Insights into Planet Formation from Exoplanets

Eric B. Ford

Astro 542: Interstellar Medium & Star FormationNovember 26, 2017

NASA/ Tim Pyle

Our Solar Solar System

NASA

Exoplanet around a Sun-like Star

Diversity of Extrasolar Planets

5yr

10yr

www.exoplanets.orgOrbital Period (days)

Ecc

entr

icity

Diversity of Extrasolar Planets

5yr

10yr

www.exoplanets.orgOrbital Period (days)

Ecc

entr

icity

Eccentric Giant Planets

Jupiter AnalogsHot Jupiters

Launch of Kepler Mission

Planets from Other SurveysP

lane

t Siz

e (E

arth

Rad

ii)

Orbital Period (days)NASA

Adding Kepler’s Planet CandidatesP

lane

t Siz

e (E

arth

Rad

ii)

Orbital Period (days)

Pla

net S

ize

(Ear

th R

adii)

Orbital Period (days)NASA/Burke et al. in prep

Fabrycky et al. 2012Fabrycky et al. 2012

Inspiration for New Theories of Planet FormationP. Armitage

Illustration by E. Chiang; Adaptations E. Ford

A New View of Planetary Systems• Most stars host a planetary system.

• Small planets (<3 Earth radii) are much more common than larger planets (at least for short orbital periods).

• Nature produces a wide diversity of planetary architectures.

• Most planetary systems are qualitatively different than our solar system.

Borucki+ 2011; Batalha+ 2012; Howard+ 2012; Fressin+ 2013; Burke+ 2015

Our Solar System is Not Typical

• Our solar system has no planets with orbital periods less than Mercury

• Our inner solar system does not have a super-Earth-size to Neptune-size planet

• Most planetary systems don’t have a Jupiter analog

→ Planet formation theories should typically produce planetary systems unlike our own

Borucki+ 2011; Batalha+ 2012; Howard+ 2012; Fressin+ 2013; Burke+ 2015

15Hot Jupiters viaDisk Migration

?

Illustration Adapted from E. Chiang

Orbital Migration due to Disk?

Very Early: Terrestrial Planets: Giant Planets:Protoplanets pushed Gas drag could cause Planet can clear gaparound by chaotic planet to spiral inwards and migrate inwards variations in density rapidly (perhaps too fast?) with the disk

Radial Velocities of GJ 876

Laughlin et al. 2004

Giant Planets in 2:1 Orbital Resonance

Lee

Migration Predicts Orbital Resonances

Cresswell & Nelson 2006

GLS

Hot Jupiters viaPlanet Scattering + Tidal Circularization

Rasio & Ford 1996; Weidenschilling & Marzari 1996 Illustration Adapted from E. Chiang

Stars & Hot-Jupiter’s can be Misaligned

Amaury Triaud; adapted from Winn et al. 2010Host Star Temperature (K)

Pro

ject

ed A

ngle

bet

wee

nS

tella

r R

otat

ion

Axi

s &

Orb

it N

orm

al

37

GLS

Eccentric Giant Planets viaPlanet Scattering

Illustration Adapted from E. Chiang

Movie of Planet Scattering

Simulation: Ford, Lystad, Rasio 2005 Animation: Trent Schindler (NSF)

exoplates.org

υ And: Radial Velocities

υ And: Radial Velocities

exoplates.org

Secular Evolution of Ups And

Ford, Lystad, Rasio 2005 see also Malhotra (2002), Chiang et al. (2002)

d

d

c

c

ara

rp

ara

rp

Impulsive Formation Scenario for Ups And

Ford, Lystad, Rasio 2005See also Malhotra 2002

Initial:Pd = 5.8 yrmd = 3.8 MJuped = 0.003Pe = 8.7 yrme = 1.9 MJupee = 0.004

Final:Pd = 3.7 yred = 0.29d

d

c

c

e

e

N

NASA’sKepler Mission

• Photometry of >160,000 stars• Looking for Earth-like planets in transit

• 50µmag in 6 hours; 30 minute cadence• All data public as of Oct 28, 2012

NASA

Planetary Systems from Kepler Mission

74Formation Theories for STIPS*:1. Large Scale Disk Migration

TimeLog

Sem

i-maj

or A

xis

Grow

Halt?

Snow Line

* = Short-Period, Tightly-Spaced, Inner Planet Systems

75Formation Theories for STIPS*:

2. In Situ Formation

TimeLog

Sem

i-maj

or A

xis

Grow…

Snow Line

* = Short-Period, Tightly-Spaced, Inner Planet Systems

76Formation Theories for STIPS*:

3. Radial Drift + Late Stage Accretion

TimeLog

Sem

i-maj

or A

xis

Grow

Snow Line

* = Short-Period, Tightly-Spaced, Inner Planet Systems

What are Observational Constraints on Planetary Architectures?

• Frequency of systems with n-transiting planets detected

• Period ratios• Planet radius ratios• Transit duration ratios• Mass & density ratios (sometimes)

• Frequency of additional planets not detected via transit

Insensitive to stellar properties

What affects fraction of stars with N-transiting planets?

� Need true/underlying/intrinsic typical multiplicity� Entangled with mutual inclination distribution� Use awesome multi-transiting systems!

Incl

inat

ion

True Multiplicity Ragozzine

Period Ratios of Kepler’s Systems

• Most planets are not near-MMR with another transiting planet

• Transiting planets are clustered in period

• Pronounced excesses at 5/4, 4/3, 3/2, 2/1, and 2.16

• Pronounced deficit slightly less than 2/1

Period Ratio

Num

ber

Ford/Data from Kepler DR25 Planet Candidates (NExScI 3/24/2017)

Kepler’s Architectural Gems

• Kepler-60: 3:4:5 Mean Motion Resonance (Jontof-Hutter+ 2016)

• Kepler-80: A pair of interlocking 2:3 Mean Motion Resonances (MacDonald+ 2016)

• Kepler-223: A 3:4:6:8 Resonance (Mills+ 2016)

Kepler’s Architectural Gems

• Kepler-60: 3:4:5 Mean Motion Resonance (Jontof-Hutter+ 2016)

Kepler’s Architectural Gems

• Kepler-60: 3:4:5 Mean Motion Resonance (Jontof-Hutter+ 2016)

• Kepler-80: A pair of interlocking 2:3 Mean Motion Resonances (MacDonald+ 2016)

Kepler’s Architectural Gems

• Kepler-60: 3:4:5 Mean Motion Resonance (Jontof-Hutter+ 2016)

• Kepler-80: A pair of interlocking 2:3 Mean Motion Resonances (MacDonald+ 2016)

• Kepler-223: A 3:4:6:8 Resonance (Mills+ 2016)

Resonances in Kepler Multi-Planet Systems

• Rarer than inRV systems– Predicted!

• Most near, but not in resonance

• Near resonantgreat for TTVs– esp. closely

spaced pairs!

Rein et al. 2012; Ford & Rasio 2008; Veras et al. 2012

RV Multi-Planet Systems

Kepler Multi-Planet Candidates

Period Ratio

Cum

ulat

ive

Num

ber

of P

lane

t Pai

rs

Tota

l Pla

net M

ass

(MJu

p)

Migrating Planets Trap Into Resonances

Rein et al. 2012

Migration Timescale (years)Mig

ratio

n Ti

mes

cale

/Ecc

entr

icity

Tim

esca

le

Late Stage Evolution of Rocky Planets

Rein et al. 2012

Time (years)

Orb

ital P

erio

d (d

ays)

Dissipation Removed

Planetesimal Scattering & Accretion can Break Resonances

Pout/Pin = 2 + εε ~ 10-2-10-2

md = 0.1-1.5 mplN < 2000

mcoll ~ 1-4% mplChatterjee & Ford 2014

Planetessimal disk can break Resonances

Chatterjee & Ford 2014

Forced Migration via Gas Disk Interaction w/ Planetesimal Disk

Dissipation Removed

Period-Radius Distribution of Kepler’s Planets(including strong planet candidates)

Kepler/Burke+ 2015/Jontof-Hutter

Planet Masses Measured with Doppler Follow-up Observations

Kepler/Burke+ 2015/Jontof-Hutter

Planet Masses Measured with Doppler Follow-up Observations

Kepler/Burke+ 2015/Jontof-Hutter

Planet Masses Measured with Doppler or Transit Timing Variations

Kepler/Burke+ 2015/Jontof-Hutter+ 2016

TTV

Apparent Differences in Planetary Mass-Radius Relationship

RV

Figure: D. Jontof-Hutter; incl. Jontof-Hutter+2016; Mills+ 2016; McDonald+ 2016

Mass from RV Follow-Up

Mass from Transit Timing Variations

Distributions of planet-planet mass ratios & density ratios are consistent for planet pairs near MMR and far from MMR

D. Jontof-Hutter+ in prepMillholland+ 2017; see also Ciardi+ 2012

Kepler’s Planetary Systems show Clustering

Masses and radii of transiting planets in a given system are correlated.

Late-stage Giant Impacts

• Can break resonance• Potential to explain distributions of

planet size, mass and density ratios• Affect retention of

– Water– Atmosphere

Daniel Carrera+ in prep; see also Inamdar & Schlichting 2016

Towards a Formation Model• Evolution of gas disk (Bitsch+ 2015)

• Migration of planetary embryos (Paardekooper+ 2011)

• Gas accretion by planetary cores (Lopez & Fortney 2014)

• Photoevaporation of disk• Giant impacts

– Direct n-body– Mass loss

(Inamdar & Schlichting 2016)

Eventually• Outgassing (Kite)

Daniel Carrera+ in prep; see also Dawson+ 2016

Follow-Up Space Missions

CHEOPS (launch 2017)Characterize known planets

Kepler/K2 (now)Same Spacecraft, New Mission

ESANASA

Future Space Missions

PLATO (launch 2024)Earth-size planets in the Habitable Zone of Bright Stars

TESS (launch 2018)Small Planets around Bright Stars

ESA/Thales Alenia SpaceNASA/MIT

Next-Generation Spectrographs for High-Precision Radial Velocity Follow-Up

Credit: Frank Cianciolo/McDonald Observatory Credit: NOAO/WIYN

Hobby-Eberly Telescope (10m)Habitable Zone Planet Finder

WIYN Telescope (3.5m)NEID Spectrograph

How to Separate Signals of Planets & Stellar Activity?

X. DumusqueS. Berdyugina

James Webb Space Telescope

Debris Disks: Fomalhaut

NASA, ESA, & Kalas (UC, Berkeley & SETI Institute)

Boley et al. 2012ALMA: ESO/NAOJ/NRAO + HST: NASA/ESA

ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)

HL Tau Protoplanetary Disk from ALMA