Report from the Oort Cloud Simulations of the Formation of the Comet Reservoir Luke Dones Hal Levison Paul Weissman Martin Duncan

Report from the Oort CloudReport from the Oort Cloud

Simulations of the Formation of the Comet ReservoirSimulations of the Formation of the Comet Reservoir

Luke DonesLuke DonesHal LevisonHal Levison

Paul WeissmanPaul WeissmanMartin DuncanMartin Duncan

KBO Workshop, 9/1/2003KBO Workshop, 9/1/2003


Scenario for Oort Cloud Formation

Icy planetesimals formed in the region of the giant planets Some formed the cores of Jupiter, Saturn, Uranus, and Neptune Some stayed small and were scattered into big orbits Most were ejected from the Solar System, but the orbits of some were lifted from the planetary region by galactic tides and passing stars and reached the Oort Cloud This scenario neglects gas, interactions between planetesimals due to gravity or collisions, … Tides and stars perturb some comets back into orbits that approach the Sun within a few AU, making them sublime


Tremaine, in Planets AroundPulsars (1993)


GoalsGoalsTo determine …To determine …

where Oort cloud [OC] comets originated where Oort cloud [OC] comets originated (Conventional wisdom: Uranus-Neptune region, but (Conventional wisdom: Uranus-Neptune region, but

compositions are diverse)compositions are diverse)

the fraction of comets that end up in the Oort cloud the fraction of comets that end up in the Oort cloud the original mass in solids in the giant planets regionthe original mass in solids in the giant planets region

the spatial distribution of comets in the OCthe spatial distribution of comets in the OC– Does a massive inner OC exist? Does a massive inner OC exist?

If so, big comet showers are possibleIf so, big comet showers are possible

the temperatures reached by OC comets as their orbits the temperatures reached by OC comets as their orbits evolvedevolved


200,000 AU

20,000

200050

5

Outer Oort Cloud

Inner Oort cloud

Kuiper Belt, scattered disk

Comets ejected

Long period comets


Wiegert and Tremaine (1999)


Observed• 109 new long-period comets (a > 10,000 AU)• 178 returning long-period comets (34 AU < a < 10,000 AU)

There are 1.6 returning comets for each new comet.

Predicted57 returning comets for each new comet (gambler’s ruin model)34 returning comets for each new comet (Paul Wiegert’s thesis)

We’re still off by a factor of 20.

Fading ProblemFading Problem


CalculationsCalculations Direct integrations of 3000 “comets” for up to 4 billion yearsDirect integrations of 3000 “comets” for up to 4 billion years

Integrations include Integrations include – SunSun– Jupiter, Saturn, Uranus, Neptune with current masses and orbitsJupiter, Saturn, Uranus, Neptune with current masses and orbits– Present-day Galactic tides (Present-day Galactic tides (rr and and zz components) components)– Passing starsPassing stars

Two sets of runs, both with aTwo sets of runs, both with a0 0 between 4 and 40 AUbetween 4 and 40 AU– ColdCold: 2000 particles, root-mean-square e: 2000 particles, root-mean-square e00 = 0.02, i = 0.02, i00 = 0.01 = 0.01

– WarmWarm: 1000 particles, root-mean-square e: 1000 particles, root-mean-square e00 = 0.2, i = 0.2, i00 = 0.1 = 0.1

Integrate orbit of each comet until it:Integrate orbit of each comet until it:– is ejected from the Solar Systemis ejected from the Solar System– impacts the Sun or a planetimpacts the Sun or a planet– survives for 4 billion yearssurvives for 4 billion years







Duncan, Quinn,Tremaine(1987)




KBO Workshop, 9/1/2003KBO Workshop, 9/1/2003Everhart, Astron. J. 72, 1002 (1967)

Hale-Bopp Halley


Mass of the Oort CloudMass of the Oort Cloud Outer Oort cloud: 0.5 x 10Outer Oort cloud: 0.5 x 1012 12 comets comets with absolute magnitude Hwith absolute magnitude H10 10 < 11< 11

Number in inner Oort cloud ~ Number in outer Oort cloud Number in inner Oort cloud ~ Number in outer Oort cloud Total of Total of 101012 12 comets in the entire Oort cloud comets in the entire Oort cloud

Calibrate to Halley, which has HCalibrate to Halley, which has H10 10 ~ 6 and known size, assume ~ 6 and known size, assume density of 0.6 g cmdensity of 0.6 g cm-3-3 and Everhart’s size distribution and Everhart’s size distribution

mean mass of a comet ~ 4 x 10mean mass of a comet ~ 4 x 101616 g = g = 7 x 107 x 10-12-12 Earth massesEarth masses Present-dayPresent-day mass of Oort cloud M mass of Oort cloud Mnownow ~ ~ 7 Earth masses7 Earth masses Fraction of comets in the Oort cloud at present: Fraction of comets in the Oort cloud at present: 0.0460.046 Original Original mass in planetesimals between 4 and 40 AU: mass in planetesimals between 4 and 40 AU:

MMdiskdisk MMnow/now/ ~ ~ 150 Earth masses150 Earth masses


Hahn & Malhotra (1999)





Science 280, 1250 (1998)



Cometary Impact RatesCometary Impact Rates

Impact rates on Earth and galilean satellites Impact rates on Earth and galilean satellites due to due to activeactive long-period comets are low long-period comets are low at presentat present (Zahnle (Zahnle et al.et al. 1998) 1998)

Two uncertainties:Two uncertainties:– Inner Oort cloud: Many or few comets?Inner Oort cloud: Many or few comets?– ““Fading”Fading”

My my, hey hey,My my, hey hey,Rock and roll is here to stayRock and roll is here to stayIt's better to burn out, than to fade awayIt's better to burn out, than to fade awayMy my, hey heyMy my, hey hey



57P/du Toit-Neujmin-Delporte


Levison et al., Science 296, 2212 (2002)


Oort Cloud “To Do” ListOort Cloud “To Do” List

1.1. Assume the Sun formed in a clusterAssume the Sun formed in a cluster2.2. Let planets grow and migrateLet planets grow and migrate3.3. Include other perturbers: Include other perturbers:

planet or brown dwarf in the Oort cloudplanet or brown dwarf in the Oort cloud molecular cloudsmolecular clouds residual gas in solar nebularesidual gas in solar nebula

4.4. Model collisionsModel collisions5.5. Include fading on the way outInclude fading on the way out


Icarus 150, 151–162 2001)°

Adams and Laughlin, Icarus 150, 151 (2001)


Ida et al., Ap. J. 528, 351 (2000)


First 5 Myr First 50 Myr

Thommes et al., Astron. J. 123, 2862 (2002)


KBO Workshop, 9/1/2003KBO Workshop, 9/1/2003Nature 409, 589 (2001)


ConclusionsConclusions

The fraction of comets that reach the Oort cloud and The fraction of comets that reach the Oort cloud and survive to the present is small, < 5%.survive to the present is small, < 5%.

Efficiency is low because most comets evolve inward and Efficiency is low because most comets evolve inward and are ejected from the Solar System by Jupiter or Saturn. are ejected from the Solar System by Jupiter or Saturn.

Two-stage formation:Two-stage formation:– Early by Jupiter and SaturnEarly by Jupiter and Saturn– Late by Uranus and Neptune (peaks at 1 billion years)Late by Uranus and Neptune (peaks at 1 billion years)

Typical comet evolves inward to ~10 AU (Saturn’s distance Typical comet evolves inward to ~10 AU (Saturn’s distance from Sun) before being placed in the Oort cloud.from Sun) before being placed in the Oort cloud.

Inner Oort cloud does Inner Oort cloud does not not appear to be the Phantom appear to be the Phantom MenaceMenace

More observations and modeling are needed to work out More observations and modeling are needed to work out the cosmogonic implications. the cosmogonic implications.

Documents

Report from the Oort Cloud Simulations of the Formation of the Comet Reservoir Luke Dones Hal Levison Paul Weissman Martin Duncan