Inspecting	  Exoplanet	  Atmosphereswith	  High-Resolution	  Spectroscopy

Florian	  Rodler
Alexander-von-Humboldt	  Fellow
Max-Planck-Institute	  for	  Astronomy
Harvard-Smithsonian	  CfA	  •SETI	  Institute1[	  flo@mpia.de	  ]exoplanets ... they are everywhere ...

Since 1995, more than 2000 exoplanets discovered

planet mass (Jupiters)

10

Jupiter

1

Saturn0.1

Neptune0.01

Earth0.01

0.1

1
10
orbital distance (AU)
21001000different types of planets

Since 1995, more than 2000 exoplanets discovered
Brown dwarfs
10planet mass (Jupiters)

Hot Jupiters
10.1

Warm Neptunes
0.010.01``Jupiters

`
`
0.1

Super Earths
110orbital distance (AU)
3100

1000

exoplanet detection methods

Since 1995, more than 2000 exoplanets discovered

most planets
found byIndirect
Detection
Methods

planet mass (Jupiters)

101

DirectImaging

0.1

0.01

0.01

0.1

1
10
orbital distance (AU)
41001000

Radial Velocity Method

We do not see the planet! Observeback-forth movement (RV) of starObtain:- orbital period of planet- only estimate of planet mass
(orbital inclination unknown)

Radial velocity of star

indirect detection methods`timeindirect detection methods

Radial Velocity Method

Transit Technique

Measure flux variations of star
We do not see the planet! Observeback-forth movement (RV) of starObtain:- orbital period of planet- only estimate of planet mass
(orbital inclination unknown)

Obtain:- orbital period- planet size (radius)- orbital inclination (~90 deg)+inspecting exoplanet atmospheres

How can we study the atmospheres of exoplanets?
Challenges:
simultaneously observe star + planet
planets are faint; stars outshine their planets by many magnitudes:- Sun/Earth: . . . . . . visual: ~1010; IR ~109
- Sun/hot Jupiters: visual ~105; IR ~103
need strategies to identify the stellar flux andseparate it from the weak planetary signal“getting rid of the star” ...

inspecting exoplanet atmospheres

transiting planets:- transmission spectroscopy at transit- secondary eclipse measurementinspecting exoplanet atmospheres

Transmission spectroscopy of transiting planets:- measure area ratio planet / star- atmosphere is opaque at certain λdue to molecular absorption- planet appears larger at those λRpλinspecting exoplanet atmospheres

Transmission spectroscopy of transiting planets:- measure area ratio planet / star- atmosphere is opaque at certain λdue to molecular absorption- planet appears larger at those λRpλinspecting exoplanet atmospheres

Present
From hot Jupiters ...

Futureto Earth-like exoplanets

Part 1: Inspecting the Atmospheres ofnon-transiting Hot Jupiters- Jupiter-sized planets a few stellar radii away from host stars- they are hot (T up to 2800 K; usually around 1500 K)- they are unique labs to study exotic atmospheres- they glow at near-infrared λ (1 - 2.5 micron)inspecting the atmospheres of non-transiting hot Jupiters

How can we separate the planetary signal?
that’s what we want!

that’s what we mostly get!

disentangling the planetary signal from the stellar one

How can we separate theplanetary signal from the star?

Trick:- stellar spectrum is almost stationary (<0.5 km/s)- spectrum of companion travels due toorbital motion (~100 km/s)

go to the largest telescopes andtake a time-series of hi-res spectra!

disentangling the planetary signal from the stellar one

to observerdisentangling the planetary signal from the stellar one

to observerinspecting the atmospheres of non-transiting hot Jupiters

What kind of object is
producing the RV shiftsof the star?

we measure RV:

to observer- is it a planet?
- is it a brown dwarf, oreven a star?
to observer

By directly measuring the RV ofthe companion, we can derive:- exact mass of companion
mp = m★ K★/Kp

inspecting the atmospheres of non-transiting hot Jupiters

Shape of RV curve reveals mass of companion: mp = m★ K★/Kp(φ, known)

0.9

Orbital Phase

10.630º
8.2 mJup

0.890º
4.1 mJup

60º
4.7 mJup
45º
5.8 mJup

0.7

0.5
0.4
0.3
0.2
0.1
0-200

Kp Kp Kp Kp
-150

-100

-50
050
Relative RV [km/s]

100150200

what can we observe in the planet atmospheres?

Day-side spectrum of planet

Visual: reflected starlight;
revealing absorption features
Infrared: thermal emission fromplanet; revealing molecularemission and absorption

what can we observe in the planet atmospheres?

Hot Jupiter with 0.05 AU around a Solar-type starplanet/star flux

1.0e-03

thermal emission

1.0e-04

reflected light
1.0e-05?
0.5
500

12
1000
2000
wavelength(micron)wavelength[nm]

344000what can we observe in the planet atmospheres?
Planet spectrum in the IR:1★ what does it look like?

0.9

deep spectral features!
★ the deeper, the better!

transmission★ need large number of

0.8
0.7
0.6

target molecules which
are likely to be present
in planet atmosphere:
CO, H2O, CH4, ...

0.5
0.4
2.295

2.3

2.305
2.31
2.315
wavelength (micron)

2.32

2.325

blue ...... 20k
green .... 35k
red ...... 100k

what can we observe in the planet atmospheres?

Hi-res spectroscopy of
exoplanet atmospheres:

H2O

H2O

- feasible with ground-based
telescopes- robust and unambiguous

H2O

H2O

COCO

measurement of molecules- inversion layer?

COCOCOno inversion

inversionCOwhat can we observe in the planet atmospheres?

With high-res spectra, wecan measure atmosphericcirculation ...
Observe the presence of★ strong winds★ atmospheric super-rotation(cf. Snellen+ 2010, 2014)

test case: the hot jupiter tau boo b

In 2012, finally, this method started to work ...
- CO in the planet atmosphere of Tau Boo b (Rodler+12, Brogi+12)- CO in HD 189733b (Rodler+ 13b, de Kok+ 13)- CO and H2O in 51 Peg (Brogi+ 13, 14)- H2O in HD 189733b (Birkby+ 13)- H2O in Tau Boo b (Lockwood+14)- rotation in Bet Pic b (Snellen+14)- CO in Ups And b, determine i ~ 24º (Rodler+, in prep)...

The Bloated Planet Upsilon Andromedae bthe bloated planet upsilon and b

Multiplanet system:
3 companions found to F8 V star with RV-method(Butler+ 1997, 1999); c+d on eccentric orbits!

b4.6 d>0.7 mJupi=?

planets c + d:
astrometry orbital inclinations ic
0.33 yrs
14 mJupi = 7º?

(McArthur+2010)

3.5 yrs
10 mJupi = 23º?

dthe bloated planet upsilon and b

Observed Ups And b with Keck / NIRSPEC at 2.3 micron:
Detection of CO absorption in day-side spectrum of planet!

(Rodler+ in prep.)

4160

3140
2120
100

180060-14020-20-100 -80 -60 -40 -20-3020 40 60 80 100

relative
RV velocity
to Earth (kms-1)
systemic(km/s)

correlation degree (m)2) determine planet mass
mp = 1.6-1.8 Jup

RV semi-amplitude Kp (km s-1)

1) measure orbital motion andfind orbital inclination 18-30º 180

the bloated planet upsilon and b

24 micron Spitzer lightcurve(Crossfield+ 2010)

the bloated planet upsilon and b

Phase curve of Ups And b can be explained by large radius):
Rp, min = 1.8 RJup (assuming day side T = 1600 K, night side T = 900 K,
spin-orbit alignment)- this planet is probably extremely inflated- among the largest exoplanets!
- observe CO in absorption, which suggests
the absence of a thermal inversion layerinspecting the atmospheres of hot Jupiters

High-res spectroscopy of exoplanet atmosphere reveals ...
1) orbital motion of companion➝ orbital inclination i, solve for exact mass mp2) molecule species in planet atmosphere3) thermal inversion layer in planetary atmosphere
4) Doppler broadening: circulation pattern in planet atmosphere
5) planet radius (with phase curve)!

inspecting the atmospheres of hot Jupiters

Outlook:With current instrumentation, we canonly investigate hot Jupiters with brighthost stars (K<6; ~10 hot Jupiters)!
With the upcoming ELTs we will:★ inspect ~80 hot Jupiters orbiting

fainter host stars (K<11)★ investigate smaller planets: super-Earths, hot Neptunes, and warm
Jupiters around bright host stars★ map the planet atmospheres of hotJupiters with Doppler imagingCrossfield+ 2014

atmospheres of transiting exoplanets

Part ii - Future: Feasibility studies for the observation ofoxygen in the atmospheres of rocky exoplanets

The key to find habitable planets is to study
the atmospheres of rocky exoplanets:- presence of biomarkers (O2, O3, CH4)
- greenhouse gases (CO2, H2O, CH4)

Text
We focus on rocky, dense exoplanets with radii 1-1.5
Earths, in the “habitable zone” (i.e. surface

temperatures allowing water to be in liquid state)feasibility studies to search for oxygen in exo-earths

How can we study the atmospheres of small exoplanets?
Challenges:
simultaneously observe star + planet
planets are faint; stars outshine their planets by many magnitudes:- Sun/Earth: . . . . . . . . visual: ~1010; IR ~109... that’s pretty faint!

feasibility studies to search for oxygen in exo-earths

How can we study the atmospheres of small exoplanets?
Challenges:
simultaneously observe star + planet
planets are faint; stars outshine their planets by many magnitudes:- Sun/Earth: . . . . . . . . visual: ~1010; IR ~109
Transmission spectroscopy of small transiting planets better?
- With transmission spectroscopy, we only care about thearea ratio planet atmosphere / stellar disk!

feasibility studies to search for oxygen in exo-earths

Transmission spectroscopy:
exo-Earth around solar-type star

Question: imagine, theSun emits 106 photons
How many photons passthrough the planet atmosphere?
a) 2b) 20c) 200

feasibility studies to search for oxygen in exo-earths

Transmission spectroscopy
Earth-like planet around an M4-dwarf

Question: imagine, thestar emits 106 photonsHow many photons passthrough the planet atmosphere?
a) 2b) 20c) 200

Roadmap for the discovery and characterizationof potentially habitable exoplanets:
TESS (2017) - 6.5 m JWST (2018) - the three ELTs (mid-2020?)

Roadmap for the discovery and characterizationof potentially habitable exoplanets:

TESS (2017)- will discover hundreds of transiting super-Earths(exoplanets with radii 1-2 Earths)- most of them with orbital periods < 20 days- most of them around relatively “bright” planet host stars- planets around cool M-dwarfs will be potentially habitable

Transmission spectrum of Earth seen by some aliens ...

transmission

10.8
0.6

O3H2 OO2H2 OCH4H2 O

CH4CO2O3CO2CO2H2 O

0.4

CO20.21?

23wavelength [micron]

45How much time would we need to observe oxygen in the atmosphereof a rocky super-Earth (1.5 Earth radii) orbiting an M-dwarf star?

?

What telescope/instrument/setup is most efficient to detect oxygen?
- carry out feasibility studies for the JWST and the 39m E-ELT

JWST, 2018

E-ELT, 2025+

150 hours with JWST (transmission spectroscopy, low-res) ...
... and still no oxygen. Instead hints for water, CO2 and ozone absorption.

1.00001

H2O

transmission

O3

H2O

H2O
CO2

1.00000

0.99999
observations
model
binned data
0.99998

12
wavelength [micron]3

Flux Transmission

Transmission

The O2 band around 760 nm (R = 100k)
1.0Planetary transmission
spectrum (to be scaled
down in flux)

0.8
0.6
0.4
1.0

Telluric absorption
lines

0.5
0.0
1.07600.5762764

766768770768770wavelength (nm)0.0760762764766
Wavelength (nm)M-dwarf, 3000 K

Sun

Observing time needed to attain a3σ detection with the 39m E-ELT ...

M1V
M2V
M3V
M4V
M5V
M6V

arearatio

MIP
transitnumber on target(days) duration (h) transits
hours

85000

7.7

43

4.0

14

67000

8.3

33

3.4

16

53000

8.8

27

3.0

16

30000

10.0

16

2.1

1214000

11.2

10

1.5

188000

12.4

6

1.1

26~56~54~48~25~27~29... at a distance of 5 pc (16 ly)Conclusions- detection of O2 in the atmosphere of a super-Earth is feasible withthe E-ELT in 25+ hours.
- most suitable for M4V at < 8 pc.

- with JWST we won’t be able to measure O2 in the atmosphere of asuper-Earth.
- JWST will allow us to measure water, ozone and CO2 therein

Check out literature:
Rodler + López-Morales (2014), Snellen+ (2013), Kaltenegger + Traub (2009)