Lecture L7 AST3020

1
Lecture L7 - AST3020 Understanding dust 1.
Clearing stage do planets clear dust? 2. Comets
3. Asteroids 4. Planetoids 5. Zodiacal light 6.
IDPs (Interplanetary dust particles)
2
Clearing the junk left at the construction site

• Oort cloud formation
• Kuiper belt
• 10th planet(s)

3
Two-body interaction a small planetesimal is
scattered by a large one, nearly missing it and
thus gaining an additional velocity of up to
vesc (from the big body with mass Mp)
The total kinetic
energy after encounter, assuming that
initially both
bodies were on nearly-circular orbits is (we
neglect the random part depending on the angle
between the two components of final velocity).
If the total energy of the small body after
encounter, EEk Epot, is positive, then the
planetesimal will escape from the planetary
system.
Gravitational slingshot
4
(No Transcript)
5
Planet Earth 0.14 Mars
0.04 Jupiters core 5 Jupiter
21 Saturn 14 Uranus
10 Neptune 19
Conclusions Terrestrial planets in the solar
system cannot eject planetesimals Giant planets
(even cores) can eject planetesimals out of the
solar system Any cleared region may be seen as a
gap in SED. So far no firm detection of
exoplanets this way but the process definitely
happened in the solar system, leaving behind the
Oort Cloud.
6
Jan Oort (1902-1992) found that a (2-7)1e4
AU for most new comets.
Typical perturbation by planets 0.01 (1/AU)
E0
7
Oort cloud of comets the source of the so-called
new comets size Hill radius of the Sun in the
Galaxy 260,000 AU inner part
flattened, outer elliptical
Q Porb ?
8
Out of 152 new comets 50 perturbed recently by
2 stars (one slow, one fast passage) excess of
retrograde orbits, aphelia clustered on the sky
9
Fomation of Oort cloud
10
Kuiper belt, a theoretical entity since 1949
when Edgeworth first mentioned it and Kuiper
independently proposed it in 1951, was discovered
by D. Jewitt and J. Lu in 1993 (1st object),
who later estimated that 30000 asteroid-sized
(typically 100 km across) super-comets
reside there.
11
Gerard Kuiper (1905-1973)
Interestingly, we now observe that Kuiper belt
apparently ends at r 50 AU, so the original
drawings were incorrect! The Kuiper belt is home
to quite a Zoo of planetoids or plutinos, some
of which are larger than the recently demoted
(former) planet Pluto.
Smith Terrile (1984)
12
10th planet(s) super-Plutos Sedna,
Xena also starring Plutinos!
Dont worry its hard to see! Better image
on the next slide.
13
The 10th planet (temp. name Xena or UB313)
first seen in 2003. It has a moon (announced in
Sept. 2005)
See the home page of the discoverer of
planetoids, Michael Brown http//www.gps.caltech.
edu/mbrown/
Images of the four largest Kuiper belt objects
from the Keck Observatory Laser Guide Star
Adaptive Optics system. Satellites are
seenaround all except for 2005FY9 in 75 of
cases! In comparison, only 1 out of 9 Kuiper
belt objects, also known as TNOs (Trans-Neptunian
Objects) have satellites.
14
On October 31 2005, 2 new moons of Pluto have
been found by the Hubble Space Telescope/ACS
Charon
Pluto
15
IDPs Interplanetary Dust Particles
Comet Hale-Bopp (1997)
10 -100 km
16
(No Transcript)
17
European (ESA) Giotto mission saw comet Halleys
nucleus in 1986, confirming the basic

concept of comet nucleus
as a few-km
sized chunk
of ice and rocks stuck

together (here, in the form
of a
potato, suggesting
2 collided
cometesimals)
The bright jets are from the craters or vents
through which water vapor and the dust/stones
dragged by it escape, to eventually spread and
form head and tail of the comet.
18
Borrely-1 imaged by NASA in 2001
19
Why study comets? Comet Wild-2 is a good
example this 3km-planetesimal was thrown out in
the giant impacts era from Saturn-Neptune region
into the Oort cloud, then wandered closer to
Uranus/Jupiter has recently been perturbed by
Jupiter (5 orbits ago) to become a short-period
comet (P5 yr) Comet Temple1, on the other
hand, is a short-period comet that survived gt100
passages - so we are eager to study differences
between the more and the less pristine bodies.
Gas tail
Comet Hale-Bopp
Dust tail
20
Stardust NASA mission - reached comet Wild-2 in
2004
Storeoscopic view of comet Wild-2 captured by
Stardust
http//stardust.jpl.nasa.gov/index.html and in
particular http//stardust.jpl.nasa.gov/mission/i
ndex.html http//stardust.jpl.nasa.gov/science/det
ails.html
21
(No Transcript)
22
Stardust NASA mission - reached comet Wild-2 in
2004
The probe also carried aerogel - a ghostly
material that NASA engineered (like a
transparent, super-tough styrofoam, 2 g of it can
hold a 2.5 kg brick - see the r.h.s.
picture). Aerogel was used to capture cometary
particles (l.h.s. picture) which came back and
landed on Earth in Jan. 2006.
23
(No Transcript)
24
(No Transcript)
25
Tracks in aerogel, Stardust sample of dust from
comet Wild 2. That comet was residing in the
outer solar system until a close encounter with
Jupiter in 1974.
26
(No Transcript)
27
(No Transcript)
28
OLIVINES, Mg-Fe silicate solid state solutions
(also found by Stardust) are the dominant
building material of both our and other planetary
systems.
Forsterite, Mg2SiO4
Fayalite, Fe2SiO4
29
"I would say these materials came from the inner,
warmest parts of the solar system or from hot
regions around other stars," "The issue of
the origin of these crystalline silicates still
must be resolved. With our advanced tools, we
can examine the crystal structure, the trace
element composition and the isotope composition,
so I expect we will determine the origin and
history of these materials that we recovered from
Wild 2."
D. Brownlee (2006)
30
Deep Impact NASA probe - impacted comet Tempel1
on July 4, 2005 (v 10.2 km/s) - see the movie
frames of the actual impact of the probe taken by
the main spacecraft, taken 0.83s apart. The
study showed that Temple1 is porous the impactor
dug a deep tunnel before exploding.
31
Comet Temple 1 nucleus 10m resolution
Here is the Deep Impact description
http//deepimpact.jpl.nasa.gov/home/index.html
See http//stardust.jpl.nasa.gov/science/feature00
1.html about the differences between comets
Wild-2 and Temple 1.
32
Other missions are ongoing. Rosetta mission by
ESA (European Space Agency) will first fly by
astroids Steins and Lutetia near Mars after the
arrival at the comet Churyumov-Gerasimenko in
2014, the spacecraft will enter an orbit around
the comet and continue the journey together. A
lander will descend onto the surface.
http//rosetta.esa.int
33
These particles have been delivered to Earth for
free
Chonditic meteorite
IDP (cometary origin?)
Brownlee particles collected in the stratosphere
Donald Brownlee, UW
34
Brownlee particle
35
Brownlee particle A few out of a thousand
subgrains shows isotopic anomalies, e.g., a O(17)
to O(16) isotope ratio 3-5 times higher than all
the rest - a sign of pre-solar nature.
36
(No Transcript)
37
Glass with Embeded Metals and Sulfides - found in
IDPs
Nano-rocks composed of a mixture of materials,
some pre-solar
38
Out of this world (pre-solar isotopes, compositio
n of GEMS)
Figure 1. Transmission electron micrographs of
GEMS within thin sections of chondritic IDPs. (A)
Bright-field image of GEMS embedded in amorphous
carbonaceous material (C). Inclusions are FeNi
metal (kamacite) and Fe sulfides. (B) Dark-field
image. Bright inclusions are metal and sulfides
uniform gray matrix is Mg-rich silicate glass. (C
and D) Dark-field images of GEMS with "relict" Fe
sulfide and forsterite inclusions.
39
(No Transcript)
40
Dust modelers toolkit
Definitions of Qsca, Qabs, Qext Simplified case
of no diffraction Mie theory Mie theory program
online at http//omlc.ogi.edu/calc/mie_calc.htm
l Temperature calculation with Mie
theory Scattering patterns Polarization Radiation
coefficients How Mie theory helped understand
beta Pictoris other systems
41
The physics of dust and radiation is very
simple In the past the amount of dust
hidden by coronograph mask had to be
reconstructed using MEM maximum entropy
method or other models. Today scattered light
data often suffice (e.g., Mirzas 1501
project!) tau optical thickness
perpendicular to the disk (vertical optical
thicknass)
42
(No Transcript)
43
(No Transcript)
44
Or, as a bare minimum, an empirical model of dust
(e.g., stolen from comets)
45
Mie theory of scattering (absorption,
polarization,Qrad)
C. F. Bohren and D. R. Huffman (Editors),
Absorption and Scattering of Light by Small
Particles (Wiley-Interscience, New York, 1983).
Gustav Mie (1869-1957)
46
Resonant scattering from Mie theory
Wavelength 0.55 um Ocean water in air,
Qsca m1.343 0i
Carbon in air, Qsca m1.95 - 079i
Air bubble in seawater, Qsca
Carbon in air, Qabs m1.95 - 079i
47
Scattering of red light (0.65 um) on water
droplets of radius r
48
How Mie theory works in terms of reflection
and/or surface electromagnetic waves.
GLORY
RAINBOW
49
(No Transcript)
50
Laboratory-measured optical constants
These peaks are caused by SiO bond vibration
Wavelength (um)
51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
s3 um
s1 um
silicates
s20 um
s9 um
55
H2O
s1 um
s3 um
s9 um
s20 um
56
Radiation pressure coefficient depends
on composition, as well as porosity
57
Radiation pressure on mixture may be stronger
than on pure components
58
Radiation pressure on ISM dust in three
prototype debris disks. Notice the logarithmic
scale! ISM particles are absorbent, which
enhances the effect.
59
Radiative Rutherford scattering off a star (the
same Coulomb 1/r potential applies!)
60
A good candidate material can be found for the
beta Pictoris disk SED and broadband photometry
modeling
61
Choosing the plausible material
and Calculating the temperature of solids
62
(No Transcript)
63
EQUILIBRIUM COOLING SEQUENCE
Chemical unity of nature and its thanks to
stellar nucleosynthesis!
Silicates
silicates
T(K)
What minerals will precipitate from
a solar-composition, cooling gas? Mainly
Mg/Fe-rich silicates and water ice. Planets are
made of precisely these things.
ices
64
(No Transcript)
65
However, this may backfire.
66
(No Transcript)
67
(No Transcript)
68
T vs. r beta Pictoris
69
Temperature-distance relationship and Ice
boundary location in beta Pic
70
Equilibrium temperature of solid particles (from
dust to atmosphereless planets) A Qsca
albedo (percentage of light scattered) Qabs
absorption coefficient, percentage of light
absorbed Qabs Qsca 1 (this assumes the
size of the body gtgt wavelength of starlight,
otherwise the sum, called extinction
coefficient Qext, might be different) total
absorbing area A, total emitting area 4 A
(spherical particle) Absorbed energy/unit time
Emitted energy /unit time A Qabs(vis) L/(4 pi
r2) 4A Qabs(IR) sigma T4 L stellar
luminosity, r distance to star, L/4pi r2
flux of energy, T equilibrium temperature of
the whole particle, e.g., dust grain, sigma
Stefan-Boltzmann constant (see physical constants
table) sigma T4 energy emitted from unit area
of a black body in unit time Qabs(vis) - in the
visible/UV range where starlight is
emitted/absorbed Qabs(IR) - emissivityabsorptivi
ty (Kirchhoffs law!) in the infared, where
thermal radiation is emitted
71
Equilibrium temperature of solid bodies falls
with the square-root of r T4
Qabs(vis)/ Qabs(IR) L/(16 pi r2 sigma) which
can be re-written using Qabs(vis) 1-A as T
280 K (1-A)/Qabs(IR) (L/Lsun)(1/4)
(r/AU)(-1/2) Theoretical surface temperature T
of planets if Qabs(IR)1, and the actual
surface temperature Tp. Differences are mostly
due to greenhouse effect Body Albedo
A T(K) Tp(K) comments ________________
_____________________________________ Mercury
0.15 433 433 Venus 0.72 240 540
huge greenhouse Earth 0.45 235 280
greenhouse Moon 0.15 270 270 Mars 0.25 210
220 weak greenhouse asteroid (typical)
0.15 160 160 Ganimede 0.3 112 112 Titan 0.2 8
6 90(?) Pluto 0.5 38 38
72
Optical thickness
perpendicular to the disk in
the equatorial plane (percentage of starlight
scattered and absorbed, as seen by the outside
observer looking at the disk edge-on,
aproximately like we look through the beta
Pictoris disk)
73
What is the optical thickness ? It
is the fraction of the disk surface covered by
dust here I this example its about 2e-1 (20) -
the disk is optically thin ( transparent,
since it blocks only 20 of light)
picture of a small portion of
the disk seen from above Examples beta Pic
disk at r100 AU opt.thickness3e-3
disk around Vega
opt.thickness1e-4 zodiacal light disk
(IDPs) solar system 1e-7
74
STIS/Hubble imaging (Heap et al 2000)
Modeling (Artymowicz,unpubl.) parametric,
axisymmetric disk cometary dust phase function
Vertical optical thickness ?
Vertical profile of dust density
Radius r AU
Height z AU
75
Mirza Ahmics (2006) best fit to HST/STIS data (b
Pic)
Model of dust distribution uses empirical ZL
scattering phase function and two overlapping
disks, inclined by a few degrees
model
Fitting method multiparametric fit (18 par.)
using simplex algorithm
76
Mirza Ahmics best fit to HST/ACS data (b Pic)
Why the differences??
77
Chemistry/mineralogy/crystallinity of dust All
we see so far are silicate particles similar to
the IDPs (interplanetary dust particles from
our system) Ice particles are not seen, at
least not in the dust size range (that is also
true of the IDPs) Are all planetary systems
made of the same material?
78
Microstructure of circumstellar disks identical
with IDPs (interplanetary dust particles) mostly
FeMg silicates (Mg,Fe)SiO3 (Mg,Fe)2SiO4
79
HD142527
cold outer disk
warm disk
80
The disk particles are made of the Earth-type
minerals! (olivine, pyroxene, FeO, PAH
Polycyclic Aromatic Hydrocarbons)
81
Crystallinity of minerals Recently, for the
first time observations showed the difference in
the degree of crystallinity of minerals in the
inner vs. the outer disk parts. This was done by
comparing IR spectra obtained with single
dish telescopes with those obtained while
combining several such telescopes into an
interferometric array (this technique, long
practiced by radio astronomers, allows us to
achieve very good, low-angular resolution, observa
tions). In the following 2 slides, you will see
some inner and outer disk spectra - notice
the differences, telling us about the
different structure of materials amorphous
silicates typical dust grains precipitating
from gas, for instance in the interstellar
medium, no regular crystal structure crystalline
grains same chemical composition, but forming a
regular crystal structure, thought to be
derived from amorphous grains by some heating
(annealing) effect at temperatures up to 1000 K.
82
(No Transcript)
83
90 amorphous
60 amorphous
45 amorphous
compare
Beta Pic,
95 crystalline
84
We do not at present see in our statistics of
Vega-type stars any simple time-evolution of
dustiness or crystallinity of solids in
circumstellar disks.
Why?
Annealing could be thermal (in proximity to
stars), while transport done by outflows. Does
migration of dust explain observations??