Search

We present high resolution spectra of comet C/2017 K2 (PanSTARRS) (hereafter 17K2), obtained using the upgraded high resolution spectrometer of the VLT, CRIRES+. We will show our findings in the (2.8 – 5.3) μm range, searching for primary volatiles (e.g., H2O, HCN, NH3, CO, C2H6, CH4, ...) and studying their evolution as the comet approach the Sun. 17K2 is a long period comet, very active already at record heliocentric distances of 16 au, and represents a unique opportunity to study the composition of a mostly unaltered comet. Comets formed from the material surrounding the proto-Sun about 4.6 billion years ago, and after their formation they were scattered into their current reservoirs [1,2], where the frozen nuclei have preserved most of the chemical and mineralogical properties linked to their formation site until today. Probing the chemical diversity in comets may thus unveil the processes that were in effect within the mid-plane of our proto-planetary disk, and test the hypothesis that comets may have contributed in delivering water and prebiotics to the early Earth [3]. Among other techniques, the composition of active comets can be studied from ground based telescopes using high resolution spectroscopy in the infrared (IR - 3 to 5 μm), where it is possible to observe emission lines produced by solar-pumped fluorescence of primary species, i.e., molecules released directly from the nucleus. High spectral and spatial resolutions are necessary to resolve different molecular species in the spectra, to study their distribution within the coma and to separate emission lines of the comet from their counterpart in the atmosphere. Comet 17K2 is in excellent observing conditions in 2022, allowing infrared high resolution studies. The comet shows already activity, probably driven by CO and other hyper-volatiles that can sublimate at distances from the Sun larger than 5 au [4,5]. Discovered in 2017 at about 16 au from the Sun [6], it is most likely entering the inner solar system for the first time, and its observation offers a unique opportunity to study its mostly unaltered material. We will present the results obtained from different spectra acquired using CRIRES+ at ESO-VLT at various epochs. We acquired comprehensive high-resolution spectra of the comet as it progressively moved towards the Sun, with the goal of monitoring the evolution of sublimating material with the heliocentric distance. In particular, we have granted time at the beginning of May, beginning of July, and end of August 2022, with the Sun-17K2 distance varying from about 3.5 to 2.3 au. In this heliocentric range, the comet is crossing the CO to H2O ice sublimation regime [7]. Data are reduced using custom semi-automated procedures (see [8] and references therein) that allow a fast analysis of the spectra. Spectral calibration and compensation for telluric absorption are achieved by comparing the data with highly accurate atmospheric radiance and transmittance models obtained with PUMAS/PSG [9]. Flux calibration is obtained using the spectra of a standard star observed closely in time with the comet, and reduced with the same algorithms. Production rates and relative abundances (i.e. mixing ratios with respect to water) of different primary species in the coma are obtained using state-of-the-art fluorescence models (see for example [10] and [11]). The molecular abundances found in this comet will be compared to reference median values retrieved for the comet population [12] and with the abundances found in other Oort Cloud Comets. References: 1. Gomes, R., et al., 2005, Nature, 435, 446 – 2. Morbidelli, A., et al., 2007, AJ, 134, 1790 – 3. Mumma, M. J., Charnley, S.B. 2011, Ann. Rev. Astron. Astroph., 49 – 4. Jewitt, D., et al., 2019, AJ, 157, 65 – 5. Yang, B., et al., 2021, ApJL, 914, L17 – 6. Wainscoat, R. J., et al., 2017, CBET, 4393, 1 – 7. Jewitt, D., et al., 2007, Protostars and Planets V. Univ. Arizona Press, Tucson, 863 – 8. Lippi, M., et al., 2020, AJ, 159, 157 – 9. Villanueva, G. L., et al., 2018, JQSRT, 217, 86 – 10. Villanueva, G. L., et al., 2012b, JQSRT, 113, 202 – 11. Villanueva, G. L., et al., 2011b, JGRE, 116, E08012 – 12. Lippi, M., et al., 2021, AJ, 162, 74.

The two infrared spectrometers onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft, the Atmospheric Chemistry Suite (ACS) and the Nadir and Occultation for MArs Discovery (NOMAD) have been providing observations since April 2018 and are a unique source of information to unveil the vertical structure of the atmosphere of Mars in a level of detail never previously seen. In this work, we focus on understanding how the NOMAD data can be used to constrain the isotopic composition of atmospheric carbon. This has been measured on several occasions on the surface [1], and in near-surface atmospheric samples [2,3], and is of great interest to trace the history of atmospheric loss and differences with other inner solar system bodies. Additionally, proper characterization of the uncertainties of derived isotopic ratios is a very important proxy towards a better understanding of the instrument limitations and performances. NOMAD is a 3-channel spectrometer working in the spectral ranges 0.2-0.65 μm (UVIS channel) and 2.2-4.3 μm (SO and LNO channels). The data taken by the Solar Occultation (SO) channel measurements in the infrared channel is used in this work. SO is an echelle grating spectrometer with relatively high spectral resolution (λ/dλ~17,000), and an Acousto Optical Tunable Filter (AOTF) used to instantaneously switch the observed diffraction orders, with a typical cycle of 1 second. This yields a vertical sampling of less than 1 km from the surface to 250 km of altitude. In this work we use NOMAD Full Scan data to gather appropriate information about 12C, 13C and temperature. We use full scans acquired between Apr/2018 (LS ~160 MY34) and Dec/2021 (LS ~137 MY36), a type of data in which many diffraction orders are measured along the vertical. From these we derive the average rotational temperature along the line of sight with an accuracy of about 5 K [4], which then can be used to derive the column density at a specific tangent altitude – in particular - of 12CO2 and 13CO2. The accuracy of the retrievals is also possible thanks to recent calibration efforts for the AOTF transfer function and the ILS of the SO channel, which are fully parameterized with the diffraction order [5]. Retrievals are performed using the Planetary Spectrum Generator (PSG, [6,7]), a full general purpose radiative transfer code, which contains a dedicated retrieval module based on Optimal Estimation and is configured with all the instrumental parameters of NOMAD SO natively accounted for. Once all the retrievals are completed, we filter the values by excluding values with low SNR and those spectra where the intensity of the spectral lines is smaller than 5 times the radiometric noise. By averaging the different measurements, is possible to get an average vertical profile of the C isotopic ratio. In this work we specifically explore analytical criteria to quantify the uncertainty of the 13C/12C at each altitude and whether the dispersion in the retrieved values is of stochastic nature - meaning that it is not dominated by systematics - or it is related to the limitations of the instrument and the accuracy of spectroscopy. In particular, we conduct specific analyses that quantify the expected uncertainty of a single measurement depending on the observed column of CO2 and the prescribed radiometric noise. We find that the 13C/12C in CO2 below 50 km can be consistently quantified, complementing the current results by ACS [8] and MSL [2,3]. We estimate the 13C/12C in CO2 in the lower atmosphere (10-25 km) in 1.027+/-0.030 VPDB, largely consistent with the value observed by MSL in surface minerals and the atmosphere. The value is fairly constant throughout the atmosphere with oscillations within the error bars. Upper atmosphere values (>50 km) do not show any inconsistency with the values reported using ACS observation above 60 km [8]. The precision of the measurement is limited by the radiometric SNR, and by the precision with which the spectral continuum can be quantified, which plays an essential role when spectral lines are close to saturation. By combining several lines, the accuracy of the atmospheric temperature is not the main limiting factor. References [1] House et al. (2022), “Depleted carbon isotope compositions observed at Gale crater, Mars”, PNAS, doi: 10.1073/pnas.2115651119.[2] Webster et al. (2013), “Isotope Ratios of H, C, and O in CO2 and H2O of the Martian Atmosphere”, Science, doi: 10.1126/science.1237961.[3] Mahaffy et al. (2013), “Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover”, Science, doi: 10.1126/science.1237966.[4] Liuzzi et al. (2021), “First Detection and Thermal Characterization of Terminator CO2 Ice Clouds With ExoMars/NOMAD”, Geophys. Res. Lett., doi: 10.1029/2021GL095895.[5] Villanueva et al. (2022), Under review, Geophys. Res. Lett.[6] Villanueva et al. (2018), “Planetary Spectrum Generator: An accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets”, J. Quant. Spectrosc. Rad. Trans., doi: 10.1016/j.jqsrt.2018.05.023.[7] Villanueva et al. (2022), Handbook of the Planetary Spectrum Generator, ISBN: 978-0-578-36143-7.[8] Alday et al. (2021), Isotopic Composition of CO2 in the Atmosphere of Mars: Fractionation by Diffusive Separation Observed by the ExoMars Trace Gas Orbiter, J. Geophys. Res., doi: 10.1029/2021JE006992.

The first detection of HCl in the atmosphere of Mars was recently achieved by the IR spectrometers (ACS and NOMAD) onboard the ExoMars Trace Gas Orbiter (TGO), revealing the presence of chlorine species in the Martian atmosphere. The two instruments report HCl abundance ranging from 1 to 4 ppbv, for Ls between 250 and 350 [1,2,3,4]. Perchlorate salts [5] (ClO4-) and chloride-bearing minerals [6] are known to be widely present on the surface, so lifted surface materials may be involved in the release of Cl in the atmosphere.The TGO measurements showed that HCl detections are mainly confined in the specific period around the southern summer season, leading to a possible chemical pathway connected with lifted dust and the release of water vapor from the southern polar cap. Yet sources and sinks of Martian HCl are still unknown. Orbital and rover measurements do not permit rapid hemispheric mapping, but this is achieved with ground-based observatories in a few hours, permitting accurate measurements of the global distribution of trace gases and fundamental understanding of the distribution of present volatile reservoirs on Mars, and allowing to quantify their evolution and atmospheric loss.Importantly, with the advent of new near-IR high resolution instrumentation (e.g., Keck/NIRSPEC-II and NASA-IRTF/iSHELL) ground-based observatories are much more sensitive than before, enabling a significant contribution to understand the origin and the variability of organics on Mars. With their much broader spectral grasp, these new high resolution spectrometers also permit simultaneous mapping of trace gases, and isotopes. In 2021 we started a comprehensive Mars observing campaign with the NASA IRTF/iSHELL spectrometer.We performed full rapid hemispheric mapping of water, trace gases, HCl and its isotopes, with a highly temporal cadence and extended seasonal coverage from the beginning of the Martian Spring Equinox Ls ~ 356, in early Feb/2021 to about the Summer Solstice Ls ~ 79 at the end of Jul/2021.This strategic seasonal sampling has the primary objective to properly characterize the Martian atmospheric water cycle, since the polar cap vaporizes between Ls = 0 – 70. Moreover, HCl will be searched close to the Spring Equinox, enabling further investigations of the newly suggested correlation between the release of water and HCl evidenced by TGO measurements [1,2,3,4]. By combining the 2D-maps obtained with iSHELL with the vertical profiles measured by TGO, we will obtain a novel 3D-picture of H2O, HDO HCl and trace gases, and their circulation. References[1] Korablev, O., Olsen, K. S., Trokhimovskiy, A., Lefèvre, F., Montmessin, F., Fedorova, A. A., et al. (2021). Transient HCl in the atmosphere of Mars. Science Advances, 7, eabe4386. https://doi.org/10.1126/sciadv.abe4386[2] Olsen, K. S. et al. "Seasonal reappearance of HCl in the atmosphere of Mars during the Mars year 35 dusty season", Astronomy & Astrophysics, A161, Doi:10.1051/0004-6361/202140329 (2021)[3] Aoki, S., et al. (co-authors Villanueva, G., Liuzzi, G.) “Annual appearance of hydrogen chloride on Mars and a striking similarity with the water vapor vertical distribution observed by TGO/NOMAD”, Geophys. Res. Letters, 48, doi:10.1029/2021GL092506.[4] Liuzzi G., Villanueva, G., Faggi, S., Kofman, V. et al. “Probing the Atmospheric Cl Isotopic Ratio on Mars: Implications for Planetary Evolution and Atmospheric Chemistry”, Geophys. Res. Letters, 48, doi:10.1029/2021GL092650.[5] Hecht et al., 2009, Science, 325, 64–67.[6] Osterloo et al., 2010, J. Geophys. Res., 115, E10012.

Molecular features in the spectra of exoplanet atmospheres are diagnostics for the physical and chemical conditions present and are essential elements in understanding planet formation and evolution. The Planetary Spectrum Generator contains all of the elements required these spectra. Aside from the modulations by the atmosphere, this includes stellar fluxes, geometrical considerations, as well as telescope and detector characteristics to assess the noise level of the observations. Molecular contributions in atmospheric emission or transmission spectra, are calculated using molecular energy levels, transition strengths, and line broadening parameters. Combining spectroscopic information from several databases is required to enable accurate calculations across the parameter space where exoplanetary atmospheres are found. Over the recent years, we have collected line broadening parameters, state and transitions energies, and line intensities from HITRAN, HITEMP and ExoMol to enable the calculation of absorption spectra in all types of environments, ranging from N2-broadened such as the Earth, to CO2-broadened Mars, and hydrogen/helium broadened hot-Jupiters and brown dwarfs. The combination of databases allows calculations of molecular absorption at high temperatures and at high energies (i.e., into the near-infrared and visible). In our previous work [Kofman and Villanueva 2021], the ExoMol line lists of H2O and HDO were ingested. The need of using more the more complete theoretical databases was demonstrated in high-temperature exoplanet atmospheres, as well as in the detectability of HDO, which absorbs in an absorbance minimum of H2O. Figure 1 shows the absorbance of water at 880 K. Absorption was calculated using both HITRAN and the variational Pokazatel/VTT databases at the natural abundances of the isotopes. Note that the HDO absorbance maximum coincides with a minimum in H2O, which is a region where HITRAN is relatively incomplete for higher temperatures. In atmospheres where water has a significant presence an important component of the absorbance is the water continuum, described by the MT_CKD formalism. Although not as strong as the typical ro-vibrational features, the continuum adds a significant amount of opacity between the main features, which is especially relevant when considering that this is where one often searches for other molecules. We show that the opacity can be well described using typical collision induced absorption parameterization and demonstrate its importance. Figure 1 shows the contrast ratio of GJ 1214b transiting in front of its host star, with MT_CKD-based H2O-H2O collisional induced absorption neglected/included. For this simulation, the atmosphere consists of 83% He, 16% H2, 670 ppm H2O, and 485 ppm CH4. In this talk, in addition to the cases described above, we will highlight where in the parameters space of exoplanet atmospheres the new additions are particularly relevant. We will look at warm transiting exoplanets, water worlds, and hot-Jupiters at high-resolution using cross-correlation studies.

We will present our observations of the bright comet C/2021 A1 (Leonard) with the newly upgraded CRIRES+ high resolution IR spectrometer mounted on the ESO VLT in Paranal, Chile. C/2021 A1 is a long period comet that reached perihelion on January 3, 2022, at 0.62 AU from the Sun. It is one of the brightest comet of recent years, reaching a visual magnitude of 3 close to perihelion (Seiichi Yoshida's webpage). Originating from the cold Oort Cloud were it spent most of its dynamical lifetime, C/2021 A1 has presumably experienced little transformation or activity, keeping a pristine memory of the chemistry of the protoplanetary disk at the place where it formed. The sublimation of the nucleus volatile ices during its close approach to the Sun was an unique opportunity to have a glimpse at C/2021 A1 composition through the fluorescence of the species in its coma. We observed the comet with CRIRES+ for three nights close to its perihelion at 0.62 AU between December 28, 2021, and January 3, 2022, and derived the production rates of several parent volatiles including H2O, CH4, C2H6, H2CO and CH3OH. During the period of observation, the proximity to the Sun triggered a series of outbursts in C/2021 A1 (Jehin et al, 2022), enhancing the release of material in the coma and ultimately leading to the disintegration of the comet. The observations were made nodding on sky to subtract telluric features in the spectra, and the spectra were later corrected for atmospheric absorption (dominant in the NIR region) and wavelength calibrated by an atmospheric transmittance model computed with the ESO MOLECFIT software (Smette 2015). A flux reference star was also observed to calibrate the target's flux. The chemical composition of the comet will be compared to other comets from the same and other dynamical groups. The ongoing effort to build a chemical taxonomy of comets (A’Hearn et al., 1995; Dello Russo et al., 2016; Lippi et al., 2021) and compare it to the established dynamical classification underlies the need to better constrain the chemical composition of an increasing number individual comets. The high resolution IR spectrometer CRIRES+ is an upgrade of the CRIRES spectrometer into a cross-dispersed spectrograph, increasing the simultaneously covered wavelength by a factor 10 (Dorn et al, 2020). It has been available at the VLT since October 2021, offering a resolving power up to 100000 with a 0.2'' slit between 1 and 5 µm. This first observation of a comet with CRIRES+ will also serve to demonstrate its capabilities to target such objects in the IR.

Introduction The large enrichments of D/H currently measured in atmospheric water suggest that a large fraction, beyond 80%, of this water was lost over time1,2, and Ar and O isotopic ratios measured with MAVEN3 and TGO4 indicate Mars has lost a large fraction of its atmosphere. As we attempt to trace back the history of water on Mars, it is unknown how much water remains locked in non-labile/sub-surface reservoirs, and an important question is whether all current labile reservoirs have evolved in the same way and undergone extensive exchange. New measurements with TGOWe have analyzed data over the entirety a Martian year as measured with TGO/NOMAD, which probed the release of water from the two polar caps using the instrument’s solar occultation mode. Specifically, the measurements presented here have been collected by the NOMAD10 instrument suite onboard TGO. The data were collected employing the Solar Occultation (SO) channel/mode of the instrument. Interpretation and extraction of molecular abundances from the calibrated data is done by employing the Planetary Spectrum Generator (PSG, https://psg.gsfc.nasa.gov)11, and as reported in 12. The model employs a layer-by-layer line-by-line method in a spherical and refractive geometry. We employ the latest linelists for H2O, HDO, and CO2 as compiled in the HITRAN-2020 database13, which are complemented to include the latest H2O and HDO broadening coefficients for a CO2 atmosphere14,15. Probing the seasonal release from both capsDuring Martian Year 34, the planet was engulfed in a global dust storm (GDS) that greatly perturbed the temperature and vertical structure of the Martian atmosphere. In addition, the lingering effects of the GDS were joined by a large regional dust storm that started during late southern summer (LS 320). These two major events greatly affected the climate of Mars, primarily leading to a strong increase in atmospheric temperature, a substantial rise in altitude of the hygropause, and subsequent transport of water to unexpectedly high altitudes16–22. Interestingly, during the GDS when the northern hemisphere was in the winter season, the climate was substantially warmer there than normal23–25, leading to high-altitude water also in the northern hemisphere. Typically, the largest seasonal water columns are observed during summer in the northern hemisphere26, and that may be true in MY35, but the vertical profile of water is highly compact (confined to altitudes below 20 km), even at the peak of northern summer (LS 90-130). In all cases (all seasons and regions of the planet) the D/H declines quickly above the hygropause, from a nominal value above 5 VSMOW to a very low value near Discussions and conclusionsThe new results presented here, which probe the vertical profiles of water and D/H for both seasonal caps, together with previous ground-based and orbital measurements, suggest a common and highly enriched value for this labile reservoir of water. Atmospheric D/H behaves as an integrator of the differential individual atomic (H and D) escape rates, and therefore without any new supply of water into the system, the D/H of the labile sources will continue to increase. Among other phenomena, the chaotic changes in obliquity that Mars has experienced, and the corresponding impact on climate and regions of ice stability28,29, could lead to large exchanges between the reservoirs and further homogenization of the D/H across the planet. Thus, the D/H value of the polar caps could be similar to the modern labile D/H value observed in the seasonal releases. References1. Jakosky, B. M. Annual Review of Earth and Planetary Sciences 49, 71–93 (2021).2. Villanueva, G. L. et al.. Science 348, 218–221 (2015).3. Jakosky, B. M. et al. Science (2017) doi:10.1126/science.aai7721.4. Alday, J. et al. JGR: Planets 126, e2021JE006992 (2021).5. Scheller, E. L., et al. Science 372, 56–62 (2021).6. Plaut, J. J. et al. Science 316, 92 (2007).7. Zuber, M. T. et al. Science 282, 2053 (1998).8. Byrne, S. & Murray, B. C. JGR: Planets 107, 11-1-11–12 (2002).9. Fishbaugh, K. E. & Head, J. W. Icarus 174, 444–474 (2005).10. Vandaele, A. C. et al. Planetary and Space Science 119, 233–249 (2015).11. Villanueva, G. L., et al. JQSRT 217, 86–104 (2018).12. Villanueva, G. L. et al. Science Advances (2021) doi:10.1126/sciadv.abc8843.13. Gordon, I. E. et al. JQSRT 107949 (2022) doi:10.1016/j.jqsrt.2021.107949.14. Devi, V. M. et al. JQSRT 187, 472–488 (2017).15. Régalia, L. et al.JQSRT 231, 126–135 (2019).16. Aoki, S. et al. JGR: Planets 124, 3482–3497 (2019).17. Belyaev, D. A. et al. GRL 48, e2021GL093411 (2021).18. Chaffin, M. S. et al. Nat Astron 5, 1036–1042 (2021).19. Heavens, N. G. et al. Nature Astronomy 2, 126–132 (2018).20. Holmes, J. A. et al. Earth and Planetary Science Letters 571, 117109 (2021).21. Neary, L. et al. GRL 47, e2019GL084354 (2020).22. Stone, S. W. et al. Science (2020) doi:10.1126/science.aba5229.23. Daerden, F. et al. JGR: Planets n/a, e2021JE007079 (2022).24. Montabone, L. et al. JGR: Planets 125, e2019JE006111 (2020).25. Rossi, L. et al. GRL 48, e2020GL090962 (2021).26. Crismani, M. M. J. et al. JGR: Planets 126, e2021JE006878 (2021).27. Laskar, J. et al. Icarus 170, 343 (2004).28. Jakosky, B. M., Henderson, B. G. & Mellon, M. T. JGR: Planets 100, 1579–1584 (1995).29. Levrard, B., Forget, F., Montmessin, F. & Laskar, J. JGR: Planets 112, (2007).

Introduction: ESA’s upcoming Comet Interceptor (CI) mission will be the first to visit a long period, potentially dynamically new, comet that will consist of some of the most primitive material from the beginning of our Solar System [1]. Part of CI’s payload includes the Modular InfraRed Molecular and Ices Sensor (MIRMIS) which aims to map the thermal and compositional variation of the comet’s nucleus and coma. MIRMIS is compromised of a near-infrared hyperspectral imager (NIR, 0.9-1.6 µm), a mid-infrared point spectrometer (MIR, 2.5 – 5 µm) and, the focus of this study, a multispectral thermal imager (TIRI, 6-25 µm). TIRI’s instrument design includes one central broadband thermal imaging channel (6-25 µm) and 2 identical sets of eight narrow-band channels situated orthogonal to each other to accommodate the instrument orientation as it changes upon closest approach to the comet (Fig.1). This configuration will allow for optimal comparison between views of the comet, and analysis of photometric effects. To maximize the science return pertinent to the mission objectives, we investigated TIRI’s ability to retrieve both temperature and composition using its originally proposed filter set, described in Table 1, and new alternative filter sets. Table 1: Summation of bandpass centers for filter sets. In blue is the original baseline filter set, and those underneath (yellow and green) show proposed filter sets tested for improved science return. Starred set is the proposed ‘new baseline’. Figure 1 : Filter layout on TIRI Methods: To optimize TIRI’s narrow-band filter set, we used both synthetic nucleus spectral targets and laboratory measured analogue minerals and meteorite spectra to understand TIRI’s detection capabilities. In addition to the proposed baseline filter set, several others were proposed that consisted of band-centers evenly spaced along TIRI’s range; band-centers concentrated near 9-11 µm (a region rich in silicate features); or a mix of the two. Synthetic Spectral Analysis: Twelve synthetic spectra were generated with the Planetary Spectrum Generator (PSG) [2]. These included six featureless spectra made of single or mixed temperature blackbodies and six spectral mixtures composed of crystalline (fayalite or enstatite) and amorphous (pyroxene) silicates convolved with single or mixed temperature blackbodies. Mixed temperature blackbodies were used to account for nucleus roughness and/or pixel anisothermality. The silicate endmembers used in this study were chosen based on identified minerals of comets Tempel 1 and Hale-Bopp [3-5]. For these simulations we assumed fixed resolving power to create synthesized spectra with a specific pixel-width that already accounted for TIRI noise performance. Six filter sets were tested as defined in Table 1 (yellow). The simulated retrievals included realistic instrument noise (noise-equivalent-power) and were performed using the Retrieval Module of the PSG [5]. We used this tool to test the ability of each filter set to retrieve a sequence of information about each original synthetic spectrum: 1) temperature; 2) temperature + amorphous pyroxene; 3) temperature + crystalline fayalite; 4) temperature + crystalline enstatite; 5) temperature + crystalline fayalite and enstatite; and 6) temperature + all three silicates (Fig. 2). These retrievals showed that temperature of the featureless spectra was always reliably determined independent of filter set. For the silicate spectra, temperature was always retrieved (±1 K) if >250 K, but spectral shape determination, had a dependence on filter set. Filter set S2 (Table 1, Fig.2 blue) was determined to most accurately identify compositional features. Figure 2. Summary of the final retrieval of temperature and composition (T & three silicates) for the 6 spectra with spectral shape (rows) using the 6 filter sets (columns) defined in Table 1. The last column on the right shows the original high-resolution spectra. Laboratory Spectral Analysis: We examined laboratory spectra of minerals and meteorites likely to be present/analogous to the anticipated primitive comet. These include minerals used in the OSIRIS-REx collection [6] and carbonaceous meteorites from [7]. From these, we identified several key features for compositional determination generally centered within 8-12 µm (Subset in Table 1). We included a set of mineral mixtures with known amorphous content from [8] to test the filter set ability to identify crystalline content of the material. Differences were subtle at low amorphous content and unlikely to be captured at this spectral resolution. Another set included hydrated/altered meteorites from [7]. Tested filter sets captured the overall spectral shape of the meteorite composition and including longer wavelengths (12-15 µm region) improved differentiation of hydrous alteration. It was determined that TIRI alone would be unable to quantify surface ice content, but hydration of surface mineralogy may be detectable. Figure 3. Minerals from the OSIRIS-REx collection [6] and lizardite (unpublished) at laboratory resolution, TIRI baseline, and filter sets defined in Table 1. Discussion: The synthetic analysis showed that filters covering a large range is necessary to capture both temperature and spectral shape of the target comet. The laboratory analysis showed that, while a concentrated filter set was better at distinguishing minute differences between compositions, a wider range of filters can still provide adequate qualitative spectral information to achieve TIRI’s science objectives. We thus propose shifting to the new filter set that encompasses a slightly smaller range (8-22 µm) to retrieve temperatures and to better capture mid-range compositional features (Table 1, starred set). Investigations will continue to incorporate a larger range of compositional spectra into the synthetic analysis model to better understand possible instrument performance and further explore the challenges of compositional unmixing for our target comet. Acknowledgments: We thank the entire Comet Interceptor team for their inputs into this analysis, and the use of online databases including PSG & RELAB. References: [1] Snodgrass C. et al (2019) Nat Commun 10, 5418. [2] Villanueva G. L. et al., (2018) JQS&RT 217, 86-104. [3] Lisse C. M. et al., (2006) Icarus, 313, 635-640 [4] Lisse C. M. et al., (2007) Icarus, 191(2), 223-240. [5] Lisse C. M. (2008) Icarus 195(2), 941-944. [6] Donaldson Hanna K. L. et al. (2021) JGRP 126(2) [7] Bates H. J. et al. (2021) JGRP 126 [8] Donaldson Hanna K. L. et al. (2018) LPSC 49 #1867

Upon its discovery in 2020 March, we requested Director Discretionary Time (DDT) at the NASA/IRTF facility to observe comet C/2020 F3 (NEOWISE), with the high-resolution spectrograph iSHELL. The comet approached the Sun, down to 0.3 au, in early 2020 July, providing a spectacular perihelion passage and revealing itself as one of the brightest comets that have appeared in the northern hemisphere in recent decades. Daytime observations with iSHELL/IRTF were performed to study the comet immediately after its perihelion passage, from 9 July to 1 August. In early August, a DDT at Keck Observatory was requested to continue following the comet with NIRSPEC 2.0. We acquired comprehensive high-resolution spectra of the comet as it progressively retreated from perihelion. We detected many cometary emission lines in the (2.8–5.3) μm range, identifying 12 molecular species: 9 primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, and H2CO) and 3 product species (CN, NH2, OH). In this paper, we present the analysis and discussion of the molecular abundances found in this comet, and we compare them to reference median values for Oort Cloud Comets. Measured molecular mixing ratios showed drastic changes during our observing campaign, which spanned nearly one month from 2020 July 9 to August 6. Here, we provide a detailed discussion of the molecular spatial distributions and their role in identifying the presence of extended sources in the coma. Our investigations provided evidence for the heterogeneous chemical composition of the comet’s nucleus.

The detection of phosphine (PH3) in the atmosphere of Venus has been recently reported based on millimeter-wave radio observations (Greaves et al. 2020), and its re-analyses (Greaves et al. 2021a/b). In this Matters Arising we perform an independent reanalysis, identifying several issues in the interpretation of the spectroscopic data. As a result, we determine sensitive upper-limits for PH3 in Venus' atmosphere (>75 km, above the cloud decks) that are discrepant with the findings in G2020 and G2021a/b. The measurements target the fundamental first rotational transition of PH3 (J=1-0) at 266.944513 GHz, which was observed with the James Clerk Maxwell Telescope (JCMT) in June 2017 and with the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2019. This line's center is near the SO2 (J=309,21-318,24) transition at 266.943329 GHz (only 1.3 km/s away from the PH3 line) which represents a potential source of contamination. The JCMT and ALMA data, as presented in G2020, are at spectral resolutions comparable to the frequency separation of the two lines. Moreover, the spectral features identified are several km/s in width, and therefore do not permit distinct spectroscopic separation of the candidate spectral lines of PH3 and SO2. We present the radiative transfer modelling we have performed and then discuss the ALMA and JCMT analyses in turn.

Following the recent detection of HCl in the atmosphere of Mars by ExoMars/Trace Gas Orbiter, we present here the first measurement of the 37Cl/35Cl isotopic ratio in the Martian atmosphere using a set of Nadir Occultation for MArs Discovery (NOMAD) observations. We determine an isotopic anomaly of −6 ± 78‰ compared to Earth standard, consistent with the −51‰–−1‰ measured on Mars’ surface by Curiosity. The measured isotopic ratio is also consistent with surface measurements, and suggests that Cl reservoirs may have undergone limited processing since formation in the Solar Nebula. The examination of possible sources and sinks of HCl shows only limited pathways to short-term efficient Cl fractionation and many plausible reservoirs of “light” Cl. © 2021. American Geophysical Union., ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by the Spanish MICINN through its Plan Nacional and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1 and ST/S00145X/1 and Italian Space Agency through grant 2018-2-HH.0. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709), and the CBK PAN team from the EXOMHYDR project, carried out within the TEAM program of the Foundation for Polish Science cofinanced by the European Union under the European Regional Development Fund (TEAM/2016-3/20). This work was supported by NASA's Mars Program Office under WBS 604796, "Participation in the TGO/NOMAD Investigation of Trace Gases on Mars" and by NASA's SEEC initiative under Grant Number NNX17AH81A, "Remote sensing of Planetary Atmospheres in the Solar System and Beyond." U.S. investigators were supported by the National Aeronautics and Space Administration. S. Viscardy acknowledges support from the Belgian Fonds de la Recherche Scientifique-FNRS under grant numbers 30442502 (ET_HOME) and Belgian Science Policy Office BrainBe MICROBE Projects. S. Aoki is "Charge de Recherches" at the F.R.S-FNRS. F. Schmidt acknowledges support from the "Institut National des Sciences de l'Univers" (INSU), the "Center National de la Recherche Scientifique" (CNRS) and "Center National d'Etudes Spatiales" (CNES) through the "Program National de Planetologie". S. Robert thanks BELSPO for the FED-tWIN funding (Prf-2019-077-RT-MOLEXO).

The goal of this white paper is to provide examples where ground-based and space-based observations are combined, and used to obtain understanding or constrain parameters beyond what the separate measurements could yield.

We present an updated statistical analysis on molecular abundances retrieved from infrared spectra of 20 comets, observed with NIRSPEC-KECK since 1999. Using these results, we investigate the chemical diversity among comets, and we try to correlate them to the chemical and physical processes present during the formation of our planetary system. Introduction: Comets are considered the remnants of the solar system formation. According to recent dynamical models [1], objects that formed between 5 and 17 AU likely scattered into the Oort cloud (OC), the primary source of long period and dynamically-new comets, while those that formed in the outer proto-planetary disk (beyond 17 AU) entered both the Oort cloud and Kuiper belt (KB) reservoirs. Investigating the chemical diversity in comets may unveil the physical and chemical conditions present during the formation and early evolution of our planetary system (e.g. hydrogenation on dust grains in cold environments or photo-dissociation processes due to UV/X-rays/Cosmic-rays radiation), as well as the processes that may have changed the nucleus composition after its formation (e.g. cosmic rays impacting the outer layer of the nucleus or successive surface warming on repeated passages through the inner solar system). Since 1985, more than 60 comets have been investigated using ground based high resolution infrared spectrometers, and many efforts have been made to create a classification of these bodies [2,3]. However, some infrared results published before 2011 may contain systematic inaccuracies related to then-incomplete molecular models used to interpret the fluorescence excitation in comets, to a non-properly described atmospheric transmittance models and/or to the use of immature reduction algorithms. These inaccuracies impact mostly comets that were observed before 2011, and they need to be removed [4]. Here, we present a statistical analysis on our revised data for twenty comets and we investigate their possible connections to processes in the proto-planetary disks and/or the natal cloud. Results and discussion: We have examined the distribution of molecular species among the comet population making use of boxplots (Figure 1). The amount of dispersion that we observe for individual species is expected and could be partially related to the temperature gradient in the proto-planetary disk and/or to the intensity of the radiation field, if present. For instance, the high dispersion range for CO may be related to efficient formation of CH3OH through hydrogenation processes on dust grains at low temperatures (T < 20 K), or formation of CO2 at higher temperatures (T > 20 K) [5]. The differential loss of highly volatile species (e.g. CO and CH4) after the comet formation may also be relevant. In Figure 2, we show two selected scatterplots for some of the analyzed molecules: these trends should reflect, at least in part, the conditions that were present during the formation of comets. We notice for example that CO shows a high and positive correlation with CH4, and a much lower but still positive correlation with CH3OH (an anti-correlation is expected if hydrogenation converted significant CO to CH3OH). Aspects of the interpretation of the scatterplots will be discussed. We compared our results with recent disk models [6,7,8], where the relative amounts of CH3OH, CO, CH4 and C2H6, are expected to depend on what chemical processes and how much radiation field (UV/X/CR) were present at different heliocentric distances from the proto-sun. Considering the combination of these four species (Figure 3), we notice that most of the sampled comets fall in the third and first quadrants and follow an (almost) linear relationship. Depending on the position of the comet with respect to this line, we can define a factor K that can be associated with an increasing processing of the cometary material, and try to reconstruct the chemical and physical history of each analyzed comet. Conclusions: We report an updated statistical analysis on molecular abundances observed in 20 comets and their possible connections with protoplanetary disk models. The results reveal a diversity in comet composition, and different correlations among the observed chemical species, ultimately giving important hints about the physical and chemical condition present during the formation and evolution of our Solar System. Figure 1. Boxplot statistic for the chemical species that we observed in 20 comets; for each box we report the interquartile range (IQR), the median (Med), the skewness (Skw), and the whiskers (error bars of the boxplots). Comets characterized by outlier values are highlighted. Figure 2. Selected scatterplots showing the measured mixing ratios (% with respect to water). For each graphic, the correlation factor is indicated in the upper left corner. Jupiter family and Oort Clouds comets are shown with squares and circles, respectively. Figure 3: Relationship between relative abundances of selected species and possible connections with the formation and evolution of comets in protoplanetary disks. Jupiter family and Oort Clouds comets are shown with squares and circles, respectively. Colors indicate a possible degree of evolution of the cometary material (violet = low degree to red = high degree) due to different processes at different life stages of the comet. This work is supported by the NASA Emerging Worlds Program EW15-57 and the NASA Astrobiology Program 13-13NAI7-0032 References: [1] Morbidelli, A. et al. 2007, Astron. J., 134, 1790; [2] Mumma & Charnley, Ann. Rev A&A, 49, 471 2011; [3] Dello Russo, N. et al. 2016, Icarus, 278, 301; [4] Lippi et al 2020, Astron. J., 159, 157; [5] Tielens, A. G. G. M., Rev. Of Modern Physics, 85, 1021, 2013; [6] Bosman et al. 2018, 618, A182; [7] Walsh 2010 ApJ, 722, 1607; [8] Eistrup et al. 2018, A&A, 613, A14.

We present revised results for the main molecular species in five Oort Cloud comets observed with near-infrared echelle grating spectrometer (NIRSPEC) at the Keck Observatory between 1999 and 2012 (C/1999 S4 (LINEAR), C/2001 A2 (LINEAR), C/2007 W1 (Boattini), C/2012 F6 (Lemmon), and C/2012 S1 (ISON)). The re-evaluation of these data shows the improvement of results in some of the data sets, in particular for comets observed and analyzed before the advent of new and revised fluorescence models and terrestrial retrieval methods introduced since 2011. We observe significant improvements in the resulting rotational temperatures and the production rates for all species, and in mixing ratios of minor species (relative to water). The re-analysis also allowed us to quantify species not analyzed previously, mostly due to the lack of molecular models (e.g., ammonia and formaldehyde). We note, however, that the improvement of these revised values is less substantial for comets observed (and/or analyzed) since 2010.

We have developed an online radiative-transfer suite (https://psg.gsfc.nasa.gov) applicable to a broad range of planetary objects (e.g., planets, moons, comets, asteroids, TNOs, KBOs, exoplanets). The Planetary Spectrum Generator (PSG) can synthesize planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (UV/Vis/near-IR/IR/far-IR/THz/sub-mm/Radio) from any observatory (e.g., JWST, ALMA, Keck, SOFIA), any orbiter (e.g., ExoMars, Juno), or any lander (e.g., MSL). This is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and planetary databases (i.e., climatological and orbital). PSG has a 3D (three-dimensional) orbital calculator for most bodies in the solar system, and all confirmed exoplanets, while the radiative-transfer models can ingest billions of spectral signatures for hundreds of species from several spectroscopic repositories. It integrates the latest radiative-transfer and scattering methods in order to compute high resolution spectra via line-by-line calculations, and utilizes the efficient correlated-k method at moderate resolutions, while for computing cometary spectra, PSG handles non-LTE and LTE excitation processes. PSG includes a realistic noise calculator that integrates several telescope / instrument configurations (e.g., interferometry, coronagraphs) and detector technologies (e.g., CCD, heterodyne detectors, bolometers). Such an integration of advanced spectroscopic methods into an online tool can greatly serve the planetary community, ultimately enabling the retrieval of planetary parameters from remote sensing data, efficient mission planning strategies, interpretation of current and future planetary data, calibration of spectroscopic data, and development of new instrument/spacecraft concepts., Journal of Quantitative Spectroscopy and Radiative Transfer, submitted

Simultaneously to the ESA Rosetta mission, a world-wide ground-based campaign provided measurements of the large scale activity of comet 67P/Churyumov-Gerasimenko through measurement of optically active gas species and imaging of the overall dust coma. We present more than two years of observations performed with the FORS2 low resolution spectrograph at the VLT, TRAPPIST, and ACAM at the WHT. We focus on the evolution of the CN production, as a tracer of the comet activity. We find that it is asymmetric with respect to perihelion and different from that of the dust. The CN emission is detected for the first time at 1.34 au pre-perihelion and production rates then increase steeply to peak about two weeks after perihelion at (1.00±0.10) ×1025 molecules s−1, while the post-perihelion decrease is more shallow. The evolution of the comet activity is strongly influenced by seasonal effects, with enhanced CN production when the Southern hemisphere is illuminated.

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft, and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit-to-orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends -- in this paper we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies., Comment: Author prepared version; final published version available at journal. 22 pages

We observed short-period comet 252P/LINEAR post-perihelion during its 2016 passage, which presented a favorable opportunity to survey its chemical composition at a close Earth approach (∼0.14 au). We characterized the comet’s chemical composition on four dates (UT 2016 April 12, 19, 26, and 29) using spectroscopic measurements with the Near-infrared Spectrograph (NIRSPEC) at the Keck Observatory on Maunakea, HI. Our high-resolution infrared spectra yielded production rates for four species (H2O, CH3OH, C2H6, and HCN) and upper limits for five species (NH3, H2CO, C2H2, CO, and CH4). We measured water at an average production rate of 4.9 ± 0.1 × 10(exp 27) molec s(exp -1). The chemical properties of 252P suggest a rather typical composition, yet somewhat enriched in methanol and ethane but low in formaldehyde (upper limit) compared to other short-period comets surveyed at infrared wavelengths. Analysis of the ortho/para ratio in water indicates a nuclear spin temperature larger than ∼38 K, consistent with statistical equilibrium (2σ). Spatial distributions of gases, which are representative of possible heterogeneity in the nucleus and/or gas dynamics upon sublimation, showed rather symmetric profiles, with subtle enhancements of the more volatile species C2H6 and HCN toward the sunward hemisphere, while water showed spatial distributions that were extended toward the anti-sunward hemisphere. The continuum was characterized by a narrow distribution. We place our infrared results in the context of observations with the Discovery Channel Telescope, the James Clerk Maxwell submillimeter Telescope, and the Hubble Space Telescope.

The ESA Rosetta spacecraft, currently orbiting around comet 67P, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. A Monte Carlo dust tail code has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is $\alpha$=--3, instead of $\alpha$=--2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 au, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 au. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment., Comment: Accepted by Astronomy and Astrophysics (January 17th, 2016)

We observed the Oort cloud comet C/2014 Q2 (Lovejoy) on 2015 January 31 and February 1 and 2 at a heliocentric distance of 1.3 au and geocentric distance of 0.8 au during its approach to the Sun. Comet Lovejoy was observed with GIANO, the near-infrared high-resolution spectrograph mounted at the Nasmyth-A focus of the TNG (Telescopio Nazionale Galileo) telescope in La Palma, Canary Islands, Spain. We detected strong emissions of radical CN and water, along with many emission features of unidentified origin, across the 1-2.5 μm region. Spectral lines from eight ro-vibrational bands of H2O were detected, six of them for the first time. We quantified the water production rate [Q(H2O), (3.11 ± 0.14) × 1029 s-1] by comparing the calibrated line fluxes with the Goddard full non-resonance cascade fluorescence model for H2O. The production rates of ortho-water [Q(H2O)ORTHO, (2.33 ± 0.11) × 1029 s-1] and para-water [Q(H2O)PARA, (0.87 ± 0.21) × 1029 s-1] provide a measure of the ortho-to-para ratio (2.70 ± 0.76)). The confidence limits are not small enough to provide a critical test of the nuclear spin temperature.

In 2017 April, we acquired comprehensive high-resolution spectra of newly discovered comet C/2017 E4 (Lovejoy) as it approached perihelion, and before its disintegration. We detected many cometary emission lines in the range (2.8-5.3) μm, in four customized instrument settings (L1-c, L3, Lp1-c, and M1) of iSHELL-the new near-IR high-resolution immersion echelle spectrograph at NASA/IRTF (Maunakea, Hawaii). We identified 12 molecular species: nine primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO) and three product species (CN, NH2, OH). We detected 85 H2O emission lines from 12 water vibrational bands across L1-c and M1 settings. The many detected water emission lines enabled retrieval of accurate measures for ortho- and para-H2O independently, thereby reducing systematic uncertainty in the derived ortho-para ratio and nuclear spin temperature. Excitation analyses and emission profile analyses were performed for all species, and molecular abundance ratios relative to water are compared with values found for other Oort Cloud comets in our infrared database. Abundance ratios are consistent for most species, with the exception of underabundant methanol and overabundant ammonia in E4.

As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet. We constrain the total activity level of the comet by photometry and spectroscopy to place Rosetta results in context and to understand the large-scale structure of the comet's coma pre-perihelion. We performed observations using a number of telescopes, but concentrate on results from the 8m VLT and Gemini South telescopes in Chile. We use R-band imaging to measure the dust coma contribution to the comet's brightness and UV-visible spectroscopy to search for gas emissions, primarily using VLT/FORS. In addition we imaged the comet in near-infrared wavelengths (JHK) in late 2014 with Gemini-S/Flamingos 2. We find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. The evolution of the total activity (measured by dust) followed previous predictions. No gas emissions were detected despite sensitive searches. The comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that Rosetta results correspond to typical behaviour for this comet. The gas production (for CN at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits., 12 pages, accepted in A&A