Editorial: Remote sensing and modelling of planetary and moon surfaces

Introduction

Observations of planetary surfaces have greatly increased these last years, both in numbers and quality, thanks to ground-based telescopes and especially space missions. These data are fundamental to provide clues about Solar System formation and evolution, as well as the delivery of water and organic molecules to the Earth, which is thought to have contributed to the conditions necessary for the emergence of life. Each planetary body provides important and unique information.

Mars is considered one of the Solar System bodies with the greatest astrobiological potential because of the occurrence of subsurface water trapped in brines, ices, and even minerals. Furthermore, its geological features show analogies with terrestrial ones and give us the opportunity to study the evolution of terrestrial planets and surface-atmosphere interactions. A large amount of data from Mars has yet to be analysed, regarding the different missions launched in the recent years. Furthermore, several other missions will explore Mars in the near future with the goal of deepening our understanding of the Red Planet, such as the ESA’s ExoMars mission, and preparatory studies supporting these missions are currently in progress.

Small bodies are the target of recent and upcoming space missions because of their limited growth, which helps us to infer information about the early Solar System. In particular, NASA’s Juno mission provided the opportunity to study Jupiter moons in detail, which exhibit different characteristics and therefore provide complementary information to other planetary bodies in the Solar System.

Moreover, all Solar System bodies are studied for comparative planetology and used to understand processes occurring on the terrestrial surface and in the terrestrial atmospheres. For all these studies, data analysis is often supported by modeling. These diverse endeavors, which range from molecular simulations all the way to dynamic solar system modeling, serve to provide context, constraints, and simulated ground truth when data are limited.

This Research Topic seeks to consolidate state-of-the-art comparisons between models and remote sensing data of planetary and moon surfaces in order to support and contextualize current and past planetary mission observations. It includes nine papers, which are here classified in three categories: Mars, the Jupiter moon Io and general planetology.

Mars

Williams presents an extensive study on alluvial fans on Mars, merging several datasets (from NASA’s Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Global Surveyor as well as ESA’s Mars Express missions). These geological features record environmental transitions and their heterogeneity (debris flows, pitted deposits, and remnants of fluvio-glacial processes). Together, these features suggest that different climate periods occurred on Mars and the transitions among them were smooth and variable rather than swift.

Sheppard et al. focused on surficial carbonates, which are of scientific interest because they precipitate from water. They have been observed in Gale crater by the Curiosity rover, but were not detected by the in-orbit spectrometers MRO/CRISM and MeX/OMEGA. The authors developed laboratory mixtures of Mg-sulfates and siderite with different hydration states, concluding that Mg-sulfates mask the carbonate spectral signatures, especially the 2.3 μm absorption band.

The work by Ligeza et al. is preparatory to ESA’s ExoMars mission, that will land on Oxia Planum. Through an extensive literature review on the geology and mineralogy of this region, the authors identified some samples that are expected to be observed by the CLUPI imager (to be mounted on the ExoMars rover): these include sedimentary rocks, igneous rocks, Fe-Mg phyllosilicates, evaporites, carbonates and morphological biosignatures. These samples were procured and imaged under different illumination and viewing conditions (simulating the expected CLUPI observations). The obtained dataset will serve as valuable reference information, increasing the likelihood of detecting diverse rock textures and relevant structures.

Corchete studied the Martian polar caps and used NASA’s InSight pressure data to retrieve the total mass of the frosted CO₂ in the polar caps and its temporal variation, finding good agreement with the General Circulation Model.

Io

The studies of the Jupiter moon Io focus on the satellite’s volcanic activity.

Tosi et al. evaluated the predicted latitudinal variation of thermal emission (based on data from the M-band of Juno’s JIRAM spectrometer), which matches the magma ocean model. The authors critically analyzed the limitations of JIRAM-M band data, including saturation effects, the lack of temperature constraints and their integration with models. They conclude that the latitudinal heat flow variation is not adequately supported and that a multi-wavelength and multi-instrument analysis would be crucial.

Mura et al., Mura et al. studied Io’s hotspot by means of JIRAM data with the aid of a photometric model specifically developed for these investigations. No latitudinal variation of power emission was observed, while low-latitude hot spots show both temporal variation and higher temperatures.

General planetology

Zhang and Chang performed an extensive review of planetary landform studies, which are necessary to understand planetary formation and geological evolution, even on Earth. The authors conclude that further landform studies are needed in the future to broaden our knowledge of planetary evolution through the Solar System, involving international cooperation, higher-precision observation data, and more refined simulations.

Weiss et al. investigated how Fourier Transform Mass Spectrometry (FT-MS) can estimate the Molecular Assembly (MA) index. This is an estimate of the complexity degree of a complex molecule (e.g., organic molecules), as foreseen by the Assembly Theory. The authors identify FT-MS requirements to retrieve MA, in view of future planetary missions, including sample return ones.

Therefore, this Research Topic has provided the opportunity to study key scientific questions regarding Mars and Io in greater detail, as well as to deepen our understanding of general planetology, laying the groundwork for future research on these planetary bodies.

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Footnotes

Edited and reviewed by: Miriam Rengel, Max Planck Institute for Solar System Research, Germany