Jake D. Turner

Possible tropical lakes on Titan from observations of dark terrain

Titan has clouds, rain and lakes—like Earth—but composed of methane rather than water. Unlike Earth, most of the condensable methane (the equivalent of 5 m depth globally averaged) lies in the atmosphere. Liquid detected on the surface (about 2 m deep) has been found by radar images only poleward of 50° latitude, while dune fields pervade the tropics. General circulation models explain this dichotomy, predicting that methane efficiently migrates to the poles from these lower latitudes. Here we report an analysis of near-infrared spectral images of the region between 20° N and 20° S latitude. The data reveal that the lowest fluxes in seven wavelength bands that probe Titans surface occur in an oval region of about 60 × 40 km2, which has been observed repeatedly since 2004. Radiative transfer analyses demonstrate that the resulting spectrum is consistent with a black surface, indicative of liquid methane on the surface. Enduring low-latitude lakes are best explained as supplied by subterranean sources (within the last 10,000 years), which may be responsible for Titan’s methane, the continual photochemical depletion of which furnishes Titans organic chemistry.

Warm ice giant GJ 3470b - II. Revised planetary and stellar parameters from optical to near-infrared transit photometry

It is important to explore the diversity of characteristics of low-mass, low-density planets to understand the nature and evolution of this class of planets. We present a homogeneous analysis of 12 new and 9 previously published broad-band photometric observations of the Uranus-sized extrasolar planet GJ 3470b, which belongs to the growing sample of sub-Jovian bodies orbiting M dwarfs. The consistency of our analysis explains some of the discrepancies between previously published results and provides updated constraints on the planetary parameters. Our data are also consistent with previous transit observations of this system. The physical properties of the transiting system can only be constrained as well as the host star is characterized, so we provide new spectroscopic measurements of GJ 3470 from 0.33 to 2.42 μm to aid our analysis. We find R* = 0.48 ± 0.04 R⊙, M* = 0.51 ± 0.06 M⊙, and T_(eff) = 3652 ± 50K for GJ 3470, along with a rotation period of 20.70 ± 0.15 d and an R-band amplitude of 0.01 mag, which is small enough that current transit measurements should not be strongly affected by stellar variability. However, to report definitively whether stellar activity has a significant effect on the light curves, this requires future multiwavelength, multi-epoch studies of GJ 3470. We also present the most precise orbital ephemeris for this system: To = 2455983.70472 ± 0.00021BJD_(TDB), P = 3.336 6487^(+0.0000043)_(−0.0000033)  d, and we see no evidence for transit timing variations greater than 1 min. Our reported planet to star radius ratio is 0.076 42 ± 0.000 37. The physical parameters of this planet are R_p = 3.88 ± 0.32 R⊕ and M_p = 13.73 ± 1.61 M⊕. Because of our revised stellar parameters, the planetary radius we present is smaller than previously reported values. We also perform a second analysis of the transmission spectrum of the entire ensemble of transit observations to date, supporting the existence of an H_2-dominated atmosphere exhibiting a strong Rayleigh scattering slope.

Optical observations of the transiting exoplanet GJ 1214b

We observed nine primary transits of the super-Earth exoplanet GJ 1214b in several optical photometric bands from 2012 March to August, with the goal of constraining the shortwavelength slope of the spectrum of GJ 1214b. Our observations were conducted on the Kuiper 1.55 m telescope in Arizona and the STELLA-I robotic 1.2 m telescope in Tenerife, Spain. From the derived light curves we extracted transit depths in R (0.65µm), V (0.55µm) and g � (0.475µm) bands. Most previous observations of this exoplanet suggest a flat spectrum varying little with wavelength from the near-infrared to the optical, corresponding to a lowscale height, high-molecular-weight atmosphere. However, a handful of observations around Ks band (∼2.15µm) and g band (∼0.46µm) are inconsistent with this scenario and suggest a variation on a hydrogen- or water-dominated atmosphere that also contains a haze layer of small particles. In particular, the g-band observations of de Mooij et al., consistent with Rayleigh scattering, limit the potential atmosphere compositions of GJ 1214b due to the increasing slope at optical wavelengths. We find that our results overlap within errors the short-wavelength observations of de Mooij et al., but are also consistent with a spectral slope of zero in GJ 1214b in the optical wavelength region. Our observations thus allow for a larger suite of possible atmosphere compositions, including those with a high molecular weight and/or hazes.

Near-UV and optical observations of the transiting exoplanet TrES-3b

We observed nine primary transits of the hot Jupiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jupiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B∗ of 100 G, the Vidotto et al. method predicts a timing difference of 5–11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES3b’s magnetic field strength to range between 0.013 and 1.3 G (for a 1–100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist–Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386 +0.248 −0.144 RJup is consistent with the planet’s optical radius.

Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits

NASAs Planetary Atmospheres programme; Virginia Space Grant Consortium Graduate Research Fellowship Program; National Science Foundation [DGE-1315231]; University of Arizona Astronomy Club; Steward Observatory TAC; Lunar and Planetary Laboratory

Investigation of the environment around close-in transiting exoplanets using cloudy

It has been suggested that hot stellar wind gas in a bow shock around an exoplanet is sufficiently opaque to absorb stellar photons and give rise to an observable transit depth at optical and UV wavelengths. In the first part of this paper, we use the CLOUDY plasma simulation code to model the absorption from X-ray to radio wavelengths by 1-D slabs of gas in coronal equilibrium with varying densities (

Photometric observation of HAT-P-16b in the near-UV

10^{4}-10^{8} \, {\rm cm^{-3}}

A Revised Orbital Ephemeris for HAT-P-9b

) and temperatures (

XO-2b: A Hot Jupiter with a Variable Host Star That Potentially Affects Its Measured Transit Depth

2000-10^{6} \ {\rm K}

Investigating the physical properties of transiting hot Jupiters with the 1.5-m Kuiper Telescope

) illuminated by a solar spectrum. For slabs at coronal temperatures (