Saving Planetary Systems: the Role of Dead Zones

Saving Planetary Systems:Saving Planetary Systems:the Role of Dead Zonesthe Role of Dead Zones

Ralph Pudritz, Soko Matsumura (McMaster Ralph Pudritz, Soko Matsumura (McMaster University),University),

& Ed Thommes (CITA)& Ed Thommes (CITA)

AAS 208, CalgaryAAS 208, Calgary

Migration can acconunt for orbits of massive extrasolar planets Migration can acconunt for orbits of massive extrasolar planets – – all within 5 AUall within 5 AU Migration occurs by tidal interaction between planet and disk:Migration occurs by tidal interaction between planet and disk: Type I: migration without gap opening – Type I: migration without gap opening – planet swallowed within 1 Myr.planet swallowed within 1 Myr. Type II: migration after gap opening – Type II: migration after gap opening – planet locked to disk and migratesplanet locked to disk and migrates at rate dictated by inner disk – again lost quicklyat rate dictated by inner disk – again lost quickly

Why do planetary systems survive it? Why do planetary systems survive it? Absence of disk turbulence in “dead zone” in central disk Absence of disk turbulence in “dead zone” in central disk

significantly slows planetary migration (Matsumura, Pudritz, significantly slows planetary migration (Matsumura, Pudritz, & Thommes 2006: MPT06). Can even reverse it.& Thommes 2006: MPT06). Can even reverse it.

Ionization: X-rays from star cosmic rays radioactive elements heating from central star

Dead Zone (low viscosity region in a disk)

X-rays

Dead Zone

Cosmic rays magnetic field

RA elements

Dead Zone (Gammie, 1998):

- Magnetic turbulence is inactive in poorly ionized regions of the disk: so the disk’s viscosity is very low there.

- The DZ stretches out to about 13 Astronomical Units (1AU = Earth-Sun difference).

Eg. Matsumura & Pudritz 2006

(MNRAS)

Protoplanet

Tidal Torque

Viscous Torque

Disk

Disk

Gap opens in a disk when

Tidal Torque ~

Viscous Torque

Level of magnetic turbulence responsible for the “viscosity” of the gas

star

planet

M

M

Gap-opening masses of Planets

Disk Radius [AU] 0.01 0.1 1 10 100

100

10

1

0.1

0.01

0.001

0.0001

Gap

-ope

ning

mas

s [

MJ]

Jupiter

Uranus or

Neptune

Earth

Dead Zones and Planet Migration (MPT 06)

1. eg. Type I migration (before gap-opening)

→ 10 MEarth (< MUranus)

Dead Zone

Star Protoplanet

Numerical Technique:

We use a hybrid numerical code combining N-body symplectic integrator SYMBA (Duncan et al 1998) with evolution equation for gas (Thommes 2005)

- Allows us to follow evolution of planet and disk for disk lifetime: 3 – 10 Million years.

10 ME: Type I migration (No Gap-opening)

30

20

10

0

Dis

k R

adiu

s [A

U]

0 2×106 4×106 6×106 8×106 107

Time [years](w/o Dead Zone)

=10-5

30

20

10

0

Dis

k R

adiu

s [A

U]

0 2×106 4×106 6×106 8×106 107

Time [years](w/ Dead Zone)

Dead Zone

=10-2=10-2

If planet forms within the DZ:If planet forms within the DZ:halt migration of terrestrial planets by opening a gap in the halt migration of terrestrial planets by opening a gap in the

DZDZ

10 M_E planet started in dead zone; Left 2 million yrs Viscosity:

25 10;10 SSdz

Type II migration of Jupiter mass planet

30

20

10

0

Dis

k R

adiu

s [A

U]

0 2×106 4×106 6×106 8×106 107

Time [years](w/o Dead Zone)

30

20

10

0

Dis

k R

adiu

s [A

U]

0 2×106 4×106 6×106 8×106 107

Time [years]

(w/ Dead Zone)

=10-3 =10-3

=10-5

Dead Zone

Migration of Migration of a Jovian a Jovian planet over planet over 10 Myr.10 Myr.

- Note extent Note extent of gap of gap opened by opened by planet once planet once inside dead inside dead zone.zone.

- Planet Planet started at 20 started at 20 AU settles AU settles into orbit at into orbit at 4AU after 10 4AU after 10 MyrMyr

10 M10 MEE opens opens

gap at 3.5 gap at 3.5 AU in AU in dead zonedead zone

Also:Also:

1 M1 MEE opens opens

gap near gap near 0.1 AU 0.1 AU

Percentage of planets that migrate and stop within 5 AUPercentage of planets that migrate and stop within 5 AU

Assume uniform Assume uniform distribution of distribution of disks with disks with temperatures temperatures (1AU) between (1AU) between 150 and 450 K; 150 and 450 K; and lifetimes and lifetimes between 1 – 10 between 1 – 10 Million yrsMillion yrs

Observe 5-20% of Observe 5-20% of stars with planets stars with planets in this regime: - in this regime: - arises if disk arises if disk viscosity < 0.0001 viscosity < 0.0001 Percent of planetary systems with planets

migrating inside 5AU

Summary:Summary:

Earth massEarth mass planets, that start migration planets, that start migration outside of DZ, are reflected to larger radii outside of DZ, are reflected to larger radii

Earth mass planets that are formed inside Earth mass planets that are formed inside DZ halt migration because they can open a DZ halt migration because they can open a gap in the disk (eg. Earth mass at around gap in the disk (eg. Earth mass at around 0.1 AU).0.1 AU).

Massive planets open gaps, but their Type Massive planets open gaps, but their Type II migration very slow in low viscosity DZII migration very slow in low viscosity DZ

If viscosity parameter is < 0.0001, can If viscosity parameter is < 0.0001, can account for observed frequency of 5-20% account for observed frequency of 5-20% of stellar systems with planets inside 5AUof stellar systems with planets inside 5AU