt dynamics Physical Properties of TNOs (size & albedo & surface structure, chemistry: colours, spectra) Kuiper Belt Evolution

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News from the Kuiper Belt

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

  2. 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 Gloves & Moonboots On H. Boehnhardt:

  3. 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 Important Notes(not further explained)

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

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

  6. Plutinos, CDOs/Cubewanos, SDOs H. Boehnhardt: The KBO Zoo • Resonant Population Plutinos: a ~ 39 AU e ~ 0.1 - 0.3  2:3 Neptune resonance • Classical Disk (CDOs) or Cubewanos: a ~ 40-46 AU e < 0.1  outside of resonance • Scattered Disk (SDOs): a > 50 AU q ~ 32 AU  main populations in Kuiper Belt

  7. Centaurs: a ~ 5 - 32 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: 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 The Extremists: Centaurs & Detached Objects H. Boehnhardt:

  8. “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) Who Has Stolen The Ice Cream? H. Boehnhardt: Scenarios: KB beyond 50 AU  ‘wall’ of KBOs  truncated disk  ‘cold’ disk Deep surveys: no classical disk objects (Cubewano) beyond 50 AU (>30mag) • The important message: • solar system formation disk < 50 AU • change in physical properties > 50AU

  9. Size & Albedo: Simple Principles • FTNO ~ a R2/r4 steep r dependence • T ~ (1-a)1/4 r-1/2 weak a dependence independent of R reflected sunlight FTNO = Foπ R2 a p(φ) / (r2Δ2) thermal flux Fo π R2 (1-a) /Δ2 = σ T4 4(2) π R2 FTNO = 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

  10. Observing TNOs Distance: > 32AU (Neptune) Size: < 1000km Brightness: > 20mag & < 3”/h  reflected light: faint & slow Temperature: 50 -- 70 K  thermal: far IR & submm ISO, Spitzer, Herschel, ALMA Searches&orbits: 2-4m Physical studies: 8-10m+HST

  11. Like Dark Satellites H. Boehnhardt: 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

  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 -10 Reddening [%/100nm] +50

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

  14. Red: high-energy radiation time scales: ~ 106 - 107 y complications for high doses Gray: impact resurfacing time scales: ~ 106 - 107 y ejecta coma: 10 - 100 d (escape, impact) Gray: intrinsic activity & recondensation on surface What makes red cheeks and gray faces? H. Boehnhardt:

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

  16. Oct, 2001 Sept, 2001 Looking for Ice Cream H. Boehnhardt: Surface Chemistry • featureless vis. spectra  reddening = wide absorpt. - Tholins & amorphous carbons for continuum • H2O absorptions in IR few % in ~ ¼ of all objects • heterogeneous surface - big TNOs: CH4, N2, SO2 ices

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

  18. The Unexpected Surprise most KBOs with featureless vis. spectra 590 nm 740 nm 2000 EB173 Liquid Water in the Kuiper Belt? H. Boehnhardt: • 3 Plutinos with weak dips in red part of vis. spectrum  wide absorption similar to C asteroids? • water alteration of silicates! - liquid/gaseous water in KBOs? - 26AL radioactivity from SN explosion close to formation disk? - dust mixing in protoplanet. nebula (Boehnhardt & de Bergh et al.)

  19. - 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 mEarth 0.2 mEarth) correlation of dynamical and physical properties (colors, sizes) possible consequences for the inner solar system (late heavy bombardment) The Kuiper Belt Evolution H. Boehnhardt:

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

  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 The New Kuiper Belt Paradigm 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

  23. The TNO Binaries H. Boehnhardt: 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)

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

  25. The TNO Binaries H. Boehnhardt: Physical properties: mass determination through Kepler’s law Msys = 4π2a3/γT2 Msys with known albedo/size  bulk density of objects or system • dense & light objects ?? (low statistics!)  evolutionary effect ??

  26. The Large TNOs • large TNO ~ 1000km diam. (Pluto, Sedna et al.) • Sedna outside of Neptune grav. influence • larger (detached) population still awaiting discovery • 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

  27. 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 (!?) cumulative number

  28. The Degraded Planet -And The Early Example H. Boehnhardt: Pluto (since 1930) & Charon (since 1978) & Satellites (since 2005) • Orbit: Plutino-like • Size: large TNO • Type: multiple system • Density: ~1.9 g/cm3 (not only ices) • Albedo: 0.5/0,3 very high (resurfacing)

  29. The Degraded Planet -And The Early Example H. Boehnhardt: - Surface: non-uniform • Chemistry: Pluto: N2 ice Charon: H2O ice • Environment: temp.atmosphere produced by intrinsic activity

  30. New Horizons

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