Interferometry of
ASTEROIDS
Marco Delbo
CNRS - Observatoire de la Cote d’Azur, Nice, France
Collaborators: A. Matter (Bonn, Germany), B. Carry (ESA),
S. Ligori (Torino, Italy), P. Tanga (Nice, France),
and G. Van Belle (Flagstaff, USA)
ESAC - Madrid - Aug 25, 2011
Outline
•
•
Introduction: why to study asteroids and what do their
physical properties tell us?
•
•
Main Belt Asteroids
Size, shape, density and internal structure
Interferometry of asteroids
•
•
•
Data analysis models, potential targets.
First results of VLTI-MIDI observations.
Future projects/perspectives.
Asteroids of the main belt
Plotted here are
the positions of
the first 5000
asteroids every 5
days.
Asteroids of the main belt
Plotted here are
the positions of
the first 5000
asteroids every 5
days.
Near-Earth Asteroids (NEAs)
Some are from the main belt
Some are dead comets
dynamical lifetime:∼ 107 y
Size distribution of
main belt asteroids
Bottke et al. 2005
Assumption of
spherical shapes
Size distribution of
main belt asteroids
Bottke et al. 2005
Assumption of
spherical shapes
D(km)
θ(mas) =
0.72 ∆(AU )
1.5
∼D×
∆
θ(mas) ∼ D(km)
at the center of the Belt
Size distribution of
main belt asteroids
Bottke et al. 2005
at the center of the MB
for D=100km
F (12µm) ∼ 20(Jy)
F ∝D
2
Assumption of
spherical shapes
D(km)
θ(mas) =
0.72 ∆(AU )
1.5
∼D×
∆
θ(mas) ∼ D(km)
at the center of the Belt
NEAs: size distribution
Images of asteroids from spacecrafts
DAWN in orbit around (4) Vesta
Images of asteroids from spacecrafts
Rosetta flyby of 21 Lutetia
Covered with a regolith, estimated
to be 600 m thick,
The regolith softens the outlines of
many of the larger craters.
size: 132 × 101 × 76 km
mass: 1.7 x 1018 kg [pre Rosetta estimate: (2.2-2.6) x 1018 kg]
Images of asteroids from spacecrafts
66×48×46 km
Mission NEAR, 1998 (NASA)
18×10×9 km
54×24×15 km
Mission Galileo, 1993 (NASA)
images from the
NEAR shoemaker
mission (NASA)
(433) Eros: size = 23 km
2nd largest near-Earth asteroids
Discovered in Nice in 1898
First detailed images of the surface of
an asteroid (433 Eros)
25143 Itokawa (viewed by
Hayabusa)
size: 535 × 294 × 209 m
mass: (3.58±0.18)×1010 kg
density:1.9±0.13 g/cm³
Asteroids and the origin of our
solar system
• Debris of the planet
formation process
• Small → little alteration →
conserve pristine material
Asteroids and the origin of our
solar system
• Debris of the planet
formation process
• Small → little alteration →
conserve pristine material
• Asteroids suffered collisional
evolution.
• Sizes, shapes, and bulk
densities tell us about their
collisional histories
Simulation of disruption and reaccumulation by P. Michel
k-density measurements need to be interpreted in terms
he object’s mineralogy. The differentiated V-type aster-
Asteroid masses have been reliably determined from a
asteroid or asteroid-spacecraft perturbations. That is, t
Densities of asteroids & meteorite analogs
1E + 22
1 Ceres (G)
4 Vesta (V)
87 Sylvia (P)
16 Psyche (M)
22 Kalliope (M)
45 Eugenia (C)
20 Massalia (S)
762 Pulcova (F)
11 Parthenope (S)
21 Hermione (C)
90 Antiope (C)
Average S
253 Mathilde (C)
Phobos
1E + 16
243 Ida (S)
433 Eros (S)
Deimos
CV Grain Density
Average C
CM Grain Density
1E + 18
Ordinary Chondrite Grain Densities
1E + 20
CI Grain Density
Mass in Kilograms (log scale)
2 Pallas (B)
1E + 14
0.5
1
1.5
2
2.5
Density (g/cm3)
Britt et al. 2002
3
3.5
4
Densities of asteroids & meteorite analogs
1E + 22
1 Ceres (G)
87 Sylvia (P)
M
ρ=
V
16 Psyche (M)
22 Kalliope (M)
45 Eugenia (C)
20 Massalia (S)
762 Pulcova (F)
21 Hermione (C)
Average C
σρ
=
ρ
253 Mathilde (C)
��
Phobos
1E + 16
Deimos
Average S
σM
M
�2
243 Ida (S)
+9
433 Eros (S)
� σ �2
D
D
CV Grain Density
90 Antiope (C)
11 Parthenope (S)
CM Grain Density
1E + 18
CI Grain Density
Mass in Kilograms (log scale)
1E + 20
Ordinary Chondrite Grain Densities
4 Vesta (V)
2 Pallas (B)
1E + 14
0.5
1
1.5
2
2.5
Density (g/cm3)
Britt et al. 2002
3
3.5
4
Methods of physical characterization
Size
Volume
Shape
Mass
Density
Methods of physical characterization
Size
Radiometry in the thermal infrared (FIR∝D2)
Stellar occultation timing
Volume
Shape
Mass
Density
Visible photometry (lightcurves)
Methods of physical characterization
Size
Radiometry in the thermal infrared (FIR∝D2)
Stellar occultation timing
Volume
Shape
Mass
Density
Visible photometry (lightcurves)
Asteroid-asteroid perturbation
Asteroid-planet (mars) perturbation
Asteroid-spacecraft perturbation
Methods of physical characterization
Size
Radiometry in the thermal infrared (FIR∝D2)
Stellar occultation timing
Volume
Shape
Mass
Density
Visible photometry (lightcurves)
Asteroid-asteroid perturbation
Asteroid-planet (mars) perturbation
Asteroid-spacecraft perturbation
Period and semimajor axis
P2
4π 2
=
3
of asteroid satellites
a
GM
Adaptive optics, visible photometry
Optical interferometers
Keck
LBT
ESO-VLT
Optical interferometers
Keck
LBT
ESO-VLT
Interferometry and physical
characterization of asteroids
Size
Volume
Shape
Mass
Density
from 1 visibility
Interferometry and physical
characterization of asteroids
Size
Volume
Shape
Mass
Density
from 1 visibility
visibility as a function
of time as the
asteroid rotates
2. Data modeling
and determination
of physical
quantities
2.A Lightcurve inversion
2.B global modeling
2.C physical modeling
MDB
12
PT
8
PM
7
MM
1.6
HC
2
DH
8
SL
2
AC
6
PD
8
CDDC
16
Team members: MDB=Marco Delbo; PT= Paolo Tanga; PM=Patrick Michel; MM=Michael
Mueller (post-doc@UMR6202 Cassiopée until 08/2011); HC=Humberto Campins;
DH=Daniel Hestroffer; SL=Sebastiano Ligori; AC=Alberto Cellino; PD=post-doc recruited
with ANR funds; CDDC=Non-permanent research position (CDD chercheur) financed
through ANR; The time is given in terms of person/work/months.
Interferometry and physical
characterization of asteroids
Size
Volume
PT
from 1 visibility
visibility as a function
of time as the
asteroid rotates
3.3.1 TÂCHE 1 / TASK 1 ASTRONOMICAL OBSERVATIONS AND DATA TREATMENT
Task 1 includes all activities devoted to the acquisition of the astronomical observations
needed for the project: for each of our targets, we will obtain interferometric observations;
photometric lightcurves in visible light; thermal infrared fluxes; spectroscopic observations
in the visible and near infrared. In some cases, the data acquisition will require traveling to
the observatories. In the following we give a technical description of the subtasks:
Shape
Mass
Asteroid satellites:
P from lightcurves and a
from the visibility at
(some) epochs
1.A Interferometric data
Aim: measure the scale of the orbit of the system
with relative accuracy better than 10% (as shown
by Delbo et al. 2009)
Providers: MD, SL, PD, CDDC, HC (for LBTI)
Deliverables: distance primary-secondary projected
along the interferometer baseline at some epochs
(the distance d of Fig. 4)
Risks: objects aligned across the baseline; objects
2 10% relative2error on d;
too faint to achieve the
Description: Data will be obtained mainly at the
VLTI using the ATs3and later the UTs during the
PRIMA commissioning time (in 2010 and likely in
2011) and GTO time allocated for ESO, the Torino Figure 4 Geometry of the orbit on the
Density
P
4π
=
a
GM
plane of the sky at the
interferometric measurement.
time
of
Simple geometric models (1)
uniform disk
Visibility
first order Bessel function of first kind
Interferometric
visibility of a uniform
disk of diameter !
as function of !,
where u = B/"
Simple geometric models (2)
binary model
Visibility
Interferometric
visibility of a binary of
components of sizes
!1 and !2 separated
by a distance rho
as function of lambda
in meters
theta1=20; theta2=10; rho=200 mas
Simple geometric models (2)
binary model
Visibility
Interferometric
visibility of a binary of
components of sizes
!1 and !2 separated
by a distance rho
as function of lambda
in meters
theta1=20;
theta2=10;
rho=100
mas
theta1=20;
theta2=10;
rho=200
mas
Simple geometric models (2)
binary model
Visibility
Interferometric
visibility of a binary of
components of sizes
!1 and !2 separated
by a distance rho
as function of lambda
in meters
theta1=20;
theta1=20;
theta2=10;
theta2=10;
rho=100
rho=60mas
mas
mas
theta1=20;
theta2=10;
rho=200
Results from
interferometry
The VLTI of the ESO
• Coherent combination of the light from telescopes
(distance between them B) of the VLT
• Resolution !~"/B
• MIDI "#[8,13]µm
• AMBER "#[1.2,2.5]µm
• VLTI B#[16,120]m
!MIDI#[15,100]mas
!AMBER#[3,25]mas
Not sensitive enough for asteroids..
!PRIMA#[3,25]mas
K<9 (guide star) dual field (reference star
and asteroid need to be within ~30”)
The VLTI of the ESO
• Coherent combination of the light from telescopes
(distance between them B) of the VLT
• Resolution !~"/B
• MIDI "#[8,13]µm
• AMBER "#[1.2,2.5]µm
• VLTI B#[16,120]m
!MIDI#[15,100]mas
!AMBER#[3,25]mas
Not sensitive enough for asteroids..
!PRIMA#[3,25]mas
K<9 (guide star) dual field (reference star
and asteroid need to be within ~30”)
So far results for MIDI only
First successful observations of
asteroids with MIDI-VLTI
Obtained fringes on
• 951 Gaspra (a testbed)
• 234 Barbara (complex shape)
•
•
long rotation period (26.5 hr, Schober 1981; Harris & Young 1983)
suggestive of a possible binary system.
• interferometric observations by Delbo et al 2009
41 Daphne (complex shape)
• Matter et al 2011 (almost in press)
Results for Gaspra: size
Uniform disk fit to visibility
d =11 ± 2 km.
d=13 ± 2 or 11 ± 2 km
expected value from
Thomas et al. (1994) in-situ
observations depending of the spinpole solution adopted
Results for Barbara: size and shape
Results for Barbara: size and shape
No. 2, 2009
MIDI-VLTI OBSERVA
No. 2, 2009
Results for Barbara: size and shape
Table 3
Table 3
Results From Geometric Models
Fits From
to Measured
Visibilities
Results
Geometric
Models Fits to M
Asteroid
Gaspra
Barbara
Barbara(1)
Barbara(2)
(1)–(2)
d
D (km)
Asteroid
θ (mas)D (km)
11 ±Gaspra
1
44.6 ±Barbara
0.3
37.1 ±Barbara(1)
0.5
21.0 ±Barbara(2)
0.2
a (km)
24.2 ±(1)–(2)
0.2
17 ± 211 ± 1
51.0 ±44.6
0.4 ± 0.3
43.0 ±37.1
0.5 ± 0.5
24.2 ±21.0
0.2 ± 0.2
ρ (mas)a (km)
28.1 ± 24.2
0.2 ± 0.2
Notesθ (m
EWS mask
17 ±
poor 51.0
fit ±
primary
43.0 ±
satellite
24.2 ±
ρ (m
separation
28.1 ±
Note. Uncertainties are 1σ . Note. Uncertainties are 1σ .
Table 4
Table 4
Results from Thermal Model Results
Fits
from Thermal Mode
Asteroid
D̃ (km)
Gaspra
Gaspra
Gaspra
Barbara
Barbara
Barbara
13.8 ± 1.0
11.6 ± 0.4
24.0 ± 0.3
51 ± 2
40 ± 1
89 ± 1
pV
Asteroid
0.24Gaspra
± 0.14
0.34Gaspra
± 0.13
0.08Gaspra
± 0.04
0.17Barbara
± 0.09
0.27Barbara
± 0.09
0.06Barbara
± 0.03
η
D̃ (km)
θD p(mas)
V
Model
η
1.06
13.8 ±
± 0.17
1.0
(0.756)
11.6
± 0.4
· · 0.3
24.0 ·±
1.17
51 ±
± 0.05
2
(0.756)
40
±1
· ·1
89 ·±
22.0±±0.14
1.6
0.24
18.4±±0.13
0.6
0.34
38.1±±0.04
0.5
0.08
58±±0.09
2
0.17
46±±0.09
1
0.27
102±±0.03
1
0.06
NEATM
1.06 ± 0.
STM
(0.756)
FRM
···
NEATM
1.17 ± 0.
STM
(0.756)
FRM
···
Notes. Uncertainties are at 1σ
level.Uncertainties
D is the diameter
sphereD with
Notes.
are at of
1σ alevel.
is thethedia
No. 2, 2009
No. 2, 2009
MIDI-VLTI OBSERVA
Results for Barbara: size and shape
Table 3
Table 3
Results From Geometric Models
Fits From
to Measured
Visibilities
Results
Geometric
Models Fits to M
Asteroid
Gaspra
Barbara
Barbara(1)
Barbara(2)
(1)–(2)
d
D (km)
Asteroid
θ (mas)D (km)
11 ±Gaspra
1
44.6 ±Barbara
0.3
37.1 ±Barbara(1)
0.5
21.0 ±Barbara(2)
0.2
a (km)
24.2 ±(1)–(2)
0.2
17 ± 211 ± 1
51.0 ±44.6
0.4 ± 0.3
43.0 ±37.1
0.5 ± 0.5
24.2 ±21.0
0.2 ± 0.2
ρ (mas)a (km)
28.1 ± 24.2
0.2 ± 0.2
Notesθ (m
EWS mask
17 ±
poor 51.0
fit ±
primary
43.0 ±
satellite
24.2 ±
ρ (m
separation
28.1 ±
Note. Uncertainties are 1σ . Note. Uncertainties are 1σ .
13.8 ± 1.0
11.6 ± 0.4
24.0 ± 0.3
51 ± 2
40 ± 1
89 ± 1
0.24Gaspra
± 0.14
0.34Gaspra
± 0.13
0.08Gaspra
± 0.04
0.17Barbara
± 0.09
0.27Barbara
± 0.09
0.06Barbara
± 0.03
proposed geometric model
1.06
13.8 ±
± 0.17
1.0
(0.756)
11.6
± 0.4
· · 0.3
24.0 ·±
1.17
51 ±
± 0.05
2
(0.756)
40
±1
· ·1
89 ·±
22.0±±0.14
1.6
0.24
18.4±±0.13
0.6
0.34
38.1±±0.04
0.5
0.08
58±±0.09
2
0.17
46±±0.09
1
0.27
102±±0.03
1
0.06
km
Gaspra
Gaspra
Gaspra
Barbara
Barbara
Barbara
53
Asteroid
Table 4
Table 4
37Thermal Mode
Results from Thermal Model Results
Fits
from
km
D̃ (km)
pV
η
θD p(mas)
Model
Asteroid
D̃ (km)
η
V
NEATM
1.06 ± 0.
STM
(0.756)
FRM
···
NEATM
1.17 ± 0.
STM
(0.756)
FRM
···
Notes. Uncertainties are at 1σ
level.Uncertainties
D is the diameter
sphereD with
Notes.
are at of
1σ alevel.
is thethedia
Barbara follow up:
photometric lightcurves
2009 occultation events
Stellar occultation 1
Oct 5, 2009
Ecliptic longitude, heliocentric: 77° ;
geocentric: 103°
Phase angle: 25°
(chord n. 2 is not precisely dated)
Source: http://www.euraster.net/results/
2009/20091105-Barbara-crd_temp.gif
Stellar occultation 2
note also the
double coord
Nov 21, 2009
Ecliptic longitude, heliocentric: 89° ; geocentric: 107°
Phase angle: 18°
Source: http://www.asteroidoccultation.com/observations/Results/
Size from the MIDI-VLTI observations confirmed
KOALA shape model of Barbara from
occultations and photometry
Tanga, Carry, Delbo et al, in preparation
KOALA shape model of Barbara from
occultations and photometry
Carry’s KOALA model
Tanga, Carry, Delbo et al, in preparation
KOALA vs VLTI models
projected on the sky at the time of VLTI observations
KOALA model
from Tanga et al.
VLTI model
adapted from from Delbo et al. 2009
80
N
60
40
km
20
0
Secondary
E
ne
eli
-40
s
ba
oj.
Primary
Pr
-20
-60
-80
-80
-60
-40
-20
0
km
20
40
60
80
KOALA vs VLTI models
projected on the sky at the time of VLTI observations
KOALA model
from Tanga et al.
VLTI model
adapted from from Delbo et al. 2009
80
N
60
40
km
20
0
Secondary
E
ne
eli
-40
s
ba
oj.
Primary
Pr
-20
-60
-80
-80
-60
-40
-20
0
km
20
40
60
80
Matter et al. Icarus, in press
41 Daphne
41 Daphne: nature of the surface
Given a priori information
about the shape, we
constrained the thermal inertia.
Γ<√
50 J m−2 s−0.5 K −1
Γ∝ κ
Smooth surface
Conclusion: insulating
layer of mature and thick regolith;
Figure 7:
craters smoothed out by regolith landslides?
From observations in the thermal IR at one epoch only Matter et al. 2011
Thermal inertia (SI)
1000
YORP: by Mueller 2007
e
el l
wa
a
k
Ito
ll
u
(M
e
u
,r M
r)
Large MBAs
NEA
MBA<100km
steins
99JU3 by Campins et al. 2010
Delbo and
Tanga 2009
100
Lamy et al 2009
TG Muller et al 1998
10
0.1
1
10
Asteroid diameter (km)
100
1000
Thermal inertia (SI)
1000
YORP: by Mueller 2007
e
el l
wa
a
k
Ito
ll
u
(M
e
u
,r M
r)
Large MBAs
NEA
MBA<100km
steins
99JU3 by Campins et al. 2010
Delbo and
Tanga 2009
100
Lamy et al 2009
thermal inertia
of our Moon
TG Muller et al 1998
10
0.1
1
10
Asteroid diameter (km)
100
1000
Thermal inertia (SI)
1000
YORP: by Mueller 2007
e
el l
wa
a
k
Ito
ll
u
(M
e
u
,r M
r)
Large MBAs
NEA
MBA<100km
steins
99JU3 by Campins et al. 2010
Delbo and
Tanga 2009
100
Lamy et al 2009
thermal inertia
of our Moon
TG Muller et al 1998
Transition size from
primordial asteroids,
never disrupted and
asteroids reaccumulated
(Bottke et al. 2005)
10
0.1
1
10
Asteroid diameter (km)
100
1000
2500 bare rock value (Jakosky 1986)
Thermal inertia (SI)
1000
YORP: by Mueller 2007
e
el l
wa
a
k
Ito
ll
u
(M
e
u
,r M
r)
Large MBAs
NEA
MBA<100km
steins
99JU3 by Campins et al. 2010
Delbo and
Tanga 2009
100
Lamy et al 2009
thermal inertia
of our Moon
TG Muller et al 1998
Transition size from
primordial asteroids,
never disrupted and
asteroids reaccumulated
(Bottke et al. 2005)
10
0.1
1
10
Asteroid diameter (km)
100
1000
2500 bare rock value (Jakosky 1986)
Thermal inertia (SI)
1000
YORP: by Mueller 2007
e
el l
wa
a
k
Ito
ll
u
(M
e
u
,r M
r)
Large MBAs
NEA
MBA<100km
steins
99JU3 by Campins et al. 2010
Delbo and
Tanga 2009
100
Lamy et al 2009
thermal inertia
of our Moon
TG Muller et al 1998
Transition size from
primordial asteroids,
never disrupted and
asteroids reaccumulated
(Bottke et al. 2005)
10
0.1
0.0035
1
0.02 0.1
10
Asteroid diameter (km)
1.0
10
100
escape velocity (m/s)
1000
Future projects
Asteroids with satellites
1000
discovered by
photometry: transits
and eclipses
Apparent separation at opposition (mas)
discovered by AOs
100
10
8
10
12
14
16
Apparent magnitude at opposition (V)
18
Asteroids with satellites
1000
AOs@8m
discovered by
photometry: transits
and eclipses
Apparent separation at opposition (mas)
discovered by AOs
100
10
8
10
12
14
16
Apparent magnitude at opposition (V)
18
Asteroids with satellites
1000
AOs@8m
discovered by
photometry: transits
and eclipses
Apparent separation at opposition (mas)
discovered by AOs
100
Linc-LBTI
10
8
10
12
14
16
Apparent magnitude at opposition (V)
18
Asteroids with satellites
1000
AOs@8m
discovered by
photometry: transits
and eclipses
Apparent separation at opposition (mas)
discovered by AOs
100
Linc-LBTI
10
VLTI-ATs
8
10
12
14
16
Apparent magnitude at opposition (V)
18
Asteroids with satellites
1000
AOs@8m
discovered by
photometry: transits
and eclipses
Apparent separation at opposition (mas)
discovered by AOs
100
Linc-LBTI
10
VLTI-ATs
8
10
VLTI-UTs
12
14
16
Apparent magnitude at opposition (V)
18
Comets: 8P Tuttle
Attachments (Figures)
Geometry of observation from the VLTI on January 17, 2008
UT3-UT4
UT1-UT2
UT2-UT3
terminator
Disk integrated flux (Jy)
January 07 2008
Rn=7.6 km
Rn=5.0 km
10
1
8
9
10
11
Wavelength (um)
12
13
12
13
January 07 2008
1.0
Visibility
W
UT1-UT2 Rn=5.0 km
UT2-UT3 Rn=5.0 km
UT3-UT4 Rn=5.0 km
0.8
SUN
N
UT1-UT2 Rn=7.6 km
UT2-UT3 Rn=7.6 km
UT3-UT4 Rn=7.6 km
0.6
0.4
0.2
0.0
8
9
10
11
Wavelength (um)
Radar delay-doppler imaging of
the first bilobate comet
2008 Jan 3.9
2008 Jan 4.9
Conclusions
• Measured the sizes and shapes of some
asteroids.
• (Determined surface properties of asteroids)
• Observations of close binaries underway...
important future prospects.
• Active comet nuclei can be observed.