Barucci_Lutetia_CIAS

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Lessons from 21 Lutetia
Pasadena
M.A. Barucci
1
LESIA - Observatoire de Paris
ESA Rosetta mission
Journey to comet Churyumov-Gerasimenko
First rendezvous to a
comet, ambitious ESA
mission, cornerstone
aimed at the deciphering
of our origins
•
•
•
•
Comet RdV maneuver : 2014/05
Insertion into comet orbit : 2014/09
Lander : 2014/11
Mission end : 2015/12
• Stein flyby: 2008/9/5
• Lutetia flyby: 2010/7/10
Launch by Ariane 5G+
March, 2nd, 2004
500.000 km -9:30h
400.000 km -7:30h
215.000 km -4:00h
300.000 km –5:30h
81.000 km -1:30h
160.000 km -3:00h
40.000 km -0:46h
63.000 km -1:10h
Is (21) Lutetia a C-type or M-type
asteroid?
(Barucci et al. 2005, A&A 430, 313)
• Spectrum:
Moderately red slope (0.3-0.75 m),
generally flat (0.75-2.5 m), possible absorption band
at 3 m.
• Albedo = 0.16-0.22
OSIRIS data
V albedo = 0.19±0.01
Opposition Images
26.000 km -0:30h
20.000 km -0:22h
17.000 km -0:19h
16.000 km -0:18h
α = 4.1° α = 2.0°
α = 0.6°
α = 0.15°
(Sierks et al. 2011)
Surface age: 100 Ma-3.6Ga
by S. Marchi (OCA)
grooves
Matteo Massironi, UPD
Fascinating area with multiple crosscutting and incising of craters
Cut the groove-like structure
- depressions
A
Regolith Thickness
First estimation of d/D for different "old"
regions between 0.13 and 0.3, similar to
what has been measured on other
planetary surfaces.
"Young" region shows craters completely
buried under the regolith blanket.
If the region was similar to the rest of the
asteroid before the resurfacing, these
craters must be at least 600m deep, which
gives a lower limit on the regolith
thickness.
Crater diameter: 70 pixels ~ 4.5 km
Blanket thickness:
~600 m (for d/D = 0.13)
Work by Jean-Baptiste Vincent, MPS
Reflectance uniform within < 5%
All the variation is limited to the thermal contribution
above 3500nm
Temperature map from VIRTIS
Thermal Inertia : I ~20-30 SI units
 Thick regolith
(Coradini et al. 2011)
Temperature Vs Morphological Features
Spectroscopy of Lutetia: VIRTIS-M
Extremely homogeneous, less than 5% variability
No obvious spectral signature
No 1 µm band (pyroxenes)
Spectroscopy of Lutetia: VIRTIS-H
Calibration in progress…
No 3 µm band
(hydrated minerals)
No 3.6 µm band
(C-H in organics)
No 2 µm band (pyroxenes)
Conclusions from VIRTIS
No spectral signature identified
• No Fe-rich pyroxene / olivine
• No hydrated minerals
• No organics
• No unexpected absorption
=> Mostly matches some primitive meteorites
(chondrites)
Thermal studies
• Temperature map + reflectance spectrum & variability
Max T ~ 245K
• Thermal map implies low thermal inertia (I ~20-30 SI units)
=> thick regolith at surface
MIRO : Microwave Instrument
for Rosetta Orbiter
P.I. S. Gulkis (JPL)
LESIA coIs: J. Crovisier, E. Lellouch,,
D. Bockelee-Morvan, T. Encrenaz, N. Biver
Radio-telescope of 30 cm:
190 GHz (1,6 mm) : continuum
563 GHz (0,5 mm) : continuum + spectro
Small thermal inertia:
I ~10-30 J/(K m2 s0.5)
(comparable Moon regolith: ~25 SI)
Subsurface (depths from ~ 2 mm to ~ 2
cm) temperatures ranged from ~ 193 K
on the sunlit hemisphere to ~ 60 K on
the dark hemisphere.
Complementary informations
Herschel observed Lutetia !
O'Rourke, L. et al.
SPIRE
250, 350 & 500 µm
11 jul. 2010
PACS
70, 100 & 160 µm
21 dec. 2009
25
Inhomogeneities on the surface of 21 Lutetia
(Perna, D. et al. 2010, A&A 513, 4)
Aqueous altered
materials ?
ferric iron spinforbidden
absorptions,
phyllosilicates
(jarosite…)?
Lazzarin et al.2006
CV3 (red)
CI (green)
E6 (Blue)
(Nudelcu et al. 2007)
(Birlan et al. 2006)
(Rivkin et al. 2011, Icarus)
Birlan et al., 2006, A&A, 454, 677
Birlan et al. 2006 and Rivkin et al.
(2000) observed the 3 micron band
diagnostic of water of hydratation;
new data of Birlan et al. 2010 do
not confirm this detection
(different observed area), new data
by Rivkin et al. 2011 confirm the
band.
Birlan et al., 2006
21 LUTETIA:
Emissivity - SPITZER
CV meteorite
CO3 carb. chondrite
___0-20 micron.
Iron meteorite
… 20-50 micron.
•The Lutetia emissivity spectrum is completely
different from that of the iron meteorites
•Low thermal inertia: I ≤ 30 JK−1 m−2 s−1/2 ,
typical of main belt asteroids; Lutetia is likely
covered by a thick regolith layer
•Lutetia is similar to CV3 and CO3
carbonaceous chondrites, meteorites which
experienced some aqueous alteration
Enstatite chondrites C peak at 8.3 µm
(Izawa et al. 2010)
___0-20 micron.
--- 50-100 micron.
CV3 carb. chondrite
___100-150 micron.
--- >150 micron.
(Barucci et al., 2008)
Polarimetric properties of Lutetia’s surface
Lutetia’s has particular
polarimetric properties as
compared to all asteroids
observed so far.
Large inversion angle is
indicative of
• small particle size and/or
• high refractory material or
inclusions
Only few asteroids
(mainly L-type) have
wider negative branch of
polarization.
(Belskaya et al., 2010, A&A 515, 29)
Pmin, %
COMPARISON WITH METEORITES
0.0
Ch Aub
Aub
E How
H5
EELL5
L6
E6
E6
RL5 L4
A
How
Fe H4 H4
V H5LL
H3
SS Fe Ur
Fe
S S SSKSL
SS S
L4B
SSS S
SSS S
S
M
K
L4B(0.12)
SM
M
M
L5B(0.10)
E4(0.09)
Lutetia
0.5
1.0
Barbara
1.5
2.0
2.5
12
iron meteorites
enstatite chondrites
ordinary chondrites
achondrites
14
16
18
20
22
24
26
Inversion angle, deg
28
30
Pmin, %
COMPARISON WITH METEORITES
0.0
Ch Aub
Aub
E E6
How
H5
E6
EELL5
L6
RL5 L4
A
How
Fe H4 H4
V H5LL
H3
SS Fe SUr
Fe
SSS SSKSL
S S
L4B
SS S
SSS S
S
M
K
L4B(0.12)
CK SM M
M
L5B(0.10)
CV3
CK
E4(0.09)
CV3
0.5
1.0
F
F
1.5
2.0
2.5
12
B
Lutetia CV3 CO3
CO3
CO3
Barbara
PC
C C
C
C
C
C
C
CM2 C
C
C
iron meteorites
C
CI1
C CM2
CI1
enstatite chondrites
C
ordinary chondrites
CM2
CM2
achondrites
CM2
carbonaceous
14
16
18
20
22
24
26
Inversion angle, deg
28
30
Lutetia ground observations on the cilindrical projection
0.4-0.9 µm
0.8-2.5 µm
2-3.5 µm
5-38 µm
Barucci et al. (2011)
V albedo = 0.19±0.01
o = hemispherical
+ = bidirectional measurements
Lutetia density
3.40± 0.21 g/cm3
(Weiss et al. 2011)
- surface similar to chondrite;
- apparent high density (exceeds that of most known chondrite meteorites)
Kaidun meteorite
8-µm particle from comet 81P/Wild 2.
sulphide pyrrhotite, enstatite grain and finegrained porous aggregate material with
chondritic composition
This Kaidun meteorite (Yemen in 1980) is a mixture of “incompatible “ materials:
principal carbonaceous chondrites (CV, CI, CM, CR) and estatite chondrites
(EH and EL) and other peculiar materials.
Therefore, in a single particle, materials which formed in different
regions in a protoplanetary disk can co-exist, which was not expected.
Almahata Sitta
asteroid 2008 TC3
Sudan desert
Summary (21 Lutetia)
Lutetia is clearly an old object with a surface age of 3.5 Ga with a
primitive chondrite crust and a possible partial differentiation with a
metallic core.
The surface is a mixture of "incompatible'' types of materials:
carbonaceous chondrite (for the majority) and enstatite chondrite (in
minor percentage).
This are the consequence of impacts that are at the origin of the
present composition.
1) We need to put together all the pieces of puzzle
2) Only in situ or a Lutetia sample return will allow knowing the real
surface composition of this intriguing object.
ENSTATITE CHONDRITES
E6
E6
Reflectivity
0.20
E6
0.15
E6
E4
E5
0.10
E4
0.05
500
1000
1500
2000
2500
Wavelength
• crushed meteorites with grain sizes less than 500 µm (Gaffey 1976)
• spectral feature at 0.87-0.90 µm
Asteroid (Type)
Gaspra (S)
Mathilde (C)
Ida (S)
Eros (S)
Itokawa (S)
Steins (E)
Lutetia (M? C?)
Diameter
12 km
53 km
31 km
17 km
0.35 km
6.7 x 5.9 x 4.3 km
126 x 101 x 73
km
Period
7.09 hr
17.406 d
4.634 hr
5.267 hr
12.132 hr
6.047 hr
8.168 hr
Age
200 My
2-4.5 Gy
1 Gy
2 Gy
1-100 My
100-150 My
0.1-3,6 Gy
Density
2.7g/cm3 (b)
1.3 g/cm3 (a)
2.6 g/cm3 (b)
2.67 g/cm3 (b)
1.95 g/cm3 (b)
?(c)
3,4 g/cm3
Porosity
?
55 – 63 %
18 – 24 %
16 – 21 %
39 – 43 %
?
?
Meteorite
ordinary
chondrite
carbonaceous
chondrite
ordinary
chondrite
ordinary
chondrite
ordinary
chondrite
aubrite
condrite
(CK/CO/CV +EC)
Objective
Fly-By Galileo
(1991)
Res=54m/px
Fly-by NEAR
(1997)
Res=180m/px
Fly-by
Galileo (1993)
Res=25m/px
1 year-RD
NEAR (2000)
Res=cm/px
Hovering
Hayabusa
(2005)
Res<1cm/px
Fly-by Rosetta
(2008)
Res<80 m/px
Fly-by Rosetta
(2010)
Res >60 m/px
-First asteroid
with young age
(200 Myr)
-Absence of
large craters
-First asteroid
with low density
- Large craters (5
with D> 20 km)
suggest porous
bodies have
much higher
impact strength
than expected
- First
discovery of a
satellite
(Dactyl)
- Age estimate
(1 Byr)
- First estimate
of density of Stype
- First
constraints on
mechanical
properties
- Larger
amount of
boulders than
expected
- Lack of very
small craters
- First evidence
of thick regolith
- First evidence
of rubble-pile
structure
- First S-type
with low bulk
density
- Large
boulders
- Lack of small
craters (<10 m)
requires
unknown
process
-- First chunk of
e highly
differentiated
object
--First visit to a
body shaped by
the YORP effect?
--Larger, older
explored
asteroid
--high density
-- heterogeneity
-- Very large
craters (D>40
km)
-- Landslides
--Fields of large
boulders (>60 m)
Science return
(a) Average densities of meteorites for C type asteroids: 2.9 – 3.5 g/cm3
(b) Average densities of meteorites for S type asteroids: 3.19 – 3.40 g/cm3
(c) Average densities of aubrites 2.97 – 3.27 g/cm3
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