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We obtained high-resolution spectra of Jupiter between 4.6 and 5.4 µm using NIRSPEC on the Keck 2 telescope in February 2017. We measured the spatial variation of NH3, H2O, and the pressure level of deep (p > 3 bar) clouds using two geometries. We aligned the slit north–south on Jupiter’s Central Meridian to measure the spatial variation of the gas composition and cloud structure between 66°N and 70°S. With the slit aligned east–west, we also examined the longitudinal variation at two regions of the North Equatorial Belt (NEB) at 18°N and at 8°N near the latitude of the Galileo Probe entry site. We used the integrated line absorption, also known as the equivalent width, of deuterated methane (CH3D) at 4.66 µm to derive the pressure level of deep clouds between 3 and 7 bar. From thermochemical models, these are most likely water clouds. At the location of a deep cloud revealed by HST methane-band imaging, we found spectroscopic evidence for an opaque cloud at the 5 bar level. We also identified regions on Jupiter that lacked deep clouds but exhibited evidence for upper clouds and enhanced NH3. We estimated column-averaged mole fractions of H2O and NH3 above the opaque lower boundary of the deep cloud. The meridional scan exhibited significant belt-zone structure with retrieved NH3 abundances in the 200–400 ppm range above the opaque lower cloud, except for a depletion (down to 90 ppm) in the NEB. Water in Jupiter’s belts varies from a maximum of 7 ppm at 8°S to a minimum of 1.5 ppm at 23°S. We found evidence for water clouds and enhanced NH3 and H2O in the South Equatorial Belt Outbreak region at 13°S. The NEB is a heterogeneous region with significant variation in all of these quantities. The NH3 abundance at 18°N and 8°N varies with the longitude with mole fractions between 120 and 300 ppm. The H2O abundance at these same latitudes varies with the longitude with mole fractions between 3 and 10 ppm. Our volatile mole fractions apply to the 5 to 8 bar pressure range (or to the level of an opaque cloud top where found at shallower pressure); therefore, they imply a deeper gradient continuing to increase toward higher concentrations detected by the Galileo Probe Mass Spectrometer at 11 and 20 bar. Hot Spots in the NEB exhibit minimal cloud opacity; however, they lack prominent anomalies in the concentrations of NH3 or H2O.

Jupiter’s atmospheric water abundance is a highly important cosmochemical parameter that is linked to processes of planetary formation, weather, and circulation. Remote sensing and in situ measurement attempts still leave room for substantial improvements to our knowledge of Jupiter’s atmospheric water abundance. With the motivation to advance our understanding of water in Jupiter’s atmosphere, we investigate observations and models of deep clouds. We discuss deep clouds in isolated convective storms (including a unique storm site in the North Equatorial Belt that episodically erupted in 2021–2022), cyclonic vortices, and northern high-latitude regions, as seen in Hubble Space Telescope visible/near-infrared imaging data. We evaluate the imaging data in continuum and weak methane band (727 nm) filters by comparison with radiative transfer simulations, 5 micron imaging (Gemini), and 5 micron spectroscopy (Keck), and conclude that the weak methane band imaging approach mostly detects variation in the upper cloud and haze opacity, although sensitivity to deeper cloud layers can be exploited if upper cloud/haze opacity can be separately constrained. The cloud-base water abundance is a function of cloud-base temperature, which must be estimated by extrapolating 0.5-bar observed temperatures downward to the condensation region near 5 bar. For a given cloud base pressure, the largest source of uncertainty on the local water abundance comes from the temperature gradient used for the extrapolation. We conclude that spatially resolved spectra to determine cloud heights—collected simultaneously with spatially-resolved mid-infrared spectra to determine 500-mbar temperatures and with improved lapse rate estimates—would be needed to answer the following very challenging question: Can observations of deep water clouds on Jupiter be used to constrain the atmospheric water abundance?

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 .

Microwave measurements of water vapour from the Juno spacecraft show that Jupiter is enhanced in oxygen by roughly three times the solar abundance at the equator. The water abundance is important in understanding the formation of Jupiter, the structure of its deep interior, and the nature of its clouds and weather.

The James Webb Space Telescope (JWST), scheduled for launch in 2018, is the successor to the Hubble Space Telescope (HST) but with a significantly larger aperture (6.5 m) and advanced instrumentation focusing on infrared science (0.6-28.0 m). In this paper, we examine the potential for scientific investigation of Titan using JWST, primarily with three of the four instruments: NIRSpec, NIRCam, and MIRI, noting that science with NIRISS will be complementary. Five core scientific themes are identified: (1) surface (2) tropospheric clouds (3) tropospheric gases (4) stratospheric composition, and (5) stratospheric hazes. We discuss each theme in depth, including the scientific purpose, capabilities, and limitations of the instrument suite and suggested observing schemes. We pay particular attention to saturation, which is a problem for all three instruments, but may be alleviated for NIRCam through use of selecting small sub-arrays of the detectors-sufficient to encompass Titan, but with significantly faster readout times. We find that JWST has very significant potential for advancing Titan science, with a spectral resolution exceeding the Cassini instrument suite at near-infrared wavelengths and a spatial resolution exceeding HST at the same wavelengths. In particular, JWST will be valuable for time-domain monitoring of Titan, given a five- to ten-year expected lifetime for the observatory, for example, monitoring the seasonal appearance of clouds. JWST observations in the post-Cassini period will complement those of other large facilities such as HST, ALMA, SOFIA, and next-generation ground-based telescopes (TMT, GMT, EELT).

Saturn's slow seasonal evolution was disrupted in 2010–2011 by the eruption of a bright storm in its northern spring hemisphere. Thermal infrared spectroscopy showed that within a month, the resulting planetary-scale disturbance had generated intense perturbations of atmospheric temperatures, winds, and composition between 20° and 50°N over an entire hemisphere (140,000 kilometers). The tropospheric storm cell produced effects that penetrated hundreds of kilometers into Saturn's stratosphere (to the 1-millibar region). Stratospheric subsidence at the edges of the disturbance produced \"beacons\" of infrared emission and longitudinal temperature contrasts of 16 kelvin. The disturbance substantially altered atmospheric circulation, transporting material vertically over great distances, modifying stratospheric zonal jets, exciting wave activity and turbulence, and generating a new cold anticyclonic oval in the center of the disturbance at 41°N.

Long‐term (2004–2009) on‐orbit observations by Cassini Composite Infrared Spectrometer are analyzed to precisely measure Saturn's emitted power and its meridional distribution. Our evaluations suggest that the average global emitted power is 4.952 ± 0.035 W m−2 during the period of 2004–2009. The corresponding effective temperature is 96.67 ± 0.17 K. The emitted power is 16.6% higher in the Southern Hemisphere than in the Northern Hemisphere. From 2005 to 2009, the global mean emitted power and effective temperature decreased by ∼2% and ∼0.5%, respectively. Our study further reveals the interannual variability of emitted power and effective temperature between the epoch of Voyager (∼1 Saturn year ago) and the current epoch of Cassini, suggesting changes in the cloud opacity from year to year on Saturn. The seasonal and interannual variability of emitted power implies that the energy balance and internal heat are also varying.

We have obtained high-resolution spectra of Jupiter's Great Red Spot (GRS) between 4.6 and 5.4 microns using telescopes on Mauna Kea in order to derive gas abundances and to constrain its cloud structure between 0.5 and 5~bars. We used line profiles of deuterated methane CH3D at 4.66 microns to infer the presence of an opaque cloud at 5+/-1 bar. From thermochemical models this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570+/-30 mbar based on fitting strong ammonia lines at 5.32 microns. We identify this layer as an ammonia cloud based on the temperature where gaseous ammonia condenses. We found evidence for a strongly absorbing, but not totally opaque, cloud layer at pressures deeper than 1.3 bar by combining Cassini/CIRS spectra of the GRS at 7.18 microns with ground-based spectra at 5 microns. This is consistent with the predicted level of an NH4SH cloud. We also constrained the vertical profile of water and ammonia. The GRS spectrum is matched by a saturated water profile above an opaque water cloud at 5~bars. The pressure of the water cloud constrains Jupiter's O/H ratio to be at least 1.1 times solar. The ammonia mole fraction is 200+/-50ppm for pressures between 0.7 and 5 bar. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8+/-0.2 ppm for PH3, a factor of 2 higher than in the warm collar surrounding the GRS. We detected all 5 naturally occurring isotopes of germanium in GeH4 in the Great Red Spot. We obtained an average value of 0.35+/-0.05 ppb for GeH4. Finally, we measured 0.8+/-0.2 ppb for CO in the deep atmosphere.

The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm (\\(\\sim\\)200 -- 400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timescales increase, increasing the likelihood of disequilibrium chemistry compared to warmer classes of planets. JWST observations are revolutionizing the characterization of these worlds with high signal-to-noise, moderate resolution near- and mid-infrared spectra. The spectra have been used to measure the abundances of prominent species like water, methane, and ammonia; species that trace chemical reactions like carbon monoxide; and even isotopologues of carbon monoxide and ammonia. Here, we present atmospheric retrieval results using both published fixed-slit (GTO program 1230) and new averaged time series observations (GO program 2327) of the coldest known Y dwarf, WISE 0855-0714 (using NIRSpec G395M spectra), which has an effective temperature of \\(\\sim\\) 264 K. We present a detection of deuterium in an atmosphere outside of the solar system via a relative measurement of deuterated methane (CH\\(_{3}\\)D) and standard methane. From this, we infer the D/H ratio of a substellar object outside the solar system for the first time. We also present a well-constrained part-per-billion abundance of phosphine (PH\\(_{3}\\)). We discuss our interpretation of these results and the implications for brown dwarf and giant exoplanet formation and evolution.

Cold brown dwarfs are excellent analogs of widely separated, gas giant exoplanets, and provide insight into the potential atmospheric chemistry and physics we may encounter in objects discovered by future direct imaging surveys. We present a low resolution R \\(\\sim\\) 300 \\(M\\)-band spectroscopic sequence of seven brown dwarfs with effective temperatures between 750 K and 250 K along with Jupiter. These spectra reveal disequilibrium abundances of carbon monoxide (CO) produced by atmospheric quenching. We use the eddy diffusion coefficient (K\\(_{zz}\\)) to estimate the strength of vertical mixing in each object. The K\\(_{zz}\\) values of cooler gaseous objects are close to their theoretical maximum and warmer objects show weaker mixing, likely due to less efficient convective mixing in primarily radiative layers. The CO-derived K\\(_{zz}\\) values imply that disequilibrium phosphine (PH\\(_{3}\\)) should be easily observable in all of the brown dwarfs, but none as yet show any evidence for PH\\(_{3}\\) absorption. We find that ammonia is relatively insensitive to atmospheric quenching at these effective temperatures. We are able to improve the fit to WISE 0855's \\(M\\)-band spectrum by including both CO and water clouds in the atmospheric model.