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Exoplanets with lower equilibrium temperatures than Earth and primordial hydrogen atmospheres that evaporate after formation should pass through transient periods where oceans can form on their surfaces, as liquid water can form below a few…
In this hypothesis article, we discuss the basic requirements of planetary environments where aerobe organisms can grow and survive, including atmospheric limitations of millimeter-to-meter-sized biological animal life based on physical…
Earth is the only planet known to harbor life and, as a result, the search for habitable and inhabited planets beyond the Solar System commonly focuses on analogs to our planet. However, Earth's atmosphere and surface environment have…
Stellar activity and planetary atmospheric properties have the potential to strongly influence habitability. To date, neither have been adequately studied in the multiverse context, so there has been no assessment of how these effects…
Life arose on Earth sometime in the first few hundred million years after the young planet had cooled to the point that it could support water-based organisms on its surface. The early emergence of life on Earth has been taken as evidence…
Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, favorable chemical ingredients and energy pathways. If life ever developed on, or was transported…
Over the past two decades, enormous advances in the detection of exoplanets have taken place. Currently, we have discovered hundreds of earth-sized planets, several of them within the habitable zone of their star. In the coming years, the…
The solar system's terrestrial planets are thought to have accreted over millions of years out of a sea of smaller embryos and planetesimals. Because it is impossible to know the surface density profile for solids and size frequency…
Open-ended evolutionary dynamics remains an elusive goal for artificial evolutionary systems. Many ideas exist in the biological literature beyond the basic Darwinian requirements of variation, differential reproduction and inheritance. I…
The existence of intelligent, interstellar traveling and colonising life is a key assumption behind the Fermi Paradox. Until recently, detecting signs of life elsewhere has been so technically challenging as to seem almost impossible.…
Understanding the origin and long-term evolution of the Solar System is a fundamental goal of planetary science and astrophysics. This chapter describes our current understanding of the key processes that shaped our planetary system,…
Our planet is experiencing an accelerated process of change associated to a variety of anthropogenic phenomena. The future of this transformation is uncertain, but there is general agreement about its negative unfolding that might threaten…
For more than 100 years, humanity (both specialists and enthusiastic laics) has been searching for extraterrestrial life hoping we are not alone. The first step in the quest for extraterrestrial life is to define what and where exactly to…
Approximately one billion years (Gyr) in the future, as the Sun brightens, Earth's carbonate-silicate cycle is expected to drive CO$_2$ below the minimum level required by vascular land plants, eliminating most macroscopic land life. Here,…
Water is crucial for the emergence and evolution of life on Earth. Recent studies of the water content in early forming planetary systems similar to our own show that water is an abundant and ubiquitous molecule, initially synthesized on…
The conditions that a planet must fulfill to be habitable are not precisely known. However, it is comparatively easier to define conditions under which a planet is very likely not habitable. Finding such conditions is important as it can…
Understanding planetary habitability is one of the major challenges of the current scientific era, particularly given the discovery of a large and diverse terrestrial exoplanet population. Discerning the primary factors that contribute to…
Two habitable planetary states are proposed: an aqua planet like the Earth and a land planet that has a small amount of water. Land planets keep liquid water under larger solar radiation compared to aqua planets. Water loss may change an…
Earth's climate is influenced by over a dozen feedbacks, but only three dominate its long-term climate behavior. Models of the exoplanet habitable zone (HZ) assume that this is similar for other Earth-like planets. We used dynamical…
The relative abundances of exotic environments provides us with (uninformed) bounds on the habitability of those environments relative to our own, on the basis that our presence here is not too atypical. For instance, since red stars…