| 1. |
- Tinetti, Giovanna, et al.
(author)
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The science of EChO
- 2010
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 6:S276, s. 359-370
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Journal article (peer-reviewed)abstract
- The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life. The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole. EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates. © International Astronomical Union 2011.
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| 2. |
- de Pater, Imke, et al.
(author)
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An Energetic Eruption With Associated SO 1.707 Micron Emissions at Io's Kanehekili Fluctus and a Brightening Event at Loki Patera Observed by JWST
- 2023
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In: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:8
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Journal article (peer-reviewed)abstract
- We observed Io with the James Webb Space Telescope (JWST) while the satellite was in eclipse, and detected thermal emission from several volcanoes. The data were taken as part of our JWST-ERS program #1373 on 15 November 2022. Kanehekili Fluctus was exceptionally bright, and Loki Patera had most likely entered a new brightening phase. Spectra were taken with NIRSpec/IFU at a resolving power R ≈ 2,700 between 1.65 and 5.3 µm. The spectra were matched by a combination of blackbody curves that showed that the highest temperature, ∼1,200 K, for Kanehekili Fluctus originated from an area ∼0.25 km2 in size, and for Loki Patera this high temperature was confined to an area of ∼0.06 km2. Lower temperatures, down to 300 K, cover areas of ∼2,000 km2 for Kanehekili Fluctus, and ∼5,000 km2 for Loki Patera. We further detected the a1Δ ⇒ X3Σ− 1.707 µm rovibronic forbidden SO emission band complex over the southern hemisphere, which peaked at the location of Kanehekili Fluctus. This is the first time this emission has been seen above an active volcano, and suggests that the origin of such emissions is ejection of SO molecules directly from the vent in an excited state, after having been equilibrated at temperatures of ∼1,500 K below the surface, as was previously hypothesized.
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| 3. |
- Fletcher, Leigh N., et al.
(author)
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Hydrogen Dimers in Giant-planet Infrared Spectra
- 2018
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In: Astrophysical Journal Supplement Series. - : Institute of Physics (IOP). - 0067-0049 .- 1538-4365. ; 235:1
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Journal article (peer-reviewed)abstract
- Despite being one of the weakest dimers in nature, low-spectral-resolution Voyager/IRIS observations revealed the presence of (H2)2 dimers on Jupiter and Saturn in the 1980s. However, the collision-induced H2-H2 opacity databases widely used in planetary science have thus far only included free-to-free transitions and have neglected the contributions of dimers. Dimer spectra have both fine-scale structure near the S(0) and S(1) quadrupole lines (354 and 587 cm-1, respectively), and broad continuum absorption contributions up to ±50 cm-1 from the line centers. We develop a new ab initio model for the free-to-bound, bound-to-free, and bound-to-bound transitions of the hydrogen dimer for a range of temperatures (40-400 K) and para-hydrogen fractions (0.25-1.0). The model is validated against low-temperature laboratory experiments, and used to simulate the spectra of the giant planets. The new collision-induced opacity database permits high-resolution (0.5-1.0 cm-1) spectral modeling of dimer spectra near S(0) and S(1) in both Cassini Composite Infrared Spectrometer observations of Jupiter and Saturn, and in Spitzer Infrared Spectrometer (IRS) observations of Uranus and Neptune for the first time. Furthermore, the model reproduces the dimer signatures observed in Voyager/IRIS data near S(0) on Jupiter and Saturn, and generally lowers the amount of para-H2 (and the extent of disequilibrium) required to reproduce IRIS observations.
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| 4. |
- Gustafsson, Magnus, 1969-, et al.
(author)
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A computational study of hydrogen dimers in giant-planet infrared spectra
- 2019
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In: 24th International Conference on Spectral Lines Shapes 17-22 June 2018, Dublin, Ireland. - : Institute of Physics (IOP).
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Conference paper (peer-reviewed)abstract
- The absorption due to H2–H2 complexes is investigated theoretically. The potential and dipole surfaces for the complex are taken from the literature. Quantum dynamical calculations of the roto-translational absorption spectrum are performed. Special attention is paid to the fine features due to hydrogen dimers, (H2)2, at the centers of the collision-induced rotational S(0) and S(1) transitions. The computed absorption coefficients are used to analyze the spectra of the four giant planets of our solar system.
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| 5. |
- Orton, Glenn S., et al.
(author)
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Mid-infrared spectroscopy of Uranus from the Spitzer Infrared Spectrometer : 1. Determination of the mean temperature structure of the upper troposphere and stratosphere
- 2014
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In: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 243, s. 494-513
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Journal article (peer-reviewed)abstract
- On 2007 December 16-17, spectra were acquired of the disk of Uranus by the Spitzer Infrared Spectrometer (IRS), ten days after the planet's equinox, when its equator was close to the sub-Earth point. This spectrum provides the highest-resolution broad-band spectrum ever obtained for Uranus from space, allowing a determination of the disk-averaged temperature and molecule composition to a greater degree of accuracy than ever before. The temperature profiles derived from the Voyager radio occultation experiment by Lindal et al. (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987]. J. Geophys. Res. 92, 14987-15001) and revisions suggested by Sromovsky et al. (Sromovsky, L.A., Fry, P.A., Kim, J.H. [2011]. Icarus 215, 292-312) that match these data best are those that assume a high abundance of methane in the deep atmosphere. However, none of these model profiles provides a satisfactory fit over the full spectral range sampled. This result could be the result of spatial differences between global and low-latitudinal regions, changes in time, missing continuum opacity sources such as stratospheric hazes or unknown tropospheric constituents, or undiagnosed systematic problems with either the Voyager radio-occultation or the Spitzer IRS data sets. The spectrum is compatible with the stratospheric temperatures derived from the Voyager ultraviolet occultations measurements by Herbert et al. (Herbert, F. et al. [1987]. J. Geophys. Res. 92, 15093-15109), but it is incompatible with the hot stratospheric temperatures derived from the same data by Stevens et al. (Stevens, M.H., Strobel, D.F., Herbert, F.H. [1993]. Icarus 101, 45-63). Thermospheric temperatures determined from the analysis of the observed H2 quadrupole emission features are colder than those derived by Herbert et al. at pressures less than ~1μbar. Extrapolation of the nominal model spectrum to far-infrared through millimeter wavelengths shows that the spectrum arising solely from H2 collision-induced absorption is too warm to reproduce observations between wavelengths of 0.8 and 3.3mm. Adding an additional absorber such as H2S provides a reasonable match to the spectrum, although a unique identification of the responsible absorber is not yet possible with available data. An immediate practical use for the spectrum resulting from this model is to establish a high-precision continuum flux model for use as an absolute radiometric standard for future astronomical observations.
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| 6. |
- Orton, Glenn S., et al.
(author)
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Mid-infrared spectroscopy of Uranus from the Spitzer infrared spectrometer : 2. Determination of the mean composition of the upper troposphere and stratosphere
- 2014
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In: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 243, s. 471-493
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Journal article (peer-reviewed)abstract
- Mid-infrared spectral observations Uranus acquired with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope are used to determine the abundances of C2H2, C2H6, CH3C2H, C4H2, CO2, and tentatively CH3 on Uranus at the time of the 2007 equinox. For vertically uniform eddy diffusion coefficients in the range 2200-2600cm2s-1, photochemical models that reproduce the observed methane emission also predict C2H6 profiles that compare well with emission in the 11.6-12.5μm wavelength region, where the υ9 band of C2H6 is prominent. Our nominal model with a uniform eddy diffusion coefficient Kzz=2430cm2s-1 and a CH4 tropopause mole fraction of 1.6×10-5 provides a good fit to other hydrocarbon emission features, such as those of C2H2 and C4H2, but the model profile for CH3C2H must be scaled by a factor of 0.43, suggesting that improvements are needed in the chemical reaction mechanism for C3Hx species. The nominal model is consistent with a CH3D/CH4 ratio of 3.0±0.2×10-4. From the best-fit scaling of these photochemical-model profiles, we derive column abundances above the 10-mbar level of 4.5+01.1/-0.8×1019molecule-cm-2 for CH4, 6.2±1.0×1016molecule-cm-2 for C2H2 (with a value 24% higher from a different longitudinal sampling), 3.1±0.3×1016molecule-cm-2 for C2H6, 8.6±2.6×1013molecule-cm-2 for CH3C2H, 1.8±0.3×1013molecule-cm-2 for C4H2, and 1.7±0.4×1013molecule-cm-2 for CO2 on Uranus. A model with Kzz increasing with altitude fits the observed spectrum and requires CH4 and C2H6 column abundances that are 54% and 45% higher than their respective values in the nominal model, but the other hydrocarbons and CO2 are within 14% of their values in the nominal model. Systematic uncertainties arising from errors in the temperature profile are estimated very conservatively by assuming an unrealistic "alternative" temperature profile that is nonetheless consistent with the observations; for this profile the column abundance of CH4 is over four times higher than in the nominal model, but the column abundances of the hydrocarbons and CO2 differ from their value in the nominal model by less than 22%. The CH3D/CH4 ratio is the same in both the nominal model with its uniform Kzz as in the vertically variable Kzz model, and it is 10% lower with the "alternative" temperature profile than the nominal model. There is no compelling evidence for temporal variations in global-average hydrocarbon abundances over the decade between Infrared Space Observatory and Spitzer observations, but we cannot preclude a possible large increase in the C2H2 abundance since the Voyager era. Our results have implications with respect to the influx rate of exogenic oxygen species and the production rate of stratospheric hazes on Uranus, as well as the C4H2 vapor pressure over C4H2 ice at low temperatures.
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| 7. |
- Orton, Glenn S., et al.
(author)
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Revised ab initio models for H2–H2 collision-induced absorption at low temperatures
- 2007
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In: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 189:2, s. 544-549
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Journal article (peer-reviewed)abstract
- A revised ab initio calculation of the H2–H2 collision-induced absorption results in significant differences compared with the work of J. Borysow et al. [Borysow, J., Trafton, L., Frommhold, L., Birnbaum, G., 1985. Astrophys. J. 296, 644–654] for wavenumbers greater than 600 cm−1 and temperatures below 120 K. The revision has significant influence on the spectra of Uranus and Neptune, and essentially removes the need for models with “super-solar” helium abundances or stratospheric hazes to explain the spectrum of Uranus.
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| 8. |
- Saur, Joachim, et al.
(author)
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Alternating North-South Brightness Ratio of Ganymede's Auroral Ovals : Hubble Space Telescope Observations Around the Juno PJ34 Flyby
- 2022
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:23
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Journal article (peer-reviewed)abstract
- We report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on 7 June 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant timevariability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m(-2) are required for its OI 1,356 angstrom emission making Ganymede a very poor auroral emitter.
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