News from the Kuiper BeltNews from the Kuiper Belt

Hermann BoehnhardtHermann BoehnhardtMax-Planck Institute for Solar System

Research (Katlenburg-Lindau/Germany)

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Gloves & Moonboots Gloves & Moonboots OnOn

Program of the TalkProgram 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

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Important NotesImportant Notes(not further explained)(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

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Neptune

Uranus

PlutinosPlutinos

CubiwanosCubiwanos

ScatteredScattered

CentaursCentaurs

ShortP. ShortP. CometsComets

Kuiper Belt:Kuiper Belt:

Escaped from Escaped from Kuiper Belt:Kuiper Belt:

Outer Solar System:

Current Situation

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Example from ESO TNO Survey: 1999 HU11

Global Structure of the Global Structure of the Kuiper-BeltKuiper-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

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Plutinos, Plutinos, CDOs/Cubewanos, SDOs CDOs/Cubewanos, SDOs

The KBO Zoo The KBO Zoo

– Resonant PopulationResonant PopulationPlutinosPlutinos: a ~ 39 AU

e ~ 0.1 - 0.3 2:3 Neptune resonance – Classical Disk (CDOs) orClassical Disk (CDOs) or

CubewanosCubewanos: a ~ 40-46 AU

e < 0.1 outside of resonance– Scattered Disk (SDOs): Scattered Disk (SDOs):

a > 50 AU q ~ 32 AU

main populations in Kuiper Belt

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The Extremists: The Extremists: Centaurs & Detached Centaurs & Detached

ObjectsObjects– CentaursCentaurs: 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: 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

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Who Has Stolen The Ice Who Has Stolen The Ice Cream?Cream?

““Missing” Mass & Extension of EKB 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) Scenarios: KB beyond 50 AU Scenarios: KB beyond 50 AU

‘ ‘wall’ of KBOswall’ of KBOs truncated disktruncated disk ‘ ‘cold’ diskcold’ 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)

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Size & Albedo: Simple Size & Albedo: Simple PrinciplesPrinciples

reflected sunlight

FTNO = Fo π R2 a p(φ) / (r2 Δ2)

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

FTNO ~ a R2/r4

steep r dependence

T ~ (1-a)1/4 r-1/2

weak a dependence

independent of R1998 SF36 Radius - Albedo

0.00

0.10

0.20

0.30

0.05 0.15 0.25 0.35 0.45 0.55

Geometric Albedo

Radiu

s (km

)

visible_mean visible_max visible_min

MIR_mean MIR_max MIR_min

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Maximum R Filter Brightness of Solar System Bodies

-5

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80 90

Sun Distance [AU]

R Fi

lter B

right

ness

[mag

]

1kmlow 10kmlow 100kmlow 1000kmlow 1kmhigh 10kmhigh 100kmhigh 1000kmhigh

1000km

100km

10km

1km

Radius

Parameter = Albedo: low = 0.04 high = 0.50

Solar System Thermal Environment

1

10

100

1000

0.1 1.0 10.0 100.0

Sun Distance [AU]

Tem

pera

ture

T [K

]

1

10

100

Ther

mal

Con

tinuu

m P

eak

Lam

bda

[mic

ron]

T (fast) T (slow) Lambda (fast) Lambda (slow)

Temperature

Wavelength of Thermal Continuum

Peak

fast

fast

slow

slow

Observing TNOsObserving TNOs

Distance: > 32AU (Neptune) Size: < 1000km

Temperature: 50 -- 70 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

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Like Dark SatellitesLike Dark Satellites

Sizes & AlbedoSizes & 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

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- spectral slope change towards red end of visible spectrum

- bi-modality in B-V vs V-R (Tegler&Romanishin 1997): no

BVRI Colour-Colour PlotsBVRI Colour-Colour Plots

-10 +50 Reddening [%/100nm]

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Between Blue And RedBetween Blue And Red

Visible WavelengthVisible Wavelength– diversity by dynamical

type

– Cubewanos: red population with blue tail

– Plutinos&SDOs: moderately red (comparable to comets)

– Centaurs: 2 colour groups

024681012141618

Num

ber o

f Obj

ects

<-25

-25/

-15

-15/

-5-5

/+5

5/15

15/2

525

/35

35/4

545

/55

55/6

565

/75

75/8

585

/95

Gradient Range [%/100nm]

Spectral Gradient StatisticsAll ESO Data

Centaurs 0 0 0 1 8 0 2 3 0 1 0 0 0

Scattered D. 0 0 0 1 11 7 5 0 0 0 0 0 0

Plutinos 0 0 0 3 9 9 4 0 0 0 0 0 0

Cubewanos 0 0 0 5 5 13 17 3 0 0 0 0 0

<-25 -25/-15 -15/-5 -5/+5 5/15 15/25 25/35 35/45 45/55 55/65 65/75 75/85 85/95

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What makes red cheeks What makes red cheeks and gray faces?and gray faces?

Red: high-energy radiationtime scales: ~ 106 - 107 ycomplications for high doses

Gray: impact resurfacingtime scales: ~ 106 - 107 y

ejecta coma: 10 - 100 d (escape,

impact)

Gray: intrinsic activity & recondensation on surface

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Visible & Near-IR Visible & Near-IR SpectroscopySpectroscopy

- spectra confirm photometric gradient determinations

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Looking for Ice Looking for Ice CreamCream

Surface ChemistrySurface 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

Oct, 2001

Sept, 2001

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Hot/Cold Cubewanos: Hot/Cold Cubewanos: Compositional & Size DiversityCompositional & Size Diversity

5°

Different at 99%

Hot

Cold

B-R vs. vrms : 3.3

600 Km400 Km200 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

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Liquid Water in the Kuiper Liquid Water in the Kuiper

Belt?Belt? The Unexpected The Unexpected

SurpriseSurprise– most KBOs with featureless

vis. spectra

2000 EB173590 nm 740 nm

- liquid/gaseous water in KBOs?- 26AL 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!

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The Kuiper Belt EvolutionThe 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: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)

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Disk Clean-Up & Heavy Disk Clean-Up & Heavy BombardmentBombardment

early bombardment

late bombardment (KBOs?)

giant planet disk Oort Cloud

inner disk craters on moon

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The Nice ModelThe 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

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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 The New Kuiper Belt ParadigmParadigm

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The TNO BinariesThe 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)

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The TNO BinariesThe TNO Binaries

First trends:First trends:

- Small objects “over-abundant”

- cold CDOs have more binaries

– large bodies seem to have more binaries (?)

– similar colors similar composition??

higher than exponential growth

cold CDOs

hot CDOs

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The TNO BinariesThe TNO Binaries

Physical properties: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 ??

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The Large TNOsThe 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

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cumulative number

The Large TNOsThe 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 (!?)

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The Degraded Planet -The Degraded Planet -And The Early ExampleAnd The Early Example

Pluto Pluto (since 1930)(since 1930) & & Charon Charon (since 1978)(since 1978) & &Satellites Satellites (since 2005)(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)

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The Degraded Planet -The Degraded Planet -And The Early ExampleAnd The Early Example

- Surface: non-uniform

– Chemistry: Pluto: N2 ice Charon: H2O ice

– Environment: temp.atmosphereproduced by

intrinsic activity

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New HorizonsNew Horizons