3.6 AND 4.5 μm PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b

By H. Knutson, N. Lewis, Jon Fortney, Adam Burrows, A. Showman, N. Cowan, E. Agol, Suzanne Aigrain, D. Charbonneau, D. Deming and 4 more. 2012

253 citations recorded by the source corpus.

We present new, full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 μm bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 μm, these data allow us to characterize the exoplanet's emission spectrum as a function of planetary longitude and to search for local variations in its vertical thermal profile and atmospheric composition. We utilize an improved method for removing the effects of intrapixel sensitivity variations and robustly extracting phase curve signals from these data, and we calculate our best-fit parameters and uncertainties using a wavelet-based Markov Chain Monte Carlo analysis that accounts for the presence of time-correlated noise in our data. We measure a phase curve amplitude of 0.1242% ± 0.0061% in the 3.6 μm band and 0.0982% ± 0.0089% in the 4.5 μm band, corresponding to brightness temperature contrasts of 503 ± 21 K and 264 ± 24 K, respectively. We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium, consistent with the eastward advection of gas by an equatorial super-rotating jet. The locations of the flux minima in our new data differ from our previous observations at 8 μm, and we present new evidence indicating that the flux minimum observed in the 8 μm is likely caused by an overshooting effect in the 8 μm array. We obtain improved estimates for HD 189733b's dayside planet–star flux ratio of 0.1466% ± 0.0040% in the 3.6 μm band and 0.1787% ± 0.0038% in the 4.5 μm band, corresponding to brightness temperatures of 1328 ± 11 K and 1192 ± 9 K, respectively; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet. We compare our new dayside and nightside spectra for HD 189733b to the predictions of one-dimensional radiative transfer models from Burrows et al. and conclude that fits to this planet's dayside spectrum provide a reasonably accurate estimate of the amount of energy transported to the night side. Our 3.6 and 4.5 μm phase curves are generally in good agreement with the predictions of general circulation models for this planet from Showman et al., although we require either excess drag or slower rotation rates in order to match the locations of the measured maxima and minima in the 4.5, 8.0, and 24 μm bands. We find that HD 189733b's 4.5 μm nightside flux is 3.3σ smaller than predicted by these models, which assume that the chemistry is in local thermal equilibrium. We conclude that this discrepancy is best explained by vertical mixing, which should lead to an excess of CO and correspondingly enhanced 4.5 μm absorption in this region. This result is consistent with our constraints on the planet's transmission spectrum, which also suggest excess absorption in the 4.5 μm band at the day–night terminator.

Subfields: Aerospace Engineering, Atmospheric Science, Global and Planetary Change

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Citations in the corpus

The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations (2012, methodology): “However, new phase curves at 3.6 and 4.5 µm and a re-analysis of the previous Spitzer data by Knutson et al. (2012) have also overhauled previous results on the emission spectrum.”
SPITZER OBSERVATIONS CONFIRM AND RESCUE THE HABITABLE-ZONE SUPER-EARTH K2-18b FOR FUTURE CHARACTERIZATION (2016, methodology): “…aperture, our extraction includes estimating and subtracting the sky background, calculating the flux-weighted centroid position of the star on the array, and then calculating the total flux within circular apertures (Knutson et al. 2012; Lewis et al. 2013; Todorov et al. 2013; Kammer et al. 2015).”
A SYSTEMATIC RETRIEVAL ANALYSIS OF SECONDARY ECLIPSE SPECTRA. II. A UNIFORM ANALYSIS OF NINE PLANETS AND THEIR C TO O RATIOS (2013, background): “…have been made with a variety of instruments including HSTNICMOS (Swain et al. 2009), Spitzer IRAC (Deming et al. 2006; Charbonneau et al. 2008; Knutson et al. 2009; 2012; Agol et al. 2012), MIPS (Knutson et al. 2009; Charbonneau et al. 2008), and IRS (Grillmair et al. 2007; 2008) spanning…”
A CONSISTENT RETRIEVAL ANALYSIS OF 10 HOT JUPITERS OBSERVED IN TRANSMISSION (2016, background): “Evidence for these jets is found in the offset of thermal phase curve hot spots (e.g. Knutson et al. 2012; Stevenson et al. 2014b) and is predicted by GCMs. Kataria et al. (2016) find that in general the eastern terminator region is relatively warm, but for all but the most highly irradiated…”
3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b (2013, background): “A shift of the hottest point of the planet eastward from the substellar point has been dirctly observed in several exoplanets (Knutson et al. 2007, 2009, 2012; Crossfield et al. 2010) and interpreted as a direct consequence of this jet.”
SPITZER PHASE CURVE CONSTRAINTS FOR WASP-43b AT 3.6 AND 4.5 μm (2016, methodology): “Similar formulations have been used to model other exoplanet phase curves (e.g. Cowan & Agol 2008; Knutson et al. 2012; Lewis et al. 2013; Stevenson et al. 2014).”
ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS (2013, unknown): “Cool planets like HD 189733b (Knutson et al. 2007, 2009b, 2012) and HD 209458b (Cowan et al. 2007) have only modest day-night flux differences.”
WATER VAPOR IN THE SPECTRUM OF THE EXTRASOLAR PLANET HD 189733b. I. THE TRANSIT (2014, methodology): “We adopted HD 189733b’s ephemeris, orbital inclination, and normalized semi-major axis from Knutson et al. (2012).”
Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b (2013, background): “In addition, phase curve observations from the Spitzer Space Telescope suggest that the hottest point in the planet atmosphere is shifted with respect to the sub-stellar point, indicating strong longitudinal circulation in the atmosphere (Knutson et al.2009, 2012).”
HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering (2014, methodology): “…for each image with the noise pixel parameter (Mighell 2005; Knutson et al. 2012), which is described in Section 2.2.2 of the IRAC instrument handbook and has been used in previous exoplanet studies to improve the results of warm Spritzer photometry (e.g. Knutson et al. 2012; O’Rourke et al. 2014).”
 ?> -REx. II. RETRIEVAL OF EMISSION SPECTRA (2015, methodology): “We have compiled data sets ranging from the NIR (1.4µm) to the MIR (24µm), namely: HST/NICMOS (Swain et al. 2009), Spitzer/IRAC 3.6, 4.5 µm (Knutson et al. 2012), 8.0 µm (Agol et al. 2010), Spitzer/IRS spectroscopy (Grillmair et al. 2008), Spitzer/IRS 16 & 24 µm photometry (Charbonneau et al. 2008).”
STABILIZING CLOUD FEEDBACK DRAMATICALLY EXPANDS THE HABITABLE ZONE OF TIDALLY LOCKED PLANETS (2013, methodology): “To estimate the photometric precision one can expect for JWST, we begin with the 4×10−5 precision obtained at 3.6 µm for HD189733 with the Spitzer Space Telescope (Knutson et al. 2012).”
The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets (2017, background): “…relied on photometric monitoring of the exoplanet host star to ascertain the extent of photospheric heterogeneities present (Pont et al. 2008, 2013; Berta et al. 2011; Désert et al. 2011; Sing et al. 2011; Knutson et al. 2012; Narita et al. 2013; Nascimbeni et al. 2015; Zellem et al. 2015).”
ROTATION AND WINDS OF EXOPLANET HD 189733 b MEASURED WITH HIGH-DISPERSION TRANSMISSION SPECTROSCOPY (2015, background): “This planet also has some constraint on energy recirculation and day/night side contrasts from multiwavelength infrared phase curves (Knutson et al. 2007, 2009b, 2012).”
THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “This eastward shift in temperature was first predicted by Showman and Guillot (2002) and since observed in a a number of hot Jupiter’s (Knutson et al. 2007;2009;2012; Crossfield et al. 2010; Cowan et al. 2012; Lewis et al. 2013; Stevenson et al. 2014).”
C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES (2012, background): “…et al. 2008, Madhusudhan & Seager 2009, Sing et al. 2011, Bean et al. 2010, Crossfield et al. 2012, Berta et al. 2012), thermal phase curves (Knutson et al. 2007, 2012; Showman et al. 2009; Cowan et al. 2012), and direct imaging (e.g. Marois et al. 2008,2010; Bowler et al. 2010; Currie et…”