The Small Star Opportunity to Find and Characterize Habitable Planets Jacob Bean Harvard-Smithsonian Center for Astrophysics

Texas Fritz Benedict Chris Sneden Barbara McArthur Amber Armstrong (ugrad, now STScI) Germany Andreas Seifahrt (now UC Davis) Ansgar Reiners Stefan Dreizler Derek Homeier Günter Wiedemann Sweden Henrick Hartman Hampus Nilsson Japan Tomonori Usuda Bunei Sato Ichi Tanaka Harvard David Charbonneau Jean-Michel Désert Zachory Berta (grad) MIT Sara Seager UC Santa Cruz Eliza Miller-Ricci Kempton Jonathan Fortney Princeton Nikku Madhusudhan Georgia State Todd Henry Funding from: NASA, German DFG, ESO, & the EU Collaborators:

data compiled by Jean Schneider Planets detected with RV and transit

Key Results: gas giants in focus statistical properties first-order atmospheric characterization of hot planets feedback to how we view the outer Solar System

Key Results: gas giants in focus statistical properties first-order atmospheric characterization of hot planets feedback to how we view the outer Solar System Key Questions for the Future: towards other Earths statistical properties basic physical properties atmospheric properties habitability inner Solar System in context strongly coupled

Key Results: gas giants in focus statistical properties first-order atmospheric characterization of hot planets feedback to how we view the outer Solar System Key Questions for the Future: towards other Earths statistical properties basic physical properties atmospheric properties habitability inner Solar System in context strongly coupled Low-mass stars offer a shortcut using RV and transit methods

Summary Initiated a comprehensive search for planets around nearby, very low-mass stars (M * < 0.2 M sun ) NIR radial velocities with CRIRES at the VLT and IRCS at Subaru using a new gas cell Paved the way for a new instrument that will be capable of finding characterizable habitable worlds Detecting planets: near-infrared radial velocities Characterizing planets: transit spectroscopy First atmospheric study of a “super-earth” exoplanet – only possible because the planet orbits a very low-mass star Measurements obtained using a new ground-based technique First results guide new theoretical and observational work

The shortcut to habitable planets #1 Low-mass advantage for dynamical methods RV signal ∝ M * -2/3 Example – 1 M earth at 1 AU K = 0.09 m/s for M * = 1.0 M sun K = 0.42 m/s for M * = 0.1 M sun Current state-of-the art is 1 m/s Transit depth ∝ R * -2 R * = 0.2 R sun for M * = 0.15 M sun

The shortcut to habitable planets #1 Low-mass advantage for dynamical methods Transit Spectroscopy Reflection & Emission Transmission both ∝ R * -2

The shortcut to habitable planets #2 Low-mass brings in habitable zone better for RV signal ∝ a -1/2 better for transits probability ∝ a -1 frequency ∝ a -3/2 (Kasting et al. 1993) P = 3 dP = 35 d (Selsis et al. 2007)

The shortcut to habitable planets #3 Low-mass stars most numerous 75% M dwarfs 50% M * < 0.2 M sun

The shortcut to habitable planets (Deming et al 2008) light, small, low luminosity, ubiquitous Best chance to find a transiting habitable planet around a nearby star, and study its atmosphere Low-mass stars…

Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

The problem faintness Planet Detection: Technical Approach

The problem faintness normal RV measurements Planet Detection: Technical 10 pc Sun V=4.8 M0 V=9.0 M8 V=18.7

The problem faintness normal RV measurements more flux in the red/NIR Planet Detection: Technical Approach

The solution – the NIR But there is another problem… calibration! No NIR RV precision like in the visible Best previous precision around 200 m/s Planet Detection: Technical Approach

Calibration methods Emission Lamps few lines in the NIR (ThAr) existing instruments have small wavelength coverage doesn’t track image motion requires a highly stabilized instrument Planet Detection: Technical Approach

Calibration methods Emission Lamps few lines in the NIR (ThAr) existing instruments have small wavelength coverage doesn’t track image motion requires a highly stabilized instrument Gas Cells iodine only works in the visible no existing NIR gas cell tracks all important effects for non-stabilized instruments with varying illumination Planet Detection: Technical Approach

Calibration methods Emission Lamps few lines in the NIR (ThAr) existing instruments have small wavelength coverage doesn’t track image motion requires a highly stabilized instrument Gas Cells iodine only works in the visible no existing NIR gas cell tracks all important effects for non-stabilized instruments with varying illumination ? Planet Detection: Technical Approach

A NIR gas cell Important considerations for the gas cell method: cell should provide lines in a region where stars also have lines avoid telluric lines temperature stabilization necessary? gas mixture not toxic, explosive, or corrosive Planet Detection: Technical Approach

18 cm 5 cm wedged windows to eliminate fringing filled with 50 mb ammonia (NH 3 ) A NIR gas cell Planet Detection: Technical Approach

First implementation in CRIRES at the VLT ESO Planet Detection: Technical Approach

cryogenic, vacuum λ = 1 – 5 μm, Δλ = 50 nm R ≤ 100,000 AO fed long-slit no gas cell temperature stabilization possible ESO gas cell goes here Planet Detection: Technical Approach

Gas cell lines overlap for in situ calibration stellar lines gas cell lines Planet Detection: Technical Approach

Adaptation of the “iodine cell” method instrumental profile and sampling Planet Detection: Technical Approach

Velocity precision tests (Bean et al. 2010b) Planet Detection: Results

A giant planet around VB10? (Pravdo & Shaklan 2009) Star Properties spectral type: M8V M * ~ M sun distance = 5.9 pc V = 17.6 K = 8.8 Planet Properties period = 272 days (0.744 yr) mass = 6 ± 3 M jup inclination ~ edge-on e, ω, and T p not constrained expected K ~ 1 km/s Planet Detection: Results

A giant planet around VB10? (Bean et al. 2010a) Planet Detection: Results

A giant planet around VB10? (Bean et al. 2010a) Planet Detection: Results

A giant planet around VB10? – probably not (Bean et al. 2010a) Planet Detection: Results

Compare to other results Visible: Anglada-Escudé et al Magellan + MIKE rms = 250 m s -1 NIR: Zapatero Osorio et al Keck + NIRSPEC rms = 560 m s -1 | 200 m s -1 CRIRES + ammonia cell rms = 10 m s -1 Planet Detection: Results

Planet Detection: Outlook Initial 2 yr VLT survey complete Identified gas giant planet candidates that need to be followed up Started a northern hemisphere survey with Subaru + IRCS (Seifahrt PI, with Japanese collaborators) Next step is to build a specialized instrument to get to 1 m s -1

Planet Detection: Outlook Will enable the large-scale detection of planets down to a few times the mass of the Earth in the habitable zones of nearby M dwarfs PI: A. Quirrenbach, Heidelberg Operational in 2014 low-mass planet statistics and characterization Spectral coverage: 0.5 – 1.7μm Precision: 1 m s -1 for late M dwarfs Telescope: Calar Alto 3.5m

Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

Planet Characterization Reflection & Emission Transmission both ∝ R * -2 Recall small size advantage for transits…

Planet Characterization (Charbonneau et al. 2009) GJ 1214b Detection of a “super-earth” around a low-mass star planet properties: M = 6.5 M earth R = 2.7 R earth T eq < 550 K star properties: M = 0.16 M sun R = 0.20 R sun super-earth ≡ 1 < mass < 10 M earth

Planet Characterization (Charbonneau et al. 2009) Detection of a “super-earth” around a low-mass star Comparison to models should reveal composition… planet properties: M = 6.5 M earth R = 2.7 R earth T eq < 550 K star properties: M = 0.16 M sun R = 0.20 R sun Kepler-10b

Planet Characterization (Charbonneau et al. 2009) Detection of a “super-earth” around a low-mass star H/He H2OH2O 75% H 2 O / 22% Si / 3% Fe Earth-like Planet is 0.5 R earth too large to be 100% solid --> substantial gas envelope Radius of planet (R earth ) planet properties: M = 6.5 M earth R = 2.7 R earth T eq < 550 K star properties: M = 0.16 M sun R = 0.20 R sun Kepler-10b

Planet Characterization Three models for GJ1214b (Rogers & Seager 2010)

Planet Characterization Three models for GJ1214b Mini-Neptune solar composition H2OH2O FeMgSiO 3 Fe Primordial envelope approximately few percent by mass (Rogers & Seager 2010)

Planet Characterization Three models for GJ1214b Mini-Neptune Water World solar composition H2OH2O FeMgSiO 3 Fe H2OH2O FeMgSiO 3 Fe Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted (Rogers & Seager 2010)

Planet Characterization Three models for GJ1214b Mini-Neptune Water Worldtrue Super-Earth solar composition H2OH2O FeMgSiO 3 Fe H2OH2O FeMgSiO 3 Fe FeMgSiO 3 H Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted Secondary atmosphere, formation interior to the snow line (Rogers & Seager 2010)

Planet Characterization Wavelength (micron) Transit Depth (%) Transmission spectroscopy predictions for GJ1214b (Miller-Ricci & Fortney 2010) H-rich “metal”-rich

Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight scale height strength of features (Miller-Ricci, Seager, & Sasselov 2009)

Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight scale height strength of features (Miller-Ricci, Seager, & Sasselov 2009)

Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight (Miller-Ricci, Seager, & Sasselov 2009) scale height strength of features Nature low mmw high mmw

Planet Characterization Wavelength (micron) Transit Depth (%) Transmission spectroscopy predictions for GJ1214b (Miller-Ricci & Fortney 2010) H-rich “metal”-rich

Planet Characterization A transmission spectrum for GJ1214b – from the ground! (Bean, Miller-Ricci Kempton, & Homeier 2010, Nature)

Planet Characterization A transmission spectrum for GJ1214b – from the ground! (Bean, Miller-Ricci Kempton, & Homeier 2010, Nature)

Planet Characterization A transmission spectrum for GJ1214b – from the ground! (Bean, Miller-Ricci Kempton, & Homeier 2010, Nature) H-rich ruled out at 5σ >70% water by mass needed to be consistent

Planet Characterization Three models for GJ1214b Mini-Neptune Water Worldtrue Super-Earth solar composition H2OH2O FeMgSiO 3 Fe H2OH2O FeMgSiO 3 Fe FeMgSiO 3 H Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted Secondary atmosphere, formation interior to the snow line (Rogers & Seager 2010) Case closed?

Planet Characterization Three models for GJ1214b Mini-Neptune Water Worldtrue Super-Earth solar composition H2OH2O FeMgSiO 3 Fe H2OH2O FeMgSiO 3 Fe FeMgSiO 3 H Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted Secondary atmosphere, formation interior to the snow line (Rogers & Seager 2010) Case closed?

Planet Characterization Three models for GJ1214b Mini-Neptune Water Worldtrue Super-Earth solar composition H2OH2O FeMgSiO 3 Fe H2OH2O FeMgSiO 3 Fe FeMgSiO 3 H Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted Secondary atmosphere, formation interior to the snow line (Rogers & Seager 2010) Case closed?

Planet Characterization Case closed? -- not exactly… low mmw Nature high mmw low mmw with clouds Clouds at <200 mbar in a H-rich atmosphere also consistent with the data

Planet Characterization (Désert, Bean, et al. 2011) Spitzer observations Spitzer data fully consistent with VLT data >80% water by mass now required in cloud-free atmospheres Clouds still possible CH 4

Planet Characterization Clouds or haze remain a possibility although no species/model has been proposed – this is an outstanding theoretical problem Further observations are planned/ongoing to fill in between the VLT optical and Spitzer IR measurements: VLT, Magellan, HST, & etc. The next frontier will be comparative studies – this is an important general aspect of exoplanet science Final Thoughts on GJ1214b…

Outlook Characterization of a habitable exoplanet by 2020 transit radial velocity individual masses and radii transmission spectrum census