High-quality aeromagnetic data are important in guiding new knowledge of the solid earth in frontier regions, such as Antarctica, where these data are often among the first data collected. The difficulties of data collection in remote regions often lead to less than ideal data collection, leading to data that are sparse and four-dimensional in nature. Standard aeromagnetic data collection procedures are optimised for the (nearly) 2D data that are collected in industry-standard surveys. In this work we define and apply a robust magnetic data correction approach that is optimised to these four dimensional data. Data are corrected in three phases, first with operations on point data, correcting for spatio-temporal geomagnetic conditions, then operations on line data, adjusting for elevation differences along and between lines and finally a line-based levelling approach to bring lines into agreement while preserving data integrity. For a large-scale East Antarctic survey, the overall median cross-tie error reduction error reduction is 93%, reaching a final median error of 5 nT. Error reduction is are spread evenly between phase 1 and phase 3 levelling operations. Phase 2 does not reduce error directly but permits a stronger error reduction in phase 3. Residual errors are attributed to limitations in the ability to model 4D geomagnetic conditions and also some limitations of the inversion process used in phase 2. Data have improved utility for geological interpretation and modelling, in particular quantitative approaches, which are enabled with less bias and more confidence.

With radar sounders, coherent backscattering simulations from global planetary DEMs typically display a deficit in diffuse clutter, which is mainly due to the implicit assumption that roughness at scales below the resolution of the DEM is absent. Indeed, while polynomial approximations of the phase evolution across the facet allow for fast and mathematically rigorous simulators, the coarse resolution of these planetary DEMs leads to a potentially significant portion of the backscattering response being neglected. In this paper, we derive the analytical phase response of a rough rectangular facet characterised by Gaussian roughness and a Gaussian isotropic correlation function under the linear phase approximation. Formulae for the coherent and incoherent power scattered by such an object are obtained for arbitrary bistatic scattering angles. Validation is done both in isolation and after inclusion in different Stratton-Chu simulators. In order to illustrate the different uses of such a formulation, we reproduce two lunar radargrams acquired by the LRS instrument with a Stratton-Chu simulator incorporating the proposed rough facet phase integral, and we show that the original radargrams are significantly better-reproduced than with state-of-the-art methods, at a similar computational cost. We also show how the rough facet integral formulation can be used in isolation to better characterise subglacial water bodies on Earth.

The composition of impurities in ice controls the stability of liquid water and thus the distribution of potential aqueous habitats. We present a framework for modeling the brine volume fraction in impure water ice as a polynomial function of temperature and bulk ice salinity, inspired by models originally developed for sea ice. We applied this framework to examine the distribution of brine within the thermally conductive layer of Europa’s ice shell, considering binary (NaCl and MgSO4) and multi-ion “analog” (Cl-dominated and SO4-dominated) endmember impurity compositions. We found the vertical extent of brine in a conductive ice layer, expressed as a fraction of the total layer thickness, to be <12% for NaCl, <2% for MgSO4, and <18% for both the analog endmember impurity compositions, suggesting that the depth where brine is stable in an ice shell is more sensitive to composition when only two ionic species are present. For the same temperature and bulk ice salinity, the brine volume fraction is higher in a Cl-dominated ice shell than a SO4-dominated ice shell. Pressure, governed by the ice thickness, was found to have only a minor effect on the vertical extent of brine within an ice shell, relative to temperature and bulk salinity. The minimum stable bulk ice shell salinity formed through freezing of an ocean was found to be insensitive to composition and ultimately governed by the magnitude of the assumed percolation threshold.

Accreted ice retains and preserves traces of the ocean from which it formed. In this work we study two classes of accreted ice found on Earth—frazil ice, which forms through crystallization within a supercooled water column, and congelation ice, which forms through directional freezing at an existing interface—and discuss where each might be found in the ice shells of ocean worlds. We focus our study on terrestrial ice formed in low temperature gradient environments (e.g., beneath ice shelves), consistent with conditions expected at the ice-ocean interfaces of Europa and Enceladus, and highlight the juxtaposition of compositional trends in relation to ice formed in higher temperature gradient environments (e.g., at the ocean surface). Observations from Antarctic sub-ice-shelf congelation and marine ice show that the purity of frazil ice can be nearly two orders of magnitude higher than congelation ice formed in the same low temperature gradient environment (~0.1% vs. ~10% of the ocean salinity). In addition, where congelation ice can maintain a planar ice-water interface on a microstructural scale, the efficiency of salt rejection is enhanced (~1% of the ocean salinity) and lattice soluble impurities such as chloride are preferentially incorporated. We conclude that an ice shell which forms by gradual thickening as its interior cools would be composed of congelation ice, whereas frazil ice will accumulate where the ice shell thins on local (rifts and basal fractures) or regional (latitudinal gradients) scales through the operation of an “ice pump”.

Brine systems in Europa’s ice shell have been hypothesized as potential habitats that could be more accessible than the sub-ice ocean. We model the distribution of sub-millimeter-scale brine pockets in Europa’s ice shell. Through examination of three habitability metrics (water activity, ionic strength, salinity), we determine that brine pockets are likely not geochemically prohibitive to life as we know it for the chloride and sulfate-dominated ocean compositions considered here. Brine volume fraction is introduced as a novel habitability metric to serve as a proxy for nutrient transport and recycling—because of its role in governing permeability—and used to define regions where nutrient-open, nutrient-closed, and relict habitats are stable. Whereas nutrient-closed habitats could exist wherever brine is stable, nutrient-open habitats are confined to meter-scale regions near the ice-ocean interface where freezing is occurring. This classification scheme can help guide future life-detection missions to ocean worlds.