91̽»¨

Abstract:

Titan is renowned for its complex atmosphere, where ongoing photochemistry leads to a rich mixture of organic molecules. Beginning with the splitting of methane by sunlight and other energetic particles, multi-carbon molecules are built up by successive addition of CxHy radicals and ions to one another. This process leads to the formation of ever-larger  molecules and eventually particulates, that sediment out on the surface. Our experimental knowledge of the molecular inventory comes from two techniques: direct sampling mass spectrometry, and remote sensing.  While the former has shown the presence of species at a very wide range of masses from 1-100+ Da, their structure and even stoichiometry is poorly known. In this respect, remote sensing spectroscopy is more robust, providing definitive detections of individual molecular types via unique patterns of IR and sub-millimeter energy transitions, however for a more limited range of species. Currently, 25 species have been definitively identified by remote sensing, ranging in size from H2 to benzene (C6H6). These include 12 hydrocarbons, with the rest a mixture of diatomics, nitriles and small oxygen compounds (H2O, CO, CO2). With direct sampling currently impossible before the Dragonfly mission returns a spacecraft to Titan in 2034, astronomers have been pushing forward with chemical identifications using a range of ground and space-based observatories. We report here on recent attempts to identify new C3 and C4 hydrocarbons in Titan’s atmosphere using the high-resolution (R~100000) TEXES spectrometer at the Infrared Telescope Facility (IRTF) – see examples in Fig. 1. Associated laboratory spectroscopy work is ongoing at the Jet Propulsion Laboratory (JPL) using a Bruker FTS spectrometer to identify the positions and intensities of the strongest gas bands, to assist with targeting the telescope searches, and interpretation of the data.  Identifications of new, heavy molecular species are urgently needed to constrain photochemical and dynamical models, and make advances in our understanding of the workings of Titan’s atmosphere, and its potential for astrobiology. Such work is also important for planning data collection and analysis from the upcoming NASA Dragonfly mission, where a sensitive mass spectrometer will assess the composition of surface materials and their relation to the atmospheric constituents, as well as Titan atmospheric data from other telescopes such as ALMA and JWST.Figure 1: Examples of currently undetected molecules in Titan's atmosphere: isomers of C4H8 and C4H10. We report on ongoing searches for these species with IRTF/TEXES.

Abstract:

Over four decades have elapsed since the last in situ spectrophotometric observations of the Venusian atmosphere, specifically from the Venera 11 (1978) and Venera 13 and 14 (1982) missions. These missions recorded spectral data during their descent from approximately 62 km to the surface. Unfortunately, the original data were lost; however, a portion has been reconstructed by digitising the graphical outputs that were generated during the initial data processing phase of each of the three missions [1]. This reconstructed data is crucial as it remains the sole set of in situ spectrophotometric observations of Venus’s atmosphere and is likely to be so for the foreseeable future.While re-analysing the reconstructed Venera datasets, we identified several artefacts, errors and sources of noise, necessitating the implementation of some corrections and validation checks to isolate the most unaffected part of the reconstructed data. Then, using NEMESIS, a radiative transfer and retrieval tool [2], we conducted a series of retrievals to simultaneously fit the downward-going spectra at all altitudes. During this process, several parameters were retrieved. The first set of retrievals focused on the structure of the main cloud deck (MCD), which includes the cloud base altitude and abundance profiles of all four cloud modes. Previous corrections that were used to account for the effect of the unknown UV absorber did not result in good fits with the spectra shortward of 0.6 µm. Hence, we derived a new correction by retrieving the imaginary refractive index spectra of the Mode 1 particles.In the next phase, the MCD retrievals were used to update the model atmospheres for each of the missions. Then, the H2O volume mixing ratio profiles were retrieved and compared with the previous retrievals using the same data by [1] along with other remote sensing observations. The final retrieval phase concentrated on characterising particulate matter in the deep atmosphere. In [3], we outlined a methodology for retrieving a near-surface particulate layer using the reconstructed Venera 13 dataset. In this new work, we apply this methodology to encompass the Venera 11 and 14 datasets and compare the retrievals from the three datasets.This research thus provides a comprehensive overview of three distinct retrievals: 1) main cloud deck, 2) H2O, and 3) near-surface particulates using the reconstructed spectrophotometric data of Venera 11, 13, and 14.References: [1] Ignatiev, N. I., Moroz, V. I., Moshkin, B. E., Ekonomov, A. P., Gnedykh, V. I., Grigor’ev, A. V., and Khatuntsev, I. V. Cosmic Research 35(1), 1–14 (1997).[2] Irwin, P. G., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J., Tsang, C. C., Wilson, C. F., Calcutt, S. B., Nixon, C. A., and Parrish, P. D. Journal of Quantitative Spectroscopy and Radiative Transfer 109(6), 1136–1150 (2008).[3] Kulkarni, S. V., Irwin, P. G. J., Wilson, C. F., & Ignatiev, N. I. Journal of Geophysical Research: Planets, 130, e2024JE008728, (2025).

Abstract:

We present a re-analysis of archival data-cubes of Neptune obtained with the GEMINI Near-Infrared Integral Field Spectrometer (NIFS), aiming to refine constraints on the abundance of hydrogen sulphide (Hâ‚‚S) in Neptune's atmosphere. To enhance spatial and spectral fidelity, we employ a modified CLEAN algorithm that effectively deconvolves the data while conserving flux. To mitigate observational and instrumental artifacts, we utilize Singular Spectrum Analysis (SSA) on single-wavelength images and apply Principal Component Analysis (PCA) across the full data-cube to suppress both random and systematic noise. Spectral retrievals are conducted using ArchNemesis, an optimal estimation inverse modeling tool. We retrieve vertical profiles at individual locations, and use Minnaert-corrected reflectivity functions across latitude bands to investigate latitudinal variability. Using the deconvolution and data analysis techniques, we are able to extract more scientific utility from legacy datasets and describe a template that can be repeated for similar datasets.

Abstract:

Introduction: Enceladus Thermal Mapper (ETM) is an 91̽»¨-built high-heritage instrument that is being developed for outer solar system operations. ETM is based upon the design of Lunar Thermal Mapper (LTM, launched on Lunar Trailblazer, Fig. 1). It has a strong heritage story, including MIRMIS (on Comet Interceptor), Compact Modular Sounder (on TechDemoSat-1) and filters shared with Lunar Diviner (on Lunar Reconnaissance Orbiter). ETM is a miniaturized thermal infrared multispectral imager, with space for 15 spectral channels (bandpasses) that can be tailored to the mission requirements. It consists of a five-mirror telescope and optical system and an uncooled microbolometer detector array. Real-time calibration is achieved using a motorized mirror to point to an onboard blackbody target and empty space. ETM has an IFOV of 35 mm, so assuming a 100 30 km orbit it will have a spatial resolution of 40 to 70 m/pixel and a swath width of 14 - 27 km. ETM Updates: Through UK Space Agency funding we have developed three areas of ETM: its filter profile, radiation tolerance and sensitivity to Enceladus-like surfaces. Filters: ETM is a push broom thermal mapper, which works by the detector being swept over a surface. Each of the detector’s 15 channels is made up 16 rows, which are coadded to increase the signal to noise. A recently completed preliminary study has updated ETM’s bandpasses to include filters between 6.25 mm and 200 mm to enable it to detect Enceladus’ polar winter (170 K). Depending on the mission goals not all channels need to be utilised to achieve this, making some available for additional studies (e.g. searching for salt). Radiation: The radiation environments of Enceladus are vastly different to those of the Moon. Recent radiation testing and analysis showed that the majority of ETM’s existing design is already highly radiation tolerant. With some additional shielding and one component change all parts can reach the radiation hardness required to operate in the Saturn-system. The additional shielding may be provided by the spacecraft structure, depending on the adopted design. Sensitivity: ETM’s sensitivity to cryogenic surfaces is currently predicted through a well-characterised model. However, as part of the LTM calibration campaign we plan to directly measure its sensitivity to

Abstract:

Introduction: The origins of Mars' moons, Phobos and Deimos, remain uncertain, with two main hypotheses under consideration: formation from debris following a high-energy impact between Mars and an asteroid [1], or capture of primitive asteroids [2]. To address this, JAXA's Martian Moons eXploration (MMX) mission aims to return samples from Phobos by 2031 [3]. The characterisation of these samples will determine the origin of Phobos.To ground-truth remote observations of Phobos, we have used X-ray diffraction (XRD), and Fourier transform infrared (FTIR) reflectance spectroscopy to characterise the bulk mineralogy and IR spectral properties of ureilites, carbonaceous and ordinary chondrites, the composition of which could be indicative of a captured asteroid [4], and Martian meteorites that could represent a collisional formation. By acquiring XRD and IR data from the same material, mineral abundances can be directly correlated with features in reflectance spectra [5]. When MMX reaches Phobos, meteorite data collected in the laboratory will play a crucial role towards interpreting the mineralogy and composition of materials on its surface.Methods: We have characterised the mineralogy and spectral properties of six CM (Mighei-like) carbonaceous chondrites, Tarda (C2-ung), the CO (Ornans-like) chondrite Kainsaz, a range of shock darkened ordinary chondrites (mostly falls) including L4-6, and H5-6, four CR2 chondrites, four ureilites, Martian meteorites Nakhla and Tissint, and a Tagish Lake (C2-ung) based simulant created by the University of Tokyo, known as UTPS-TB [6]. For the meteorites, chips of approximately 200 mg were ground to produce powders with grain sizes of less than 40 microns. The UTPS-TB sample came in a powdered form which was ground to the same grain size as the meteorites.Diffuse reflectance spectra (1.7 - 50 μm) were collected using a Bruker VERTEX 70V FTIR spectrometer at the 91̽»¨ Planetary Spectroscopy Facility. Spectra were calibrated at the start of each measurement day and between measurements of samples using a gold standard. The powdered sample was measured under a vacuum to reduce terrestrial atmospheric contributions.XRD patterns of the same powders were collected using an INEL X-ray diffractometer with a position-sensitive detector at the Natural History Museum, London. Around 50 mg of powdered sample was measured for 16 hours to achieve good signal-to-noise. Measurements of well-characterised standard minerals were collected for 30 minutes and compared with meteorite patterns to identify minerals and quantify their abundance in the sample [e.g. 7].Results & Discussion: The mineralogical and spectral characteristics of meteorites in this investigation are compared the reflectance spectra of Phobos’ surface. The CR chondrites are primitive, containing both anhydrous silicates (e.g. olivine and pyroxene) and aqueous alteration phases such as phyllosilicates, carbonates, magnetite, and sulfides. Their albedo is ~3-5% reflectance with a weak red slope in the visible to near-infrared (VNIR). The CRs have a 3 μm hydration band, due to partial aqueous alteration. Their low VNIR reflectance, red-sloped continuum, and weak 3 μm spectral absorption feature is like that of Phobos, 91̽»¨ing the captured asteroid origin theory. The CM chondrites share similar spectral features but have a lower albedo and a stronger μm hydration band, corresponding to a higher phyllosilicate composition.   The ureilites are achondritic ultramafic meteorites containing olivine, pyroxene and carbon phases. These samples have a low albedo (~6-15% in VNIR) due to their opaque carbonaceous composition. However, their VNIR spectra are blue-sloped, inconsistent with Phobos’ red-sloped spectra. Ureilites are also anhydrous and therefore lack the 3 μm hydration band seen in Phobos spectra. Their low reflectance and feature-poor spectra could resemble Phobos, however there is a significant difference in spectral slope and hydration features. Therefore, Phobos were composed of ureilitic material, its surface would need to be significantly modified by space weathering.Martian meteorites Nakhla (a nakhlite) and Tissint (a shergottite) have mineralogical and spectral features consistent with their basaltic origin. XRD measurements of these meteorites are dominated by pyroxene (augite, pigeonite), and olivine, consistent with their origin in the Martian crust. Their reflectance spectra have relatively high albedo, mafic absorption bands at ~1 and 2 μm, and a lack of hydration features. These features are inconsistent with the spectra of Phobos, which lack 1 or 2 μm bands and show significantly lower reflectance.CR and CM chondrites are the closest spectral match to Phobos from the samples studied. Their low albedo, red-sloped, hydrated spectra are consistent with surface measurements of Phobos. Ureilites share low reflectance but differ significantly in slope and hydration, while Martian meteorites differ in more spectral characteristics. These results 91̽»¨ the interpretation that Phobos is composed of primitive, carbon-rich material, likely of outer solar system origin, and favour a capture scenario over a collisional formation from Martian ejecta. The similarities between the carbonaceous chondrites and Phobos indicates that the Martian moons may be captured asteroids and further demonstrates the importance of the MMX mission sample return for solving the mystery of their origin definitively.References: [1] R. Citron et al. (2015) Icarus 252:334-338. [2] M. Pajola et al. (2013) The Astrophysical Journal 777:127. [3] K. Kuramoto et al. (2022) Earth, Planets and Space 74:12. [4] K. D. Pang et al. (1978) Science 199(4324):64-66. [5] H. C. Bates et al. (2023) Meteoritics & Planetary Science 1-23. [6] H. Miyamoto et al. (2021) Earth, Planets and Space 73:1-17 [7] G. Cressey et al. (1996) Powder Diffraction 11:35-39.