With an equilibrium temperature of 1200 K, TrES-1 is one of the coolest hot Jupiters observed by {Spitzer}. It was also the first planet discovered by any transit survey and one of the first exoplanets from which thermal emission was directly observe
d. We analyzed all {Spitzer} eclipse and transit data for TrES-1 and obtained its eclipse depths and brightness temperatures in the 3.6 {micron} (0.083 % {pm} 0.024 %, 1270 {pm} 110 K), 4.5 {micron} (0.094 % {pm} 0.024 %, 1126 {pm} 90 K), 5.8 {micron} (0.162 % {pm} 0.042 %, 1205 {pm} 130 K), 8.0 {micron} (0.213 % {pm} 0.042 %, 1190 {pm} 130 K), and 16 {micron} (0.33 % {pm} 0.12 %, 1270 {pm} 310 K) bands. The eclipse depths can be explained, within 1$sigma$ errors, by a standard atmospheric model with solar abundance composition in chemical equilibrium, with or without a thermal inversion. The combined analysis of the transit, eclipse, and radial-velocity ephemerides gives an eccentricity $e = 0.033^{+0.015}_{-0.031}$, consistent with a circular orbit. Since TrES-1s eclipses have low signal-to-noise ratios, we implemented optimal photometry and differential-evolution Markov-chain Monte Carlo (MCMC) algorithms in our Photometry for Orbits, Eclipses, and Transits (POET) pipeline. Benefits include higher photometric precision and sim10 times faster MCMC convergence, with better exploration of the phase space and no manual parameter tuning.
WASP-8b has 2.18 times Jupiters mass and is on an eccentric ($e=0.31$) 8.16-day orbit. With a time-averaged equilibrium temperature of 948 K, it is one of the least-irradiated hot Jupiters observed with the Spitzer Space Telescope. We have analyzed s
ix photometric light curves of WASP-8b during secondary eclipse observed in the 3.6, 4.5, and 8.0 {microns} Infrared Array Camera bands. The eclipse depths are $0.113pm 0.018$%, $0.069pm 0.007$%, and $0.093pm 0.023$%, respectively, giving respective brightness temperatures of 1552, 1131, and 938 K. We characterized the atmospheric thermal profile and composition of the planet using a line-by-line radiative transfer code and a Markov-chain Monte Carlo sampler. The data indicated no thermal inversion, independently of any assumption about chemical composition. We noted an anomalously high 3.6-{microns} brightness temperature (1552 K); by modeling the eccentricity-caused thermal variation, we found that this temperature is plausible for radiative time scales less than $sim 10^{2}$ hours. However, as no model spectra fit all three data points well, the temperature discrepancy remains as an open question.
We report the detection of UCF-1.01, a strong exoplanet candidate with a radius 0.66 +/- 0.04 times that of Earth (R_{oplus}). This sub-Earth-sized planet transits the nearby M-dwarf star GJ 436 with a period of 1.365862 +/- 8x10^{-6} days. We also r
eport evidence of a 0.65 +/- 0.06 R_{oplus} exoplanet candidate (labeled UCF-1.02) orbiting the same star with an undetermined period. Using the Spitzer Space Telescope, we measure the dimming of light as the planets pass in front of their parent star to assess their sizes and orbital parameters. If confirmed, UCF-1.01 and UCF-1.02 would be called GJ 436c and GJ 436d, respectively, and would be part of the first multiple-transiting-planet system outside of the Kepler field. Assuming Earth-like densities of 5.515 g/cm^3, we predict both candidates to have similar masses (~0.28 Earth-masses, M_{oplus}, 2.6 Mars-masses) and surface gravities of ~0.65 g (where g is the gravity on Earth). UCF-1.01s equilibrium temperature (T_{eq}, where emitted and absorbed radiation balance for an equivalent blackbody) is 860 K, making the planet unlikely to harbor life as on Earth. Its weak gravitational field and close proximity to its host star imply that UCF-1.01 is unlikely to have retained its original atmosphere; however, a transient atmosphere is possible if recent impacts or tidal heating were to supply volatiles to the surface. We also present additional observations of GJ 436b during secondary eclipse. The 3.6-micron light curve shows indications of stellar activity, making a reliable secondary eclipse measurement impossible. A second non-detection at 4.5 microns supports our previous work in which we find a methane-deficient and carbon monoxide-rich dayside atmosphere.
We have studied plume formation after a Jovian comet impact using the ZEUS-MP 2 hydrodynamics code. The three-dimensional models followed objects with 500, 750, and 1000 meter diameters. Our simulations show the development of a fast, upward-moving c
omponent of the plume in the wake of the impacting comet that pinches off from the bulk of the cometary material ~50 km below the 1 bar pressure level, ~100 km above the depth of greatest mass and energy deposition. The fast-moving component contains about twice the mass of the initial comet, but consists almost entirely (>99.9%) of Jovian atmosphere rather than cometary material. The ejecta rise mainly along the impact trajectory, but an additional vertical velocity component due to buoyancy establishes itself within seconds of impact, leading to an asymmetry in the ejecta with respect to the entry trajectory. The mass of the upward-moving component follows a velocity distribution M(>v) approximately proportional to v^-1.4 (v^-1.6 for the 750 m and 500 m cases) in the velocity range 0.1 < v < 10 km/s.
The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets (WASP) project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzers Infrared Array Camera (IRAC) in t
he 3.6 micron and 5.8 micron bands on 2008 December 20, and in the 4.5 micron and 8.0 micron bands on 2008 December 24. We report eclipse depths of 0.30 +/- 0.02%, 0.39 +/- 0.02%, 0.37 +/- 0.03%, 0.41 +/- 0.02%, and brightness temperatures of 3100 +/- 90, 3310 +/- 130, 3080 +/- 140 and 3120 +/- 110 K in order of increasing wavelength. WASP-18b is one of the hottest planets yet discovered - as hot as an M-class star. The planets pressure-temperature profile most likely features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day-side to the night side of the planet.
We present a comparative study of the thermal emission of the transiting exoplanets WASP-1b and WASP-2b using the Spitzer Space Telescope. The two planets have very similar masses but suffer different levels of irradiation and are predicted to fall e
ither side of a sharp transition between planets with and without hot stratospheres. WASP-1b is one of the most highly irradiated planets studied to date. We measure planet/star contrast ratios in all four of the IRAC bands for both planets (3.6-8.0um), and our results indicate the presence of a strong temperature inversion in the atmosphere of WASP-1b, particularly apparent at 8um, and no inversion in WASP-2b. In both cases the measured eclipse depths favor models in which incident energy is not redistributed efficiently from the day side to the night side of the planet. We fit the Spitzer light curves simultaneously with the best available radial velocity curves and transit photometry in order to provide updated measurements of system parameters. We do not find significant eccentricity in the orbit of either planet, suggesting that the inflated radius of WASP-1b is unlikely to be the result of tidal heating. Finally, by plotting ratios of secondary eclipse depths at 8um and 4.5um against irradiation for all available planets, we find evidence for a sharp transition in the emission spectra of hot Jupiters at an irradiation level of 2 x 10^9 erg/s/cm^2. We suggest this transition may be due to the presence of TiO in the upper atmospheres of the most strongly irradiated hot Jupiters.
We report the results of infrared (8 micron) transit and secondary eclipse photometry of the hot Neptune exoplanet, GJ436b using Spitzer. The nearly photon-limited precision of these data allow us to measure an improved radius for the planet, and to
detect the secondary eclipse. The transit (centered at HJD = 2454280.78149 +/-0.00016) shows the flat-bottomed shape typical of infrared transits, and it precisely defines the planet-to-star radius ratio (0.0839 +/-0.0005), independent of the stellar properties. However, we obtain the planetary radius, as well as the stellar mass and radius, by fitting to the transit curve simultaneously with an empirical mass-radius relation for M-dwarfs (M=R). We find Rs=Ms=0.47 +/-0.02 in solar units, and Rp=27,600 +/-1170 km (4.33 +/-0.18 Earth radii). This radius significantly exceeds the radius of a naked ocean planet, and requires a gasesous hydrogen-helium envelope. The secondary eclipse occurs at phase 0.587 +/-0.005, proving a significant orbital eccentricity (e=0.15 +/-0.012). The amplitude of the eclipse (5.7 +/-0.8e-4) indicates a brightness temperature for the planet of T=712 +/-36K. If this is indicative of the planets physical temperature, it suggests the occurrence of tidal heating in the planet. An uncharacterized second planet likely provides ongoing gravitational perturbations, to maintain GJ436bs orbit eccentricity over long time scales.
