HATNet

Keck

KMTNet

Kepler

Mayor & Queloz (1995)

Charbonneau et al. (2000)

Gillon et al. (2017)

Bond et al. (2003)

Hot Jupiters

Cold Jupiters

Cold Neptunes

Super Earths

Data from NASA Exoplanet Archive

(1%)

(10%)

(30%)

(?)

Image from Maruyama & Ebisuzaki (2017)

A Comprehensive Picture of

Planet Formation & Evolution

What is the initial condition (i.e., disk model)?

Do planets migrate in the gas disk?

Anything happens after disk disappears?

(See also R. Dong's talk)

Snow line

Minimum-mass solar/extra-solar nebula:

Weidenschilling (1977); Hayashi (1981)

\Sigma(r) \propto r^{-3/2}

\Sigma(r) \propto r^{-3/2}

The outer region dominates the mass and angular momentum budget

Nebula Model

Mimimum mass extra-solar nebula

Mimimum mass solar nebula

Chiang & Laughlin (2013)

(see also Schlichting 2014)

Planet Migration

Image credit: P. Armitage

Transfers mass
Changes orbital configuration: more mean-motion resonance

Image credit: M. Rex

Dynamical Instability

Credit: Raymond, Izidoro, & Morbidelli (2018)

Transfers angular momentum (deficit)

Modifies orbital spacing, eccentricity, inclinations

Cold giants, if exists, play dominant roles

Super Earths alone

w/ outer Giants

HATNet

Keck

KMTNet

Understanding Planet Formation from Data

(by correlating different planets and planet populations)

Hot Jupiters

(~1%)

Cold Jupiters

(~10%)

Cold Neptunes

(?)

Super Earths

(30%)

Kepler Mission

1-m space telescope
10^5 target stars
4-yr observations
~5000 exoplanet detection (incl. 0 Earth-like)

Image credit: NASA/Ames, Batalha (2014)

Cui et al. (2012); Zhao et al. (2012); De Cat et al. (2015); Zong et al. (2018)

LAMOST-Kepler Survey

4mx6m; 5 deg^2 FoV
4000 fibers/plate
~40% of Kepler stars surveyed by 2017

If no dynamical instability...

Planets very often reside in multi-planet systems

Multi-planet systems are flat (<~5 deg); planets have (nearly) circular orbits

Multi-planet systems should be well regulated (size & spacing)

Planets very often reside in multi-planet systems

Architecture Revealed by

Kepler Mission

Multi-planet systems are flat
Multi-planet systems should be well regulated (size & spacing)

Image credit: NASA/Ames, Shallue & Vanderburg (2017)

Kepler Dichotomy?

Ballard & Johnson (2016)

(See also Lissauer et al. 2011, Johansen et al. 2012)

If assuming small mutual inclinations, two populations are needed:
- compact systems
- 1-planet systems (or 2-planet with large mutual inclinations)

Transiting Planets (Tranets) vs. Planets

mutual inclination

No Sign for Kepler Dichotomy

Zhu et al. (2018)

(See also Xie et al. 2016, Weiss et al. 2018)

One-tranet hosts

Multi-tranet hosts

Transit Timing Variation (TTV)

No interaction

Interaction with additional planet

Holman & Murray (2005); Agol et al. (2005)

TTV Applications

Becker et al. (2015); Almenara et al. (2018)

Characterizing known planets
Detecting additional planets

Transit + TTV

Number of systems with k transiting planets
- ~50% in transit singles
# of systems with k transiting planets AND at least one showing TTV signals (Holczer++16)
- ~50% in transit singles
Majority of transit singles are actually multi-planet systems with large mutual inclinations

Zhu, Petrovich, Wu et al., 2018

Transit singles

Transit multis

Intrinsic Architecture

{\rm inclination~dispersion~of~} \\ k{\rm -planet~system} \propto k^\alpha

{\rm inclination~dispersion~of~} \\ k{\rm -planet~system} \propto k^\alpha

Zhu, Petrovich, Wu et al., 2018

Planet-planet mutual inclinations affect the occurrence rate of planetary systems

{\rm \#~of~planetary~systems} = \frac{\rm \#~of~detected~systems}{\rm detectability~of~individual~system}

{\rm \#~of~planetary~systems} = \frac{\rm \#~of~detected~systems}{\rm detectability~of~individual~system}

mutual inclination

Planet-planet mutual inclinations affect the occurrence rate of planetary systems

{\rm \#~of~planetary~systems} = \frac{\rm \#~of~detected~systems}{\rm detectability~of~individual~system}

{\rm \#~of~planetary~systems} = \frac{\rm \#~of~detected~systems}{\rm detectability~of~individual~system}

Fraction of Sun-like stars with planets

>50% (Fressin et al. 2013; Petigura et al. 2013; Winn & Fabrycky 2015)

30% (Zhu, Petrovich, Wu et al. 2018)

Kepler Planets Also Have Significant Eccentricities

\frac{P^2}{4\pi^2} = \frac{a^3}{GM_\star} = \frac{3(a/R_\star)^3}{4\pi G\rho_\star}

\frac{P^2}{4\pi^2} = \frac{a^3}{GM_\star} = \frac{3(a/R_\star)^3}{4\pi G\rho_\star}

\rightarrow T_0 \propto P^{1/3} \rho_\star^{-1/3}

\rightarrow T_0 \propto P^{1/3} \rho_\star^{-1/3}

T_0 = \frac{2R_\star}{2\pi a /P}

T_0 = \frac{2R_\star}{2\pi a /P}

Seager & Mallen-Ornellas (2003)

Xie, Dong, et al. (2016)

(see also Van Eylen et al. 2018)

Intrinsic Architecture of

Inner Planetary System

30% of Sun-like stars have Kepler planets

Fewer-planet systems are dynamically hotter

Each system has on average 3 planets

Our solar systems fits "well" in this picture

i,~e \propto k^\alpha

i,~e \propto k^\alpha

Zhu, Petrovich, Wu et al., 2018

Orbital eccentricity

Planets very often reside in multi-planet systems: Yes

Multi-planet systems are flat: No
Multi-planet systems should be well organized (size & spacing): Maybe

Zhu, Petrovich, Wu et al., 2018

Intrinsic Architecture of

Inner Planetary System

Dynamical Instability Excites e, i

Kai Wu (吴开), et al. (in prep)

(see also Hansen & Murray 2013, Huang et al. 2017, etc)

Inner system alone cannot excite large enough mutual inclinations and eccentricities

Where Super Earths Form?

In situ
- Requires a massive disk

Migration
- Normal disk can work
- Mean-motion resonance pile-ups

Evidence for In Situ Formation?

Period ratio distribution shows no preference for MMR pile-ups (Lissauer et al. 2011; Fabrycky et al. 2014)
Asymmetry around period commesurability is a natural outcome of in situ formation (Petrovich et al. 2013)

Image from Winn & Fabrycky (2015)

Not conclusive: dynamical instability can modify the dynamical state

Where Super Earths Form?

In situ
- Requires a massive disk
- More inner super Earths, more outer cold Jupiters

Migration
- Normal disk can work
- More inner super Earths, fewer outer cold Jupiters

Super Earth-cold Jupiter relation

Cold Jupiters

Super Earths

Using data from NASA Exoplanet Archive

P({\rm CJ}|{\rm SE})

P({\rm CJ}|{\rm SE})

(Plus another 22 systems from Kepler)

Zhu & Wu, 2018, AJ, 156, 92

(see also Bryan et al.2018)

Super Earth-cold Jupiter relation

Cold Jupiters

Super Earths

Using data from NASA Exoplanet Archive

P({\rm CJ}|{\rm SE}) \approx 33\% {\rm ~vs.~} P({\rm CJ})=10\%

P({\rm CJ}|{\rm SE}) \approx 33\% {\rm ~vs.~} P({\rm CJ})=10\%

Cold Jupiters are more likely found in super Earth systems.

Zhu & Wu, 2018, AJ, 156, 92

(see also Bryan et al.2018)

(Plus another 22 systems from Kepler)

Super Earth-cold Jupiter relation

Cold Jupiters

Super Earths

Using data from NASA Exoplanet Archive

Zhu & Wu, 2018, AJ, 156, 92

(see also Bryan et al.2018)

P({\rm CJ}|{\rm SE}) \approx 33\% {\rm ~vs.~} P({\rm CJ})=10\%

P({\rm CJ}|{\rm SE}) \approx 33\% {\rm ~vs.~} P({\rm CJ})=10\%

Cold Jupiters are more likely found in super Earth systems.
Cold Jupiters are (almost) always accompanied by super Earths.

P({\rm SE}) = 30\%

P({\rm SE}) = 30\%

P({\rm SE}|{\rm CJ}) = \frac{P({\rm SE})}{P({\rm CJ})} P({\rm CJ}|{\rm SE}) \approx 100\%

P({\rm SE}|{\rm CJ}) = \frac{P({\rm SE})}{P({\rm CJ})} P({\rm CJ}|{\rm SE}) \approx 100\%

(Plus another 22 systems from Kepler)

Being confirmed by TESS!

10 M_{\rm J}\\ 3~{\rm AU}\\ e=0.6

10 M_{\rm J}\\ 3~{\rm AU}\\ e=0.6

5 M_\oplus\\ 6~{\rm d}

5 M_\oplus\\ 6~{\rm d}

Huang et al., (2018)

(see also Gandolfi et al. 2018)

All-sky survey, bright stars
27 days per sector
Looking for close-in planets around nearby stars

Transiting Exoplanet Survey Satellite

HATNet

Keck

KMTNet

Kepler

Hot Jupiters

(~1%)

Cold Jupiters

(~10%)

Cold Neptunes

Super Earths

(30%)

Data from NASA Exoplanet Archive

Hot Jupiters have distant companions

(Knutson et al. 2014, etc)

Hot Jupiters are lonely(?) (Steffen et al. 2010)

Super Earths & cold Jupiters tend to co-exist

(Zhu & Wu 2018)

An Inclusive View of Planetary Systems

(Un)Popularity of Solar system

P({\rm no~SE,~CJ}) = [1-P({\rm SE}|{\rm CJ})] \times P({\rm CJ}) \\ \approx 1\%

P({\rm no~SE,~CJ}) = [1-P({\rm SE}|{\rm CJ})] \times P({\rm CJ}) \\ \approx 1\%

Zhu & Wu, 2018, AJ, 156, 92

Hot Jupiters

(~1%)

Cold Jupiters

(~10%)

Cold Neptunes

Super Earths

(30%)

Hot Jupiters have distant companions

(Knutson et al. 2014, etc)

Hot Jupiters are lonely(?) (Steffen et al. 2010)

Super Earths & cold Jupiters tend to co-exist

(Zhu & Wu 2018)

Solar system has no super Earth (~70%)
Solar system has cold Jupiter (10%)

Inner-outer correlation

P({\rm SE}|{\rm CJ}) = 100\% \left( \frac{N_{\rm in,out}/N_{\rm out}}{5/12} \right) \left( \frac{R_\star/a_{\rm in}}{0.03} \right)^{-1} \left( \frac{i_0}{4^\circ} \right)

P({\rm SE}|{\rm CJ}) = 100\% \left( \frac{N_{\rm in,out}/N_{\rm out}}{5/12} \right) \left( \frac{R_\star/a_{\rm in}}{0.03} \right)^{-1} \left( \frac{i_0}{4^\circ} \right)

Herman, Zhu, & Wu (in prep)

i_0 \propto k^{-2}

i_0 \propto k^{-2}

1 yr

12 long-period giants in Kepler data
5 have inner transiting companions
1 has five inner planets:

Inner and outer regions correlate in occurrence rate & dynamical states

HATNet

Keck

Summary & Future Directions

Hot Jupiters

(~1%)

Cold Jupiters

(~10%)

Cold Neptunes

(?)

Super Earths

(30%)

Planet formation is a global process
Systems with more planets are dynamically colder --> dynamical instability happened
- How was the gas envelop preserved/regained?
Inner and outer planetary systems show strong correlations --> in situ formation for super Earths
- What suppressed disk migration?
What is the architecture of outer region down to lower masses (i.e., cold Neptune population)?

Inner

Outer

Hot Jupiters have distant companions

(Knutson et al. 2014, etc)

Hot Jupiters are lonely(?) (Steffen et al. 2010)

Super Earths & cold Jupiters tend to co-exist

(Zhu & Wu 2018)

Gaia, TESS, & RV Follow-ups

TESS (2018-2020?) looks for close-in small planets; 1000s detections
Gaia (2014-2024?) looks for distant giant planets; 1000s detections
A ground-based RV instrument (2-4M USD) on a 2-4 m telescope has lots of science to do!

Space-based Microlensing

WFIRST: NASA mission; 2.4 m; 1yr/5yr dedicated to microlensing; >2028
Chinese Space Telescope (CST): ~2 m, detached to space station; early 2020s?

Penny et al. (2018)

(see also Zhu et al. 2014; 2017)

HATNet

Keck

Summary & Future Directions

Hot Jupiters

(~1%)

Cold Jupiters

(~10%)

Cold Neptunes

(?)

Super Earths

(30%)

Planet formation is a global process
Systems with more planets are dynamically colder --> dynamical instability happened
- How was the gas envelop preserved/regained?
Inner and outer planetary systems show strong correlations --> in situ formation for super Earths
- What suppressed disk migration?
What is the architecture of outer region down to lower masses (i.e., cold Neptune population)?

Inner

Outer

Wei Zhu (祝伟), CITA

Thanks for your attention!

Backup Slides

Things to improve on:

Too much material to cover --> remove the microlensing part (could briefly mention it in the end, with 1 slide)
Segmented topics --> unify everything into a single big question: how super Earths form?
- Theoretical motivation: in situ vs. migration
- Studying relations with CJ can help distinguish them
- This requires knowing P(SE)
More theoretical stuff on the architecture(?):
- Why large mutual inclinations are hard to produce?
- Why 3 planets/system is an important result?
- Future explorations?

Talk Structure

1-slide overview of observations (techniques & results)
Comprehensive overview of planet formation and evolution
Kepler's puzzles
1. How common are Kepler-like systems?
2. Kepler dichotomy?
3. How do super Earths form? (With focus on where they form)
Summary
Future directions
1. TESS, Gaia follow-ups
2. Space-based microlensing surveys