The detection of benzene in Saturn's upper atmosphere

Koskinen, Tommi; Moses, J. I.; West, Robert A.; Guerlet, Sandrine; Jouchoux, A.

doi:10.1002/2016gl070000

Cited by 40 publications

(47 citation statements)

References 25 publications

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“…Such hazes have been observed as dark regions in the ultraviolet (West, 1988;Pryor and Hord, 1991) in Jupiter's polar regions, coincident with regions of auroral emissions (Carlson, 1997;Grodent et al, 2015). A similar effect has also been observed at Saturn's poles (Gérard et al, 1995;Karkoschka and Tomasko, 2005) and recent analyses by Guerlet et al (2015) and Koskinen et al (2016) confirm the presence of C 6 H 6 and aerosols in Saturn's polar atmosphere.…”

Section: Introductionsupporting

confidence: 77%

Jupiter’s auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

Sinclair

Orton

Greathouse

et al. 2017

Icarus

107

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Auroral processes are evident in Jupiter's polar atmosphere over a large range in wavelength (X-ray to radio). In particular, previous observations in the mid-infrared (5 to 15 µm) have shown enhanced emission from CH 4 , C 2 H 2 and C 2 H 4 and further stratospheric hydrocarbon species in spatial regions coincident with auroral processes observed at other wavelengths. These regions, described as auroral-related hotspots, observed at approximately 160• W to 200• W (System III) at high-northern latitudes and 330• W to 80• W at high-southern latitudes, indicate that auroral processes modify the thermal structure and composition of the neutral atmosphere. However, previous studies have struggled to differentiate whether the aforementioned enhanced emission is a result of either temperature changes and/or changes in the concentration of the emitting species. We attempt to address this degeneracy in this work by performing a retrieval analysis of Voyager 1-IRIS spectra (acquired in 1979) and Cassini-CIRS spectra (acquired in 2000/2001) of Jupiter. Retrievals of the vertical temperature profile in Cassini-CIRS spectra covering the auroral-related hotspots indicate the presence of two discrete vertical regions of heating at the 1-mbar level and at pressures of 10-µbar and lower. For example, in Cassini-CIRS 2.5 cm −1 'MIRMAP' spectra at 70• N (planetographic) 180• W (centred on the auroral oval), we find temperatures at the 1-mbar level and 10-µbar levels are enhanced by 15.3 ± 5.2 K and 29.6 ± 15.0 K respectively, in comparison to results at 70• N, 60• W in the same dataset. High temperatures at 10-µbar and lower pressures were considered indicative of joule heating, ion and/or electron precipitation, ion-drag and energy released form exothermic ion-chemistry. However, we conclude that the heating at the 1-mbar level is the result of either a layer of aurorally-produced haze particles, which are heated by incident sunlight and/or adiabatic heating by downwelling within the auroral hot-spot region. The former mechanism would be consistent with the vertical profiles of polycyclic aromatic hydrocarbons (PAHs) and haze particles predicted in auroral-chemistry models (Wong et al., 2000(Wong et al., , 2003. Retrievals of C 2 H 2 and C 2 H 6 were also performed and indicate C 2 H 2 is enriched but C 2 H 6 is depleted in auroral regions relative to quiescent regions. For example, using CIRS ∆ν = 2.5 cm −1 spectra, we determined that C 2 H 2 at 0.98 mbar increases by 175.3 ± 89.3 ppbv while C 2 H 6 at 4.7 mbar decreases by 0.86 ± 0.59 ppmv in comparing results at 70• N, 180• W and 70• N, 60• W. These results represent a mean of values retrieved from different initial assumptions and thus we believe they are robust. We believe these contrasts in C 2 H 2 and C 2 H 6 between auroral and quiescent regions can be explained by a coupling of auroral-driven chemistry and horizontal advection. Ion-neutral and electron recombination chemistry in the auroral region enriches all C 2 hydrocarbons but in particular, the unsaturated ...

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Section: Introductionsupporting

confidence: 77%

Jupiter’s auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

Sinclair

Orton

Greathouse

et al. 2017

Icarus

107

View full text Add to dashboard Cite

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“…This is proactive for the study of large molecules through the unique fingerprint features offered by the LWIR spectral region, for example molecules of the BTEX (benzene, toluene, ethylbenzene, xylenes) family that are of high interest for environmental modelling applications. In the case of benzene, which lacks a permanent dipole moment and, therefore, cannot be detected by pure rotational spectroscopy, infrared bands such as the ν 11 explored here represent the clue to assess their presence in remote spatial environments, such as planetary atmospheres 6,37,38 . On another front, by the use of a sub-hertz linewidth comb and phase-locking loops for pump and signal lasers, the spectrometer could reach the level of stability and spectral purity needed for tests of fundamental physics on molecular samples 39,40 in a spectral region not explored so far.…”

Section: Discussionmentioning

confidence: 99%

Optical frequency metrology in the bending modes region

et al. 2020

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Optical metrology and high-resolution spectroscopy, despite impressive progress across diverse regions of the electromagnetic spectrum from ultraviolet to terahertz frequencies, are still severely limited in the region of vibrational bending modes from 13 to 20 µm. This long-wavelength part of the mid-infrared range remains largely unexplored due to the lack of tunable single-mode lasers. Here, we demonstrate bending modes frequency metrology in this region by employing a continuous-wave nonlinear laser source with tunability from 12.1 to 14.8 µm, optical power up to 110 µW, MHz-level linewidth and comb calibration. We assess several CO2-based frequency benchmarks with uncertainties down to 30 kHz and we provide an extensive study of the v11 band of benzene, a significant testbed for the resolution of the spectrometer. These achievements pave the way for long-wavelength infrared metrology, rotationally-resolved studies and astronomic observations of large molecules such as aromatic hydrocarbons.

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“…The composition of photochemical aerosols has not been clearly identified yet. Both observations and modelling suggest that they are hydrocarbon based (Ben-Jaffel et al 1995;Wong et al 2003;Koskinen et al 2016), but contributions from phosphine chemistry on Saturn and sulfur chemistry on Jupiter are also anticipated, although not yet verified. Average particle sizes range between ∼0.01 µm in the stratosphere to ∼0.1 µm in the upper troposphere.…”

Section: Introductionmentioning

confidence: 99%

Aerosol Properties of the Atmospheres of Extrasolar Giant Planets

Lavvas

Koskinen

2017

ApJ

101

186

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We use a model of aerosol microphysics to investigate the impact of high-altitude photochemical aerosols on the transmission spectra and atmospheric properties of close-in exoplanets, such as HD 209458 b and HD 189733 b. The results depend strongly on the temperature profiles in the middle and upper atmospheres, which are poorly understood. Nevertheless, our model of HD 189733 b, based on the most recently inferred temperature profiles, produces an aerosol distribution that matches the observed transmission spectrum. We argue that the hotter temperature of HD 209458 b inhibits the production of high-altitude aerosols and leads to the appearance of a clearer atmosphere than on HD 189733 b. The aerosol distribution also depends on the particle composition, photochemical production, and atmospheric mixing. Due to degeneracies among these inputs, current data cannot constrain the aerosol properties in detail. Instead, our work highlights the role of different factors in controlling the aerosol distribution that will prove useful in understanding different observations, including those from future missions. For the atmospheric mixing efficiency suggested by general circulation models, we find that the aerosol particles are small (∼nm) and probably spherical. We further conclude that a composition based on complex hydrocarbons (soots) is the most likely candidate to survive the high temperatures in hot-Jupiter atmospheres. Such particles would have a significant impact on the energy balance of HD 189733 b's atmosphere and should be incorporated in future studies of atmospheric structure. We also evaluate the contribution of external sources to photochemical aerosol formation and find that their spectral signature is not consistent with observations.

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The detection of benzene in Saturn's upper atmosphere

Cited by 40 publications

References 25 publications

Jupiter’s auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

Jupiter’s auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

Optical frequency metrology in the bending modes region

Aerosol Properties of the Atmospheres of Extrasolar Giant Planets

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