Prof. Patrick Irwin

Abstract:

The design of a versatile dual-telescope thermal-infrared radiometer spanning the spectral wavelength range 8–200 µm, in five spectral pass bands, for outer planet fly-by missions is described. The dual-telescope design switches between a narrow-field-of-view and a wide-field-of-view to provide optimal spatial resolution images within a range of spacecraft encounters to the target. The switchable dual-field-of-view system uses an optical configuration based on the axial rotation of a source-select mirror along the optical axis. The optical design, spectral performance, radiometric accuracy, and retrieval estimates of the instrument are discussed. This is followed by an assessment of the surface coverage performance at various spatial resolutions by using the planned NASA Europa Mission 13-F7 fly-by trajectories as a case study.

Abstract:

We use high-resolution ground-based observations from the VLT CRIRES instrument in November 2012 to identify sixteen previously undetected H3+ emission lines from Jupiter’s ionosphere. These emission lines are located in Jupiter’s 5-micron window (4.5−5.2 μm), an optically-thin region of the planet’s spectrum where the radiation mostly originates from the deep troposphere. The H3+ emission lines are so strong that they are visible even against this bright background. We measure the Doppler broadening of the H3+ emission lines in order to evaluate the kinetic temperature of the molecules, and we obtain a value of 1390 ± 160 K. We also measure the relative intensities of lines in the ν2 fundamental in order to calculate the rotational temperature, obtaining a value of 960 ± 40 K. Finally, we use the detection of an emission line from the 2ν2(2)-ν2 overtone to measure a vibrational temperature of 925 ± 25 K. We use these three independent temperature estimates to discuss the thermodynamic equilibrium of Jupiter’s ionosphere.

Abstract:

We report interferometric observations of carbon monoxide (CO) and its isotopologues in Titan's atmosphere using the Atacama Large Millimeter/submillimeter Array (ALMA). The following transitions were detected: CO (J = 1-0, 2-1, 3-2, 6-5), 13CO (J = 2-1, 3-2, 6-5), C18O (J = 2-1, 3-2), and C17O (J = 3-2). Molecular abundances and the vertical atmospheric temperature profile were derived by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code. We present the first spectroscopic detection of 17O in the outer solar system with C17O detected at >8σ confidence. The abundance of CO was determined to be 49.6 ± 1.8 ppm, assumed to be constant with altitude, with isotopic ratios 12C/13C = 89.9 ± 3.4, 16O/18O = 486 ± 22, and 16O/17O = 2917 ± 359. The measurements of 12C/13C and 16O/18O ratios are the most precise values obtained in Titan's atmospheric CO to date. Our results are in good agreement with previous studies and suggest no significant deviations from standard terrestrial isotopic ratios.

Abstract:

The climate on Earth is generally determined by the amount and distribution of incoming solar radiation, which must be balanced in equilibrium by the emission of thermal radiation from the surface and atmosphere. The precise routes by which incoming energy is transferred from the surface and within the atmosphere and back out to space, however, are important features that characterize the current climate. This has been analysed in the past by several groups over the years,based on combinations of numerical model simulations and direct observations of theEarths climate system. The results are often presented in schematic form to show the main routes for the transfer of energy into, out of and within the climate system. Although relatively simple in concept, such diagrams convey a great deal of information about the climate system in a compact form. Such an approach has not so far been widely adopted in any systematic way for other planets of the Solar System, let alone beyond, although quite detailed climate models of several planets are now available, constrained bymany new observations and measurements. Here we present an analysis of the global transfers of energy within the climate systems of a range of planets within the Solar System,including Mars, Titan, Venus a nd Jupit er, a s mo delled by rela t ively co mprehens iveradiative transfer and (in some cases) numerical circulation models. These results are presented in schematic form for comparison with the classical global energy budget analyses (e.g.Trenberth et al. 2009; Stephenset al.2012; Wildet al.2013; IPCC 2013)for the Earth, highlighting important similarities and differences. We also take the first steps towards extending this approach to other Solar System and extra-solar planets,including Mars, Venus, Titan, Jupiter and the ‘hot Jupiter’ exoplanet HD189733b, presenting a synthesis of `both previously published and new calculations for all of these planets.