The technique of Mössbauer spectroscopy is the gold standard for measurements of the redox state, coordination environment, and site occupancy of iron in geologic materials. Laboratory measurements typically involve measurements on 5–300 mg of powdered material. Mössbauer is also used to identify mineralogy of iron oxide phases and in some cases to constrain the distribution of Fe among mixed silicate phases in a rock. Together, these uses fill a need in the terrestrial and extraterrestrial communities for understanding Fe redox states, and by inference, oxygen fugacity, as oxygen evolves on planetary bodies. This chapter provides a background for understanding the Mössbauer effect and interpretation of its hyperfine parameters.

Laser-Induced Breakdown Spectroscopy (LIBS) is the remote elemental analysis technique used by the ChemCam instrument on the Curiosity rover. LIBS involves remotely ablating material from rocks and soils with a focused high-energy laser, which generates an optically excited plasma from which the elements in the rock or soil sample are quantitatively determined. The LIBS technique offers many advantages for remote chemical analysis. LIBS provides very rapid analyses without the need for any sample preparation. LIBS is capable of detecting all elements present above the detection limits independent of the atomic mass. LIBS quantitative analysis continues to evolve and produce accurate compositions with decreasing uncertainties. Furthermore, the matrix effects that tend to complicate most elemental analysis techniques like LIBS are increasingly exploited to extract more sample details. The focus of this chapter is to describe the current state of LIBS chemical analysis for remote planetary science.

Ices of various compositions and in various phases and combinations with one another are found on planetary surfaces through remote sensing techniques, of which optical spectroscopy is the most powerful and diagnostic. Ices also are found in combination with minerals and organic materials; some complex organic materials are the result of energetic processing of ices, while some may represent organic matter from other sources. Remote spectroscopic observations from Earth-based telescopes and planetary probes are usually interpreted with the aid of radiative transfer models that account for the compositions, particle properties, mixing configurations and other parameters relevant to the materials under consideration. This chapter reviews the spectroscopic character of planetary ices in pure states and in combinations with one another, and with minerals and organic solid materials found by remote sensing techniques and by the analysis of analog materials, both naturally occurring and synthesized in the laboratory and thus available for analytical studies.

Neutrons, gamma rays, and X-rays are used to measure the subsurface elemental composition of Solar System bodies, providing insights into their formation and evolution. Neutrons and gamma rays are highly penetrating particles made by the steady bombardment of the regolith of airless bodies by galactic cosmic rays. Gamma rays are also made by the decay of natural radioelements. The escaping radiation can be detected in close-proximity orbits and analyzed to determine subsurface elemental composition to depths of a few decimeters. Because the radiation sensors have nearly omnidirectional response, spatial resolution depends on orbital altitude. X-ray fluorescence is induced by solar X-rays. Consequently, X-ray spectroscopy is most useful for studies of objects in the inner Solar System. Characteristic elemental X-rays are made within the uppermost ~100 micrometers of the surface. The suite of elements analyzed overlaps that of nuclear spectroscopy, providing complementary geochemical information. Because X-rays are easily collimated, relatively high spatial resolution measurements are possible. This chapter presents the fundamentals of neutron, gamma-ray, and X-ray production, transport, and detection along with an overview of the measurement principles, including modeling, analysis, and mapping methods.

New visible and infrared data of minor bodies, including minor planet 1 Ceres, asteroids 4 Vesta, 21 Lutetia, 2867 Steins and comet 67P/Churyumov–Gerasimenko (hereafter 67P/CG) have been collected in the last years by remote sensing instruments aboard NASA-Dawn and ESA-Rosetta missions. These minor bodies are among the most primitive bodies in the Solar System, and the understanding of their composition, surface morphology and evolution history is a fundamental step to shed light on the processes that occurred during planetary formation.By merging spatial and spectral information retrieved from the surfaces of these objects it is possible to infer their composition and physical properties and to correlate them with local morphology and geological processes. A discussion about spectral indicators, modeling, and mapping is given for both asteroids and comet 67P/CG. Given that the remote sensing observation techniques are very similar between Dawn and Rosetta missions, a comparative approach is used for the entire chapter and methods and interpretation for the results of these different objects are given together.

Imaging radars are all-weather instruments that can image planetary surfaces regardless of local atmospheric or solar illumination conditions. Radar images provide information about surfaces that are complementary to the chemistry usually inferred from visible and infrared images. Instead, radar images are strongly influenced by surface roughness and geomorphology, and to a lesser extent by the bulk electrical properties of the surface. This chapter describes the basic principles of high-resolution synthetic aperture radars (SARs), as well as advanced SAR implementations. Radar polarimetry provides information about surface roughness and electrical properties, while radar interferometry allows the measurement of surface topography and surface deformation following events such as earthquakes or volcanic inflation. Radar imagers have returned spectacular information about the surfaces of both Venus and Titan, bodies with dense, opaque atmospheres that are difficult to image using traditional camera systems. Examples of both planetary and Earth observations with SAR are discussed to illustrate the utility of these images.

Asteroids represent a time capsule, storing information about the composition of and conditions in the solar nebula as well as processes that have affected the Solar System. The asteroid population includes primitive bodies, partially melted material, and the result of full melting and differentiation of planetesimals. Asteroidal minerals, organic molecules, and ices that are relevant to uncovering the history of the Solar System are accessible spectroscopically. Reflection and thermal emission spectroscopy from ground-based telescopes, space telescopes, and spacecraft provide a rich view of asteroid surfaces. Analysis techniques, including taxonomic classification, direct comparisons to meteorites and pure materials, band parameter analysis, and physical models of light scattering, are customized to the specific science question under study. In recent years, spacecraft missions to asteroids have provided ground-truth to more remote spectral analyses, corroborating many inferences from ground-based observations, while enabling new discoveries and a richer, deeper view of asteroid surfaces. These compositional studies provide an important complement to and constraint on dynamical investigations of Solar System evolution. The future of asteroid science is bright, with advances expected in the areas of sample return, additional reconnaissance missions, improved wavelength coverage spectroscopy, and significant increases in the size of the database of asteroid spectra.

This chapter describes the phenomenon of Raman scattering from the point of view of classical electrodynamics and quantum mechanics. Raman scattering is a type of inelastic scattering of light by molecules that changes the energy of a photon by the energy equal to a vibrational transition of that molecule. The symmetry of vibrational modes and the activity of vibrational modes in Raman spectra is discussed via group theory for molecules and minerals. The chapter describes how the information gleaned from Raman spectra can be used to identify structural information about a given sample and how this information can be useful to Earth and planetary scientists. The principal components of laboratory and remote Raman instrumentation are defined, including excitation sources, spectrographs, and detectors, and the ways in which recent advances in technology have facilitated the application of Raman spectroscopy for Earth and planetary science are discussed. Some technological advances include the development of reliable continuous wave (CW) and pulsed lasers at a variety of wavelengths, the advancement of multichannel detectors such as two-dimensional charge-coupled devices and photodiode arrays, and the coupling of optical accessories such as microscopes and telescopes. The applications of these advanced Raman systems in the fields of Earth and planetary science are highlighted.

Mössbauer instruments were included on the Mars Exploration Rover (MER) Mission to determine the mineralogic composition, diversity, and oxidation state of Fe-bearing igneous materials and alteration products. A total of 16 Fe-bearing phases (consistent with bulk-sample chemistry) were identified, including Fe associated with rock-forming minerals (olivine, pyroxene, magnetite, ilmenite, and chromite), Fe3+-bearing oxyhydroxides (nanophase ferric oxide, hematite, and goethite), sulfates (jarosite and an unassigned Fe3+ sulfate phase), and Fe2+ carbonate. Igneous rock types ranged from basalts to ultramafic rocks at Gusev crater. Jarosite-hematite bedrock was pervasive at Meridiani Planum, and concretions winnowed from the outcrop were mineralogically hematite. Because their structures contain hydroxyl, goethite, and jarosite provide mineralogic evidence for aqueous processes on Mars, and jarosite and Fe3+ sulfate are evidence for acid-sulfate processes at both Gusev crater and Meridiani Planum. A population of rocks on the Meridiani Planum outcrop was identified as iron and stony meteorites by the presence of Fe metal (kamacite) and the sulfide troilite. The MER mission demonstrates that Mössbauer spectrometers landed on any Fe-bearing planetary surface provide first-order information on igneous provinces, alteration state, and alteration style and provide well-constrained criteria for sample selection on planetary sample-return missions including planets, moons, and asteroids.

The near-infrared reflectance spectra of Pluto and its satellites are rich with diagnostic absorption bands of ices of CH4, N2, CO, H2O, and an incompletely identified ammonia-bearing molecule. Following years of investigation of the spectra of Pluto and Charon with ground-based telescopes, NASA’s New Horizons spacecraft obtained spectral maps of these bodies and three small satellites on its passage through the system on July 14, 2015, showing the distribution of these ices, as well as a colored, non-ice component. Spectral modeling mapped the distribution of the various ices and showed their abundance and mixing details in relationship to regions of differing surface elevation, albedo, and geologic structure. Additionally, owing to their greatly different degrees of volatility, the ices of Pluto are distributed in patterns responsive to Pluto’s climatic changes on both short and long terms. The surface of Charon is dominated spectrally by H2O ice with one or more ammoniated compounds, and three of the four very small satellites show both H2O ice and the ammonia signature.

Middle infrared (~2000 to 200 cm–1 or 5 to 50 μm) data are extremely useful for compositional determination of geologic materials because this wavelength region hosts the fundamental (“Reststrahlen”) vibrational bands of most minerals. Analysis of remotely sensed data requires comparison to well-developed spectral libraries populated with a wide variety of mid-IR mineral spectra (and additional rock or meteorite spectra). Here we present the theory behind molecular vibrations of mineral structures and the simple harmonic oscillators that define them mathematically. We present dispersion theory that describes how energy travels through a crystal and how propagating energy is affected by the crystal lattice structure, specifically along the various crystal axes. The equipment required for these types of laboratory measurements (both emissivity and reflectivity) is presented as well as a discussion about how mid-IR data are affected by particle size and how related volume scattering affects spectral data. Finally, mid-IR emissivity spectra acquired in a dry, 1-atm environment are provided for 93 different minerals and meteorites. These spectra are available as ancillary data files.

The theory of reflectance and emittance spectroscopy is based on the fundamental principles of radiative transfer (the propagation of energy in the form of electromagnetic radiation) in particulate media. This chapter outlines key models for radiative transfer in particulate media that can be forward-modeled to predict reflectance and emittance spectra or inverted to obtain the abundance of geologic materials from remote observations. The models are rooted in the optical properties of geologic materials, namely the complex index of refraction, and the scattering of light controlled by particulate texture, shape, and size. The chapter is divided into reflectance modeling and emittance modeling because of the key difference in the origin of the electromagnetic radiation: external to the grain’s surface and internal to the grain’s surface, though the principles are common across this division. The key models presented for reflectance spectroscopy are the Hapke model for scattering and reflectance and the Shkuratov model for reflectance. For emittance spectroscopy, the Hapke model forms the backbone upon which hybrid models incorporating Mie T-matrix concepts are integrated.

The Cassini Visual Infrared Mapping Spectrometer (VIMS) spans a wavelength range of 0.34 to 5.2 µm. Executing numerous close targeted flybys of the major moons of Saturn, as well as serendipitous flybys of the smaller moons, VIMS gathered millions of spectra of these bodies during its 13-year mission, some at spatial resolutions of a few hundred meters. The surfaces of the inner moons are dominated by water ice, while Iapetus, Hyperion, and Titan have substantial amounts of dark materials, including hydrocarbons, on their surfaces. Phoebe is grayer in color in the visible than Saturn’s other low-albedo moons. The surfaces of the inner small moons are also dominated by water ice, and they share compositional similarities to the main rings. The optical properties of the main moons are affected by particles from Saturn’s rings: the inner moons are coated by the E-ring, which originates from cryoactivity on Enceladus, while Iapetus and Hyperion are coated by particles from the Phoebe ring. Cassini VIMS detected previously unknown volatiles and organics on these moons, including CO2, H2, organic molecules as complex as aromatic hydrocarbons, nano-iron, and nano-iron oxides.

Visible and near-infrared reflectance spectroscopy using reflected sunlight is an ideal tool for remote detection of many compounds. Surfaces can be measured in the field at close range (mm), or from a distance with aircraft or spacecraft. The technology works throughout the Solar System. Advancements have recently been made in sensor calibration and atmospheric correction, enabling faster and more accurate calibration to surface reflectance (or apparent surface reflectance). Parallel to these advancements have been advancements in radiative transfer models, including a better understanding of the scattering effects of submicrometer particles and the ability to model those effects. There has also been progress in spectral analysis, including methods to rapidly analyze imaging spectrometer data to identify and map hundreds of compounds. Finally, with the advancements in computer technology, both in compute speed and in storage, analysis of very large imaging spectrometer data sets is now feasible in a relatively short time. With some additional development, imaging spectroscopy could be used in real time or near real time applications, including exploration of resources to autonomous robots such as spacecraft rovers searching for resources or life on remote planets and satellites.