N.23 dotto physica-characterization-of-trans-neptunian-objec

Physical characterization of
Trans-Neptunian Objects and Centaurs

Elisabetta Dotto
(INAF-Osservatorio Astronomico di Roma)

Elisabetta Dotto
Pisa 14-16 June 2010 Workshop on Paolo Farinella INAF-Osservatorio Astronomico di Roma

Centaurs and TNOs

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Extended scattered disk

Sedna:
(announced on
March 15, 2004)

a = 532 AU
q = 76 AU
Q = 988 AU

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Centaurs

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30 A.U. < ∆ < ? A.U.
~ 1130 TNOs
~ 161 SDO
few 104 with D ≥ 100 km

5 A.U. < ∆ < 30 A.U.
95 Centaurs
about 107 D ≥ 1 km

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Centaurs and TNOs: light curves & densities

•
Rotational period, shape,
surface structure
•
Density (with some assumptions...),
9 estimations (45% literature)
06/15/10Antonella Barucci
LESIA, Observatoire de Paris


Prot
Jacobi ellipsoids
Density estimation
(Chandrasekhar)

(a/bMAX = 2.31)
[otherwise unstable to rotation]

06/15/10Antonella Barucci
LESIA, Observatoire de Paris
Haumea (Illustration: Ann Feild/STScI/ESA/NASA)

ension/density trend? (Sheppard et al. 2008)

Pearson correlation coefficient:
r = -0.46

Probability of no correlation:
~ 4.8%
(with 19 objects)

(Perna et al. 2009)

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Pearson correlation coefficient:
r = -0.46 -0.29

Probability of no correlation:
~ 4.8% ~ 23%
(with 19 objects)

(Perna et al. 2009)

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increase the statistics

albedo measurements

a new model for densities

(Perna et al. 2009)

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Taxonomical classification

G-mode statistical
method according to the
Barucci et al. (2005)
system

(Barucci et al. 2010)

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s
ct
je
ob
al
s ic
as
Cl

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Hot and Cold Classicals, True Compositional Diversity?
Cold

s
Hot

ct
je
ob
al
s ic
as
Cl

•dynamically cold: red colors, low i, small
•dynamically hot: diverse colors, moderate

and high i, larger sizes

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Cold = RR = old

Hot = BB = young

(Gomes 2003)

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Visible Spectra

Slope:

1 < S < 51 %/103 Å

(Fornasier et al. 2009)
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Synthetic Spectra

Geographical mixtures of :

tholins + amorphous carbon
(+ water ice + olivine)

kerogene + olivine (+ water ice)

V+NIR spectroscopy

• > 50% of objects have H2O ice
(amorph+crystalline)
• CH4, CH3OH, C2H6 , N2, NH3………………
• aqueous alteration (2003 AZ84, Chariklo and
Typhon)
• surface heterogeneities

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Featureless spectra

Irradiation mantle

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50000 Quaoar

(Dalle Ore et al. 2009)

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

(Emery et al. 2007)

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90377 Sedna (2003 VB12)
VLT-ESO

Surface heterogeneity

Surface model:
H2O+Tritan&Titan Tholins+Serpentine+
CH4+N2+CH3OH (Barucci et al. 2010)

TNO 55638 and on Centaur Pholus:
Methanol

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(55638) 2002 VE95

11/2008

18%CH3OH+3%H20+40%TrTh+26%TTh+7%K+6%Ca

12/2007

11% CO3OH+11%H2O+26%TrTh+37%TTh+15%Ca

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Origin of the spectral diversity among TNOs
The color of an object depends on its level of resurfacing

Formation of an irradiation mantle

Resurfacing

• Resurfacing vs. Irradiation (Luu & Jewitt, 1996)

Red spectra can be flattened by ion
irradiation (Moroz et al. 2002; 2003)

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Ion Irradiation of an Organic Sampe:
ASPHALTITE – natural solid complex hydrocarbon material (solid oil bitumen)
 Consists of aliphatic and polyciclic aromatic hydrocarbons (PAHs)
 Carbon aromaticity (fraction of aromatic C) is 0.33
 H/C ratio is 1.4
 Density ~1 g/cm3
 Soluble in organic solvents (true bitumen)

(Moroz et al. 2002)
4.0 4.0
Asphaltite Dust1 (IN SITU)
3.5 15 + 2
3.5 Asphaltite "Dust"
Dust1+7,3x10 H /cm (30 keV)
Scaled Reflectance

15 ++ 2

Scaled Reflectance
15 + 2 Asphaltite "Dust" + 0.5x10 Ar /cm
3.0 Dust1+7,3x10 H /cm (30 keV)
15 + 2
+ 6,6x10 N /cm (15 keV)
3.0 15 ++
Asphaltite "Dust" + 1.5x10 Ar /cm
2

2.5 15 +
Dust1+7,3x10 H /cm (30 keV)
2

16 + 2
2.5
2.0 + 5,9x10 N /cm (15 keV)
2.0
1.5
1.0 1.5

0.5 1.0

0.0 0.5
0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.3 0.4 0.5 0.6 0.7 0.8
Wavelength (microns) Wavelength (microns)

Ratio of icy bodies as a function of their taxonomy

• all objects classified as BB were found to have ice on their surfaces

• for other taxonomic classes it seems that a ratio of icy and non-icy
bodies is approximately the same

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Scott Sheppard (2010) in AJ:
« The color of extreme outer solar system objects »

Inner Oort cloud:

(90377) Sedna, 2006 SQ372 & (87269) 2000 OO67

ultra red (S>25)

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The reddest objects

RR class objects are present in all
dynamical populations

reddest in Centaurs & detached

higher concentration in the classical group
(cold=primitive?)

ultra red objects in the inner Oort cloud
(characteristic of objects kept far from the
Sun?)

Does red mean « primitive »?
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Summarizing:
•
The wide difference in surface composition and colour could be
connected to different original composition and/or different
experienced processes.

• Collisions must have played a fundamental role
on the evolution of TNOs including
heating and chemical changes.
The consequence of collisions is
not only the alteration of the surface
properties but also the modification
of the internal structure.
Collisions are relevant for small
and large objects
(e.g. Charon-Pluto).
Elisabetta Dotto

N.23 dotto physica-characterization-of-trans-neptunian-objec

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