arXiv subjects

C. A. Nixon

Publications and source records attributed to C. A. Nixon.

18 recordsLinked to original sources

arXiv2026

An unidentified absorption feature at 5.11 $μ$m on the surface of Titan and Pluto from JWST spectroscopy

Titan possesses a thick N$_2$-CH$_4$ atmosphere that makes it difficult to study its surface spectroscopically. The chemical composition of the solid surface of Titan thus remains very uncertain. By leveraging JWST's high sensitivity and large spectral coverage, we searched for any signature from Titan's surface in the broad and less explored 5-$μ$m atmospheric window. We also investigated the JWST spectrum of Pluto which has a thin Titan-like atmosphere. We made selections of JWST NIRSpec and MIRI spectra around Titan's disk center and compared the NIRSpec average spectrum with a radiative transfer model including gas and haze opacity. We detected an unidentified absorption in both NIRSpec and MIRI spectra of Titan centered at 5.113 $μ$m (1956 cm$^{-1}$) and 6-7% deep. The width of the feature is 0.024$\pm$0.0008 $μ$m (9.2$\pm$0.3 cm$^{-1}$) in the NIRSpec spectrum recorded on the trailing side and is possibly 25% narrower in the MIRI spectrum of the leading side. This absorption most likely originates from the surface. We could not identify this signature among published laboratory spectra of ices relevant to Titan's atmospheric compounds but present a few plausible candidates. A 4-5% deep absorption is also present in the MIRI spectrum of Pluto but is about 3 times broader than on Titan's trailing side.

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arXiv2025

Improved Carbon and Nitrogen Isotopic Ratios for CH$_3$CN in Titan's Atmosphere Using ALMA

Titan, Saturn's largest satellite, maintains an atmosphere composed primarily of nitrogen (N$_2$) and methane (CH$_4$) that leads to a complex organic chemistry. Some of the nitriles (CN-bearing organics) on Titan are known to have substantially enhanced $^{15}$N abundances compared to Earth and to Titan's dominant nitrogen (N$_2$) reservoir. The $^{14}$N/$^{15}$N isotopic ratio in Titan's nitriles can provide better constraints on the synthesis of nitrogen-bearing organics in planetary atmospheres as well as insights into the origin of Titan's large nitrogen abundance. Using high signal-to-noise ratio ($>13$), disk-integrated observations obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 receiver (211-275 GHz), we measure the $^{14}$N/$^{15}$N and $^{12}$C/$^{13}$C isotopic ratios of acetonitrile (CH$_3$CN) in Titan's stratosphere. Using the Nonlinear optimal Estimator for MultivariatE spectral analySIS (NEMESIS), we derived the CH$_3$CN/$^{13}$CH$_3$CN ratio to be 89.2 $\pm$ 7.0 and the CH$_3$CN/CH$_3$$^{13}$CN ratio to be 91.2 $\pm$ 6.0, in agreement with the $^{12}$C/$^{13}$C ratio in Titan's methane, and other Solar System species. We found the $^{14}$N/$^{15}$N isotopic ratio to be 68.9 $\pm$ 4.2, consistent with previously derived values for HCN and HC$_3$N, confirming an enhanced $^{15}$N abundance in Titan's nitriles compared with the bulk atmospheric N$_2$ value of $^{14}$N/$^{15}$N = 168, in agreement with chemical models incorporating isotope-selective photodissociation of N$_2$ at high altitudes.

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arXiv2024

The D/H ratio in Titan's acetylene from high spectral resolution IRTF/TEXES observations

We report observations of deuterated acetylene (C$_2$HD) at 19.3 $μ$m (519 cm$^{-1}$) with the Texas Echelon Cross Echelle Spectrograph on the NASA Infrared Telescope Facility in July 2017. Six individual lines from the Q-branch of the $ν_4$ band were clearly detected with a S/N ratio up to 10. Spectral intervals around 8.0 $μ$m (745 cm$^{-1}$) and 13.4 $μ$m (1247 cm$^{-1}$) containing acetylene (C$_2$H$_2$) and methane (CH$_4$) lines respectively, were observed during the same run to constrain the disk-averaged C$_2$H$_2$ abundance profile and temperature profile. Cassini observations with the Composite Infrared Spectrometer (CIRS) were used to improve the flux calibration and help to constrain the atmospheric model. The measured D/H ratio in acetylene, derived from the C$_2$HD/C$_2$H$_2$ abundance ratio, is (1.22$^{+0.27}_{-0.21})$ $\times$ 10$^{-4}$, consistent with that in methane obtained in previous studies. Possible sources of fractionation at different steps of the acetylene photochemistry are investigated.

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arXiv2024

ALMA Spectroscopy of Europa: A Search for Active Plumes

The subsurface ocean of Europa is a high priority target in the search for extraterrestrial life, but direct investigations are hindered by the presence of a thick, exterior ice shell. Here we present spectral line and continuum maps of Europa obtained over four epochs in May-June 2021 using the Atacama Large Millimeter/submillimeter Array (ALMA), to search for molecular emission from atmospheric plumes, with the aim of investigating subsurface processes. Using a 3D physical model, we obtained upper limits for the plume abundances of HCN, H$_2$CO, SO$_2$ and CH$_3$OH. If active plume(s) were present, they contained very low abundances of these molecules. Assuming a total gas production rate of $10^{29}$ s$^{-1}$, our H$_2$CO abundance upper limit of $<0.016$\% is more than an order of magnitude less than measured in the Enceladus plume by the Cassini spacecraft, implying a possible chemical difference between the plume source materials for these two icy moons.

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arXiv2024

Variability in Titan's Mesospheric HCN and Temperature Structure as Observed by ALMA

The temperature structure of Titan's upper atmosphere exhibits large variability resulting from numerous spatially and temporally irregular external energy sources, seasonal changes, and the influence of molecular species produced via photochemistry. In particular, Titan's relatively abundant HCN is thought to provide substantial cooling to the upper atmosphere through rotational emission, balancing UV/EUV heating and thermal conduction. Here, we present the analysis of ALMA observations of Titan from 2012, 2014, 2015, and 2017, corresponding to planetocentric solar longitudes of ~34-89$^{\circ}$, including vertical HCN and temperature profiles retrieved from the lower mesosphere through the thermosphere (~350-1200 km; $3\times10^{-2}$-$2\times10^{-8}$ mbar). Throughout the atmosphere, temperature profiles differ by 10 to 30 K between observations approximately one Earth year apart, particularly from 600-900 km. We find evidence for a large imbalance in Titan's upper atmospheric energy budget between 2014 and 2015, where the mesospheric thermal structure changes significantly and marks the transition between a mesopause located at ~600 km ($2\times10^{-4}$ mbar) and at ~800 km ($3\times10^{-6}$ mbar). The retrieved HCN abundances vary dramatically during the 2012 to 2017 time period as well, showing close to 2 orders of magnitude difference in abundance at 1000 km. However, the change in HCN abundance does not appear to fully account for the variation in mesospheric temperatures over the $L_S\sim$34-89$^{\circ}$ period. These measurements provide additional insight into the variability of Titan's mesospheric composition and thermal structure following its 2009 vernal equinox, and motivate continued investigation of the origins of such rapid changes in Titan's atmosphere throughout its seasonal cycle.

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arXiv2022

Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations

The presence of phosphine (PH$_3$) in the atmosphere of Venus was reported by Greaves et al. (2021a), based on observations of the J=1-0 transition at 267 GHz using ground-based, millimeter-wave spectroscopy. This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of atmospheric phosphorous-bearing gases. Here we present results from a search for PH$_3$ on Venus using the GREAT instrument aboard the SOFIA aircraft, over three flights conducted in November 2021. Multiple PH$_3$ transitions were targeted at frequencies centered on 533 GHz and 1067 GHz, but no evidence for atmospheric PH$_3$ was detected. Through radiative transfer modeling, we derived a disk-averaged upper limit on the PH$_3$ abundance of 0.8 ppb in the altitude range 75-110 km, which is more stringent than previous ground-based studies.

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arXiv2022

The Isotopic Links from Planet Forming Regions to the Solar System

Isotopic ratios provide a powerful tool for understanding the origins of materials, including the volatile and refractory matter within solar system bodies. Recent high sensitivity observations of molecular isotopologues, in particular with ALMA, have brought us new information on isotopic ratios of hydrogen, carbon, nitrogen and oxygen in star and planet forming regions as well as the solar system objects. Solar system exploration missions, such as Rosetta and Cassini, have given us further new insights. Meanwhile, the recent development of sophisticated models for isotope chemistry including detailed gas-phase and grain surface reaction network has made it possible to discuss how isotope fractionation in star and planet forming regions is imprinted into the icy mantles of dust grains, preserving a record of the initial isotopic state of solar system materials. This chapter reviews recent progress in observations of molecular isotopologues in extra-solar planet forming regions, prestellar/protostellar cores and protoplanetary disks, as well as objects in our solar system -- comets, meteorites, and planetary/satellite atmospheres -- and discusses their connection by means of isotope chemical models.

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arXiv2021

Detection of Dynamical Instability in Titan's Thermospheric Jet

Similar to Earth, Saturn's largest moon, Titan, possesses a system of high-altitude zonal winds (or jets) that encircle the globe. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in August 2016, Lellouch et al. (2019) discovered an equatorial jet at much higher altitudes than previously known, with a surprisingly fast speed of up to ~340 m/s, but the origin of such high velocities is not yet understood. We obtained spectrally and spatially resolved ALMA observations in May 2017 to map Titan's 3D global wind field and compare our results with a reanalysis of the August 2016 data. Doppler wind velocity maps were derived in the altitude range ~300-1000 km (from the upper stratosphere to the thermosphere). At the highest, thermospheric altitudes, a 47% reduction in the equatorial zonal wind speed was measured over the 9-month period (corresponding to L_s = 82-90 degrees on Titan). This is interpreted as due to a dramatic slowing and loss of confinement (broadening) of the recently-discovered thermospheric equatorial jet, as a result of dynamical instability. These unexpectedly-rapid changes in the upper-atmospheric dynamics are consistent with strong variability of the jet's primary driving mechanism.

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arXiv2020

Detection of CH$_3$C$_3$N in Titan's Atmosphere

Titan harbors a dense, organic-rich atmosphere primarily composed of N$_2$ and CH$_4$, with lesser amounts of hydrocarbons and nitrogen-bearing species. As a result of high sensitivity observations by the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6 ($\sim$230-272 GHz), we obtained the first spectroscopic detection of CH$_3$C$_3$N (methylcyanoacetylene or cyanopropyne) in Titan's atmosphere through the observation of seven transitions in the $J = 64\rightarrow63$ and $J = 62\rightarrow61$ rotational bands. The presence of CH$_3$C$_3$N on Titan was suggested by the Cassini Ion and Neutral Mass Spectrometer detection of its protonated form: C$_4$H$_3$NH$^+$, but the atmospheric abundance of the associated (deprotonated) neutral product is not well constrained due to the lack of appropriate laboratory reaction data. Here, we derive the column density of CH$_3$C$_3$N to be (3.8-5.7)$\times10^{12}$ cm$^{-2}$ based on radiative transfer models sensitive to altitudes above 400 km Titan's middle atmosphere. When compared with laboratory and photochemical model results, the detection of methylcyanoacetylene provides important constraints for the determination of the associated production pathways (such as those involving CN, CCN, and hydrocarbons), and reaction rate coefficients. These results also further demonstrate the importance of ALMA and (sub)millimeter spectroscopy for future investigations of Titan's organic inventory and atmospheric chemistry, as CH$_3$C$_3$N marks the heaviest polar molecule detected spectroscopically in Titan's atmosphere to date.

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arXiv2019

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

The Cassini mission performed 127 targeted flybys of Titan during its 13-year mission to Saturn, culminating in the Grand Finale between April-September 2017. Here we demonstrate the use of the Atacama Large Millimeter/submillimeter Array (ALMA) to continue Cassini's legacy for chemical and climatological studies of Titan's atmosphere. Whole-hemisphere, interferometric spectral maps of HCN, HNC, HC3N, CH3CN, C2H3CN, C2H5CN and C3H8 were obtained using ALMA in May 2017 at moderate (~0.2'', or 1300 km) spatial resolution, revealing the effects of seasonally-variable chemistry and dynamics on the distribution of each species. The ALMA sub-mm observations of HCN and HC3N are consistent with Cassini infrared data on these species, obtained in the same month. Chemical/dynamical lifetimes of a few years are inferred for C2H3CN and C2H5CN, in reasonably close agreement with the latest chemical models incorporating sticking of C2H5CN to stratospheric aerosol particles. ALMA radial limb flux profiles provide column density information as a function of altitude, revealing maximum abundances in the thermosphere (above 600 km) for HCN, HNC, HC3N and C2H5CN. This constitutes the first detailed measurement of the spatial distribution of HNC, which is found to be confined predominantly to altitudes above 730 $\pm$ 60 km. The HNC emission map shows an east-west hemispheric asymmetry of (13$\pm$3)%. These results are consistent with very rapid production (and loss) of HNC in Titan's uppermost atmosphere, making this molecule an effective probe of short-timescale (diurnal) ionospheric processes.

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arXiv2018

Spatial Variations in Titan's Atmospheric Temperature: ALMA and Cassini Comparisons from 2012 to 2015

Submillimeter emission lines of carbon monoxide (CO) in Titan's atmosphere provide excellent probes of atmospheric temperature due to the molecule's long chemical lifetime and stable, well constrained volume mixing ratio. Here we present the analysis of 4 datasets obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA) from 2012 to 2015 that contain strong CO rotational transitions. Utilizing ALMA's high spatial resolution in the 2012, 2014, and 2015 observations, we extract spectra from 3 separate regions on Titan's disk using datasets with beam sizes of ~0.3''. Temperature profiles retrieved by the NEMESIS radiative transfer code are compared to Cassini Composite Infrared Spectrometer (CIRS) and radio occultation science results from similar latitude regions. Small seasonal variations in atmospheric temperature are present from 2012 to 2015 in the stratosphere and mesosphere (~100-500 km) of spatially resolved regions. We measure the stratopause (320 km) to increase in temperature by 5 K in northern latitudes from 2012-2015, while temperatures rise throughout the stratosphere at lower latitudes. While retrieved temperature profiles cover a range of latitudes in these observations, deviations from CIRS nadir maps and radio occultation measurements convolved with the ALMA beam-footprint are not found to be statistically significant, and discrepancies are often found to be less than 5 K throughout the atmosphere. ALMA's excellent sensitivity in the lower stratosphere (60-300 km) provides a highly complementary dataset to contemporary CIRS and radio science observations. The demonstrated utility of CO emission lines in the submillimeter as a tracer of Titan's atmospheric temperature lays the groundwork for future studies of other molecular species, as temperature profiles are found to consistently vary with latitude in all three years by up to 15 K.

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arXiv2018

Abundance Measurements of Titan's Stratospheric HCN, HC$_3$N, C$_3$H$_4$, and CH$_3$CN from ALMA Observations

Previous investigations have employed more than 100 close observations of Titan by the Cassini orbiter to elucidate connections between the production and distribution of Titan's vast, organic-rich chemical inventory and its atmospheric dynamics. However, as Titan transitions into northern summer, the lack of incoming data from the Cassini orbiter presents a potential barrier to the continued study of seasonal changes in Titan's atmosphere. In our previous work (Thelen et al., 2018), we demonstrated that the Atacama Large Millimeter/submillimeter Array (ALMA) is well suited for measurements of Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km) through the use of spatially resolved (beam sizes <1'') flux calibration observations of Titan. Here, we derive vertical abundance profiles of four of Titan's trace atmospheric species from the same 3 independent spatial regions across Titan's disk during the same epoch (2012 to 2015): HCN, HC$_3$N, C$_3$H$_4$, and CH$_3$CN. We find that Titan's minor constituents exhibit large latitudinal variations, with enhanced abundances at high latitudes compared to equatorial measurements; this includes CH$_3$CN, which eluded previous detection by Cassini in the stratosphere, and thus spatially resolved abundance measurements were unattainable. Even over the short 3-year period, vertical profiles and integrated emission maps of these molecules allow us to observe temporal changes in Titan's atmospheric circulation during northern spring. Our derived abundance profiles are comparable to contemporary measurements from Cassini infrared observations, and we find additional evidence for subsidence of enriched air onto Titan's south pole during this time period. Continued observations of Titan with ALMA beyond the summer solstice will enable further study of how Titan's atmospheric composition and dynamics respond to seasonal changes.

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arXiv2018

Solar system science with the Wide-Field InfraRed Survey Telescope (WFIRST)

We present a community-led assessment of the solar system investigations achievable with NASA's next-generation space telescope, the Wide Field InfraRed Survey Telescope (WFIRST). WFIRST will provide imaging, spectroscopic, and coronagraphic capabilities from 0.43-2.0 $μ$m and will be a potential contemporary and eventual successor to JWST. Surveys of irregular satellites and minor bodies are where WFIRST will excel with its 0.28 deg$^2$ field of view Wide Field Instrument (WFI). Potential ground-breaking discoveries from WFIRST could include detection of the first minor bodies orbiting in the Inner Oort Cloud, identification of additional Earth Trojan asteroids, and the discovery and characterization of asteroid binary systems similar to Ida/Dactyl. Additional investigations into asteroids, giant planet satellites, Trojan asteroids, Centaurs, Kuiper Belt Objects, and comets are presented. Previous use of astrophysics assets for solar system science and synergies between WFIRST, LSST, JWST, and the proposed NEOCam mission are discussed. We also present the case for implementation of moving target tracking, a feature that will benefit from the heritage of JWST and enable a broader range of solar system observations.

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arXiv2018

Interferometric imaging of Titan's HC$_3$N, H$^{13}$CCCN and HCCC$^{15}$N

We present the first maps of cyanoacetylene isotopologues in Titan's atmosphere, including H$^{13}$CCCN and HCCC$^{15}$N, detected in the 0.9 mm band using the Atacama Large Millimeter/submillimeter array (ALMA) around the time of Titan's (southern winter) solstice in May 2017. The first high-resolution map of HC$_3$N in its $v_7=1$ vibrationally excited state is also presented, revealing a unique snapshot of the global HC$_3$N distribution, free from the strong optical depth effects that adversely impact the ground-state ($v=0$) map. The HC$_3$N emission is found to be strongly enhanced over Titan's south pole (by a factor of 5.7 compared to the north pole), consistent with rapid photochemical loss of HC$_3$N from the summer hemisphere combined with production and transport to the winter pole since the April 2015 ALMA observations. The H$^{13}$CCCN/HCCC$^{15}$N flux ratio is derived at the southern HC$_3$N peak, and implies an HC$_3$N/HCCC$^{15}$N ratio of $67\pm14$. This represents a significant enrichment in $^{15}$N compared with Titan's main molecular nitrogen reservoir, which has a $^{14}$N/$^{15}$N ratio of 167, and confirms the importance of photochemistry in determining the nitrogen isotopic ratio in Titan's organic inventory.

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arXiv2017

Mapping Vinyl Cyanide and Other Nitriles in Titan's Atmosphere Using ALMA

Vinyl cyanide (C$_2$H$_3$CN) is theorized to form in Titan's atmosphere via high-altitude photochemistry and is of interest regarding the astrobiology of cold planetary surfaces due to its predicted ability to form cell membrane-like structures (azotosomes) in liquid methane. In this work, we follow up on the initial spectroscopic detection of C$_2$H$_3$CN on Titan by Palmer et al. (2017) with the detection of three new C$_2$H$_3$CN rotational emission lines at submillimeter frequencies. These new, high-resolution detections have allowed for the first spatial distribution mapping of C$_2$H$_3$CN on Titan. We present simultaneous observations of C$_2$H$_5$CN, HC$_3$N, and CH$_3$CN emission, and obtain the first (tentative) detection of C$_3$H$_8$ (propane) at radio wavelengths. We present disk-averaged vertical abundance profiles, two-dimensional spatial maps, and latitudinal flux profiles for the observed nitriles. Similarly to HC$_3$N and C$_2$H$_5$CN, which are theorized to be short-lived in Titan's atmosphere, C$_2$H$_3$CN is most abundant over the southern (winter) pole, whereas the longer-lived CH$_3$CN is more concentrated in the north. This abundance pattern is consistent with the combined effects of high-altitude photochemical production, poleward advection, and the subsequent reversal of Titan's atmospheric circulation system following the recent transition from northern to southern winter. We confirm that C$_2$H$_3$CN and C$_2$H$_5$CN are most abundant at altitudes above 200 km. Using a 300 km step model, the average abundance of C$_2$H$_3$CN is found to be $3.03\pm0.29$ ppb, with a C$_2$H$_5$CN/C$_2$H$_3$CN abundance ratio of $2.43\pm0.26$. Our HC$_3$N and CH$_3$CN spectra can be accurately modeled using abundance gradients above the tropopause, with fractional scale-heights of $2.05\pm0.16$ and $1.63\pm0.02$, respectively.

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arXiv2015

Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA

We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter array (ALMA). The presence of C$_2$H$_5$CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27 rotational lines from C$_2$H$_5$CN (in 19 separate emission features detected at $>3σ$ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were also obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in Titan's northern (spring) hemisphere, the emission from C$_2$H$_5$CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C$_2$H$_5$CN. Radiative transfer models show that most of the C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)$\times10^{14}$ cm$^{-2}$.

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arXiv2014

ALMA measurements of the HNC and HC$_3$N distributions in Titan's atmosphere

We present spectrally and spatially-resolved maps of HNC and HC$_3$N emission from Titan's atmosphere, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) on 2013 November 17. These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC$_3$N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and atmospheric circulation. Differences between the spectrally-integrated flux distributions of HNC and HC$_3$N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC being concentrated predominantly in the mesosphere and above (at altitudes $z\gtrsim 400$ km), whereas HC$_3$N is abundant at a broader range of altitudes ($z\approx70$-600 km). From spatial variations in the HC$_3$N line profile, the locations of the HC$_3$N emission peaks are shown to be variable as a function of altitude. The peaks in the integrated emission from HNC and the line core (upper-atmosphere) component of HC$_3$N (at $z\gtrsim300$ km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally-variable than previously thought. The spatially-integrated HNC and HC$_3$N spectra are modeled using the NEMESIS planetary atmosphere code and the resulting best-fitting disk-averaged vertical mixing ratio (VMR) profiles are found to be in reasonable agreement with previous measurements for these species. Vertical column densities of the best-fitting gradient models for HNC and HC$_3$N are $1.9\times10^{13}$ cm$^{-2}$ and $2.3\times10^{14}$ cm$^{-2}$, respectively.

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arXiv2009

Titan's Prolific Propane: The Cassini CIRS Perspective

In this paper we select large spectral averages of data from the Cassini Composite Infrared Spectrometer (CIRS) obtained in limb-viewing mode at low latitudes (30S--30N), greatly increasing the path length and hence signal-to-noise ratio for optically thin trace species such as propane. By modeling and subtracting the emissions of other gas species, we demonstrate that at least six infrared bands of propane are detected by CIRS, including two not previously identified in Titan spectra. Using a new line list for the range 1300-1400cm -1, along with an existing GEISA list, we retrieve propane abundances from two bands at 748 and 1376 cm-1. At 748 cm-1 we retrieve 4.2 +/- 0.5 x 10(-7) (1-sigma error) at 2 mbar, in good agreement with previous studies, although lack of hotbands in the present spectral atlas remains a problem. We also determine 5.7 +/- 0.8 x 10(-7) at 2 mbar from the 1376 cm-1 band - a value that is probably affected by systematic errors including continuum gradients due to haze and also an imperfect model of the n6 band of ethane. This study clearly shows for the first time the ubiquity of propane's emission bands across the thermal infrared spectrum of Titan, and points to an urgent need for further laboratory spectroscopy work, both to provide the line positions and intensities needed to model these bands, and also to further characterize haze spectral opacity. The present lack of accurate modeling capability for propane is an impediment not only for the measurement of propane itself, but also for the search for the emissions of new molecules in many spectral regions.

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