Zodiacal Cloud: The Local Circumstellar Disk

Sumita Jayaraman

PSI Why do we study the Zodiacal Cloud?

Yields information on the formation and evolution of the interplanetary dust disk in our Solar System.

For the Solar System

For Exo-zodi Disks and Planetary For Exo-zodi Disks and Planetary SystemsSystemsDirect application to the structure of Direct application to the structure of

exo- zodi disks and planetary exo- zodi disks and planetary detection.detection.

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Structures in the zodiacal cloud• Earth’s Resonant Ring

• Dynamical Asymmetries

• Dust Bands

Structures in Exo-zodiacal disks

Contents

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Structures in the zodiacal cloud

• Earth’s Resonant Ring• Dynamical Asymmetries

• Dust Bands

Structures in Exo-zodiacal disks

Contents

PSI Zodiacal Peak-Flux Variation (COBE-DIRBE)

Average Trailing: 70.26 MJ/Sr

Average Leading: 68.5 MJy/Sr

Ring Flux : 1.7 MJy/Sr

(~2.5%)

PSI Resonant Trapping of Dust Particles

PSI Resonance Capture Probability vs Particle Size

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Earth’s Resonant Ring Model

Sun

Spitzer’s Orbit

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At Spitzer Launch…

…After 2 years

Estimated Ring Flux: ~ 5.5 MJy/Sr (8% of Zody)

All-Sky View of RingTrailing Leading

PSI Resonant Ring Obs. 25μm (COBE-DIRBE)

SN

S

LeadingTrailing

(Reach et al., 1995)

PSI All Sky Model for Extended Spitzer Mission

Year 1

Year 2

Year 3

Year 4

Year 5

At Launch

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Goals of the Spitzer Project

• Track measurements of the Earth’s Resonant Ring as Spitzer traverses it.

• Monitor variations in the Ecliptic Pole flux.

• Measure the absolutely calibrated zodiacal flux and estimate background radiation levels during the mission.

• Obtain very high resolution images of the asteroidal dust bands.

PSI Spitzer Zodical Obs.

Obs. Mode Direction of Obs. Instrument

Fast Scan-Map

~ -6 ° to +6 ° Ecliptic Latitude

MIPS

TPM Poles +90 ° and -90 ° IRAC & MIPS

TPM Ecliptic

(Trailing and Leading)

0 ° Ecliptic Latitude

ε =70 °, 90 °, 110 °

60 ° Ecliptic Latitude

ε =90°

IRAC & MIPS

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Spitzer Project: Planned ObsS

N

S

LeadingTrailing

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IRAC North Ecliptic Pole Flux

2004

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IRAC North Ecliptic Pole Flux

2004

2005

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IRAC North Ecliptic Pole Flux

2004

2005

2006

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MIPS North Ecliptic Pole Flux

2004

2005

2006

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Ring: Model vs Observations

EarthRing Model:

10 micron particles into

First order resonances

Spitzer Earthring Observations

2004: None

2006: 10% increase of in the NEP Flux at the maximum point

2004: None

2006 (May): 6% (1.1MJy increase in the NEP Flux)

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Next Steps

• Analysis of Ecliptic Plane Observations (predicted increase in ring flux from 2.5%(1.7 MJy/Sr) of zody to 8% (5.5 MJy/Sr) of zody)

• Multiple Wavelength observations (3.6 and 70 microns) from IRAC, MIPS as well as IRS Peak-up mode.

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Science Questions

• What is number density of particles in the ring?• What is the background number density required

to produce the flux variations?• What is the efficiency of capture into resonance

by an Earth-mass planet?• How do we distinguish a feature like trailing dust

cloud in ring from the planetary perturber in an exozodiacal disk?

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Structures in the zodiacal cloud• Earth’s Resonant Ring

• Dynamical Asymmetries• Dust Bands

Structures in Exo-zodiacal disks

Contents

PSI Dynamical Asymmetries in the Zodiacal cloud

• Off-center shift of the zodiacal cloud shown by the pole observations.

• Warps in the cloud due to the inclination and shift measured by the variations in peak flux.

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Sun-Centered Cloud

SunEarth Orbit

Zodiacal Center

Earth Aphelion

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Off-Center Cloud

SunEarth Orbit

Zodiacal Center

Earth Aphelion

PSI Evidence for an off-center cloud

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Inclination of the cloud

PSI Zodiacal Peak-Flux Variation (COBE-DIRBE)

Ring Flux : 1.7 MJy/Sr

(~2.5%)

PSI Zodiacal Peak-Flux Variationwithout the Ring

PSI Zodiacal Peak-Flux Variationdue to Earth’s eccentricity

PSI Warps in the Zodiacal cloud

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Structures in the zodiacal cloud• Earth’s Resonant Ring

• Dynamical Asymmetries

• Dust BandsStructures in Exo-Zodiacal disks

Contents

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Asteroidal Dust Bands

Scan

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Structures in the zodiacal cloud

• Earth’s Resonant Ring

• Dynamical Asymmetries

• Dust Bands

Structures in Exo-zodiacal disks

Contents

PSI Dynamical Effects in Circumstellar Disks

• Resonant trapping – determined by the number and co-rotation of the clumps

• Recent planetesimal collisions in the disk – young dust bands

• Planetary perturbations on the disk due to one or more planets causing an inclined and off-center disk.

PSI Planetary Signatures in Observed Disks

• Resonant Rings caused by larger Planets - ε Eridani

• Off-center disk – HR4796A• Gaps in the disk due to Resonant

Trapping and scattering due to Large Planet – β Pictoris ?

• Warps in the disk due to planetary perturbations - β Pictoris.

• Bands due to stochastic collisions.

PSI What do the structures tell us?

• Location of the planet(s), eccentricity of the orbit

• Mass of the planet(s)

• Size of the dust particles (lower limits)

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ε Eridani

(Quillen & (Quillen & Thornedike, Thornedike, 2002)2002)

e = 0.3

M = 10- 4 MSun

A = 40 A.U.

PSI HR 4796A (Wyatt et al. 2002)

Estimate of Planet Mass > 10 Mass of Earth with e >0.02

Flux Asymmetry ~ 5%

PSI Challenges in Planetary Detection in Disks

• Young disks have dust and gas

• Structures observed in images do not provide unique solutions for planetary masses or location

• Source of dust is uncertain – especially for disks with small dust grains.