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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
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
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
WhatwelearnedfromDSCOVRobserva4onsofEarth
Rotation Period and Hydrological Cycle
Jiangetal.2018
Minimumsamplingrateis10hours
13
Howdoweknowwhetheranexoplanethasanatmosphere?whetheranexoplanet’satmospherehasevolved?whetheranexoplanethasgeological/biologicalacDviDes?
14
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
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
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)
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