Forming Planets: when and how

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Forming Planets when and how


Nuria Calvet Department of Astronomy University
of Michigan
To Sra. Magris
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Our Planetary System
Sun
Pluto and Kuiper Belt bodies
Rocky Planets
Giant Planets
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Extrasolar planets
340 and counting (NYT 03/03/09)
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20 1 known multi-planetary systems
Large diversity
How do they form? Why so diverse?
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Other planetary systems


Common properties Star at center Planets and
other bodies in disk rotating around the star
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Solar System in the Galaxy
Solar System
Our twin galaxy
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Star-forming regions in the plane of the Galaxy
Most star formation along spiral arms of
galaxy Spiral arms regions of high density of
gas and dust
Infrared
Optical
Dust is cold and emits infrared radiation
Dust traces arms and star-forming regions
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Electromagnetic radiation
10-7 10-5 5x10-5
10-3 1 100
cm
X rays Ultraviolet Visual
Infrared Microwaves Radio
Rainbow colors
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Blackbody emission
UV V IR
A blackbody emits all the energy it absorbs The
temperature of a blackbody decreases as it
absorbs less energy A blackbody emits at longer
wavelength the cooler it gets Interstellar dust
is heated by absorbing radiation from distant
stars Cold, 10 279F Bright in the infrared
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The Three Great Observatories
Star Forming Regions
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Molecular clouds
Molecular cloud
Spiral arm
Molecular cloud core
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Molecular clouds and cores
Hubble image
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The Orion Nebula


The closest massive star forming region
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What is in the disk?


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The youngest objects
Hidden inside molecular clouds
infrared
visual
Barnard dark cloud
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Dust shines in Spitzer images
Infrared
Optical
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Multi-wavelength view of Young cluster


Courtesy NASA/JPL-Caltech
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Multi-wavelength view of Star-forming region


Courtesy NASA/JPL-Caltech
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Molecular cloud cores collapse


Core collapses under its own gravity. Too cold to
build enough pressure to counteract
gravity Collapse conserving angular momentum A
disk is formed around central object
?1
0.1 pc 20,000 AU
100 AU
1 AU distance earth-sun 1.5 x 108 km 9 x
107 Miles
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Disk formation

• Collisions between opposing flows make the disk.

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Protostars images of (rotating) infall forming
rotating disks

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Disks in silhouettes and photoevaporating in
Orion Nebula cluster
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Disks and associated jets


HH 30
Credits Alan Watson (Universidad Nacional
Autonoma de Mexico, Mexico), Karl Stapelfeldt
(NASA Jet Propulsion Laboratory), John Krist
(STScI), and Chris Burrows (ESA/STScI)
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A new edge-on disk around a low mass star


200 AU
Discovered 2 weeks ago by Kevin Luhman,
collaborator at Penn State
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Spectral energy distribution Spitzer data


Disk heated by the star Temperature decreases
with distance to the star Each disk ring emits at
longer wavelength
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What are these disks?


Gas with 1 of dust particles, circling around
the star Mass 1-5 mass of star, 10-50
Jupiter masses Rotational velocity is Keplerian,
increases as distance to star decreases
Disks are changing with time Mass is accreted
onto the star Dust particles collide with each
other, grow, settle towards the midplane of the
disk
Disks evolve
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Disks are accreting matter onto the star


Differential rotation causes rubbing between the
rings of the disk Rubbing transfers angular
momentum outwards - Inner rings tend to rotate
slower, outer rings faster Inner rings move
inward, outer rings outwards Matter spirals in
and finally is accreted onto the star Disk
expands to conserve angular momentum
faster
slower
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Dust particles collide and stick together


Starting with sizes 1 micron Collide with each
other, stick together, grow
1 micron 0.0001 cm
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Dust settles toward the midplane of the disk


Dust starts small and is well mixed with
gas Particles stick together and grow Larger
particles sink toward miplane Particle collisions
and growth continues at midplane Planetesimals (
m - km size) are formed
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What materials?
Depends on temperature Metals, rocks can survive
to high temperature Ices only below 150K
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Composition of particles in disk


Disk is heated by central star Only rocky
planetesimals in inner disk, ices also beyond
snow line
Snow line
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Our Planetary System
Sun
Snow line
Pluto and Kuiper Belt bodies
Rocky Planets
Giant Planets
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Accretion model for forming giant planets


Jupiter
Timescales 10 million years
H, He rich envelope
Planetesimal core
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Building giant planets

• Each giant planet formed its own miniature disk
  
• The biggest moons formed out of this disk.

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Disk with multiple giant planets


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When do giant planets form?
Giant planets need gas to form But disk gas is
accreting onto the star Eventually disk runs out
of gas How long does the gas last in the disk?


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When do giant planets form?


Find the disks in stellar groups of different
ages Disks detected by emission in Spitzer
bands Gas in disk is gone by 10 million years!
Giant planets form during the first 10 million
years of the life of the star
Study by Jesus Hernandez postdoc at Michigan
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Opening a gap


Planets as they grow drive density waves into the
disks nearby These waves carry angular momentum
and can push gas away from planet opening a gap
Simulations Frederik Masset
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Planet-disk interaction migration


When planet mass is low, disk pushes it
inward Planet may fall into star!
Hydrodynamical simulations by Frederic Masset
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Planet-disk interaction stopping migration and
opening gap


When/if planet accretes enough mass, migration
stops Planet opens a gap in disk
Frederic Masset
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Disk Evolution


Courtesy NASA/JPL-Caltech
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What do we observe? Inner disk clearing


Full disk
Hot inner regions gone
IRS disk team
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Signature of gaps


Inner clearing
Inner clearing
Less emission at intermediate wavelengths
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Clear evidence of gaps!


full disk
Disk with gap
star
Catherine Espaillat et al 2007, 2008 Michigan
graduate student
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Evolutionary sequence the first stages of giant
planet formation
Disk Gaps
Full disk
Inner Disk Holes
Spitzer Science Center
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Formation of terrestrial planets
After gas in essentially gone - and danger of
migrating into star is over! Collisions between
left-behind planetesimals can build up
terrestrial planets
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Diversity?
Because of chaotic/random motions, different sets
of planets result from slightly different initial
conditions
Chambers Wetherill 1998
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Diversity
Range of initial conditions and disk properties
can explain large diversity of exoplanets!
observations
models
Research by Althea Moorhead and Fred Adams,
Michigan Physics
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Formation of the planets quick summary

• cold gas core collapses under gravity to form

protostar with disk and jet. accretes mass from
disk
planets form in dusty rotating disk
dust and gas gets swallowed up (accreted) in
larger bodies
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Scientific American Top 10 Exoplanets


at Michigan
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Proto-Jupiter Flyby


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IAU 2006 General Assembly definition of Planet

• The International Astronomical Union members
  gathered at the 2006 General Assembly agreed that
  a planet is defined as a celestial body that
• Is in orbit around the Sun
• Has sufficient mass for its self-gravity to
  overcome rigid body forces so that it assumes a
  hydrostatic equilibrium (nearly round) shape, and
• Has cleared the neighborhood around its orbit

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IAU 2006 General Assembly definition of Planet


Eris
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The outer Solar System


Dwarf Planets and Small Solar-System Bodies
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Alternative theory formation by gravitational
instabilities


Region of high density in disk collapse under its
own gravity, forming a giant planet
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Planets detected by transit
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Planet detection by Doppler shift
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Scientific American Top 10 Exoplanets


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Scientific American Top 10 Exoplanets


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Scientific American Top 10 Exoplanets


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Scientific American Top 10 Exoplanets


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Scientific American Top 10 Exoplanets


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A planet in a debris disk
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Planet-interactions gap opening


Frederic Masset
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What is in the disk?


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Pre-Transitional Disk of LkCa 15

• Truncated outer disk at 46 AU (Pietu et al. 2006)
• Binary? No companion M 0.1 Msun 3-22 AU
  (Ireland Krauss 2008) or larger separations
  (White Ghez 2001)

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Pre-Transitional Disk of LkCa 15
Increasing flux/ optically thick disk
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Detailed near-IR spectrum of pre-transitional
disk LkCa 15
Blackbody at T 1500K
Espaillat et al. 2008, Poster by Espaillat 91
2-5 mm SpeX spectrum
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Blackbody-like near-IR excess between 2-5 mm in
full disks of CTTS
Muzerolle et al. 2003
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Dust-gas Transition
Monnier Millan-Gabet 2002
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Detailed near-IR spectra of transitional disks
No hot optically thick gas!
Poster by Espaillat 91