Prospects for ground-based characterization of Proxima Centauri b

Prospects for ground-based characterization of Proxima Centauri b Ma#eo Brogi Hubble Fellow, CU-Boulder Ignas Snellen, Remco de Kok, Henrie5e Schwarz (Leiden, NL) Jayne Birkby (CfA, USA), Simon Albrecht (Aarhus, DK) Image credits: ESO/M.Kornmesser Searching for life across space and Ime, Irvine, CA Dec 5, 2016

The planet around Proxima Centauri The closest star to the Sun (1.3 pc)

The planet around Proxima Centauri The closest star to the Sun (1.3 pc) α Cen AB Hubble/WFC2 The star M5.5V, 3050±100 K 0.120±0.015 M Sun 0.141±0.021 R Sun Proxima The planet m sin(i) = 1.27 M E K S = 1.38±0.21 m/s a = 0.0485 AU P = 11.186 d

Small exoplanets are common ExtrapolaIons from Kepler detecions of transiing planets around FGK stars (Fressin+ 2013) 0.20 Planets per star (P < 85 days) 0.15 0.10 0.05 Earths Super-! Earths Small! Neptunes Large! Neptunes P = 0.8-85 days η any = (52 ± 4) % η = (16.6 ± 3.6) % Giant! Planets 1.0 1.4 2.0 2.8 4.0 5.7 8.0 11.3 16.0 23.0 Planet radius (R )

Small planets around small stars are very abundant! Based on Kepler detecions around M dwarfs (Dressing & Charbonneau 2015) 80 All planets (R<4 R, P<200 d) 2.5±0.2 planets/star! Occurrence (%) 60 40 20 Habitable planets +0.17 0.16 0.07 planets/star (1.0-1.5 R ) +0.10 0.12 0.05 planets/star (1.5-2.0 R ) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Planet radius (R Earth ) ConservaIve HZ (runaway / max. greenhouse) 4

Smaller & fainter stars higher planet/star contrast Solar-type star Transit depth D = (R P /R S ) 2 You are here! M5-dwarf Earth-Sun: D 0.008% Earth-M5: D 0.25% Similar gain for reflected-light and thermal-emission contrasts

Small planets around small stars are nearby! Data from the RECONS project: www.recons.org Solar neighborhood within 10 pc Sun WD:20 O:0! B:0! A:4 F:6 G:20 K:44 M:248 L:5 T:10 Planets:34+8 Dressing & Charbonneau: the nearest transiing exoplanet in the HZ is at 10.6±1.7 pc, but the nearest non-transiing is only 2.6±0.4 pc away we found Proxima Cen b! 6

Habitable zones around M dwarfs Classical habitable zone (moist / max greenhouse) Kopparapu+ 2013 Proxima Cen b PotenIally-habitable planets orbit very close to M-dwarfs! Reflected-light signal enhanced (dependence on semi-major axis) Increased geometric probability of a transit Transits are frequent and S/N can be stacked

Atmospheric characterization: transiting planets Star and planet are not spaially resolved Monitoring of the total light from the star+planet system, at various wavelengths

Atmospheric characterization: transiting planets Star and planet are not spaially resolved Monitoring of the total light from the star+planet system, at various wavelengths Eclipse (Dayside spectra) Planet occulted by the stellar disk Measuring the missing planet flux Transit (Transmission spectra) Starlight filtering through the planet atmosphere Measuring the planet radius

High-dispersion spectroscopy to observe exoplanet atmospheres SeparaIng the planet from the star in the spectral domain

HDS detects the fingerprint of each molecule Transmission spectrum of HD 189733 b 0.159 CO Radius ratio (+ arbitrary shift) 0.158 0.157 0.156 0.155 0.154 H 2 O CH 4 Molecules resolved into individual lines 0.153 2290 2300 2310 2320 2330 2340 2350 Wavelength (nm) 10

HDS detects the orbital motion of exoplanets HJs sensibly move along the orbit during few hours of observaions Carbon monoxide - 2.3 µm 0.8 Planet mozon resolved 0.6 red-shifted 0.4 blue-shifted Orbital phase 0.2 Telluric and planet signal disentangled Planet radial velocity can be measured Star & planet can be treated as spectroscopic binaries 11 Earth s atmosphere Hot Jupiter 0.0-0.2 2.308 2.310 2.312 2.314 Wavelength (μm)

The data analysis: a two-step process 1 Removing telluric lines The Earth s atmospheric absorpion is staionary in wavelength The planet moves along the orbit and it is Doppler-shiued 5 hours of real data + 20x planet signal (CO) Time Wavelength 2 Cross-correlaZng with model spectra (Models by Remco de Kok) Time / orbital phase Planet radial velocity 13

High-resolution studies of hot Jupiters ~150 hrs VLT/CRIRES (R=100,000) 2.3µm, 3.2µm Masses and orbital inclinazons of non-transizng planets τ Boo b, HD 179949 b, 51 Peg b CO and H2O confidently detected CH4 not yet detected Consistent with expectaions for hot planets and solar abundances No thermal inversions detected All emission spectra are well fit by models containing absorp3on lines RotaZon and winds of exoplanets measured The planet line profile, and hence the cross-correlaion funcions, are broadened 14

Spectral and spatial resolution combined The contrast from high-resoluion spectroscopy alone (10-6 -10-5 ) is not enough! y sky posiion GPi - β Pic b x sky posiion

Spectral and spatial resolution combined The contrast from high-resoluion spectroscopy alone (10-6 -10-5 ) is not enough! y sky posiion GPi - β Pic b Speckles = star (scaled, distorted) Planet spectrum + speckle noise x sky posiion Wavelength Current implementazon with VLT-CRIRES: Aligning the slit with the planet-star direcion DetecZons for a few directly-imaged planets β Pic b (Snellen+ 2014, Nature); GQ Lup b (Schwarz+ 2016)

Spectral and spatial resolution combined SimulaIons for METIS@E-ELT: Snellen+ 2015 Starlight suppression factor at planet posiion Number of lines to cross-correlate with Sky y-distance ( ) 0.4 0.2 0.0-0.2-0.4 Thermal emission of Earth-like planet (R=1.5 R, T=300K) orbiing α Cen B HCI only E-ELT/METIS w/ IFU CCF sliced at RV=30 km/s 0.0 0.5 1.0 Sky x-distance ( ) 0.0 0.5 1.0 HCI+HDS 8σ (30 hrs) 5σ (10 hrs)

10-7 Proxima Centauri b: thermal emission R = 1.1 R, T = 250-265K, a = 0.0485 AU 0.0373 separaion Contrast curve 350 K Contrast (1σ) 10-8 300 K α Cen B planet (Snellen+ 2015) 10-9 250 K 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Angular separation ( ) METIS observaions centered at 4.85 µm, 30 hrs

10-7 Proxima Centauri b: thermal emission R = 1.1 R, T = 250-265K, a = 0.0485 AU 0.0373 separaion Contrast curve 350 K Contrast (1σ) 10-8 1σ @ 0.037 ~ 2e-8 300 K α Cen B planet (Snellen+ 2015) 10-9 250 K 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Angular separation ( ) METIS observaions centered at 4.85 µm, 30 hrs

10-7 Proxima Centauri b: thermal emission R = 1.1 R, T = 250-265K, a = 0.0485 AU 0.0373 separaion 265K - 1.1e-7 260K - 9.3e-8 255K - 7.4e-8 250K - 5.9e-8 350 K Contrast curve Contrast (1σ) 10-8 1σ @ 0.037 ~ 2e-8 300 K α Cen B planet (Snellen+ 2015) 10-9 250 K 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Angular separation ( ) METIS observaions centered at 4.85 µm, 30 hrs

Proxima Centauri b: reflected light The star is faint in the opical (B=12.95, V=11.13, R=9.45) low S/N 1.0 0.8 Sun HD 189733 (K1V) Normalized flux 0.6 0.4 0.2 0.0 300 400 500 600 700 800 900 1000 Wavelength (nm) Proxima Cen Current spectrographs are not opimized for M stars, future spectrographs will be VLT-ESPRESSO VLT-HARPS GMT-GCLEF EELT-HIRES MMT-MAROONX Gain in S/N from cross-correlaing with thousands of lines: 65-80

Proxima Centauri b: reflected light The planet/star contrast is in the range (7e-7, 2e-6) Albedo 10-6 FP,refl / Fstar 10-7 i = 30º i = 60º i = 90º 0.2 0.4 0.6 0.8 1.0 Planet albedo

Proxima Centauri b: reflected light The planet/star contrast is in the range (7e-7, 2e-6) Albedo 10-6 100 hrs GMT 100 hrs E-ELT FP,refl / Fstar 10-7 i = 30º i = 60º i = 90º 10 hrs E-ELT (HCI+HDS) 0.2 0.4 0.6 0.8 1.0 Planet albedo High-resoluZon spectroscopy only (350-1000nm, 10% throughput): challenging even with 100 hours of Extremely Giant Telescopes Spectral and spazal resoluzon combined would easily succeed! (Revised Snellen+ 2015 esimates, strehl raio 0.3, 10% throughput)

Terrestrial planets around M-dwarfs are our best short-term chance to characterize potenially-habitable worlds Thank you!

Terrestrial planets around M-dwarfs are our best short-term chance to characterize potenially-habitable worlds High-resoluIon spectroscopy is reliable, can complement space observaions and produce unique measurements (rotaion, masses, inclinaions ) Combined spectral and spaial resoluion: suitable for characterizing poten3ally habitable planets from the ground, even if they non transit! Thank you!