Using the Inner Oort Cloud to Explore the History of the Earth

and Sun

Nathan KaibAdvisor: Tom Quinn

Collaborators: Andrew Becker, Lynne Jones

University of Washington

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

Classical Kuiper Belt (pre ~1995)

• Leftover primordial disk

• Low inclination

• Low eccentricity

Scattered Disk• Objects that have had Neptune encounter

• Inclinations inflated

- ( 0 – ~20o)

• Higher eccentricities

- (0.1 – ~1)

• Source of short-period comets

Outer Solar System

Oort Cloud extends to ~200,000 AU (1 pc)

Source of Long-Period Comets

Long-Period Comets

The tide of the Milky Way also perturbs the Oort Cloud

(COBE, NASA)

Galactic tide causes perihelion and inclination to oscillateAbout 2x as powerful as stellar passages (Heisler & Tremaine 1986)

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

X

Jupiter-Saturn Barrier• Comets must have large

perihelion shift to make it past Jupiter/Saturn in one orbital period

• Only weakly bound comets will have large perihelion changes

• Jupiter/Saturn shield inner solar system from inner 20,000 AU of Oort Cloud

25000 AU

25000 AU• LPCs near Earth only constrain outer Oort Cloud

• LPCs beyond Saturn will sample inner Oort Cloud as well

LPCs and Oort Cloud

a > 20,000 AUa > 1,000 AU~

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

SDSS-II SN Survey Observations2006 SQ372

SDSS-II SN Survey Observations2006 SQ372

SDSS-II SN Survey Observations2006 SQ372

SDSS-II SN Survey Observations2006 SQ372

Orbit Summary

a = 796 AU q = 24.2 AU i = 19.5°

Orbital Evolution

Current orbit is transient - unstable after ~200 Myrs!

Two Different Origin Scenarios1. Scattered Disk

sem

imaj

or a

xis

perihelion

x

Two Different Origin Scenarios2. Oort Cloud

sem

imaj

or a

xis

perihelion

x

OC

SD

Simulations

Scattered Disk

• 2,500 particles• Orbit distributions

based on SDO observations

• Run for 4.5 Gyrs

Oort Cloud

• 106 particles• Orbit distributions

based on Kaib & Quinn (2008) sims

• Run for 1.4 Gyrs

Non-symplectic variable timestep integrator based on SWIFT (Levison & Duncan, 1994; Kaib & Quinn, 2008)

Results – OC Sim.(10° < i < 30°)

Results – OC Sim. (10° < i < 30°)

Results – OC Sim.(10° < i < 30°)

Results – OC Sim.(10° < i < 30°)

Results – OC Sim. (10° < i < 30°)

Orbital Residence Map (OC)

X2006 SQ372

10° < i < 30°

Calibrating Simulation Output

• For scattered disk simulation, assume:

- NJFCs = 250

- Dormant:Active Comet ratio = 2 (Morbidelli & Fernandez, 2006)

•For Oort Cloud simulation, assume:- LPC flux (q < 5 AU) = 1.5 comets/yr (Neslusan, 2007)

- Inner:Outer OC population ratio = 3 (Kaib & Quinn, 2008)

Orbital Residence Map (OC)

X2006 SQ372

10° < i < 30°

POC/PSD Map

SQ372

For 2006 SQ372: POC/PSD 16

2006 SQ372

2000 OO67

(Kaib et al., 2009)

Origin Implications

• 2006 SQ372 is at least 16 times more likely to come from the Oort Cloud compared to the Scattered Disk

• Which region of the Oort Cloud?

Inner Oort Cloud Origin

Semimajor axis drawdown time

vs.

Perihelion drift time

q = -10 AU Ejection by Saturnq = 10 AU a is fixed

Inner Oort Cloud Origin

tq ~ a-2

ta ~ 100 MyrsSampled by Known LPCs

(~2.5%)

a < 800 AU20 AU < q < 30 AU

(Kaib et al., 2009)

2006 SQ372 Summary

• 2006 SQ372 and 2000 OO67 (Elliot et al. 2005) are first detected members of inner Oort Cloud population inside planetary region

• Pan-STARRS, LSST will discover 100’s to 1000’s of similar bodies

• Population statistics will constrain structure and population size of inner Oort Cloud

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

How did the Oort Cloud form?

Pat Rawlings, NASA

q is ~fixed, but a undergoes random walk

Planetesimal Scattering

If q > 40 AU then growth in a stops

~ 104 AU

Inclination also changes

Semimajor axis (AU)

Per

ihel

ion

(AU

)

(Kaib & Quinn, 2008)

t = 2 Gyrs

Semimajor axis (AU)

Per

ihel

ion

(AU

)

(Kaib & Quinn, 2008)

x

x x x

t = 2 Gyrs

LPCs

SDKB OC

Sedna

2000 CR105

Buffy2004 VN112

Extended Scattered Disk~ 103 AU

• If q was always big, orbit should be circular, low i

• a is too small for current external forces to shift q

Early Strong Perturbations

Embedded Cluster Environment

(Brasser et al., 2006)

Open Cluster Environment

(Kaib & Quinn, 2008)

Reproducing ESDOs

Med

ian

OC

Dis

tanc

e (A

U)

med

min

Kaib & Quinn (2008)

Brasser et al. (2006)

Birthplace Consequences

Kaib & Quinn (2008)

Inner OC: a < 20,000 AUOuter OC: a > 20,000 AU

• Sun’s birth environment controls inner Oort Cloud enrichment and radial distribution

OutlineBackground• Outer Solar System primer• Inner vs. outer Oort Cloud

Observations• Candidate inner Oort Cloud objects• Prospects from future surveys

What We Can Learn• Oort Cloud formation and the Sun’s birth

environment• Comet showers and mass extinctions

Comet Showers

25000 AU• Rare close stellar

encounters (< 5000 AU) are able to perturb more tightly bound orbits

• The Earth is temporarily exposed to the entire Oort Cloud

M* = MSun v = 20 km/s,

Dmin = 3000 AU t = 105 yrs

25,000 AU 4 AU

Quantifying Shower Strength

LPC defined as q < 5 AU

M* = 0.8 MSun

v = 20 km/sDmin = 1300 AU

v = 20 km/s

Simulation ResultsR

elat

ive

Sho

wer

Stre

ngth

Use impulse approximation to calculate vSun for each stellar passage:

vSun = (2GM*)/(bv)

One parameter controls shower strength

Rel

ativ

e S

how

er S

treng

th

Finding Shower Frequency

• Use Rickman et al. (2008) stellar encounter code to generate ~106 passages

• Find dN(vSun)/dt

One parameter controls shower strength

Rel

ativ

e S

how

er S

treng

th

1/ ~ (vSun)-2

Rel

ativ

e S

how

er S

treng

th

Regions Sampled by LPCs

Effects of Solar Formation Setting

Inner Oort Cloud population very sensitive to formation environment of Sun (Fernadez & Brunini, 2000; Brasser et al., 2006; Kaib & Quinn, 2008)

Summary• Inner Oort Cloud objects should be abundant

beyond 10-15 AU

• First few objects have been discovered

• LSST and Pan-STARRS will discover 100’s to 1000’s and constrain inner OC

• This will reveal clues about the Sun’s birthplace

• Indicate if comet showers are source of mass extinctions

Divide LPC distribution by Oort Cloud distribution

Probability of LPC as a function of a

semimajor axis (AU)

perih

elio

n (A

U)

Random walkIn a

Random walkIn q

Duncan et al. (1987)

30

300

3000

1000

100

1600 2500 4000 6300 1600010000