13 C‐Ethane in the Atmospheres of Jupiter and Saturn

Icarus, 1998

C 2 H 2 ). Neither of these molecules should exist under thermochemical equilibrium (Barshay and Lewis 1978).

1998

We performed high-resolution (lambda /Delta lambda ~ 2,000) spectral observations at mid-infrared wavelengths of C2H6 (12.16 mu m) and C2H2 (13.45 mu m)on Saturn during November and December 1994. These emission features probe the stratosphere of the planet and provide information on the carbon-based photochemical processes taking place in that region of the atmosphere. We used CELESTE, a Goddard-developed cryogenic echelle spectrometer, in conjunction with the 1.5-m McMath-Pierce Solar Telescope (NSO/NOAO) at Kitt Peak National Observatory. For our initial analysis we have used the average temperature profile derived from the Voyager Radio Occultation Experiment, and constant mixing ratios throughout the atmosphere for the hydrocarbons. Preliminary global abundances (excluding polar regions) are 5.0x10(-6) for ethane and 2.5x10(-7) for acetylene. For this presentation we will refine these results by using an updated temperature profile derived from Voyager-IRIS methane observations of the same latitude range as our measurements. We will also use altitude-dependent hydrocarbon mixing ratios derived from recent photochemical models.

Data Archiving and Networked Services (DANS), 2020

The chemical composition of planetary atmospheres has long been thought to store information regarding where and when a planet accretes its material. Predicting this chemical composition theoretically is a crucial step in linking observational studies to the underlying physics that govern planet formation. As a follow-up to a study of hot Jupiters in our previous work, we present a population of warm Jupiters (semi-major axis between 0.5-4 AU) extracted from the same planetesimal formation population synthesis model as used in our previous work. We compute the astrochemical evolution of the protoplanetary disks included in this population to predict the carbon-to-oxygen (C/O) and nitrogen-to-oxygen (N/O) ratio evolution of the disk gas, ice, and refractory sources, the accretion of which greatly impacts the resulting C/O and N/O in the atmosphere of giant planets. We confirm that the main sequence (between accreted solid mass and atmospheric C/O) we found previously is largely reproduced by the presented population of synthetic warm Jupiters. And as a result, the majority of the population fall along the empirically derived mass-metallicity relation when the natal disk has solar or lower metallicity. Planets forming from disks with high metallicity ([Fe/H] > 0.1) result in more scatter in chemical properties which could explain some of the scatter found in the mass-metallicity relation. Combining predicted C/O and N/O ratios shows that Jupiter does not fall among our population of synthetic planets, suggesting that it likely did not form in the inner 5 AU of the solar system before proceeding into a Grand Tack. This result is consistent with recent analysis of the chemical composition of Jupiter's atmosphere which suggests that it accreted most of its heavy element abundance farther than tens of AU away from the Sun. Finally we explore the impact of different carbon refractory erosion models, including the location of the carbon erosion front. Shifting the erosion front has a major impact on the resulting C/O ratio of Jupiter and Neptune-like planets, but warm Saturns see a smaller shift in C/O, since their carbon and oxygen abundances are equally impacted by gas and refractory accretion.

Icarus, 2008

We have analyzed infrared spectra of Titan recorded by the Cassini Composite Infrared Spectrometer (CIRS) to measure the isotopic ratio 12 C/ 13 C in each of three chemical species in Titan's stratosphere: CH 4 , C 2 H 2 and C 2 H 6 . This is the first measurement of 12 C/ 13 C in ...

Planetary and Space Science, 1999

We present our current understanding of the composition, vertical mixing, cloud structure and the origin of the atmospheres of Jupiter and Saturn. Available observations point to a much more vigorous vertical mixing in Saturn's middle-upper atmosphere than in Jupiter's. The nearly cloud-free nature of the Galileo probe entry site, a 5-micron hotspot, is consistent with the depletion of condensible volatiles to great depths, which is attributed to local meteorology. Somewhat similar depletion of water may be present in the 5-micron bright regions of Saturn also. The supersolar abundances of heavy elements, particularly C and S in Jupiter's atmosphere and C in Saturn's, as well as the progressive increase of C from Jupiter to Saturn and beyond, tend to support the icy planetesimal model of the formation of the giant planets and their atmospheres. However, much work remains to be done, especially in the area of laboratory studies, including identi®cation of possible new microwave absorbers, and modelling, in order to resolve the controversy surrounding the large discrepancy between Jupiter's global ammonia abundance, hence the nitrogen elemental ratio, derived from the earth-based microwave observations and that inferred from the analysis of the Galileo probe-orbiter radio attenuation data for the hotspot. We look forward to the observations from Cassini± Huygens spacecraft which are expected to result not only in a rich harvest of information for Saturn, but a better understanding of the formation of the giant planets and their atmospheres when these data are combined with those that exist for Jupiter.

The Journal of …, 2009

The 12 C/ 13 C abundance ratio in ethane in the atmosphere of Titan has been measured at 822 cm -1 from high spectral resolution ground-based observations. The value, 89(8), coincides with the telluric standard and also agrees with the ratio seen in the outer planets. It is almost identical to the result for ethane on Titan found by the composite infrared spectrometer (CIRS) on Cassini. The 12 C/ 13 C ratio for ethane is higher than the ratio measured in atmospheric methane by Cassini/Huygens GCMS, 82.3(1), representing an enrichment of 12 C in the ethane that might be explained by a kinetic isotope effect of approximately 1.1 in the formation of methyl radicals. If methane is being continuously resupplied to balance photochemical destruction, then we expect the isotopic composition in the ethane product to equilibrate at close to the same 12 C/ 13 C ratio as that in the supply. The telluric value of the ratio in ethane then implies that the methane reservoir is primordial. † Part of the special issue "Chemistry: Titan Atmosphere".

2021

The origins of gas giant planets orbiting close to their host stars (``hot Jupiters'') remain a mystery despite more than a quarter-century of study (Fortney et al. 2021). The atmospheric compositions of these planets are highly sought after to provide insight to their formation location in protoplanetary disks, how they migrated to be so close to their host stars, and the relative role of solid versus gas accretion during their assembly (Madhusudhan 2019). However, simultaneous, bounded constraints on both carbon and oxygen abundances, which are key for understanding giant planet formation (Oeberg et al. 2011, Mordasini et al. 2016, Madhusudhan et al. 2017,Cridland et al. 2016), have been elusive (Kreidberg et al. 2014,Wakeford et al. 2018,Pelletier et al. 2021). Here, we report precise abundance measurements of both water and carbon monoxide in a hot Jupiter atmosphere via ground-based, high resolution spectroscopy. From these constraints on the primary carbon- and oxygen-...

Icarus, 2003

This paper presents the first detailed analysis of acetylene absorption features observed longward of 190.0 nm in a jovian spectrum by the Faint Object Spectrograph on board the Hubble Space Telescope. The presence of two features located near 207.0 nm can only be explained by a substantial abundance of acetylene in the upper troposphere. Using a Rayleigh-Raman radiative transfer model, it was determined that the acetylene vertical profile is characterized by a decrease in the mole fraction with increasing pressure in the upper stratosphere, a minimum around 14 to 29 mbar, followed by an increase to about 1.5 ϫ 10 Ϫ7 in the upper troposphere. Longward of 220 nm, the relatively high contrast of Raman features to the continuum precludes the existence of an optically significant amount of clouds from 150 to 500 mbar unless they are highly reflective. Instead, the reflectivity at these long wavelengths is determined by stratospheric, not tropospheric, scatterers and absorbers. Analysis of the data also suggests that ammonia is extremely undersaturated at pressures below 700 mbar. However, no firm conclusions can be reached because of the uncertainties surrounding its cross section longward of 217.0 nm, which are due to vibrationally excited states.

Nature, 2021

209458b formed far from its present location and subsequently migrated inwards 11,13. Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions. We observed four transits of HD 209458b, the archetype of transiting hot Jupiters, with the near-infrared echelle spectrograph GIANO-B 14 , mounted at the 3.6-m Telescopio Nazionale Galileo located in La Palma, Spain. The transits happened on

arXiv (Cornell University), 2023

Isotope ratios have recently been measured in the atmospheres of directly-imaged and transiting exoplanets from ground-based observations. The arrival of JWST allows us to characterise exoplanetary atmospheres in further detail and opens up wavelengths inaccessible from the ground. In this work we constrain the carbon and oxygen isotopes 13 C, 18 O and 17 O from CO in the atmosphere of the directly-imaged companion VHS 1256 b through retrievals of the ∼4.1-5.3 µm NIRSpec G395H/F290LP observations from the early release science programme (ERS 1386). We detect and constrain 13 C 16 O, 12 C 18 O and 12 C 17 O at 32, 16 and 10σ confidence respectively, thanks to the very high signal-to-noise observations. We find the ratio of abundances are more precisely constrained than their absolute values, with 12 C/ 13 C = 62 +2 −2 , in between previous measurements for companions (∼30) and isolated brown dwarfs (∼100). The oxygen isotope ratios are 16 O/ 18 O = 425 +33 −28 and 16 O/ 17 O = 1010 +120 −100. All of the ratios are lower than the local inter-stellar medium and Solar System, suggesting that abundances of the more minor isotopes are enhanced compared to the primary. This could be driven by isotope fractionation in protoplanetary disks, which can potentially alter the carbon and oxygen ratios through isotope selective photodissociation, gas/ice partitioning and isotopic exchange reactions. In addition to CO, we constrain 1 H 2 16 O and 12 C 16 O 2 (the primary isotopologues of both species), but find only upper limits on 12 C 1 H 4 and 14 N 1 H 3. This work highlights the power of JWST to constrain isotopes in exoplanet atmospheres, with great promise in determining formation histories in the future.

The Astrophysical Journal, 2004

The Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft made infrared observations of Jupiter's atmosphere during the flyby of

Astronomy & Astrophysics, 2005

The 12 C 14 N/ 12 C 15 N and 12 C 14 N/ 13 C 14 N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12 C/ 13 C 90 and 14 N/ 15 N 145 for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets.

Reviews in Mineralogy and Geochemistry, 2008

Giant planet atmospheric composition and satellite densities provide insights into protoplanetary disk conditions. Abundances of condensable species and noble gases in wellmixed atmospheres can distinguish among several giant planet formation scenarios, and satellite densities are fi rst order measurements of ice:rock ratios. Recent work on protosolar abundances, relying on three-dimensional spectroscopic modeling of the solar photosphere, provides the framework for the interpretation of measurements. Model densities of protoplanetary disk condensates are shown as a function of carbon partitioning between CO, CH 4 and organics. Comparison with observed satellite densities shows that Saturn's icy satellites are inconsistent with solar composition, and must either have formed in a water-rich environment or have suffered a complex collisional history. The larger satellites of the giant planets are consistent with solar composition, with densities that speak of variation in the partitioning of carbon. 220 Wong et al. Thermochemical equilibrium calculations predict water as the deepest tropospheric cloud on Jupiter, the planet with the best-constrained bulk water abundance. Yet cloud base pressure levels, remote spectroscopic water vapor measurements, and in situ mass-spectral measurements have all been unable to distinguish conclusively between subsolar and supersolar Jovian bulk water abundances, due to modeling assumptions and/or the spatially-variable water vapor distribution in Jupiter's troposphere. Modeling of images of lightning fl ashes is consistent with supersolar water abundances. Galileo probe measurements are consistent with an enrichment factor of 4±2 over the protosolar values for most volatiles other than water (C, N, S, and the noble gases Ar, Kr, and Xe). With that of oxygen unknown, Jupiter's enrichments of other volatiles could be explained in terms of enrichment by heretofore unidentifi ed solar composition icy planetesimals, by planetesimals containing volatiles trapped in water ice clathrates, or by enriched gas in the evolved disk. All models involving delivery of elements by planetesimals require planetesimal formation at temperatures below 40 K, to trap argon and molecular nitrogen. Although atmospheric C/H ratios have been measured for all four giant planets, a conclusive test of the competing formation scenarios cannot be made until O/H is measured on all four planets (extremely diffi cult on Uranus and Neptune), and abundances of the other volatiles and noble gases are measured for the outer three.

Icarus, 2007

Hydrocarbons such as acetylene (C 2 H 2 ) and ethane (C 2 H 6 ) are important tracers in Jupiter's atmosphere, constraining our models of the chemical and dynamical processes. However, our knowledge of the vertical and meridional variations of their abundances has remained ...

Icarus, 2009

Hydrocarbons in the upper atmosphere of Saturn are known, from Voyager, ground-based, and early Cassini results, to vary in emission intensity with latitude. Of particular interest is the marked increase in hydrocarbon line intensity near the south pole during southern summer, as ...