Transcript Great Migrations & other natural history tales

UTSC
Astronomy and Astrophysics - what’s its purpose
in the society?
0. Model for freedom of thinking & cooperation
1. Understanding
- solar system functioning and origin
- extrasolar planets, and the place of solar system
among other systems
- sun-Earth connection
- chaos
2. Prediction
- global warming
- impacts
Understanding of extrasolar and solar planetary
systems through theory of their formation
Introducing extrasolar systems
Protoplanetary disks
Disk-planet interaction: resonances and torques,
numerical calculations, mass buildup, migration of planets
Dusty disks in young planetary systems
Origin of structure in dusty disks
HD107146
Source: P. Kalas
At the age of 1-10 Myr the primordial solar nebulae =
protoplanetary disks = T Tau accretion disks
undergo a metamorphosis
A silhouette disk in Orion
star-forming nebula
Beta Pictoris
They lose almost all H and He and after a brief period as
transitional disks, become low-gas high-dustiness
Beta Pictoris systems (Vega systems).
Prototype of Vega/beta-Pic systems
Beta Pictoris
11 micron image analysis
converting observed flux
to dust area
(Lagage & Pantin 1994)
B Pic b(?) sky?
Chemical basis for universality of exoplanets:
cosmic composition (Z=0.02 = abundance of heavy elem.)
cooling sequence: olivines, pyroxenes dominant,
(Mg+Fe+SiO), then H2O
Hubble Space Telescope/ NICMOS infrared camera
HD 141569A is a Herbig emission star
>2 x solar mass, >10 x solar luminosity,
Emission lines of H are double, because they
come from a rotating inner gas disk.
CO gas has also been found at r = 90 AU.
Observations by Hubble Space Telescope
(NICMOS near-IR camera).
Age ~ 5 Myr
transitional disk
HD 14169A disk (HST observations), gap confirmed
by the new observations
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Gas-dust coupling?
Planetary
perturbations?
Dust avalanches?
HD 141569A: Spiral structure
detected by (Clampin et al. 2003)
Advanced Camera for Surveys
onboard Hubble Space Telescope
Radiation-pressure instability of opaque disks
found at UTSC
r
r
Radial-velocity planets
around normal stars
-450: Extrasolar systems predicted (Leukippos, Demokritos). Formation in disks
-325 Disproved by Aristoteles
1983: First dusty disks in exoplanetary systems discovered by IRAS
1992: First exoplanets found around a millisecond pulsar (Wolszczan & Dale)
1995: Radial Velocity Planets were found around normal, nearby stars,
via the Doppler spectroscopy of the host starlight,
starting with Mayor & Queloz, continuing wth Marcy & Butler, et al.
Orbital radii + masses of the extrasolar planets (picture from 2003)
Radial migration
Hot jupiters
These planets were found
via Doppler spectroscopy
of the host’s starlight.
Precision of measurement:
~3 m/s
Marcy and Butler (2003)
2005
~2003
Like us?
NOT REALLY
Why?
Diversity of exoplanetary systems likely a result of:
disk-planet interaction
a
m?
(low-medium) e
planet-planet interaction
a
X
m?
(high) e
star-planet interaction
disk breakup
(fragmentation into GGP)
a
m
X
X
e
a
m
X
X
e?
X
metallicity
Disk-planet interaction:
observation + numerics
A gap-opening body in a disk:
Saturn rings, Keeler gap region (width =35 km)
This new 7-km satellite of Saturn was announced 11 May 2005.
To Saturn
Masset and Papaloizou (2000); Peale, Lee (2002)
Some pairs of exoplanets may be caught in a 2:1 resonance
Mass flows through the gap
opened by a jupiter-class exoplanet
----> Superplanets can form
An example of modern Godunov (Riemann solver) code:
PPM VH1-PA. Mass flows through a wide and deep gap!
Surface density
Log(surface density)
Binary star on circular orbit
accreting from a circumbinary disk through a gap.
simulation of a Jupiter in a standard solar nebula. PPM
What permeability of gaps teaches us about
our own Jupiter:
- Jupiter was potentially able to grow to 5-10 m_j, if left
accreting from a standard solar nebula for ~1 Myr
- the most likely reason why it didn’t:
the nebula was already disappearing and not enough mass
was available.
Disk-planet interaction:
new strange migration
mode
Migration Type I :
embedded in fluid
Migration Type II :
in the open (gap)
Migration Type III
partially open (gap)
Type I-III Migration of protoplanets/exoplanets
Timescale
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Ward (1997)
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I
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II
M/M_Earth
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Disks repel planets:
Type I (no gap)
Type II (in a gap)
Currently THE
problem is:
how not to lose
planetary embryos
(cores) ?
Type I-III Migration of protoplanets/exoplanets
Timescale
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If disks repel
planets:
Type I (no gap)
Type II (in a gap)
I
II
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M/M_Earth
If disks attract
planets: Type III
Q’s:
Which way do they
migrate?
How fast?
Can the protoplanets
survive?
Variable-resolution
PPM (Piecewise
Parabolic Method)
[Artymowicz 1999]
Jupiter-mass planet,
fixed orbit a=1, e=0.
White oval = Roche
lobe, radius r_L= 0.07
Corotational region out
to x_CR = 0.17 from
the planet
disk
gap
(CR region)
disk
Consider a one-sided disk (inner disk only). The rapid inward migration is
OPPOSITE to the expectation based on shepherding (Lindblad resonances).
Like in the well-known problem of “sinking satellites” (small satellite galaxies
merging with the target disk galaxies),
Corotational torques cause rapid inward sinking.
(Gas is trasferred from orbits inside the perturber to the outside.
To conserve angular momentum, satellite moves in.)
Now consider the opposite case of an inner hole in the disk.
Unlike in the shepherding case, the planet rapidly migrates outwards.
Here, the situation is an inward-outward reflection of the sinking satellite problem.
Disk gas traveling on hairpin (half-horeseshoe) orbits fills the inner void and moves the planet
out rapidly (type III outward migration). Lindblad resonances produce spiral waves and try to
move the planet in, but lose with CR torques.
Outward
migration type III
of a Jupiter
Inviscid disk with an
inner clearing & peak
density of 3 x MMSN
Variable-resolution,
adaptive grid
(following the planet).
Lagrangian PPM.
Horizontal axis shows
radius in the range
(0.5-5) a
Full range of azimuths
on the vertical axis.
Time in units of initial
orbital period.
Edges or gradients in disks:
Magnetic
cavities around
the star
Dead zones
Summary of type-III migration
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New type, sometimes extremely rapid (timescale < 1000
years). CRs >> LRs
Direction depends on prior history, not just on disk properties.
Supersedes a much slower, standard type-II migration in disks
more massive than planets
Very sensitive to disk density gradients.
Migration stops on disk features (rings, edges and/or
substantial density gradients.) Such edges seem natural (dead
zone boundaries, magnetospheric inner disk cavities,
formation-caused radial disk structure)
Offers possibility of survival of giant planets at intermediate
distances (0.1 - 1 AU),
...and of terrestrial planets during the passage of a giant planet
on its way to the star.
If type I superseded by type III then these conclusions apply to
cores as well, not only giant protoplanets.
1. Early dispersal of the primordial nebula ==> no material, no mobility
2. Late formation (including Last Mohican scenario)