news from the kuiper belt
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News from the Kuiper BeltNews from the Kuiper Belt
Hermann BoehnhardtHermann BoehnhardtMax-Planck Institute for Solar System
Research (Katlenburg-Lindau/Germany)
2
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
3
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]
13
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
15
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)
20
Disk Clean-Up & Heavy Disk Clean-Up & Heavy BombardmentBombardment
early bombardment
late bombardment (KBOs?)
giant planet disk Oort Cloud
inner disk craters on moon
21
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
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 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)
24
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 ??
26
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
27
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 (!?)
28
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)
29
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
30
New HorizonsNew Horizons
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