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… 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” ?

Pluto 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 ideas 1930, Leonard see Pluto as the first member of a swarm of distant objects Edgeworth 1943, 1949 Kuiper 1951 Independently described the existence of a disk of a large number of small (kilometer sized) objects beyond Neptune

The discovery of 1992 QB 1 August Hawai`i UH 2.2m telescope Jewitt and Luu discovered The first Kuiper Belt Object Mauna Kea

The Kuiper Belt Objects Now, about 1,000 objects have been discovered (bright end of the distribution) ~ objects D>100km ~ 10 objects D>1000 km They might retain the most pristine material of the Solar System ~ 340 objects lost !!! ~ 230 objects in critical situation -> strong need for follow up and recovery !!! 1999 KR 16, D. Jewitt Website

Current Outer Solar System view Classical belt Plutinos Scattered disk Centaurs Comets Neptune Pluto Saturn Jupiter Uranus

The giant Sedna November 2003 Sedna’s orbit

The outer Solar System ?

Surface density profile

Ecliptic surveys Hainaut & Delsanti, survey ESO 2.2m + 8x8K, 20 deg 2 on sky, m R ~23, 40 new objects Trujillo et al. (2001) CFHT 4m + 12K×8K, 73 deg 2 on sky, m R ~ 23.7, 86 new objects Allen et al. (2001) CTIO 1.5m + BTC, 1.5 deg 2 on sky, m R ~ , 24 new objects Hainaut & Delsanti, survey ESO 2.2m + 8x8K, 20 deg 2 on sky, m R ~23, 40 new objects Trujillo et al. (2001) CFHT 4m + 12K×8K, 73 deg 2 on sky, m R ~ 23.7, 86 new objects Allen et al. (2001) CTIO 1.5m + BTC, 1.5 deg 2 on sky, m R ~ , 24 new objects No objects with Perihelion > 50 UA

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 (m V ~18-26) distant objects spatially not resolved Difficult to observe  4 to 8m class telescopes needed The bulk of physical information comes from Broadband photometry (Spectroscopy) In the visible & near IR domain HST image of Quaoar (Brown & Trujillo, 2004) Studying Kuiper Belt Objects properties

The surface color diversity of KBOs Near-IRVisible ESO Large Program

Reflectivities Meech & Jewitt (1986) Normalization at 1. In V band Spectral slope (%/100nm)

Visible near-infrared reflectivity spectra

The reddening curve

The 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 (H 2 O, CO, CO 2, CH 4, NH 3, …) - 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) HOCH 2 CH 2 OH

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 Mg 2 SiO 4 (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 (26181) 1996 GQ % Titan tholin 35 % Ice tholin 50 % Amorphous carbon Visible albedo: 5%

Tholins: example of composition NameInitial MixtureReferences Titan tholin90% N 2 – 10% CH 4 (gas)Khare et al. (1984) McDonald et al. (1994) Triton tholin99.9% N 2 – 0.1% CH 4 (gas)McDonald et al. (1994) Ice tholin I86% H 2 O – 14% C 2 H 6 Khare et al. (1993) McDonald et al. (1996) Ice tholin II80% H 2 O – 16% CH 3 OH 3.2% CO 2 – 0.8% C 2 H 6 McDonald et al. (1996)

Scattered-disk object Red visible colors Neutral IR colors … 99% kerogen 1% tremolite p V = 2% __ 24% titan tholin 15% ice tholin 54% amorphous carbon 7% water ice p V = 10% Jewitt et al (2001): Water ice Hydroxyl group with possible interaction with an Al or Mg compound (26375) 1999 DE9 Doressoundiram et al. 2003

Kerogen and water ice 2000 QC Centaur 1998 SG 35 - Centaur Suggestion of interpretation for both objects % kerogen - 1% olivine - 3-2% water ice Other results Water ice on 1999 TC 36 (Plutino) Dotto et al. 2003

(90482) 2004 DW April 11, 2004 VLT + ISAAC - 38% kerogen - 7% water ice - 55% amorphous carbon Albedo 0.07 at 0.55 µm VLT + FORS2

Summary of the current situation Lack of surface albedos Geographical mixture: spectra modeling does not drive to unique solutions  intimate mixture models Lack of optical constants n & k for most components  Laboratory experiments

THE END