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

The giant SednaThe giant Sedna

November 2003

Sedna’s orbit

The outer Solar System

?

Surface density profileSurface density profile

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

The surface color diversity of KBOs

Near-IRVisible

ESO Large Program

ReflectivitiesReflectivities

Meech & Jewitt (1986)

Normalization at 1.In V band

Spectral slope (%/100nm)

Visible near-infrared reflectivity spectraVisible near-infrared reflectivity spectra

The reddening curveThe reddening curve

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 ?

Spectroscopic study of bright KBOs & Centaurs

KBOs Centaurs

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

THE END