Ge/Ay133 What can transit observations tell us about (exo)-planetary science? Part II – “Spectroscopy” & Atmospheric Composition/Dynamics Kudos to Heather Knutson, now at Caltech!

Rapid Progress: Transiting Planets, 1 May 2007

One year later (2008): 43 Systems And Counting Ice/Rock Planets

Updates from exoplanets.org :

Hot Jupiter/Neptune atmospheres?

M L T In the optical/near-IR, the spectra of M → T dwarfs (similar temp. as the hot Jupiters) show strong alkali metal lines:

Transit Secondary Eclipse See thermal radiation and reflected light from planet disappear and reappear See radiation from star transmitted through the planet’s atmosphere Orbital Phase Variations See cyclical variations in brightness of planet Transiting Planets as a Tool for Studying Exoplanet Atmospheres

Characterizing Atmospheres With Transmission Spectroscopy Probes composition of atmosphere at day-night terminator Can search for clouds, hazes, condensates HST STIS transits of HD b from nm (Knutson et al. 2007a) Atmosphere Star Planet

First detection of an extrasolar planet atmosphere: Look for the transit depth in filters on and off the Na D- line with HST. Charbonneau, D. et al. 2001, ApJ, 568, 377

Atmospheres Part II: Most atoms have their so called resonance lines in the UV. The H I depth is VERY large. EXOSPHERE? Vidal-Madjar, A. et al. 2004, ApJ, 604, L69

Water and Haze on HD b Figure from Pont, Knutson et al. (2007) showing atmospheric transmission function derived from HST ACS measurements between nm Figure from Swain et al (2008) showing infrared atmospheric transmission function derived from HST NICMOS spectra compared to models for the planet’s transmission spectrum with (orange) and without (blue) additional methane absorption (Tinetti et al. 2008). Featureless visible light spectrum indicates hazes… … which disappear in infrared, revealing water absorption features.

What about day/night chemistry? Need IR observations: GL 229B (BD) T dwarf IR opacities dominated by CH 4, H 2 O. Oppenheimer, B. et al. 1998, ApJ, 502, 932

A Broadband Emission Spectrum For HD b Charbonneau, Knutson et al. (2008), Barman (2008) Use secondary eclipses to acquire dayside fluxes:

Can even collect R~ spectra: IRS Data for HD b Grillmair et al., Nature 456, 767 (Dec ) Gillett, Low, & Stein (1969), “The Micron Spectrum of Jupiter” “Most of the features of the μm spectrum of Jupiter can be accounted for on the basis of absorption by NH 3, CH 4, and H 2.”

A Near-IR Emission Spectrum for HD b “Most of the features of the μm spectrum of Jupiter can be accounted for on the basis of absorption by NH 3, CH 4, and H 2.” Swain et al. (2009) HST NICMOS observations of a secondary eclipse of HD b

Even in space, these measurements are at the limits of current detectors: HST NICMOS Spitzer

A Surprise: The Emission Spectrum of HD b Why would two hot Jupiters with similar masses, radii, compositions, and temperatures have such different pressure- temperature profiles? Requires a model with a temperature inversion and water features in emission instead of absorption. Knutson et al. (2008c), Burrows et al. (2007)

Gas Phase TiO/VO Temperature Inversion? Problem: Cold Trap Figure from Fortney et al. (2008) As described in Hubeny et al. (2003), Burrows et al. (2007, 2008), and Fortney et al. (2008) TrES-4 is a great test case! T eq = 1760 K Inverted Non-Inverted One alternative: photochemistry (tholins, polyacetylenes?)

Possible Explanation: UV Chromospheric Stellar Activity? Figure from Knutson et al. 2010, ApJ, 720, 1569 Increasing UV

Ultimately want many objects/wavelengths; Problem: Switch from inverted to non-inverted states can artificially increase day-night contrast Observations of HD b from Knutson et al. (2008a) Model for HD b from Showman et al. (2008) Solution: Use 3.6 and 4.5 μm phase curves to map extent of inversion

Ultimately want many objects/wavelengths; Observations of HD b from Knutson et al. (2008a) Solution: Use 3.6 and 4.5 μm phase curves to map extent of inversion The warm Spitzer mission has done another 18 planets at 3.6/4.5  m (H. Knutson, P.I.). Test of Spitzer color index with stellar UV activity Knutson et al. 2010, ApJ, 720, 1569

Ground? Line shape would give pressure at the photosphere, center/shift the wind profiles. Challenge is the Earth’s atmosphere! Limits only just beginning to reach sufficient sensitivity… CO Search Terrestrial CH 4 Deming, D. et al. 2005, ApJ, 622, 1149

First possible ground based high spectral resolution detection: Gives orbital velocity and thus absolute mass of the planet & star (w/RV), is the blueshift due to strong winds across the terminator? Snellen, I. et al. 2010, Nature, 465, 1049

A Diversity of Worlds Super-Earths & Mini- Neptunes Mass range: 1-10 Earth masses

Prospects for Studies of Terrestrial Planets With the James Webb Space Telescope (launches 2018?) Seager, Deming, & Valenti (2008) Neptune-mass planets are observable with Spitzer and HST…. … but observations of earth- like planets orbiting M dwarfs will require JWST- level precision Predicted transmission spectrum for a 0.5 M earth, 1 R earth, 300 K planet orbiting a M3V, J=8 star

Imaging extrasolar planetary systems? Jovian-mass planets cool slowly, so few-few 10s of MYr old objects are fairly bright… And have emission peaks in the near-IR atmospheric windows where AO systems perform well. Marois et al. (2008), Science

Signatures of “young” planetary systems? One group of systems to try are the so-called ‘debris disks’ that we’ll learn about later. These are young stars with “2 nd generation dust” caused by planetesimal collisions.  Pictoris (VLT, proper motion now confirmed) HR 8799 Marois et al. (2008), Science

Can also use coronography/PSF subtraction in space: Too 600 nm? Circum- planetary disk? If so, M p ? Use dynamics!

Fomalhaut dynamical analysis of companion mass: Kalas, P. et al. (2008), Science Neptune-mass planets are observable with Spitzer and HST…. Modeling of the dust ring suggests an upper limit to the companion of ~3 M J. Photometry-based mass estimate uncertainties are dominated by possible age(s). Formation? (In situ/scattering?)