Depletion and excitation of the asteroid belt by migrating planets Kevin J. Walsh, Alessandro Morbidelli (SwRI,OCA-Nice) Sean N. Raymond (Obs. Bordeaux), Dave P. O’Brien (PSI), Avi M. Mandell (GSFC)

Motivation: a solution to the Mars problem? Problem: Mars analogs are 5-10x larger than Mars in standard simulations. Raymond et al Mars analogs are bad

A solution to the Mars problem? Mars analogs are great Hansen 2009 Solution: Hansen (2009) solved this problem with ad-hoc initial conditions, a narrow annulus of material between 0.7— 1.0 AU. Question: Is there a mechanism to create these initial conditions? Problem: Mars analogs are 5-10x larger than Mars in standard simulations.

Migration of Jupiter and Saturn in a gas-disk 3:2 res Masset and Snellgrove, 2001, Morbidelli and Crida, 2007; Pierens and Nelson, 2008 For a wide range of possible gas-disk parameters Jupiter will open a gap and migrate inwards via type II migration Saturn migrates inwards, getting captured in resonance with Jupiter. Saturn in resonance with Jupiter can halt and reverse the inward migration of Jupiter. Saturn Jupiter

Jupiter’s migration - truncating the disk Jupiter migrates inward to ~1.5, Saturn migrates inward, getting captured in the 3:2 resonance with Jupiter, while increasing in mass, Saturn reaching near full mass halts their migration, and reverses it. They migrate out together as the gas-disk dissipates. Semimajor axis ?

Problem? The Asteroid Belt Jupiter’s outward migration scatters bodies into the asteroid belt Thus, seeking to produce taxonomic distributions, we envision reservoirs of primitive bodies between and beyond the giant planets. The asteroid belt provides strict constraints in its taxonomic and orbital distribution. Gradie and Tedesco 1982

Jupiter’s migration - truncating the disk Jupiter migrates inward to ~1.5, Saturn migrates inward, getting captured in the 3:2 resonance with Jupiter, while increasing in mass, Saturn reaching near full mass halts their migration, and reverses it. They migrate out together as the gas-disk dissipates. S-type C-type Semimajor axis ? ? scattered S-types

X,Y movie

Repopulating the Asteroid Belt The “S-type” bodies from the inner disk are scattered back roughly where they originated. This means that they largely repopulated the inner part of the asteroid belt region a<2.8. Semimajor axis (AU)

Asteroids Gradie and Tedesco 1982 Bodies are implanted in the asteroid belt ~10 -3 efficiency, ~10x current asteroid belt mass for an initial MMSN, ~Taxonomic distributions largely recreated Orbital distribution matches pre-LHB expectations e = i=0-25°

We We are not done. There is ~500 Myr until the LHB We have a component of high-e bodies that will accrete onto planets or could collide with each other.

Asteroid Belt implications Separate parent populations – AU and ~6-13 AU – Requires diversity in both populations to explain the significant observed diversity among asteroids. – Suggests that our primitive asteroids may originate closer to comets than our more metamorphosed asteroids Pre-Depleted asteroid belt – The asteroid belt was depleted rapidly before the gas-disk had fully dissipated. Pre-Excited asteroid belt – Asteroid belt gets its inclination distribution at this early time, – Eccentricities will be re-shuffled later (LHB) Chondrules/CAIs – Need to be formed/transported to ~ 13 AU and beyond?

Conclusions Conclusions: Jupiter migrating to 1.5 AU can solve some outstanding problems – Small mass of Mars – Physical dichotomy of the asteroid belt – Freedom for Jupiter to form very near the Snow Line Implications: – Jupiter and Saturn migrated significantly in the gas-disk: Jupiter reached 1.5 AU – The asteroid belt was repopulated from two distinct parent populations

Asteroids Gradie and Tedesco 1982 Bodies are implanted in the asteroid belt ~10 -3 efficiency, ~10x current asteroid belt mass for MMSN, ~Taxonomic distributions recreated Orbital distribution matches pre-LHB expectations e = i=0-25°

Asteroid Distributions: e and i The Grand Tack is not the last event to alter the orbital distribution in the asteroid belt. – The orbital instabilities related to the LHB will happen 500 Myr later. The sweeping of resonances across the asteroid belt when the giant planets migrate will – Deplete the population 2-5x, – Not change a distribution substantially, – Not change i distribution substantially, – Likely change the e distribution substantially,

Eccentricity Asteroids post-Grand Tack Average e = 0.2 Current-Day Asteroid belt H<10.8 Average e = 0.15

Minton & Malhotra did this for us! This analytical work found a good match for a rapid, and smooth, sweeping of resonances in τ < 1 Myr.

The post-Grand Tack distribution is similar post-Grand Tack

We don’t trust Minton, so we test this numerically…. What is the parameter space for giant planet migration? – Differing smooth migration rates, exponential with τ < 0.5 Myr τ = 0.5 Myr – match Minton et al τ = 0.2, 0.1, 0.05 Myr as a proxy for even more rapid migrations (e.g. jumping Jupiter) – “Jumping-Jupiter” migration, using the rapid and non-smooth evolution of the giant planets -> “jumping-Jupiter” Morbidelli et al “jump”

Smooth Migration τ=1e5 yr