Climate and radiative properties of a tidally-locked planet around Proxima Centauri

Transcription

1 Climate and radiative properties of a tidally-locked planet around Proxima Centauri D. Galuzzo 1,2 F. Berrilli 1 C. Cagnazzo 2 L. Giovannelli 1 F. Fierli 2 1 Department of Physics, University of Rome Tor Vergata 2 Istituto di Scienze dell Atmosfera e del Clima (ISAC), Centro Nazionale delle Ricerche (CNR) 10/10/18 ESA M4 ARIEL-IT Meeting

2 Bordi, Berrilli & Pietropaolo, Ann. Geo., 2015 UV new proxies suitable for Str. O 3 UV Color, Mg II, UV recons., O 3 (ML) Climate and possible role of stratospheric ozone UV Color and fluxes in 3D GCM (DG) Earth s thermosphere UV Color Stellar Application Lovric+, J. Space Weather Space Climate, 2017 Criscuoli+, ApJ, 2018 (Exo)planetary-Stellar Connection 3D GCM + 1D RTM (exoplanets) Galuzzo+, ApJ submitted, 2018 Galuzzo+, J. Climate in preparation, 2018

3 Goals 1. From solar and atmospheric physics to exoplanet climate and star/planet interactions; 2. Explore a wide range of parameters for habitabilityconditions; 3. Develop a procedure to assess space and ground based detection limits for exoplanets; 4. Supply a method to evaluate the required performances of future detectors. 10/10/18 ESA M4 ARIEL-IT Meeting

4 Why the atmosphere? Habitability Liquid environment (Bains, W., 2004)? Water Atmosphere No atmosphere known habitable planets: 1 known habitable planets: 0 Other fundamental requirements: Characterization of the central star: activity and variability Use what we learned from Sun and Solar System Planetary magnetic fields Orbital stability conditions 10/10/18 ESA M4 ARIEL-IT Meeting

5 A case study: Proxima b Anglada-Escudé, G. et al., 2016 European Southern Observatory High Accuracy Radial velocity Planet Searcher and Ultraviolet and Visual Echelle Spectrograph Intruments 10/10/18 ESA M4 ARIEL-IT Meeting

6 Planet properties Proxima b: derived parameters from radial velocity (Anglada-Escudé, G. et al., 2016) Parameter Symbol Value Orbital period T Earth days Orbital semi-major axis a AU Orbit eccentricity e < 0.35 Planet minimum mass m M Eq. blackbody temperature T K Proxima b: Unknown planetary parameters (extrapolated for the simulation) Parameter Symbol Value Mean density ρ 1 ρ Radius r R Surface gravity acceleration g m/s? Axial tilt α 0 deg Rotation rate ω FG rad/s m 1 = M 1 sin ι ρ = 5514 kg m O Rotation period = Orbital period (Ribas, I. et al., 2016) 10/10/18 ESA M4 ARIEL-IT Meeting

7 Host star properties a) Sun Stellar property Symbol Value Spectral type - M5.5 Mass M M Proxima Radius R R Bolometric flux F STU FVV W m F? Irradiance at Planet b TOA F XTY W m F? Effective temperature 6ZZ T 3050 K Ribas, I. et al., 2017 c) b) AU b Howard, W. S. et al., 2018 Proxima data from 10/10/18 ESA M4 ARIEL-IT Meeting

8 Simulating an exoplanetary atmosphere 3D Intermediate Complexity GCM Planet Simulator (PlaSim) 1D RTM Library for radiative transfer (libradtran) (Fraedrich, K. et al., 2005) (Emde, C. et al., 2016) Keplerian parameters atmospheric composition surface properties Host star Geometryof incident radiation Clouds properties 10/10/18 ESA M4 ARIEL-IT Meeting

9 Simulation initial conditions Earth-like preindustrial atmosphere with 360 ppm of CO? ; Stationary vertical profiles for gasses (no seasonal changes), parameterized O O profile, taken from Green (1980); Aquaplanet with a slab thermodynamic ocean of 50 meters depth; Surface pressure of 1000 hpa (1000 millibars) and top of the atmosphere (TOA) fixed at 50 hpa.

10 North Pole Dawn zowe Anti-stellar point Dusk zone Sub-stellar point South Pole

11 Results: Synthetic spectra AIRS broad-bands e f e f e f ] F^_`a b _ca λ dλ ] F^_`a b _ λ dλ ] F^_`a b _`a λ e a e a e a dλ Planet reflection spectra Planet thermal flux F^,b λ e f e f e f ] F^_b _ca λ dλ ] F^_b _ λ dλ ] F^_b _`a λ e a e a e a dλ μm μm e f e f ] F^_ca b _ca λ dλ ] F^_ca b _ λ e a e a dλ ] F^_ca b _`a λ e f e a dλ 10/10/18 ESA M4 ARIEL-IT Meeting

12 Results: Atmosphere/climate detectability A0 Star G2 Star M5 Star Earth-like planet Superrotation 10/10/18 ESA M4 ARIEL-IT Meeting

13 Results: PlaSim + libradtran output Integrated fluxratio μm 10/10/18 ESA M4 ARIEL-IT Meeting

14 Simulate an observation: From space with the Mid-Infrared Imager on the James Webb Space Telescope From ground based instruments by photometry in the Earth s atmospheric windows 10/10/18 ESA M4 ARIEL-IT Meeting

15 James Webb Space Telescope Medium Infrared Instrument Imager (MIRIM) MIRIM input field of view FULL = ; BRIGHTSKY = ; SUB256 = ; SUB128 = ; SUB64 = /10/18 ESA M4 ARIEL-IT Meeting

16 JWST MIRIM Filters and relative signal amplitude Not face-on Specular by symmetry Non-transiting Not face-on 10/10/18 ESA M4 ARIEL-IT Meeting

17 James Webb Space Telescope Exposure Time Calculator Orbital period Earth s days Exposure Time 5 hours 10/10/18 ESA M4 ARIEL-IT Meeting

18 Color variation Ground based observation simulation M N = 2.5 log Vn o p F e p F q F n F e Fo N Q = 2.5 log e Vn o n F q F n e s o F n s ESO IR photometric passbands M = μm N = μm Q = μm 10/10/18 ESA M4 ARIEL-IT Meeting

19 CONCLUSIONS AND PERSPECTIVES 3D GCM can be used to evaluate the instrumental observation limits for exoplanets; Exoplanet climatic conditions can be inferred by fitting model results to observational data; Habitability can be studied under a wide range of conditions; Ongoing collaboration between UniToV, ISAC-CNR, UniCal and INAF-IAPS to develop a 3D radiative, magnetic and particles model for planet/star interaction; We are able to simulate atmospheric spectra in the observing range of ARIEL. 10/10/18 ESA M4 ARIEL-IT Meeting

20 Bibliography Anglada-Escude, G et al. - A terrestrial planet candidate in a temperate orbit around proxima centauri. Nature, 536(536), Bains, W. - Many chemistries could be used to build living systems. Astrobiology, 2004 Emde, C. et al. - The libradtran software package for radiative transfer calculations (version 2.0.1) - Geoscientific Model Development, 2016 Fraedrich, K. et al. - PUMA Portable University Model of the Atmosphere - World Data Center for Climate (WDCC) at DKRZ, 2005 Green, A. E. S. Attenuation by Ozone and the Earth's Albedo in the Middle Ultraviolet. OSA, 1964 Güdel, M. et al. Flares from small to large: X-ray spectroscopy of Proxima Centauri with XMM-Newton. A&A, 2004 Howard, W. S. et al. The First Naked-Eye Superflare Detected from Proxima Centauri. The Astrophysical Journal Letters, 2018 Ressler, M. E. et al. The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System, Publications of the Astronomical Society of the Pacific, Ribas, I. et al. The habitability of Proxima Centauri b - I. Irradiation, rotation and volatile inventory from formation to the present. A&A, 2016 Ribas, I. et al. The full spectral radiative properties of Proxima Centauri. A&A, 2017 Van der Bliek, N. S. et al. - Infrared aperture photometry at ESO ( ) and its future use - Astron. Astrophys. Suppl. Ser., /10/18 ESA M4 ARIEL-IT Meeting

21 Work s aims and motivations A case study: Proxima b Presentation Overview Simulating an exoplanetary atmosphere: models Method for line-by-line planetary emission spectrum Proxima b atmosphere: photometric and spectral features Conclusions 10/10/18 ESA M4 ARIEL-IT Meeting

22 Simulating an exoplanetary atmosphere: PlaSim Grid-box Simple radiative scheme Lev n 3D Navier-Stokes equations: Conservation of momentum: u, v, w Conservation of mass: uv + q ρu = 0 ux Conservation of energy: T, z Lev n 1 θ = latitude (64) φ = longitude (128) φ φ }V Spectral transform method for non-linear terms Surface / atmosphere interface Lev 0 Surface / Sea-ice / ocean submodels 10/10/18 ESA M4 ARIEL-IT Meeting

23 Simulating an exoplanetary atmosphere: PlaSim - Simple Radiation scheme - shortwave The stellar spectral range is divided into two regions: Star spectral flux UV / VIS spectrum, for λ < 0.75 µm: pure clouds scattering, O O absorption and Rayleigh scattering; NIR spectrum, for λ > 0.75 µm: clouds scattering E V = Energy flux fractions: ƒ a n E n F ƒdλ E n = ] F ƒ dλ n E? = 1 E V and absorption, H? O absorption. Sun E V = 0.51 E? = 0.49 Proxima E V = 0.23 E? = /10/18 ESA M4 ARIEL-IT Meeting

24 Method for line-by-line planetary emission spectrum FV FV W m F? cm ν Planet thermal flux W m F? nm FV Energy input E V E? Stellar input λ Layer 20 TOA libradtran off-line radiative transfer PlaSim simulation: Planetary atmosphere caratterization Dynamical evolution T H? O ˆ O O CO? H? O U Layer 1 p, T z, r Thermal structure 10/10/18 ESA M4 ARIEL-IT Meeting

25 RESULTS Check for system steady state Dynamics 10/10/18 ESA M4 ARIEL-IT Meeting

26 Results: Dynamics R T = U fl 1 rotationally dominated atmosphere 1 Hadley-cell dominated atmosphere Mass streamfunction: ψ = 2πr 1 g 1 ] [v ] cos θ dp n [#] Showmann, A. P. et al., ArXive 2010 [#] Showmann, A. P. and Polvani, L. M., ApJ 2011 [#] Showmann, A. P. et al., book 2013 ψ < 0 anticlockwise circulation ψ > 0 clockwise circulation U 10 m s L 10 G m f = 2ω 1 sin θ 10 F sin θ ψ in 10 G kg s 10/10/18 ESA M4 ARIEL-IT Meeting

27 Results: Dynamics - Superrotation M Y > M n r 1 cos θ ω 1 r 1 cos θ + u > ω 1 r 1? u > u ž u ž = ω 1 r 1 sin θ? cos θ Showman, A. P., et al., 2010 & /10/18 ESA M4 ARIEL-IT Meeting

28 10/10/18 ESA M4 ARIEL-IT Meeting