A meteoritical perspective of
giant planet migration

Graham H. Edwards

Earth & Environmental Geosciences, Trinity University

Rice University

17 September 2026

My science spans two broad categories…

Quaternary climate

Isotope geochemistry

Cosmochemistry

Reconstructing early solar system processes from meteorites

Contextualizing the formation of planetary systems

Giant planet migration

is a quotidian feature of planetary systems

Planetary migration is common in the galaxy

Hot Jupiters likely migrated inward from larger radii

Dawson+Johnson 2018

Planetary migration is common in the galaxy

Exoplanet spacing and eccentricity distributions reflect dynamical excitation

Pu+Wu 2015, Raymond+ 2010

Giant planet migration

is a quotidian feature of planetary systems

…including our solar system

Evidence of migration in the outer solar system

Evidence of migration in the outer solar system

Orbital eccentricities and inclinations of giant planets and Kuiper Belt objects.

Fernández+Ip 1984, Tsiganis+ 2005, Gomes+ 2003

Evidence of migration in the inner solar system

Heavy bombardment of rocky bodies

The heavily cratered terrains of the Moon and other bodies…provide clear physical evidence for an elevated flux of impactors across the Solar System that continued for several hundred million years after the initial accretion and differentiation of the terrestrial planets.

Bottke+Johnson 2017

The Late Heavy Bombardment

∼3.9 Ga

Wikimedia

The Late Heavy Bombardment

Illusory Late Heavy Bombardments

Boehnke+Harrison 2016, PNAS

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Evidence against a Late Heavy Bombardment event on Vesta

Cartwright+ 2022, EPSL

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Evidence for very early migration of the Solar System planets from the Patroclus–Menoetius binary Jupiter Trojan

Nesvorný+ 2018, Nature Astronomy

Lots of evidence for giant planet migration!

But how?

Mechanisms & timing of migration

Mechanisms of giant planet migration

The classics:

1. The Grand Tack
2. Giant planet instability

Giant planets carve gaps in gaseous protoplanetary disks and migrate inwards

ALMA, NASA/ESA

Adapted from Kley+Nelson 2012

The Grand Tack

The Grand Tack

Proto-Jupiter carves out a gap in the disk.

Jupiter migrates inward as Saturn becomes large enough to migrate, too.

Saturn catches Jupiter in a mean motion resonance, and they tack outward.

Mixed inner and outer solar system material and a small Mars.

Giant planet instability

Giant planet instability

A large and compact Kuiper Belt remains after gas (disk) dissipation.

Disk-planet interactions. Jupiter and Saturn drift into 2:1 resonance.

Dynamical instability!

Modern architecture.

Mechanisms of giant planet migration

Variations on instability

3. Gas dissipation and rebound
4. Self-unstable systems

Gas dissipation & planet rebound

Gaseous disks apply inner and outer torques on embedded planets

Gas dissipation & planet rebound

1. Photoevaporation of inner disk terminus
2. Saturn pulled outward by retreating gas (rebound)
3. Outward migration of Saturn compresses outer orbits, increases close encounters

Liu+ 2022

Gas dissipation & planet rebound

Dynamical instability ensues

Self-unstable systems

Self-unstable systems

Planetary architecture forms embedded within a gaseous disk.

The disk dissipates…

…and dissipates…

…and dissipates…

Dynamical instability!

Mechanisms & timing of migration

Solar system time-zero

Ca-Al-rich inclusions (CAIs)

Allende (CV3), American Museum of Natural History

CAIs = “solar age”

0 My_ss = 4567.3 Ma

When did giant planets migrate?

When did giant planets migrate?

Four mechanisms, four timescales

1. Gas-driven migration (Grand Tack)
2. Planetesimal disk-triggered instability
3. Gas dissipation (and rebound)
4. Self-unstable systems

When did giant planets migrate?

So…a meteoritical perspective?

Dynamical excitation → chaos in the inner solar system

Asteroids are witnesses (and participants) of inner solar system dynamics

Asteroid collisions release energy and generate heat

Davison+ 2012, Bland+ 2014

Meteorites sample the asteroid population

Meteorite thermochronology

The radioactive ⁴⁰K decay system

K-Ar radiochronometer

K-Ar thermochronometer

At high temperatures, Ar is lost from the mineral.

≫500 K

At low temperatures, Ar is retained and records time.

≪500 K

When did giant planets migrate?

Can we reconstruct asteroid belt collisional history (and system-scale dynamical excitation) from meteorite thermochronology?

Modeling asteroid-scale thermochronology

Modeling asteroid-scale thermochronology

• midplane temperature
• heat-producing element abundances
• Ar closure temperature
• planetesimal radius
• time of accretion
• material properties

Carslaw+Jaeger 1959, Hevey+Sanders 2006

Modeling asteroid-scale thermochronology

\[ \begin{aligned} F_o &:~\text{Initial flux}\\ t_o &:~\text{onset time}\\ \tau &:~e\text{-folding time} \end{aligned} \]

Exponentially decaying bombardments (impact fluxes)

Asteroid ⇆ meteorite thermochronologic data

Compiling chondritic ⁴⁰K-⁴⁰Ar system ages

Wikimedia

Chondrites are common in the meteorite record

Chondrite parent bodies did not melt

Inner solar system chondrites had similar parent bodies with (roughly) similar histories

Compiling chondritic ⁴⁰K-⁴⁰Ar system ages

Compiled >200 ages from >70 sources…

• Journals
• Reports
• Conference proceedings
• Conference abstracts

Database of chondritic ⁴⁰K-⁴⁰Ar system ages

Database of chondritic ⁴⁰Ar-³⁹Ar ages

• early peak
• monotonic decline
• recent break-up events →

Database of chondritic ⁴⁰Ar-³⁹Ar ages

Fitting thermochronologic
(forward) models to data

Markov chain Monte Carlo

MCMC inversion of chondrite thermochronologic data

Prior

Posterior

Methods

Methods

MCMC inversions of simulations employing different bombardment scenarios

0. No bombardment (flux of impactors)
1. One bombardment
2. Two bombardments
3. Three or more bombardments

Results

Prior & posterior ⁴⁰Ar-³⁹Ar age distributions

Prior & posterior ⁴⁰Ar-³⁹Ar age distributions

\[ \ell = -1016 \pm 2 \]

\[\ell = -992 \pm 2 \]

\[ \ell = -989 \pm 3 \]

Prior & posterior ⁴⁰Ar-³⁹Ar age distributions

\[ \ell = -992 \pm 2 \]

\[ \ell = -989 \pm 3 \]

One impact flux

Thermochronologic parameters

One impact flux

Posterior distributions

One impact flux

A mild and protracted primordial impact flux

Two impact fluxes

Thermochronologic parameters

Two impact fluxes

Bombardment intensity & duration

An intense and brief post-accretion bombardment

A mild and protracted primordial impact flux

Two fluxes are sufficient reproduce the prior

More than 2 fluxes are not necessary to reproduce the prior

Bombardment histories with two impact fluxes are necessary and sufficient to reproduce chondrite thermochronology with a migration event

Posterior distributions of impact fluxes in a two-bombardment history

Posterior distribution of post-accretion bombardment onset

No evidence for a Late Heavy Bombardment

Embedded in a gaseous disk

20%

Dissipation of gaseous disk

<20%

Self-unstable system after gas dissipation

45%, incl. median & mean (μ=15.0)

Outer planetesimal disk-triggered instability

38%

Giant planets migrated during an instability

(≥75% confidence)

Instability followed dissipation of the gaseous disk

(∼50% confidence)

Conclusions

Conclusions

• Giant planets migrated during an early instability, likely associated with dissipation of the gaseous disk.
• Importance of <20 My (exo)planetary systems to understand ours…
• Ar-Ar geochronologists should date more chondrites.

Appendix

Methods

Age distributions by meteorite classification

Thermochronologic simulation methods

Model validation

Appendix

Extended data

No bombardments

Two “free” bombardments

Three bombardments

Appendix

Decay constants and age of CAIs

Decay constants

Age of CAIs (t_ss)

Appendix

Exploring more realistic impactors

Impactor D = 1 km

Impactor D = 15 km