Explore the vast range of titles available.

The overarching theme of the Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) , an Astrophysics MIDEX-class mission concept, is Following water from galaxies, through protostellar systems, to Earth’s oceans . The OASIS science objectives address fundamental questions raised in “Pathways to Discovery in Astronomy and Astrophysics for the 2020s (National Academies of Sciences and Medicine, Pathways to Discovery in Astronomy and Astrophysics for the 2020s, 2021 , https://doi.org/10.17226/26141 , https://www.nap.edu/catalog/26141/pathways-to-discovery-in-astronomy-and-astrophysics-for-the-2020s )” and in “Enduring Quests and Daring Visions” (Kouveliotou et al. in Enduring quests-daring visions (NASA astrophysics in the next three decades), 2014 , arXiv:1401.3741 ), in the areas of: 1) the Interstellar Medium and Planet Formation, 2) Exoplanets, Astrobiology, and the Solar System, and 3) Galaxies. The OASIS science objectives require space-borne observations of galaxies, molecular clouds, protoplanetary disks, and solar system objects utilizing a telescope with a collecting area that is only achievable by large apertures coupled with cryogenic heterodyne receivers. OASIS will deploy an innovative 14-meter inflatable reflector that enables >16× the sensitivity and >4× the angular resolution of Herschel , and complements the short wavelength capabilities of James Webb Space Telescope . The OASIS state-of-the-art cryogenic heterodyne receivers will enable high spectral resolution (resolving power > 10 6 ) observations at terahertz (THz) frequencies. These frequencies encompass far-IR transitions of water and its isotopologues, HD, and other molecular species, from 660 to 63 μm that are otherwise obscured by Earth’s atmosphere. From observations of the ground state HD line, OASIS will directly measure gas mass in a wide variety of astrophysical objects. Over its one-year baseline mission, OASIS will find water sources as close as the Moon, to galaxies ∼4 billion light years away. This paper reviews the solar system science achievable and planned with OASIS .

Benzene ice contributes to an emission feature detected by the Cassini Composite InfraRed Spectrometer (CIRS) near 682 cm^{-1} in Titan's late southern fall polar stratosphere. It is as well one of the dominant components of the CIRS-observed High Altitude South Polar (HASP) ice cloud observed in Titan's mid stratosphere during late southern fall. Titan's stratosphere exhibits significant seasonal changes with temperatures that spatially vary with seasons. A quantitative analysis of the chemical composition of infrared emission spectra of Titan's stratospheric ice clouds relies on consistent and detailed laboratory transmittance spectra obtained at numerous temperatures. However, there is a substantial lack of experimental data on the spectroscopic and optical properties of benzene ice and its temperature dependence, especially at Titan-relevant stratospheric conditions. We have therefore analyzed in laboratory the spectral characteristics and evolution of benzene ice's vibrational modes at deposition temperatures ranging from 15 K to 130 K, from the far- to mid-IR spectral region (50 - 8000 cm^{-1}). We have determined the amorphous to crystalline phase transition of benzene ice and identified that a complete crystallization is achieved for deposition temperatures between 120 K and 130 K. We have also measured the real and imaginary parts of the ice complex refractive index of benzene ice from 15 K to 130 K. Our experimental results significantly extend the current state of knowledge on the deposition temperature dependence of benzene ice over a broad infrared spectral range, and provide useful new data for the analysis and interpretation of Titan-observed spectra.

The results from ground- and space-based observations aimed at exploring the aerosol vertical structure in the lower atmosphere of Titan, the methane abundance in Titan's troposphere, and the dust abundance in the martian atmosphere are presented. Investigating the vertical distribution of Titan's lower atmospheric haze and tropospheric methane, as well as martian atmospheric dust, provides insight into dynamical, radiative, and thermal properties of both atmospheres. Titan's lower atmospheric haze profile indirectly provides evidence for atmospheric circulation and condensation processes (i.e., methane rain and clouds). Similarly, suspended martian dust heats up the atmosphere, thus driving the thermal structure. For the Titan portion of this project, ground-based narrowband images of Titan from 1999 were utilized at 5 wavelengths surrounding 0.94 μm, as well as Titan images obtained in 2004 at 4 shorter wavelengths, to examine the haze distribution at altitudes below 100 km. Analysis of these observations indicated a clearing haze abundance at altitudes in Titan's upper troposphere/lower stratosphere. Additionally, HST STIS spectra acquired in 2000 at 122 wavelengths between 0.6 μm and 1 μm were utilized to expand the altitude sensitivity below 100 km by exploiting the transition between optically thick haze at shorter wavelengths and optically thin haze at longer wavelengths. Analysis of the STIS data suggests a strong reduction in haze concentration above Titan's tropopause that varies in degree as a function of latitude. Titan's methane abundance profile is fairly consistent with latitude and longitude and there is evidence for local areas of methane saturation in the troposphere. For the Mars portion of this project, near-infrared observations of Mars recorded in 2003 using the SpeX instrument at the NASA/IRTF. H- and K-band spectroscopy of Mars was acquired across the 1.6 μm and 2.0 μm CO 2 absorption bands to measure the total extinction optical depth of dust as a function of time-of-day. This work quantifies the variations in the dust abundance over a course of a martian day. The results are consistent with small time-of-day variations in the abundance of martian dust. The implications regarding the aerosol distribution in two Earth-analog objects will be discussed.

In response to ESA Voyage 2050 announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn largest moon Titan. Titan, a \"world with two oceans\", is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a \"heavy\" drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan northern latitudes with an orbiter and in situ element(s) would be highly complementary with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan equatorial regions in the mid-2030s.

From 2004 to 2017, the Cassini spacecraft orbited Saturn, completing 127 close flybys of its largest moon, Titan. Cassini's Composite Infrared Spectrometer (CIRS), one of 12 instruments carried on board, profiled Titan in the thermal infrared (7-1000 microns) throughout the entire 13-year mission. CIRS observed on both targeted encounters (flybys) and more distant opportunities, collecting 8.4 million spectra from 837 individual Titan observations over 3633 hours. Observations of multiple types were made throughout the mission, building up a vast mosaic picture of Titan's atmospheric state across spatial and temporal domains. This paper provides a guide to these observations, describing each type and chronicling its occurrences and global-seasonal coverage. The purpose is to provide a resource for future users of the CIRS data set, as well as those seeking to put existing CIRS publications into the overall context of the mission, and to facilitate future inter-comparison of CIRS results with those of other Cassini instruments, and ground-based observations.

The SALTUS Probe mission will provide a powerful far-infrared (far-IR) pointed space observatory to explore our cosmic origins and the possibility of life elsewhere. The observatory employs an innovative deployable 14-m aperture, with a sunshield that will radiatively cool the off-axis primary to <45K. This cooled primary reflector works in tandem with cryogenic coherent and incoherent instruments that span the 34 to 660 micron far-IR range at both high and moderate spectral resolutions.

Chemistry along the star- and planet-formation sequence regulates how prebiotic building blocks -- carriers of the elements CHNOPS -- are incorporated into nascent planetesimals and planets. Spectral line observations across the electromagnetic spectrum are needed to fully characterize interstellar CHNOPS chemistry, yet to date there are only limited astrochemical constraints at THz frequencies. Here, we highlight advances to the study of CHNOPS astrochemistry that will be possible with the Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS). OASIS is a NASA mission concept for a space-based observatory that will utilize an inflatable 14-m reflector along with a heterodyne receiver system to observe at THz frequencies with unprecedented sensitivity and angular resolution. As part of a survey of H2O and HD towards ~100 protostellar and protoplanetary disk systems, OASIS will also obtain statistical constraints on the inventories of light hydrides including NH3 and H2S towards protoplanetary disks, as well as complex organics in protostellar hot corinos and envelopes. Line surveys of additional star-forming regions, including high-mass hot cores, protostellar outflow shocks, and prestellar cores, will also leverage the unique capabilities of OASIS to probe high-excitation organics and small hydrides, as is needed to fully understand the chemistry of these objects.

In this chapter we describe the remote sensing measurement of nitrogen-bearing species in Titan's atmosphere by the Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft. This instrument, which detects the thermal infrared spectrum from 10-1500 cm-1 (1000-7 microns) is sensitive to vibrational emissions of gases and condensates in Titan's stratosphere and lower mesosphere, permitting the measurement of ambient temperature and the abundances of gases and particulates. Three N-bearing species are firmly detected: HCN, HC3N and C2N2, and their vertical and latitudinal distributions have been mapped. In addition, ices of HC3N and possibly C4N2 are also seen in the far-infrared spectrum at high latitudes during the northern winter. The HC(15)N isotopologue has been measured, permitting the inference of the 14N/15N ratio in this species, which differs markedly (lower) than in the bulk nitrogen reservoir (N2). We also describe the search in the CIRS spectrum, and inferred upper limits, for NH3 and CH3CN. CIRS is now observing seasonal transition on Titan and the gas abundance distributions are changing accordingly, acting as tracers of the changing atmospheric circulation. The prospects for further CIRS science in the remaining five years of the Cassini mission are discussed.

Since Cassini's arrival at Titan, ppm levels of benzene (C6H6) as well as large positive ions, which may be polycyclic aromatic hydrocarbons (PAHs). have been detected in the atmosphere. Aromatic molecules. photolytically active in the ultraviolet, may be important in the formation of the organic aerosol comprising the Titan haze layer even when present at low mixing ratios. Yet there have not been laboratory simulations exploring the impact of these molecules as precursors to Titan's organic aerosol. Observations of Titan by the Cassini Composite Infrared Spectrometer (CIRS) in the far-infrared (far-IR) between 560 and 20/cm (approx. 18 to 500 microns) and in the mid-infrared (mid-IR) between 1500 and 600/cm (approx. 7 to 17 microns) have been used to infer the vertical variations of Titan's aerosol from the surface to an altitude of 300 km in the far-IR and between 150 and 350 km in the mid-IR. Titan's aerosol has several observed emission features which cannot be reproduced using currently available optical constants from laboratory-generated Titan aerosol analogs, including a broad far-IR feature centered approximately at 140/cm (71 microns).