Astrobiology and SETI search for life-not-as-we-know-it (yet). Researchers aspire to an understanding not yet found. With that in mind, knowledge about three types of context can inform and improve the search. Observational context: knowing our location as humans (anthropism) can mitigate biases introduced by our desire to over-value humanity (anthropocentrism). Historical context: knowing the history of the search, not just the last 10–30 years, can clarify concepts and significance. Disciplinary context: understanding the rules by which different disciplines operate can reveal the limitations of a single perspective (astronomy, biology, ecology, sociology, law, medicine, philosophy, theology…). Astrobiology and SETI tell epic stories about the place of life in the cosmos. They locate humans morally as well as physically. We should ask why we tell them and how our context shapes the telling, because the stories shape human interactions with the world.

We are in the age of the direct and indirect search for extraterrestrial life. The major question is: what are we looking for and to what extent can life on Earth provide an analogy for extraterrestrial life. We will address these questions by examining the emergence of life and its evolution through geological time, based on consideration of the Earth as an exoplanet. We conclude that, with the exception of a couple of hundred million years during the Great Oxydation Event 2.3-2.1 Ga, it would not have been possible for an extraterrestrial observer to detect traces of terrestrial life until the advent of planktonic eukaryotic algae after the Neoproterozoic Oxydation Event about 800 Ma. Thus, for most of the history of life on Earth, there would be no externally observable evidence of its existence. We address the implications of this for the search for extraterrestrial life.

This abstract explores the application of quantitative information theory measures and linguistic features to analyze animal communication systems and extends this methodology to contemplate the possibilities of interstellar communication as a part of CETI practice. We will assess some early findings by using information theory on social species with sophisticated acoustic communication abilities, such as bottlenose dolphins and humpback whales (Hanser, Sean F., et al.) as well as birds, as examples of how the complex interplay between notions, data, and misinterpretations can become established as reliable knowledge and cognition about and understanding of an ETI civilization and culture. The study also looks into the potential implications of extraterrestrial contact. Given the diversity of language instances in Earth’s evolutionary history, we discuss the choice of syntactic complexity of an “intelligent message” for potential alien civilizations. The central point of this paper is to examine the advantages and limitations of acoustic and visual communication, considering linguistical and mathematical constraints that may apply universally.

The discovery of phosphine in Venus’s atmosphere provides lessons for the search for life. The detection has survived all challenges and has acquired independent support from archival data from PVP. The presence of phosphine in Venus’ oxidising environment is perplexing, and comprehensive studies rule out all known abiotic sources. More data is needed to understand the origin of phosphine, leading to JCMT-Venus, a long term atmospheric monitoring programme. This can find how phosphine varies in relation to other species providing clues to its origin. We present the latest JCMT-Venus results. The discovery and subsequent papers were explicit that they did not constitute evidence for life, only of phosphine. Media and public reaction to the discovery and its implications provide lessons for future life searches, as does the reaction of the scientific community. How this was handled by the team, media, and general public will be reviewed.

A long-standing issue in astrobiology is whether planets orbiting the most abundant type of stars, M-dwarfs, can support liquid water and eventually life. Often previous studies have raised doubts for the habitability of planets orbting M-stars, due to the intense stellar activity during the early evolution. Those include solar-wind-like eruptions of the host star that could erode the planetary atmosphere, as well as the intense XUV radiation from the host. A new study shows that subglacial liquid water that accumulates on the night-side of tidally locked planets may provide an answer, significantly extending the habitability region, in particular around M-dwarf stars, which are also the most promising for biosignature detection with the present and near-future technology.

How may life be defined? This is a question that has growing importance as humanity develops the ability to explore beyond the Earth and searches for evidence of life being present on other astronomical bodies from the planets and moons in our own solar system to the thousands of exoplanets we are detecting around other stars. Such a definition is non-trivial and, as we discover life in ever more diverse and ‘extreme’ environments on Earth broadening the regions of ‘habitability’, increasingly complex. In this short article, we review the different definitions of ‘life’, the need for such a definition and the implications that such a definition may have on the future development of astrobiology and the search for evidence of life in the universe.

It is argued that a central challenge to the task of developing a foundational model for life lies within the implicit propositions of the Western scientific view. These propositions constrain thinking about the concept of life. Three implicit boundary conditions in particular - life as a property of a system, life as a purely biological phenomenon, and life as a binary concept - are identified, and it is suggested to replace them with three operational principles - synonymity of ’life’ with ’processes of change’; the foundation of change upon interaction; the recursion and integration of change over boundary conditions.

Conway’s Game of Life is a cellular automaton noted for its rich, complex, and emergent behaviour, which seems qualitatively ‘lifelike’. It exists within a wider space of different rulesets of cellular automata, none of which have been found to display behaviours that seem as rich as Conway’s selected example. We present here a set of three quantitative tests for ‘lifelike’ behaviour, based on the critical brain theory, Shannon’s theory of information entropy and integrated information theory, all of which are successfully able to select Conway’s Game of Life as an outlier within this set, which is a non-biological analogue to the selection of a habitable planet or universe amongst a wider space of similar settings that cannot support the same kinds of living systems.

Context. Modern polarimeters enable precise measurements of exoplanetary systems, providing valuable constraints on orbital geometry and atmospheric scattering properties.

Aims. We aim to investigate the orbital parameters of the non-transiting Jupiter-like exoplanet ʋ And b, which orbits close to its host star, using polarized scattered light observed with the DiPol-2 polarimeter on a 60 cm telescope.

Methods. Over nearly three years, we collected high-precision polarimetric data of the ʋ And system. Using Lomb-Scargle periodograms, we identified variability close to the planetary orbital phase and modeled the signal with the Rayleigh-Lambert approximation.

Results. A weak polarimetric signal at half the orbital period of ʋ And b was detected. The V-band MCMC fits yielded an orbital inclination of , an argument of periastron , a longitude of ascending node , and a geometric albedo of . Although uncertainties remain large, the inclination result agrees with earlier estimates, supporting a low-inclination, non-transiting geometry.

Conclusions. While the detection is not definitive, these results demonstrate the capability of high-precision polarimetry to probe the orbital parameters of non-transiting exoplanets. Further observations with larger telescopes and improved sensitivity will be required to refine the constraints on the orbital parameters.

In the JCMT-Venus project, we conducted three multi-week disc-integrated observations of Venus’ atmosphere using the JCMT ‘Ū‘ū receiver. This paper focuses on the HDO 2(2,0)-3(1,3) transition line at 266.1611 GHz, employed as a proxy for water abundance under the assumption of a constant D/H ratio. Based on the HDO line depth, we observed significant and rapid short-term variations, and have tentatively identified potential long-term effects. Water vapor abundance values were retrieved daily, and their variations will be displayed and discussed in our forthcoming publications.

We present the progress of work to streamline and simplify the process of exoplanet observation by citizen scientists. International collaborations such as ExoClock and Exoplanet Watch enable citizen scientists to use small telescopes to carry out transit observations. These studies provide essential supports for space missions Such as JWST and ARIEL. Contributions include maintenance or recovery of ephemerides, follow up confirmation and transit time variations. Ongoing observation programs benefit from a large pool of observers, with a wide variety of experience levels. Our projects work closely with these communities to streamline their observation pipelines and enable wider participation. Two complementary approaches are taken: Star Guide applies human-centric design and community consultation to identify points of friction within existing systems and provide complementary online tools and resources to reduce barriers to entry to the observing community. Machine Learning is used to accelerate data processing and automate steps which are currently manual, providing a streamlined tool for citizen science and a scalable solution for large-scale archival research.

The title of the Kavli–IAU Symposium (Toward) Discovery of Life Beyond Earth and its Impact invites us to speculate upon the consequences for humanity of the detection of biological processes out there in the cosmos. The discovery of any form of life beyond Earth would be a momentous event for science, but for many people it is the discovery of intelligent life that would have the most profound impact—not just on science, but on philosophy, religion, and society in general. Equally profound, however, might be the impact of a continuing non-discovery of extraterrestrial intelligence. In this paper I outline some personal thoughts regarding the implications of continuing non-discovery.

In this article, I analyze the claim that alien life could be “weird”. I propose to distinguish between two types of astrobiological weirdness: a naturalistic and an epistemic one. Weirdness, naturalistically construed, is an attribute for astrobiological traits. Weirdness, epistemically construed, is an attribute for scientific hypotheses and theories about the nature of such traits.

The contention of this paper is that alien visitation claims are a societal problem when they (a) move into the mainstream of discourse to the extent that government policy has to respond to them; (b) when they generate background noise which impedes science communication; and (c) when they become entangled with indigenous origin narratives, making it hard to recover the latter. Where this is the case, periodic debunking looks like a failed paradigm. Something closer to a scientific research program (SRP) might be called for, at some point. This is an idea which has already been advanced by Avi Loeb and Martin Elvis (albeit in significantly different ways and for different reasons). It is not clear that we are already at the stage where an SRP is required, but such a requirement does seem to be on the near horizon.) The paper concludes by setting out a number of framing requirements for any such SRP.

Planetary Protection is an effort to prevent inadvertent biological or organic contamination in solar system exploration. That effort cannot be perfect in actual exploration missions, but the price of not attempting it can be seen in numerous actual contamination events on Earth (e.g., kudzu and starlings in the US, Australia-released rabbits) and the more fanciful, but possibly valid, works of fiction (The War of the Worlds, The Andromeda Strain). Extraterrestrial contamination spread by Earth missions is known as forward contamination, while backward, or back contamination refers to contamination brought to Earth. Both robotic and human missions may be affected by planetary protection practices, which strive to apply the most current science to those efforts, but it is clear that those same missions may discover new information (the hope of most missions) that could argue for new and potentially altered requirements on the next mission, or on the ongoing missions themselves.

With billions of planets in the galaxy, advanced civilizations could relocate planets within or into their planetary systems rather than destroy entire planetary systems to construct megastructures. Such shifts could create Strange Exoplanetary Architectures (SEA), with unusual planetary arrangements potentially indicating deliberate actions by extraterrestrial intelligence (ETI). Searching for biosignatures and technosignatures in these systems could be a promising method for detecting ETI activities.

It is generally believed that it is unlikely that our civilization is alone in this galaxy. This belief is central to the premise of the Search for Extraterrestrial Intelligence (SETI), which has focused mainly on searching for radio signals originating from extraterrestrial communications, since it is believed that extraterrestrial craft visiting Earth would be an extremely unlikely event. However, the fact that we ourselves are currently working on developing probes to send to the Alpha Centauri system by 2069, strongly suggests that other civilizations may make similar, or more ambitious, efforts. Therefore, it is reasonable to inform our expectations by considering what characteristics and capabilities would be required for an interstellar civilization to find and visit Earth. In this paper, a physics-based analytic model of expanding interstellar civilizations is developed. A million civilizations that encounter Earth are simulated and their statistics are studied to determine their characteristics.

Astronomers are now able to peer into the atmospheres of distant planets and search for signs of life. With the large diversity in exoplanets being found, confidently identifying remote signs of life is a complex process. E.g. while the high level of oxygen in Earth’s atmosphere is the product of life, different planetary scenarios can produce oxygen rich atmospheres without any life-processes. Therefore we will need multiple lines of evidence to confidently declare a planet inhabited. Earth has been dramatically shaped by life for over 4 billion years and life plays a key role in regulating Earth’s surface chemistry and climate, providing multiple detectable signals a remote observer would be able to detect from afar. The biosphere-Earth co-evolving system is known as ‘Gaia’. Understanding the likelihood of Gaian-systems emerging on inhabited planets will inform us on the probability of confidently identifying an inhabited planet.

Human civilization continues to experience rapid growth in energy consumption, while projections of population stabilization remain uncertain. A continued trajectory of exponential energy use would cause direct heating of the planet by ∼2300, which would also coincide with a transition to a Kardashev type-I civilization. If such patterns of energy consumption are typical for other technological civilizations, then the lack of evidence for extraterrestrial life suggests that Earth may be among the first. This implies that a “Great Filter” may exist in the near future, which would mark a critical juncture of whether civilization on Earth becomes spacefaring or extinct. Any extant technological civilizations are likely those that have achieved long-term equilibrium with energy consumption and population growth. The search for technosignatures by ongoing ground- and space-based observatories will provide a way to test the Great Filter hypothesis and examine the extent to which energy-intensive civilizations occur in the galaxy.