Antonella Barucci

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TNO surface Ices analysis of the populations
spectral properties
 
M.A. Barucci F. Merlin (LESIA, Paris
Observatory, France)
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Visible and near-Infrared spectroscopy
Sedna
Asbolus
Huya
Chariklo
Thereus
Ixion
Oxyrnoe
Bienor
Orcus
Chiron
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Taxonomy BB, BR, IR and RR
2000 OK 67
(Barucci et al. 2005, A.J.)
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Taxonomy BB, BR, IR and RR Different
composition or The trend from neutral (BB) to
very red (RR) groups indicates the possible
sequence of alteration processes (collisions,
recurfacing, craters, UV and/or energetic
particle bombardment, etc. Each group would
represent an evolutionary stage of the
population, indicating the duration for which
each object has been exposed to these different
alteration processes. The relative number of
objects in each group would account for the time
spent in the different evelutionary stages.
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Sedna
Orcus
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Visible spectra Aqueous altered
silicates ?
(Fornasier et al. 2004)
(Lazzarin et al. 2003)
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Surface heterogeneity 32532 Thereus
(Merlin et al. 2005, AA)
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Grouping TNOs by Spectroscopic Characteristic

• H2O ice bodies (50 - 67)
• CH4 ice bodies - dissolved in N2
• - pure
• CH3OH ice bodies
• Mantled ice bodies (featureless spectra)

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• H2O Ice bodies
• Crystalline water ice

50000 Quaoar (D1300 km)
2003 EL61 (D2000 km)
(Jewitt and Luu, 2005)
(Trujillo et al. 2006)
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90482 Orcus (2004 DW)
Fornasier et al. 2004 38 kerogen60 amorphous
carbon 2water ice albedo0.044
De Berg et al. 2004 42 kerogen 53 amorphous
carbon, 5 c water ice albedo 0.07
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II. CH4 Ice bodies
(Brown et al. 2005)
(Brown et al. 2005)
2003 UB313 (larger than Pluto)
(Dumas et al., poster)

• On 2003 UB313, from the positions of the bands,
  it appears to be present as pure methane ice (and
  no nitrogen ice is detected).
• A 0.60 D. 3000 km. (Bertoldi et a 2006,
  Nature 439, 563)
• A 0.86 D. 2400 km. (Brown et al. 2006, ApJ
  643, L61)

(VLT-Sinfoni)
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II. CH4 Ice bodies
(Brown et al. 2005)
(Brown et al. 2005)
2003 UB313 (larger than Pluto)
(Dumas et al., poster)
N2 ?

• On 2003 UB313, from the positions of the bands,
  it appears to be present as pure methane ice (and
  no nitrogen ice is detected).
• A 0.60 D. 3000 km. (Bertoldi et a 2006,
  Nature 439, 563)
• A 0.86 D. 2400 km. (Brown et al. 2006, ApJ
  643, L61)

(VLT-Sinfoni)
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II. CH4 Ice bodies
2005 FY9 (D1800 km)
(Licandro et al. 2005)
A 0.6. D. 1800 km. Methane bands stronger
than for Pluto. .
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II. CH4 Ice bodies
N2 ?
90377 Sedna (2003 VB12)
24 Triton tholin 7 amorphous carbon 10 N2
26 CH3OH 33 CH4 (contaminated by small
inclusion of Titan tholin) , albedo 0.15
(Barucci et al. 2005, AA, 439, L1)
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Sedna - Triton
(Barucci et al. 2005, A.A., 439, L1)
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III. CH3OH ice bodies
55638 2002VE95 5145 Pholus
(Barucci et al. 2006, AA, in press)
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Similarity
? dynamical classes

• S UB313 Pluto
• R 2005 FY9
• R 2003 EL61 Charon
• R Orcus
• ES Sedna Triton
• R 55630 Pholus

?
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Presence of ices with taxonomic groups
BB
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Presence of ices
(Barucci et al. 2006)
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Conclusion

• Visible and near-Infrared spectroscopy
• Large difference in spectral behaviour
• Models by mixtures of organics, silicates, ices,
  amorphous carbon
• Traces of aqueous altered silicates on three
  objects ?
• Evidence for surface variations (collision
  resurfacing.)

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Compositional summary

• All large TNOs have ices on their surface
• Methane ice on two large TNOs (similarity to
  Pluto)
• Crystalline water ice on 2-3 objects ( Charon).
• Detection of N2 and CH4 on Sedna (similarity
  to Triton)
• Methanol in 1 TNO 1 Centaur
• Water ice is detected on blue objects as well as
  on red objects. Its detection does not depend on
  the dynamical class to which belongs the objects
  or on its perihelion distance.

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Grouping TNOs by Spectroscopic Characteristic

• H2O ice bodies (50 - 67)
• CH4 ice bodies - dissolved in N2
• - pure
• CH3OH ice bodies
• Mantled ice bodies (featureless spectra)

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Possible mechanisms for surface evolution

• Solar and cosmic ray irradiation, collisions,
  outgassing
• Importance of the interior
• Large objects - Cryovolcanism (crystalline H2O
  and CH4)
• - Formation of a thin
  atmosphere with sublimation and
  recondensation of surface ices.

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THE END
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Ammonia and/or ammonia hydrate on Charon and
Quaoar ?
An absorption feature present at 2.2 micron in
spectra of Charon has been tentatively assigned
(Brown and Calvin 2000) to a combination of
ammonia and ammonia hydrate (see below). This is
surprising, as ammonia hydrate ices are destroyed
by radiation. (Also detected in spectra of
Miranda, satellite of Uranus). A comparable
feature is found in spectra of TNO Quaoar (Jewitt
and Luu, 2004, Subaru telescope). But the spectra
are quite noisy (see below). There is a need for
more laboratory data on ammonia hydrates and a
need for better spectra of Quaoar.

• 
  

Quaoar
Charon
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Space weathering effects

• Surface materials of small airless bodies of the
  outer Solar System are exposed to a flux of
  energetic ions throughout their evolution.
• When ice-rich surfaces are bombarded by solar
  wind, cosmic ray and microimpacts, chemical
  modifications are induced including formation of
  more and less volatile species.
• If ices contain simple hydrocarbons, irradiation
  often forms a complex, refractory residue which
  remains stable after warming.
• After long-time exposure to irradiation, the
  residue evolves to hydrogenated carbon with a
  neutral color.

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• Titan Tholin synthetic macromoecular compound,
  produced from irradiation of a gaseous mixture of
  N2CH4.
• Ice Tholin produced from ice mixture of
  H2OC2H6
• Triton Tholin compound produced from a more
  Nitrogen-rich N2CH4 mixture
• Kerogen complex organic compound

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90377 Sedna (2003 VB12)
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Phoebe
115x110x105 km
Cassini-Huygens mission June 11, 2004 at 32,500
km
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Space weathering effects Asphaltite
(Moroz et al. 2004, Icarus, 170, 214 )
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Cross-correlation diagram
c) Triton-Sedna model b) Sedna-Triton
spectrum a) Sedna-N2CH4 model
(Barucci et al. 2005, A.A., 439, L1)
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47171 1999 TC36 57 T t25 i t10 a c8 H2O
26375 1999 DE9 24 T t15 i t54 a c
2001 BL41 17Tr t10 H2O73 a c
Orcus 85 a c 4 T t11 H2O
(Barucci et al. 2005, A.J)
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