Earths and super-Earths Science Enabled by Direct Imaging Technology Renyu Hu, Ph.D. Jet Propulsion Laboratory California Institute of Technology WorkshoponTechnologyforDirectDetec4onandCharacteriza4onofExoplanetsApril 9, 2018 Pasadena CA

CommonalityofSmallPlanetsExoplanet Demography

2

Earth

Neptune

Jupiter

Transit RadialVelocity

Imaging Microlensing

IntransitDetecting ExoPlanet Atmospheres

3 Fraine et al. 2014

HAT-P-11b, a Neptune-sized planet

DetectableviatransitH2 Atmospheres

4

HAT-P-11b, a Neptune-sized planet

100 120 140 160 180 200 220 240 260 280 300 320Equ. Temp [K]

0

2

4

6

8

10

12

14

Obs

Inde

x of

HST

Obs

Inde

x of

JW

ST /

2.7

HST Observable

JWST Observable

PH-2 bLHS-1140 b

K2-18 b

K2-3 dK2-9 b

K-16 bK-167 e

TRA-1 h (2)

TRA-1 e (3)

TRA-1 f (4)

TRA-1 g (6)

TRA-1 d (12)

Complica4onwithstellarvariabilityNon-H2 Atmospheres?

5 Rackham et al. 2018

TransitFeature-  Upto10%forH2

atmospheres-  <1%fornon-H2

atmospheres

EmissionFeature-  1-2%

StarshadeRendezvousMissionsimulatedimageofanearbystarDirect Detection of a Solar System

6 Seager et al. 2015

EXO-SFinalReport2015

Detecting Earths

7

8

Howdoweknowwhetheranexoplanethasanatmosphere?whetheranexoplanet’satmospherehasevolved?whetheranexoplanethasgeological/biologicalacDviDes?

9

Spectralfeaturesofrockyplanetarysurfaces

wavelength wavelength

Refle

c4vity

Refle

c4vity

Detect Rocky Exoplanet Surfaces

10

Directdetec4onofrockyexoplanets

Detect Rocky Exoplanet Surfaces

Huetal.2012

Metal-richPrimarycrustwithmantlerippedoff

UltramaficPrimarycrustwithmantleoverturnor

secondarycrustfromhotlavasFeldspathic

PrimarycrustwithoutmantleoverturnBasal4c

SecondarycrustGranitoid

Ter4arycrustClay

AqueouslyalteredcrustIce-richsilicate

Ice-richsurfaceFe-oxidized

Oxida4veweathering

11

Fromphasecurvesofarockyplanet

Delineate Land and Sea

Cowanetal.200912

WhatwelearnedfromDSCOVRobserva4onsofEarth

Rotation Period and Hydrological Cycle

Jiangetal.2018

Minimumsamplingrateis10hours

13

Howdoweknowwhetheranexoplanethasanatmosphere?whetheranexoplanet’satmospherehasevolved?whetheranexoplanethasgeological/biologicalacDviDes?

14

Water,Oxygen,andCarbonDioxide

Detecting an Earth-like Atmosphere

15Turnbulletal.2006

O2

ImportanceofClouds

Detecting an Earth-like Atmosphere

16

H2O

500 600 700 800 900 1000Wavelength [nm]

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35Al

bedo

No CloudCumulus CloudCirrus CloudMean

Diverseatmosphericcomposi4onofrockyplanets

Detecting Earths and Super-Earths

17Gaillard&Scaillet2014

H2O

0.1 0.2 0.5 1 2 5 1000.10.20.30.40.50.60.70.80.9

1

XC/XO

X H

Water-richAtmosphere

Oxygen-richAtmosphere

Chemically as Gas Giant Atmospheres

Hydrocarbon-rich Atmosphere

H2, CO,CH4, CO2,H2O

CO,CO2

Depend on Temperature

DiversityofAtmospheres

Continuum from Super-Earths to Sub-Neptunes

18 Hu & Seager 2014

H2 – Rich

H2 – Poor

Carbon – Poor

Carbon – Rich

Condensible-RichAtmospheres

A Special Case for Water Worlds

19 Ding & Pierrehumbert 2016

InreflectedlightDistinguish Water Worlds vs. Giant Planets

20Hu 2014; Filippatos & Hu in prep.

InterplaybetweencloudsandC,N,Oabundances

HazeProduc4oninPhotochemicalProcesses

NeptunesandH2O-richSuper-Earths

SpectralDegeneraciesandInforma4onContent

500 550 600 650 700 750 800 850 900 950 10000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Wavelength [nm]

Geom

etric

Albe

do

H2−Dominated Atmosphere, Cloud Deck at 0.4 BarsH2−Dominated Atmosphere, Cloud Deck at 2 BarsH2O−Dominated Atmosphere, Cloud Deck < 10−3 Bars

CH4

CH4

CH4

CH4

CH4

CH4

CH4

CH4CH4

CH4 H2O

H2O

H2O

NH3

Howdoweknowwhetheranexoplanethasanatmosphere?whetheranexoplanet’satmospherehasevolved?whetheranexoplanethasgeological/biologicalacDviDes?

21

The image part with relationship ID rId2 was not found in

JWST/WFIRST/Otherspacetelescopes

Planetary Spectrum

Atmospheric Composition

Surface Source flux

Radiative Transfer

Atmosphere Chemistry

TowardsCharacterizingRockyExoplanets’Atmospheres

22

VolcanicemissioncontrolsO2buildupinCO2atmospheresCharacterize Rocky Exoplanets’ Atmospheres

10−14 10−12 10−10 10−8 10−6 10−4 10−2 100

10−1

100

101

102

103

104

105

Mixing Ratio

O2

OO3

Pres

sure

[Pa]

Hu et al. 2012

Solid:Earth-likevol.emissionDashed:Lowvol.emissionDoged:Novol.emission

23

Escapeofhydrogenisbalancedbyanetoxidizingfluxfromtheatmospheretotheocean

O2andCH4togetherasabiosignatureCharacterize Rocky Exoplanets’ Atmospheres

Domagal-Goldman et al. 2014 24

MeasuringvolcanicoutgassingCharacterize Rocky Exoplanets’ Atmospheres

25

0.1 0.2 0.3 0.5 1 2 30

0.1

0.2

0.3

0.4

0.5

0.6

Wavelength [microns]

Refle

ctivit

y

N2 AtmospheredP = 0.1 µm

S8 Aerosol ReflectionS8 Absorption

Earth X 3000Earth X 1000Earth X 100

Earth X 10Earth X 1

0.1 0.2 0.5 1 2 5 10 20 50 1000

0.2

0.4

0.6

0.8

1

Wavelength [microns]

Tran

smiss

ion

N2 AtmospheredP = 0.1 µm

S8 Aerosols

Earth X 1

Earth X 10

Earth X 100

Earth X 3000Earth X 1000 H2SO4

AerosolsCO2

CO2

SO2H2SH2OSO2

5 8 10 20 30 50 80 100180

200

220

240

260

280

300

Wavelength [microns]

Brigh

tnes

s Tem

pera

ture

[K] H2SH2OH2O CO2

SO2

SO2

SO2

CH4

N2 AtmospheredP = 0.1 µm

Hu et al. 2013

Transit-  Ground-basedtransitsurveys,TESS-  JamesWebbSpaceTelescope

(JWST,launch2018)

Directimaging-  StarshadeRendez-vouswithWFIRST-  Flagshipconceptsfor2020

AstrophysicsDecadalSurvey(HabEx+LUVOIR)

§  Direct imaging will enable characterization of Earths and super-Earths

§  We may learn about: surface type, atmospheric H2O, O2, CO2, rotation period, variability of clouds

§  It may be hard to directly measure: size of planet, mass of atmosphere, liquid water ocean

§  Intrinsic widths of spectral features will determine the required resolution, and the need to measure variability will determine the required collection area

Conclusion

27

Wecouldnotguesshowdifferentfromusthey(extraterrestrials)mightbe.CarlSagan,Contact,1985

Sensi4vitytoatmosphericsurfacepressureCharacterize Rocky Exoplanets’ Atmospheres

James & Hu, in prep.

Oxygenbuilduppeaksat~1bar

28

10-1 100 101

Surface Pressure [Bar]

10-10

10-8

10-6

10-4

10-2

100

Colu

mn

Mixi

ng R

atio

H2 O2 O3 CO CH4

Tre’ShundaJamesInternatJPL

HowdoesO2buildupdependonsurfacepressureandirradia4on?

SynergybetweentransitanddirectimagingAtmospheres of Wide-Separation Exoplanets

29

Transitspectrumofa229-day-periodexoplanetKepler16-b(HSTGO14927,PIRenyuHu)

Copyright 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.