Water and Volatiles in the Outer Solar System

Abstract

Space exploration and ground-based observations have provided outstanding evidence of the diversity and the complexity of the outer solar system. This work presents our current understanding of the nature and distribution of water and water-rich materials from the water snow line to the Kuiper Belt. This synthesis is timely, since a thorough exploration of at least one object in each region of the outer solar system has now been achieved. Next steps, starting with the Juno mission now in orbit around Jupiter, will be more focused on understanding the processes at work than on describing the general characteristics of each giant planet systems.

Infrared Observations of Ganymede From the Jovian InfraRed Auroral Mapper on Juno

“…The most prominent spectral feature is the absorption band of water ice centered at 2 µm, which has been discussed in the Introduction and whose band depth varies over Ganymede's surface. To map crystalline versus amorphous water ice based on near-infrared spectra, one needs to measure three diagnostic spectral indices: the depth of the 1.65-µm band, the shape and center of the 2.0-µm band, and the strength and shape of the 3.1-µm reflectance peak coming from the Fresnel reflection off the facets of the water ice grains on the surface (e.g., Grasset et al, 2017;Mastrapa et al, 2009). Unfortunately, the 1.65-µm feature is out of the JIRAM range of sensitivity, while only half of the 2.0-µm band is seen, ruling out the possibility of using these two features.…”

Prediction of the near-IR spectra of ices byab initiomolecular dynamics

“…Ices formed by mixtures of these species and other molecules, like NH 3 , CO 2 or CH 3 OH, are also frequently found on other bodies of the solar system and in the interstellar medium. 1,[19][20][21] In this paper we continue previous theoretical studies 3,22-25 on ices of astrophysical relevance, and intend now to theoretically simulate the near-IR spectra of these amorphous solid systems using molecular dynamics. A brief description of the most relevant methodological aspects is included in the next section.…”

Low-temperature synthesis of polycyclic aromatic hydrocarbons in Titan’s surface ices and on airless bodies

“…Therefore, the facile, GCR-mediated synthesis of PAHs in low-temperature acetylene ices represents a fundamental shift from currently accepted perceptions leading to PAH formation in hydrocarbon-rich atmospheres of planets and their moons, followed by their precipitation to the ground ( 4 ). The versatile concept of PAH synthesis in acetylene ices has vital implications to the surface chemistry and interpretation of reflection spectra of airless bodies, on which either hydrocarbon ices were detected such as Makemake or which reveal areas of lower albedos proposing “dark organic surface material” of hitherto unknown origin and composition such as on Hyperion, Iapetus, and Phoebe ( 42 , 43 ), throughout our Solar System. Cassini’s VIMS observations of “dark material” on Phoebe and Iapetus revealed absorption in the spectral range of 3.0 to 3.6 μm, centered at 3.29 μm, which was assigned to C─H stretching modes of PAHs ( 44 , 45 ).…”