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Composition and Surface Diversity
of the Kuiper Belt objects
Composition and Surface Diversity
of the Kuiper Belt objects
Audrey Delsanti
IFA - University of Hawai`i - NAI
Audrey Delsanti
IFA - University of Hawai`i - NAI
An historical overview…An historical overview…
With naked eyes:• Venus and Mercury • Mars, Jupiter, Saturn
With telescopes:• Uranus discovered in 1781 by William Herschell• 1801: discovery of Ceres by Piazzi• 1851: 15 objects known as the “Asteroid Belt”
• 1846: discovery of Neptune• “Planet X” ?
PlutoPluto
• discovered in 1930• by Clyde Tombaugh• at the Lowell Observatory 33cm telescope• Tombaugh looked for other objects for 13 years
The outer solar system: First ideasThe outer solar system: First ideas
• 1930, Leonard see Pluto as the first member of a swarm of distant objects
• Edgeworth 1943, 1949
• Kuiper 1951
Independently described theexistence of a disk of a large number of small (kilometer sized) objects beyond Neptune
The discovery of 1992 QB1The discovery of 1992 QB1
• August 1992 - Hawai`i• UH 2.2m telescope• Jewitt and Luu discoveredThe first Kuiper Belt Object
Mauna Kea
The Kuiper Belt ObjectsThe Kuiper Belt Objects
• Now, about 1,000 objects have been discovered (bright end of the distribution)
~ 70 000 objects D>100km~ 10 objects D>1000 km
• They might retain the most pristine material of theSolar System
~ 340 objects lost !!!~ 230 objects in critical situation-> strong need for follow up and recovery !!!
1999 KR16, D. Jewitt Website
Current OuterSolar System
view
Classical belt
Plutinos
Scattered disk
Centaurs
CometsNeptune
Pluto
Saturn
Jupiter
Uranus
Ecliptic surveysEcliptic surveys
• Hainaut & Delsanti, survey 1999-2001 ESO 2.2m + 8x8K, 20 deg2 on sky, mR ~23, 40 new objects
• Trujillo et al. (2001)CFHT 4m + 12K×8K, 73 deg2 on sky, mR ~ 23.7, 86 new objects
• Allen et al. (2001) CTIO 1.5m + BTC, 1.5 deg2 on sky, mR~24.9-25.9, 24 new
objects
• Hainaut & Delsanti, survey 1999-2001 ESO 2.2m + 8x8K, 20 deg2 on sky, mR ~23, 40 new objects
• Trujillo et al. (2001)CFHT 4m + 12K×8K, 73 deg2 on sky, mR ~ 23.7, 86 new objects
• Allen et al. (2001) CTIO 1.5m + BTC, 1.5 deg2 on sky, mR~24.9-25.9, 24 new
objects
No objects with Perihelion > 50 UA
A truncature at 50 AU ?A truncature at 50 AU ?
• No objects • Truncature of proto-solar nebula by a passing star• Existence of a Martian-mass body, a~60 AU, 1Gy • Initial truncature at 30 AU + further migration• Other
• Objects• “cold disk” ?• Change of regime in albedo/size distribution ?
• No objects • Truncature of proto-solar nebula by a passing star• Existence of a Martian-mass body, a~60 AU, 1Gy • Initial truncature at 30 AU + further migration• Other
• Objects• “cold disk” ?• Change of regime in albedo/size distribution ?
• Faint (mV~18-26)• distant objects• spatially not resolved• Difficult to observe 4 to 8m class telescopes needed
The bulk of physical informationcomes from• Broadband photometry • (Spectroscopy)
In the visible & near IR domain
HST image of 50000 Quaoar(Brown & Trujillo, 2004)
Studying Kuiper Belt Objects propertiesStudying Kuiper Belt Objects properties
ReflectivitiesReflectivities
Meech & Jewitt (1986)
Normalization at 1.In V band
Spectral slope (%/100nm)
The surface color diversityThe surface color diversity
• Intrinsic different composition
• Same initial composition but different evolution
- Surface irradiation by high energy particles(solar UV, cosmic rays, …)
- Non disruptive collisions between KBOs - Cometary activity ?
Constraints for KBO spectra modeling
1) The presence or absence of absorption bands arising from
- minerals- ices (H2O, CO, CO2, CH4, NH3, …)- organic solids
2) The spectral range
3) The spectral gradient (ex: V-J color)
4) The surface albedo
KBO spectra modeling
Radiative transfert model (Douté & Schmitt, 1998)
Synthetic spectra of several geographical (spatial) mixtures
LIMITATIONS : the component grain size used should be greater than the wavelength of the spectrum
THE SOLUTION IS NOT UNIQUE !!!
= linear combination of the spectra of the components
= juxtaposition of regions covered by a single component Collisions between KBOs
Organics signatures in Solar System objects
Ex: carbonaceous chondrites contain• amino acids • hydrocarbons• insoluble polymers close to terrestrial kerogen• nitrogen compounds
Ex: comets contain• Methanol + more complex organics
(Bockelée-Morvan et al. 1995)• Ethylene glycol in Hale-Bopp (Crovisier et al. 2004) HOCH2CH2OH
Organics in Solar System objects
Organic compounds may be - primordial- or the result of on-going chemical reactions Ex: KBO surface irradiation by high energy particles (solar UV, cosmic rays, …)
Minerals and silicates
• Abundant on asteroids surfaces
• Enter in cometary grains composition Ex: fosferite Mg2SiO4 (magnesium-rich olivine)
on comet Hale-Bopp also crystalline pyroxenes, amorphous silicates (Crovisier et al. 2000)
• centaur Pholus (Cruikshank et al. 1998)
Doressoundiram et al. 2003
(26181) 1996 GQ21
15 % Titan tholin35 % Ice tholin50 % Amorphous carbonVisible albedo: 5%
Tholins: example of composition
Name Initial Mixture References
Titan tholin 90% N2 – 10% CH4 (gas) Khare et al. (1984)McDonald et al. (1994)
Triton tholin
99.9% N2 – 0.1% CH4 (gas)
McDonald et al. (1994)
Ice tholin I 86% H2O – 14% C2H6 Khare et al. (1993)McDonald et al. (1996)
Ice tholin II 80% H2O – 16% CH3OH
3.2% CO2 – 0.8% C2H6
McDonald et al. (1996)
Scattered-disk objectRed visible colorsNeutral IR colors
… 99% kerogen 1% tremolite pV = 2%
__ 24% titan tholin 15% ice tholin 54% amorphous carbon 7% water ice pV = 10%
Jewitt et al (2001):• Water ice• Hydroxyl group with possible interaction withan Al or Mg compound
(26375) 1999 DE9(26375) 1999 DE9
Doressoundiram et al. 2003
Kerogen and water ice 2000 QC243 - Centaur
1998 SG35 - Centaur
Suggestion of interpretationfor both objects
- 96-97 % kerogen- 1% olivine- 3-2% water ice
Other results
Water ice on 1999 TC36
(Plutino)
Dotto et al. 2003
(90482) 2004 DW(90482) 2004 DW
April 11, 2004
VLT + ISAAC
- 38% kerogen - 7% water ice- 55% amorphous carbonAlbedo 0.07 at 0.55 µm
VLT + FORS2
Summary of the current situation
• Lack of surface albedos
• Geographical mixture: spectra modeling does not driveto unique solutions intimate mixture models
• Lack of optical constants n & k for most components Laboratory experiments