Scattering in Planetary Atmospheres Svetlana Berdyugina Kiepenheuer Institut für Sonnenphysik, Freiburg, Germany SPW3, Tenerife, 2002 Hot Molecules in Exoplanets and Inner Disks

Content Polarized scattering Model Observations Earth Rayleigh scattering Mie scattering Observations Solar system Exoplanets SPW3, Tenerife, 2002

Scattering in a stellar atmosphere polarization depends on the scattering angle polarization is determined by the projection of dipoles towards observer polarization is perpendicular to the scattering plane polarization arises because of the spatial symmetry braking anisotropic radiation non-spherical geometry magnetic/electric field

Scattering in a planetary atmosphere polarization depends on the scattering angle polarization is determined by the projection of dipoles towards observer polarization is perpendicular to the scattering plane polarization arises because of the spatial symmetry braking anisotropic radiation non-spherical geometry magnetic/electric field

Rayliegh Scattering: Earth on bound electrons Sky color and polarization  Intensity and polarization are larger for higher frequency (shorter wavelength) light Hegedüs et al. (2007)

Can humans sense polarization? 1846, von Haidinger Viking navigation tool

Earth-shine polarization Earth shine polarized spectra: Rayleigh, O2, H2O, vegetation(?) Sterzik et al. (2012)

Scattering in a stellar atmosphere Radiative transport equation: Scattering source function: HotMol tools: StarPol Chandrasekhar (1960), Fluri & Stenflo (1999), Kostogryz & Berdyugina (2014)

Scattering in a planetary atmosphere Radiative transport equation for Stokes parameters: Scattering source function: Formal solution: * = 0: I-(, <0, ) = stellar incident radiation from the top * = : I+(, >0, ) = planet intrinsic radiation from the bottom Boundary conditions Sobolev (1956), Chandrasekhar (1960),…, Berdyugina (2017), JSQRT

Polarized scattering on molecules Hot Jupiter at 0.02 AU: single scattered stellar photons dominate planetary radiation limb brightnening, high polarization (Berdyugina 2017, JQSRT) I/I0 Q/I Source Function: Black: thermal radiation of the planet, Green: single scattered stellar radiation, Magenta: multiple scattered stellar and planetary radiation, Red dotted: the total source function Relative opacities: Blue dashed: total scattering Blue solid: total absorption Blue dashed-dotted: particle scattering

Polarized scattering on molecules Hot Jupiter at 0.05 AU: single scattered stellar photons ~ multiply scattered photons moderate limb brightnening & polarization (Berdyugina 2017, JQSRT) I/I0 Q/I Source Function: Black: thermal radiation of the planet, Green: single scattered stellar radiation, Magenta: multiple scattered stellar and planetary radiation, Red dotted: the total source function Relative opacities: Blue dashed: total scattering Blue solid: total absorption Blue dashed-dotted: particle scattering

Polarized scattering on molecules Hot Jupiter at 0.1 AU: multiply scattered photons dominate planetary radiation low limb brightnening & polarization (Berdyugina 2017, JQSRT) I/I0 Q/I Source Function: Black: thermal radiation of the planet, Green: single scattered stellar radiation, Magenta: multiple scattered stellar and planetary radiation, Red dotted: the total source function Relative opacities: Blue dashed: total scattering Blue solid: total absorption Blue dashed-dotted: particle scattering

Polarized scattering on molecules H2O example (Berdyugina 2017, JQSRT) Q I

Molecular polarizability Polarization amplitudes scale with intrinsic polarizability, W2 opacity Rayleigh scattering: positive intrinsic polarizability with two asymptotic values 0.4 in Q branch lines 0.1 in R and P branch lines Raman scattering: positive and negative intrinsic polarizability with asymptotic values 0.1 in RP and PR transitions –0.2 in QP and RQ transitions Rayleigh scattering Raman scattering Berdyugina et al. (2002)

Polarized scattering on particles (Berdyugina 2017, JQSRT) Scattering on droplets: nr = 1.6 & 1.9 Forward scattering Rayleigh limit Geometrical optics limit Rainbow near165-170 “Glory” near 140-150 and at 180 “Anomalous diffraction“ near 20-30 Intensity Polarization

Polarized scattering on particles Hot Jupiter at 0.02 AU: Scattering with different cloud depths: 70km 80km 90km (Berdyugina 2017, JQSRT) I I I Q Q Q Source Function: thermal radiation of the planet (black), single scattered stellar radiation (green), multiple scattered stellar and planetary radiation (magenta), and the total one (red dotted line), Relative opacities: total scattering (dashed blue) and absorption (solid blue), particle scattering (dashed-dotted blue)

Effects of atmosphere composition Particles of 1m Incident light Seager et al. (2000) Molecules (1), tropospheric clouds (2), stratospheric haze (3) Stam et al. (2004)

Earth Polarized Cloudbow: POLDER Breon & Goloub (1998)

Venus Polarization measurements: Lyot (1929), Dollfus (1969) Models: Sobolev (1968), Coffeen (1968,1969), Hansen & Hovenier(1971) Clouds: 1.05 m droplets of 75% H2SO4 + 25% H2O

Gas Giants I Q U Jupiter Uranus Neptune Schmid et al. (2006), Joos & Schmid (2007)

Unresolved Exoplanets Detection of reflected light  direct probe of planetary environment Physics: scattering polarization Polarization is perpendicular to the scattering plane Max. polarization at 90 scattering angle Stellar light is unpolarized (or modulated with a different period) Polarization varies as planet orbits the star (Fluri & Berdyugina 2010) polarimeter

i=98, =270, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=98, =270, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=98, =225, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=98, =180, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=135, =270, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=180, =270, e=0 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

i=130, =270, e=0.5, =270 R = 1.2RJ a = 0.03 AU P = 2.2 d (Fluri & Berdyugina 2010)

First Detection: HD189733b Transiting hot Jupiter (Berdyugina et al. 2008) Transiting hot Jupiter mass 1.15 MJ period 2.2 d semimajor axis 0.03 AU B band (440nm, DiPol, KVA60) (Berdyugina et al. 2008) 93 nightly measurements (3h) Errors ~510–5 UBV (360,440,550nm, TurPol) (Berdyugina et al. 2011a) 35 nightly meas. (3-4h) 29 standard stars for calibration: ~(1-2)10–5 Errors ~110–5 Monte Carlo error analysis Amplitude (9  1)x10–5 B (Berdyugina et al. 2011) UB

HD189733b: Blue Planet Geometrical Albedo, Ag: Strong function of  (Berdyugina et al. 2011) Geometrical Albedo, Ag: Strong function of  0.60.3 at 370 nm 0.610.12 at 450 nm, 0.280.15 at 550 nm, <0.2 at 600 nm <0.1 at >800 nm Similar to that of Neptune blue: Rayleigh and Raman scattering on H2 red: absorption by molecules P ~ scatt/abs ratio Blue Planet

Model with Condensates: HD189733b Berdyugina 2011 Polarimetry and transit data fit with one model Semi-empirical model Rayleigh/Mie scattering: H, H2, He, CO, H2O, CH4, e–, MgSiO3 Absorption: H, H–, H2–, H2+,He, He–, metals Haze: High-altitude condensate layer with 20-30nm particles R=1/RJ(U)~1.190.24  Scat R=1/RJ(B)~1.180.10  Scat (in agreement with Sing et al. 2011) R=1/RJ(V)<0.750.20  Abs R=1/RJ(RI)<0.43  Abs Polarization  scat/abs () Berdyugina et al. (2008, 2011) Wiktorovicz (2009) Lucas et al. (2009) ++ Pont et al. (2007), 550 nm

HD189733b: Blue Planet Primary transit spectroscopy, HST (Sing et al. 2011): Raleigh scattering – opacity increases to the blue Additional opacity (absorption?) at 300-400nm R(~1)  Total opacity = absorption+ scattering

HD189733b: Blue Planet Secondary eclipse spectroscopy, HST (Evans et al. 2013): Geometrical albedo: 0.400.12 @300-450nm, <0.1 @450-590nm Reflected flux ~ total opacity = scattering+absorption

What does it mean, blue planet?

New Trend in Hot Jupiter Art Before: After:

Blue Gas Planets Neptune geometrical albedo model GA of a pure Rayleigh scattering atmosphere = const (white) Raman scattering & haze absorption reduces GA in near UV CH4 & CIA absorption reduces GA in the red 0.78 (Sromovsky 2005)

Blue Gas Giants Spectropolarimetry of Neptune Methane bands are polarized Single scattered photons avoide the absorption Multiply scat.phot.are absorbed Depends on scat/abs ratio Search in blue Jupiters: identify absorption source and determine chemical composition! 100% 30% (Joos & Schmid 2007)

Key Points: Polarized scattering on molecules In planetary atmospheres polarization arises due to its anisotropic irradiation, both from the top and from the bottom. Polarimetry is a differential technique for direct detection of exoplanets Albedo, atmos.composition, weather, rot. periods, magnetospheres Rayleigh scattering with the strong wavelength dependence dominates the reflected light  blue planets Rayleigh scattering: Polarization is sensitive to the incident stellar flux: hotter stars hosting closer-in planets are systems potentially producing larger polarization in the blue. Limb brightening for large fluxes of single-scattered stellar photons Molecular band polarization can be stronger than continuum Mie scattering (nr = 1.6 & 1.9): Forward scattering is dominant Rainbow (near165-170) “Glory” (near 140-150 and at 180) “Anomalous diffraction“ (near 20-30)