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The discovery of Europa's subsurface ocean has spawned a strong desire by the planetary community to return and assess the ocean's habitability using the magnetic induction signal that Europa generates. NASA has since formulated and developed the Europa Clipper mission with that same goal, anticipating its arrival in the Jovian system in the early 2030s. In parallel, ESA has developed the JUpiter Icy moons Explorer mission to further investigate the interior of Ganymede and other Jovian moons, scheduled to arrive approximately one year later. As a result, extensive work has now been devoted to developing and refining methods to analyse magnetic induction measurements with the goal of characterizing oceans within icy moons, including those in the Neptune and Uranus systems, which are ideal laboratories for such investigations. We present one such method, involving a distance-based inverse and forward modelling approach that leverages self-consistent interior models used to infer ocean and ice-shell properties of various moons that respond inductively to the dynamic magnetic environments in which they reside. We demonstrate the method on a hypothetical ocean within Umbriel, showing the ocean thickness and conductivity constraints that can be inferred from a Monte Carlo error analysis using a three-flyby mission concept. This article is part of the theme issue 'Magnetometric remote sensing of Earth and planetary oceans'. [ABSTRACT FROM AUTHOR]

Spacecraft magnetic field measurements are able to tell us much about the planets' interior dynamics, composition, and evolutionary timeline. Magnetic fields also serve as the source for passive magnetic sounding of moons. Time‐varying magnetic fields experienced by the moons, due to relative planetary motion, interact electrically with conductive layers within these bodies (including salty subsurface oceans) to produce induced magnetic fields that are measurable by nearby, magnetometer‐equipped spacecraft. Many factors influence the character of the induced field, including the precise amplitude and phase of the time‐varying field, known as the excitation or driving field and represented by excitation moments. In this work, we present an open‐source Matlab software package named PlanetMag that features calculation of planetary magnetic field models available in the literature at arbitrary positions and times. The implemented models enable simultaneous inversion of the excitation moments across a range of oscillation frequencies using linear least‐squares methods and ephemeris data with the SPICE toolkit. Here we summarize the available magnetic field models and their associated coordinate systems. Precisely determined excitation moments are a critical input to forward models of global induced fields. Our results serve as a prerequisite to any precise comparison to spacecraft data for magnetic sounding investigation of giant planet moons—connecting the induced magnetic field to a moon's interior requires accurate representation of the oscillating excitation field. We calculate complex excitation moments relative to the J2000 epoch and share the results as ASCII tables compatible with related software packages intended for induction response calculations. Plain Language Summary: Planetary magnetic fields tell us much about a planet's interior, composition, and history. Magnetic fields are also useful for remotely probing the interior of their moons, especially for finding and characterizing potential subsurface oceans. Liquid‐water oceans within the solar system are ideal places to search for habitable environments beyond Earth. Relating spacecraft magnetic measurements to the interior properties of the moons requires an understanding of various related components, including the manner in which the magnetic field applied to the moon changes with time. We have developed an open‐source software package called PlanetMag that uses published magnetic field models to estimate the magnetic field at any point in time and space. It also has the ability to precisely estimate the planetary field oscillations at the location of each large moon in the solar system, which is needed for prediction of the magnetic field response from the moon. Calculations of these magnetic oscillations are provided in text files compatible with existing software. Key Points: We developed an open‐source software package in Matlab called PlanetMag for evaluating planet magnetic field models from the literaturePlanetMag uses ephemeris data and least‐squares inversion methods to determine amplitudes and phases of magnetic excitations for moonsComplex excitation moments are determined for all outer planet large moons in support of magnetic sounding investigations [ABSTRACT FROM AUTHOR]

The open‐source PlanetProfile framework was developed to investigate the interior structure of icy moons based on collectively matching their observed properties and comparative planetology. The software relates observed and measured properties, assumptions such as the type of materials present, and laboratory equation‐of‐state (EOS) data through geophysical and thermodynamic models to evaluate radial profiles of mechanical, thermodynamic, and electrical properties, as self‐consistently as possible. We have created a Python version of PlanetProfile. In the process, we have made optimization improvements and added parallelization and parameter‐space search features to utilize fast operation for investigating unresolved questions in planetary geophysics, in which many model inputs are poorly constrained. The Python version links to other scientific software packages, including for evaluating EOS data, magnetic induction calculations, and seismic calculations. Physical models in PlanetProfile have been reconfigured to improve self‐consistency and generate the most realistic relationships between properties. In this work, we focus on the description of the software design and algorithms in detail, summarize model results for major moons across the outer solar system, and discuss new inferences about the interior structure of several bodies. The high values and narrow uncertainty ranges reported for the axial moments of inertia for Callisto, Titan, and Io are difficult to reconcile with the realistic physical and chemical approximations applied, requiring highly porous rock layers equivalent to incomplete differentiation for Callisto and Titan, and a high rock melt fraction for Io. Radial profiles for each model and comparison to prior work are provided as Zenodo archives. Plain Language Summary: The software package PlanetProfile was developed in order to connect measurable properties of planetary bodies to each other and determine how planetary interiors might be structured. We adapted the existing Matlab version of PlanetProfile to Python and improved it in many ways in the process, to better investigate scientific questions. Python is more widely available, and PlanetProfile now connects better to other scientific software packages capable of relating measurements and observations to the interior structure of planetary bodies such as large moons. PlanetProfile is now more adaptable for new scientific investigations and adding features, includes more realistic relationships between pressures, temperatures, and physical properties of materials, and is optimized for studies that require a wide variety of models to be run. These improvements make PlanetProfile a powerful tool that will become more useful as new features are added. We summarize our models for the major large moons in the outer solar system and provide output files detailing each model. In creating these models, we found that bulk properties for Io, Callisto, and Titan are difficult to combine together into realistic models, which suggests that the reported values may contain errors. Key Points: Radial models of planetary interiors are generated from bulk properties based on geophysical models, lab data, and minimal assumptionsBodies with a high moment of inertia such as Callisto require low‐density rocks, which we model with a high effective porosityModels are optimized for wide parameter‐space searches as needed for investigating unresolved questions about planetary interiors [ABSTRACT FROM AUTHOR]

The Galileo mission to Jupiter discovered magnetic signatures associated with hidden subsurface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter's strong time‐varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager 2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with subsurface oceans. Future missions to the ice giants may therefore be capable of discovering subsurface oceans, thereby adding to the family of known "ocean worlds" in our Solar System. Here, we assess magnetic induction as a technique for investigating subsurface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single‐pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus. Plain Language Summary: The best evidence for the existence of an ocean within Jupiter's moons of Europa and Callisto comes from interpretations of measurements collected from the magnetometer on the Galileo spacecraft. Their salty oceans are able to conduct electrical currents that are driven by Jupiter's strong time‐varying magnetic field, producing a unique secondary magnetic field signature that can be measured externally by as spacecraft passing by. Some of the large moons of the Ice Giant planets of Uranus and Neptune are also thought to possibly contain subsurface oceans. Unfortunately, Voyager 2 did not pass close enough to any of these planetary bodies for its onboard magnetometer to sense magnetic field signatures associated with a subsurface ocean. In this work, we investigate the feasibility of detecting magnetic signatures of subsurface oceans within the moons of Uranus based upon various assumed interior structure profiles, thus providing guidance to required magnetometer performance and trajectory design for possible future missions. Key Points: The major moons of Uranus exhibit surface features which hint at recent geologically activity, possibly associated with subsurface oceansFavorable geometry of the Uranus system facilitates magnetic induction investigation of potential oceans within the primary moonsSubsurface ocean detection and constrained characterization is possible within these moons, even in the presence of an ionosphere [ABSTRACT FROM AUTHOR]

Prior analyses of oceanic magnetic induction within Jupiter's large icy moons have assumed uniform electrical conductivity. However, the phase and amplitude responses of the induced fields will be influenced by the natural depth‐dependence of the electrical conductivity. Here, we examine the amplitudes and phase delays for magnetic diffusion in modeled oceans of Europa, Ganymede, and Callisto. For spherically symmetric configurations, we consider thermodynamically consistent interior structures that include realistic electrical conductivity along the oceans' adiabatic temperature profiles. Conductances depend strongly on salinity, especially in the large moons. The induction responses of the adiabatic profiles differ from those of oceans with uniform conductivity set to values at the ice–ocean interface, or to the mean values of the adiabatic profile, by more than 10% for some signals. We also consider motionally induced magnetic fields generated by convective fluid motions within the oceans, which might optimistically be used to infer ocean flows or, pessimistically, act to bias the ocean conductivity inversions. Our upper‐bound scaling estimates suggest this effect may be important at Europa and Ganymede, with a negligible contribution at Callisto. Based on end‐member ocean compositions, we quantify the magnetic induction signals that might be used to infer the oxidation state of Europa's ocean and to investigate stable liquids under high‐pressure ices in Ganymede and Callisto. Fully exploring this parameter space for the sake of planned missions requires thermodynamic and electrical conductivity measurements in fluids at low temperature and to high‐salinity and pressure as well as modeling of motional induction responses. Plain Language Summary: Oscillations in a planet's magnetic fields can create magnetic signals within its companion moons if those moons have salty oceans under their icy surfaces. Fluid currents within those oceans can also create magnetic fields. Spacecraft investigating those oceans can measure such fields and thereby learn about the properties of the oceans. We compute possible magnetic properties for Jupiter's ocean moons—Europa, Ganymede, and Callisto—using available chemical data and electrical conductivity. Previous work has also computed these properties, but our methods allow us to account for how the electrical properties vary with depth due to pressure and temperature. We also model ocean currents. We find that the depth‐dependence of electrical conductivity affects the predicted magnetic fields more than 1 nT as compared with the typical assumption of a uniform conductivity. This is important because the planned Europa Clipper and JUpiter ICy moons Explorer (JUICE) missions will measure magnetic fields at these moons with roughly 1 nT precision. For Europa, we examine seawater (NaCl) and MgSO4 ocean compositions linked to more hydrogen‐rich or oxygen‐rich scenarios. With additional constraints on ice shell and ocean thickness from other spacecraft measurements, magnetic measurements may be a key tool for determining the composition of Europa's ocean, and thus its chemical evolution through time. Key Points: The signal from induction that accounts for adiabatic ocean temperatures is distinct from induction based on uniform conductivityMotional induction due to thermal convection in the satellite oceans may be significantMaterial properties and motional induction modeling are needed to obtain ocean composition from magnetic induction [ABSTRACT FROM AUTHOR]

The discovery of Europa's subsurface ocean has spawned a strong desire by the planetary community to return and assess the ocean's habitability using the magnetic induction signal that Europa generates. NASA has since formulated and developed the Europa Clipper mission with that same goal, anticipating its arrival in the Jovian system in the early 2030s. In parallel, ESA has developed the JUpiter Icy moons Explorer mission to further investigate the interior of Ganymede and other Jovian moons, scheduled to arrive approximately one year later. As a result, extensive work has now been devoted to developing and refining methods to analyse magnetic induction measurements with the goal of characterizing oceans within icy moons, including those in the Neptune and Uranus systems, which are ideal laboratories for such investigations. We present one such method, involving a distance-based inverse and forward modelling approach that leverages self-consistent interior models used to infer ocean and ice-shell properties of various moons that respond inductively to the dynamic magnetic environments in which they reside. We demonstrate the method on a hypothetical ocean within Umbriel, showing the ocean thickness and conductivity constraints that can be inferred from a Monte Carlo error analysis using a three-flyby mission concept.This article is part of the theme issue 'Magnetometric remote sensing of Earth and planetary oceans'.

The Astrobiology Primer 3.0 (ABP3.0) is a concise introduction to the field of astrobiology for students and others who are new to the field of astrobiology. It provides an entry into the broader materials in this supplementary issue of Astrobiology and an overview of the investigations and driving hypotheses that make up this interdisciplinary field. The content of this chapter was adapted from the other 10 articles in this supplementary issue and thus represents the contribution of all the authors who worked on these introductory articles. The content of this chapter is not exhaustive and represents the topics that the authors found to be the most important and compelling in a dynamic and changing field.

Although astrobiology is a relatively new field of science, the questions it seeks to answer ( e.g., "What is life?" "What does life require?") have been investigated for millennia. In recent decades, formal programs dedicated specifically to the science of astrobiology have been organized at academic, governmental, and institutional scales. Constructing educational programs around this emerging science relies on input from broad expertise and backgrounds. Because of the interdisciplinary nature of this field, career pathways in astrobiology often begin in more specific fields such as astronomy, geology, or biology, and unlike many other sciences, typically involve substantial training outside one's primary discipline. The recent origin of astrobiology as a field of science has led to strong collaborations with education research in the development of astrobiology courses and offers a unique instructional laboratory for further pedagogical studies. This chapter is intended to support students, educators, and early career scientists by connecting them to materials and opportunities that the authors and colleagues have found advantageous. Annotated lists of relevant programs and resources are included as a series of appendices in the supplementary material.

All known life on Earth inhabits environments that maintain conditions between certain extremes of temperature, chemical composition, energy availability, and so on (Chapter 6). Life may have emerged in similar environments elsewhere in the Solar System and beyond. The ongoing search for life elsewhere mainly focuses on those environments most likely to support life, now or in the past-that is, potentially habitable environments. Discussion of habitability is necessarily based on what we know about life on Earth, as it is our only example. This chapter gives an overview of the known and presumed requirements for life on Earth and discusses how these requirements can be used to assess the potential habitability of planetary bodies across the Solar System and beyond. We first consider the chemical requirements of life and potential feedback effects that the presence of life can have on habitable conditions, and then the planetary, stellar, and temporal requirements for habitability. We then review the state of knowledge on the potential habitability of bodies across the Solar System and exoplanets, with a particular focus on Mars, Venus, Europa, and Enceladus. While reviewing the case for the potential habitability of each body, we summarize the most prominent and impactful studies that have informed the perspective on where habitable environments are likely to be found.