Kepler’s Multiple Planet Systems

TITech & Kobe Univ.
February 2018

Jack J. Lissauer
NASA Ames

Outline
Solar System & Exoplanets
Kepler Mission

Kepler planets and planetery systems
Principal Kepler findings

K2 & TESS
Earth-trailing heliocentric orbit

Planets in the Solar System

Stars and Planets

TECHNIQUES FOR FINDING
EXTRASOLAR PLANETS
MethodYield

Size Limit

StatusPulsar Timingm/M ; t

Lunar

Successful (3+~3)

Radial Velocity

m sini ; tsuper-Earth

Successful (~700)

Astrometry
Ground:Space:m ; t ; Ds ; aJupiter
sub-Jupiter

Ongoing
Ongoing - GAIATransit Photometry
GroundSpace, 27 cm
Space, 1 mA ; t ; sini=1Neptune
sub-Neptune
Mercury

Successful (300)
CoRoT (~30)
Kepler (>2000 + >2000)

Microlensing:
Groundf(m,M,r,Ds,DL )super-Earth

Successful (>50)

Direct Imaging
GroundSpace

albedo*A ; t ; Ds ; a ; M
JupiterEarth

Successful (>30)
Being studied

Transit Lightcurveflux

Δf =(Rp/R*)2

Rp

RptimeJosh Pepper~1%for JupiterKeplerMission

 NASA, photometry of > 150,000 stars
 Searched for Earth-like planets in transit
 30 minute cadence; 4 years observing same FOV
 ~ 30 ppm in 6 hours for bright targets (mv < 12)Kepler Mission Goals
Explore the structure and diversity of extrasolar planetary systems

1.Determine the frequency of terrestrial planets in or near
the habitable zone of a wide variety of spectral types ofstars;
2. Determine the distributions of size and semi-major axis ofthese planets;
3. Estimate the frequency and orbital distribution of planets in multiple-starsystems;
4. Determine the distributions of semi-major axis, albedo, size, mass and densityof short-period giant planets;
5. Identify additional members of each photometrically-discovered planetarysystem using complementary techniques;
6. Determine the properties of those stars that harbor planetary systems.

SPACECRAFT & INSTRUMENT
Large focal plane:
94.6 million science pixels

42 science CCDs,
2 channels each
4 fine guidance
sensor (FGS) CCDs

CCDs controlled at -85C,
Readout electronics atroom temperatureKepler Planet Candidates & Their Stars
Jason Rowe, 2015







Kepler found a w i d e diversity ofplanets and planetary systems

Kepler-9b,cKepler-9 b,c: Transit Timing Variations

Transit timing - Planet perturbations
 Kepler-9 models
without interactions
give poor fits Models with planets
affecting each othergive good fits
 TTVs can be used
to confirm planets &measure masses

Kepler-10
10 b: R = 1.4 REarth, M = 4.6 MEarth, P = 0.8 days
10 c: R = 2.2 REarth, M < 20 MEarth, P = 45 days

Kepler-11
A really cool system with
6 transiting planets

Kepler-11 Planets
Correct sizes
relative to star(Dan Fabrycky)

Kepler-11: Six Transiting Planets Transits

TTVs Effect of Planet in Gap Between Kepler-11 f & g
on Fit to TTVs of Observed Planets
Mass of unseen planet

1 MEarth
3 MEarth
10 MEarth---- no unseen planet

No evidence for a missing planet between f & g(Jontof-Hutter et al. 2017)Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar
Densities(Carter et al. 2012)

Orbits Are Extremely Close

Kepler-36 A
M⋆ = 1.071±0.043 M⊙
R⋆ = 1.626± 0.019 R⊙
Teff⋆ = 5911 ± 66 K

Kepler-36 b
Mp = 4.32±0.20 M
Rp = 1.486±0.035 R
P= 13.83989 d

Kepler-36 c
Mp = 7.84±0.35 M
Rp = 3.679±0.054 R
P = 16.23855 d

ac = 0.1283±0.0016 AU

ab = 0.1153±0.0015 AU

Parameters from:
Carter et al. (2012)
Deck et al. (2012)Kepler-36 b Mass Measured within 4.2%,
Radius Measured within 1.8%

K36c

H2O
EarthComposition

K36bFeKepler-36 b is Consistent with an Earth-like Composition
Leslie Rogers et al., in preparation

MgFeSiO3Fe

Mp = 4.40±0.18 M
Rp = 1.481±0.027 R
Mcore/Mp = 0.33±0.05

All InitialConditionsLong-Lived Zone
Mixed LongLived Orbits• Kepler-36 b is the rocky exoplanet with best constrained mass,density, and composition: mass known within 4.2%, radius to 1.8%,density to 4.6%.

• Kepler-36 b’s mass and radius are consistent with an Earth-likecomposition. An iron-enhanced Mercury-like composition is ruledout.
• In contrast, Kepler-36 c requires several percent of its mass in ahydrogen-rich envelope.
(L. A. Rogers et al. in prep)

Figure Credit: NASA; Frank Melchior, frankacaba.com; Eric Agol

Mass vs. Radius for sub-Neptune Exoplanets

Eric Lopez 5/2016

Mass-Radius Relationship for Planets and Small Stars(Chen & Kipping 2017)

The Smallest Known PlanetA Very Small Planetary System

KOI-500
also known as

Kepler-80

Kepler-16:
A Saturn-like planet
orbiting a close binaryKepler-186 f: a planet slightly larger than
Earth in the habitable zone of an M dwarf

10

1 RJupiter

Rp [RÅ]1 RNeptune

1
One: 2117
Two: 384
Three: 134
Four: 48

1 RMars
1

10
Orbital Period [days]

100

Five: 18
Six: 2Seven: 1

Systems with 3+ planet candidates
Daniel Fabrycky

Mass Distribution of RV Planets
Difficult to observe

Real ‘dip’
Very difficult to observe

Real dropoffM starDressing & Charbonneau (2015)





 ~70% of known planets were discovered by Kepler/K2

Key Kepler Findings
Planets, especially “small” ones, are common
Planetary systems are flat, like the Solar System

Planets & planetary systems are extremely diverse

K2: Good Science from a Broken Spacecraft In May of 2013, Kepler lost its 2nd gyroscope andcould no longer point at its original field of view
 Kepler can still observe in its orbital plane

DDT Proposals forC19 due April 12• Forward facing to facilitate
simultaneous groundobservations• Return to Trappist-1• Return to Neptune• Comet 2P/Encke
DDT deadline is April 12, 2018

August 6, 2018 – October 10, 2018

keplerscience.arc.nasa.gov• Partial overlaps with C3 & C12

Exoplanets: K2 vs. Kepler Kepler had better precision, stared at the same stars formuch longer and observed more stars simultaneously K2 has observed more total stars, with the best targets(brighter stars and M dwarfs) chosen from many fieldsof view
 Kepler provided more information about properties ofplanets and planetary systems, but K2 has found manyplanets that are better for follow-up

Typical K2 Planets are

Confirmed Planets January 11, 2018

Confirmed Planets January 11, 2018
0.25

1.00

KeplerFrequency

0.75

K2

Kepler0.50

Frequency

0.20

K2

0.15

0.10

0.25

0.05

0.00

0.00
10

1000

Distance (pc)around closer stars

051015

Host Star Brightness (KepMag)around brighter stars

20

5 planet system found by K2



Vanderburg et al. 2016

Multis Observed by K2
Kepler gyros failed – Spacecraft repurposed as K2

Many FOVs, focus on bright stars and small stars

Dozens of multis discovered, with as many as 5 planets
Observed TRAPPIST-1

K2

Observations of TRAPPIST1
A 0.09 MSun Star With 7 Earth-size Transiting Planets

The period(3:2)

of TRAPPIST-1h: 18.764 d

Luger et al. 2017

Mass-Radius Diagram for TRAPPIST-1 Planets

Grimmet al.
(2018)TESS: Discovering New
Transiting Exoplanet
Survey SatelliteEarths and Super-Earths
in the Solar Neighborhood
George Ricker (MIT), PI
Launch: 2018 March 20

TESS — Discovering New Earths and Super-Earths in the Solar Neighborhood

68

TESS Sky Coverage