KITP: migration, violence and the future for the planets

Final day of the Exoplanet Rising workshop.
Start off with migration theory, then scattering and collisions.
Finish with tidal destruction and future observational prospects.

Lubow and Malhotra.
Then Thommes and Armitage.
Followed by Ogilvie and Traub.
Then we are done.

This is a public service announcement: Extreme Solar Systems II - Sep. 2011

Announcement went out a few days ago and pre-registration for the meeting is nearing capacity. If you are contemplating attending, then pre-register ASAP, please.

Lubow is up first.
Migration is still an issue, even if most planets maybe don't migrate substantially (but do most of them migrate a little bit?).
Simple models of migration just don't work. In detail. Neither do complex models...
There's yer type I, type II and at least two completely different types of type III...

Then there are the Dead Zones - these may be rather important.
But, he didn't say anything about hard x-ray flares and flash ionization!

Excellent review of the work to date and what the issues are.
Review paper coming as chapter of "Exoplanets" book coming out soon, ed. Seager.

Mahotra: migration in outer system.
Don't just get gas driven migration, planetesimal scattering also drives orbital changes in scattering planet, which can be secular.
eg. model for Neptune where it moved outwards by at least 8 AU, trapped Pluto in the 3:2 resonance and sculpted the inner Kuiper belt.

Morbidelli et al 2009 for review.

Discussion of parametric numerical simulations.
Need 30 earth masses in planetesimals to move Neptune order 10 AU

that is a lot, why did migration stop (hmm, might have an idea on that...)
an outer edge is another possibility, but why would there be an edge?

why is eccentricity not damped?

Inventory of asteroids over 50 km diameter, in the asteroid belt, is complete.
We really need it complete to 5 km, and better still down to < 0.5 km.
Where are the Planetary Defence Officers when you need them?

models suggest asteroid belt is "over depleted" - could be signature of some giant planet migration - eg if Jupiter moved about 0.5 AU or so over a few Myr or so - ν₆ sweeps impressively. Of course Jupiter moving shifts everything else, as cause or effect.
cf Minton and Mahotra 2009

Could Jupiter partial migration be due to late formation and photoevaporation of the gas disk on commensurate timescale?

Asteroid depletion lead to early heavy bombardment of inner planets.
See two crater populations, correlated with surface age and size distribution of older craters is different - bigger craters for older bombardment

younger craters have P(D) ~ D^-2.5 size distribution older are more like -2

main belt asteroids fit older crater size distribution - mass independent scattering process at early times => macro gravitational perturbation
NEOs fit younger crater distribution - NEOs come from main belt but smaller asteroids leak out - size dependent processes, and of course collisional fragmentation of parent bodies.

So where do the comets fit in?
This is a disputed conclusion.

BUT: early is ~ 3.9 Gyr (lunar highland crater dating)
ie the early bombardment is LHB - which requires the giant planet rearrangement at 3.9 Gyr

Nice model does this with slow outer migration of Jupiter/Saturn through mutual perturbation which then gets Neptune/Uranus going

Or Neptune and Uranus just formed very slowly - ie 600 Myrs.
mass growth or N/U triggered the migration.

Comets still not fitting in here. Something is missing.

Ed! Stealth and Violence among the Exoplanets.
Not Nice.

Hm, Thommes et al (Science 2008) grid simulation with hybrid pseudo-gas dynamics,
grid of disk mass vs α
Low mass lwo α gives no giants; high mass high α makes many giants
and migration, Solar system are happy medium - godilocks indeed.
Jupiter forms but relatively late in disk lifetime - seen that before.

Ties to low Z systems, happy medium moves to higher M and α corner,
so giants rare but range in M and α probably larger than range in Z and even Z²
conversely high Z systems move down and right and migration is more liklely.
Need opacity and gas instability physics, but lookin' good.

Stuff kinda coming together here.

Making Fomalhaut/HR8799 planets - model by scattering ice giant cores out and doing accretion of cold, low c_s, gas. Initially eccentric so wide sweep zone for feeding.
Circularize. Voila.
Requires flat disk surface density. What about ionization at large radii?
Touch and go on timescales, and you have narrow phase space in E-J plane to avoid scattering to infinity.
Ok if these are rare?

Professor Davies - Exoplanet Rising session chair - delivers an object lesson to people who will insist on working on laptops during KITP talks.

Phil Armitage: planet-planet-scattering - review and new result.
In scattering dominated scenarios - and scattering must occur, planetary systems are crowded - predict various e(M) and e(a) distributions - but gas contaminates and residual worries that gas can excite e - or as Murray-Clay points out, planetesimals residual in disk also do some damping
But, you can do anything if masses of adjacent planets are correlated and not random from general planetary mass function - which is also not inconceivable

Fine tuning worris - Phil worries too much, I think this self-regulates

Ultra long period planets - yes, but E-J phase space is small, so rare
Naively unstable due to periastron encounters, but inner system evolution or external perturbations torquing at aphelion could leave these long term stable

: tidal interactions - the importance of Q
well, that woke us up.
Gordon speaks math, so you better pay attention.

"bodies respond to perturbation in a more or less complicated way" - I paraphrase.

It is the imaginary part of the Love Number that determines the physical interaction: the energy transfer is proportional to the frequency and the spin depends on the multiplicity of the perturbing term.
Yes, it does.

Good discussion of limits of linear perturbation theory and where the non-linearities enter.

So what is Q?
Well, it is Not A Number - it is really a function - at least in linear theory.
But, for the Earth it is almost a number over a large range in ω as was famously noted

distinction between equilibrium tide and dynamical tide a la Zahn.

It matters whether planets are all fluid or have cores - ie is there a phase boundary in the interior - affect propagation of internal waves, reflection and refraction at boundaries - which affects dissipation and hence effective Q
also stratification and molecular weight gradients, not just density

inertial waves vs gravity waves

normal mode standing waves, or rays of wave packets ratting around?

Ekland number, it has been a long time since someone has told me an Ekland number!

Adding rigid cores leads to richer spectrum of dynamical perturbations - possibly effective Q over range of frequencies becomes almost independent of frequency and viscosity

For intermediate size cores, Q goes down as approx 5th power of core size.
Flattens out of course as core size approaches planet size

oh, and there is turbulent convection, and magnetic fields, and rotation...
so, really, anything goes, right?

Wes: Exoplanet in the Teens - International Plans To the Rescue
what space) missions are currently planned or proposed, by whom and when
what can they do
what should we be thinking about

Current: Hersche (2012), CoRoT (2013), Kepler (2014), Spitzer (2014), Hubble (2014++), Sofia (2020)

in the pipeline

GAIA 2012+5
SPICA 2017+5

JWST 2014+10
SIM 2017+5

we're kinda falling off a cliff there in 2012-2014, depending on actual lifetimes...

Microlensing mission? GEST/MPF
Small transit mission? (TESS or PLATO)

What about the TPF class missions?
Coronographs, Interferometers and Umbras