Worlds of the Solar System: Geological Evolution and Habitability of Planets and Moons

Dear Colleagues,

The Special Issue entitled “Worlds of the Solar System: Geological Evolution and Habitability of Planets and Moons” aims to bring together the latest advances on the dynamic processes that have shaped planetary bodies and their potential to support life. We welcome submissions on comparative studies of Venus, Earth, and Mars, highlighting the divergent evolutionary pathways of terrestrial planets from Venus’ runaway greenhouse conditions to Earth’s long-term climate stability and Mars’ transition from a wetter, more habitable past to its current arid state. Contributions may include, but are not limited to, an examination of how factors such as volcanism, tectonics, atmosphere–surface interactions, and mineralogical transformations influence habitability.

Beyond inner planets, this Special Issue also aims to explore the icy worlds of the outer solar system. We welcome investigations of Europa and Enceladus focusing, among other topics, on evidence for subsurface oceans, plume activity, and geophysical mechanisms that may create niches for life beneath their ice shells, as well as studies on Titan emphasizing its unique methane-based hydrological cycle, organic-rich surface, and complex interactions between the atmosphere and surface chemistry. Other icy moons are also a topic of interest for manuscripts submitted to this Special Issue.

Integrating mineralogical, geophysical, geochemical, and astrobiological perspectives, the articles in this collection will advance our understanding of planetary habitability in diverse environments. Together, they will provide a multidisciplinary foundation to interpret upcoming mission data and refine models of life-supporting conditions within the solar system.

Prof. Dr. Alberto G. Fairén
Guest Editor

Special Issue Invited Papers

The Concept of Habitability on Earth, the Solar System, and beyond.
Author: Christopher P. McKay
Brief summary: In this paper I review the concept of habitability beginning with Earth. Our concept of where life can thrive on Earth has advanced over the years to include the deep subsurface, hydrothermal vents on the deep ocean floor, extreme arid deserts, and reaching to the ice-covered lakes and high mountain valleys of Antarctica. This expanding understanding of the biosphere has informed the search for life on other water worlds in our Solar System – especially Mars, Europa, and Enceladus. Titan presents a reverse of this approach. The interesting organic solid and fluids on that world have no analog in Earth habitability but have inspired suggestions of possible biological systems unlike any on Earth. If realized the discovery of life on Titan would stretch the concept of habitability just as it stretches the concept of life as we know it. Habitability studies on exoplanets may follow both of these paths: we will look for habitability on exoplanets based on observed habitats on Earth and we will also use observations of exoplanets as grist for contemplation of life styles different from anything we know on Earth.

Mercury: The distinctive innermost planet
Authors: Sean C. Solomon, Paul K. Byrne, and Christian Klimczak
Brief Summary: Ten years after the end of Mercury orbital operations by NASA's MESSENGER spacecraft, we know a great deal more about one of our nearest planetary neighbours than before that mission. An integrated summary of our present understanding of the dynamics, composition, internal structure, environment, and geological and geophysical evolution of Mercury from MESSENGER and earlier spacecraft and Earth-based astronomical observations sets the stage for the imminent follow-on exploration of the innermost planet by the dual BepiColombo spacecraft mission of the European Space Agency and the Japan Aerospace Exploration Agency.

Astrobiology perspective on Venus
Authors: Sanjay Limaye, Diana Gentry, Rakesh Mogul, Michael Way.
Brief summary: This paper will provide the background information about Venus environment, early ideas of life (pre-space age), current knowledge, gaps in our knowledge and key questions.

Applying the Mantle Plume–Large Igneous Province–Mafic Dyke Swarm paradigm to Venus
Authors: Richard Ernst and Hafida El Bilali
Brief Summary: We introduce the Mantle Plume–Large Igneous Province–Dyke Swarm (MP–LIP–DS) paradigm as a new event-based framework for Venus. By unifying mantle plumes, LIP-scale magmatism, and mafic dyke swarm geometries, this paradigm enables the systematic identification of magmatic centers, the quantification of underlying plume head size, the reconstruction of the full spatial footprints of discrete magmatic events, and the establishment of their relative chronologies. In doing so, the framework envisages Venusian geology as a dynamic mosaic of overlapping plume-driven events rather than a collection of isolated volcanic units, offering a coherent lens through which the planet’s volcanic, tectonic, and thermal history can be reinterpreted.

The Earth from an astrobiology perspective
Author: Frances Westall
Brief Summary: The Earth is the most important astrobiological planetary body for the simple reason that it is the only planetary body we know of, to date, that is inhabited. This contribution will track the evolution of terrestrial habitability through time, from the creation of conditions for the emergence of life, or abiogenesis, to the establishment of life throughout the oceans and on land, and finally to the appearance of technologically capable beings. It will highlight the importance of geology and geophysics in the spread of life since the appearance of oxygenic photosynthesis, addressing the Earth as an exoplanet.

Evidence for life on Mars
Author: Alberto G. Fairén
Brief Summary: The search for Martian life has produced several debated findings. NASA’s Viking landers recorded reactions that could be interpreted as metabolic, but the absence of organics suggested exotic chemistry rather than biology. The ALH84001 meteorite, over 4 billion years old, contains carbonate globules, magnetite chains, and nanostructures that some interpret as being biogenic, though inorganic origins cannot be ruled out. Methane detections from orbiters and rovers may imply active processes, yet the results remain inconsistent. The Curiosity rover identified complex organics and 12C enrichment, intriguing but not definitive biosignatures. Perseverance’s exploration of Jezero Crater has revealed organics, vivianite, and greigite that resemble microbially influenced minerals on Earth. While these discoveries are inconclusive, they collectively hint at Mars’s potential for past or even present biology. Confirmation awaits the return of samples for analysis.

What Martian Mineralogy Can Tell Us About Aqueous Processes and the Habitability of Mars
Author: Janice Bishop
Brief summary: Minerals on Mars hold secrets about the geochemical history of Mars and evolution of the climate. Alteration minerals, including phyllosilicates, sulfates, carbonates, iron oxides/hydroxides, phosphates, chlorides and perchlorates, have all been observed on Mars and contribute to informing us about the geochemical environment during their formation. Many of these minerals formed on ancient Mars when the climate was much different from today, and others formed more recently, indicating niches where liquid water has been more active on Mars and habitable environments were possible. Hyperspectral remote sensing has enabled mineral detection at the tens of meters scale from orbit at numerous sites across the planet, while in situ analyses by landers and rovers have provided mineral detections up close. Coordinating these close-up mineralogy results with lab and field work on Martian analogs enables informed interpretation of the global mineralogy data from orbit. Recent mineralogy observations from the Curiosity and Perseverance rovers have expanded the types of mineral assemblages and redox processes occurring on Mars. Many of these are linked to environmental transformations on early Mars and new interpretations of habitability.

The Habitability of Europa
Authors: Cynthia B. Phillips and Morgan Cable
Brief summary: Jupiter's moon Europa appears to host all ingredients for life as we know it: liquid water, chemical building blocks, and at least one energy source, potentially sustained for a billion years or more. Spacecraft data primarily from the Galileo mission, as well as telescopic observations, laboratory work, modeling, and studies of field analogues on Earth, have all shaped our understanding of this ocean world. Here we provide a comprehensive view of Europa's geology, composition, and interior structure as it relates to habitability, including surface/subsurface exchange and the potential for life both in the ocean and in near-surface reservoirs. We also consider the future exploration of Europa by both remote sensing and in situ missions.

Enceladus: A habitable ocean beyond Earth
Authors: Alfonso Davila et al.
Brief Summary: This paper synthesizes the current understanding of Saturn’s moon Enceladus as a habitable ocean world, integrating geophysics, chemistry, and astrobiology to assess its potential for life. Drawing on data collected by the Cassini spacecraft, it highlights the moon's subsurface ocean, active plume emissions, and interior–exterior material exchange, all of which enable investigations into chemical evolution, and the possibility of extant life in a habitable water ocean beyond Earth.

The habitability of Titan in the context of its evolution
Author: Jonathan Lunine
Brief Summary: With lakes and seas of methane and ethane, methane rain, and the geological processes of fluvial and aeolian erosion superimposed on a lightly cratered and mostly subtle topography, Titan is geologically somewhat like Earth, but with different working materials. Its prodigious atmosphere’s organic chemistry suggests the possibility of a kind of photo-biological evolution at the surface. The low temperatures may not be an impediment to the chemistry if recent calculations of quantum tunnelling at 95 K are correct. Titan’s interior may be the only one of the triad of giant moons (Callisto, Titan, and Ganymede) to not have a large liquid water ocean today. How the evolution of this enigmatic body has brought it to the present state remains one of the great challenges of planetary science, and likely rests on the behaviour of hydrated silicates interacting with high-pressure ice, methane clathrates, and melting point depressants like ammonia and methanol.

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