Although so-called Dysonian SETI has been much in the air in recent times, its origins date back to the birth of SETI itself. It was in 1960 – the same year that Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia to study Epsilon Eridani and Tau Ceti – that Freeman Dyson proposed the Dyson sphere. In fiction, Olaf Stapledon had considered such structures in his novel Star Maker in 1937. As Macy Huston and Jason Wright (both at Penn State) remind us in a recent paper, Dyson’s idea of energy-gathering structures around an entire star evolved toward numerous satellites around the star rather than a (likely unstable) single spherical shell. We can’t put the brakes on what a highly advanced technological civilization might do, so both solid sphere and ‘swarm’ models can be searched for, and indeed have been, for in SETI terms we’re looking for infrared waste heat. And if we stick with Dyson (often a good idea!), we would be looking for structures...

If SETI is all about intelligence, and specifically technology, at the other end of astrobiology is the question of abiogenesis. Does life of any kind in fact occur elsewhere, or does Earth occupy a unique space in the scheme of things? Alex Tolley looks today at one venue where life may evolve, deep inside planetary crusts, with implications that include what we may find "locally" at places like Europa or Titan. In doing so, he takes a deep dive into a new paper from Jeffrey Dick and Everett Shock, while going on to speculate on broader questions forced by life's emergence. Organisms appearing in the kind of regions we are discussing today would doubtless be undetectable by our telescopes, but with favorable energetics, deep ocean floors may spawn abundant life outside the conventional habitable zone, just as they have done within our own 'goldilocks' world. by Alex Tolley Are the deep hot ocean vents more suitable for life than previously thought? In a previous article [1] I...

As we puzzle out the best observing strategies to pick up a bio- or technosignature, we're also asking in what ways our own world could be observed by another civilization. If such exist, they would have a number of tools at their disposal by which to infer our existence and probe what we do. Extrapolation is dicey, but we naturally begin with what we understand today, as Brian McConnell does in this, the third of a three-part series on SETI issues. A communications systems engineer, Brian has worked with Alex Tolley to describe a low-cost, high-efficiency spacecraft in their book A Design for a Reusable Water-based Spacecraft Known as the Spacecoach (Springer, 2015). His latest book is The Alien Communication Handbook -- So We Received A Signal, Now What? recently published by Springer Nature. Is our existence so obvious to the properly advanced observer? That doubtless depends on the state of their technology, about which we know nothing, but if the galaxy includes billion-year old...

If you were crafting a transmission to another civilization -- and we recently discussed Alexander Zaitsev's multiple messages of this kind -- how would you put it together? I'm not speaking of what you might want to tell ETI about humanity, but rather how you could make the message decipherable. In the second of three essays on SETI subjects, Brian McConnell now looks at enclosing computer algorithms within the message, and the implications for comprehension. What kind of information could algorithms contain vs. static messages? Could a transmission contain programs sufficiently complex as to create a form of consciousness if activated by the receiver's technnologies? Brian is a communication systems engineer and expert in translation technology. His book The Alien Communication Handbook (Springer, 2021) is now available via Amazon, Springer and other booksellers. by Brian S McConnell In most depictions of SETI detection scenarios, the alien transmission is a static message, like...

If we ever do receive a targeted message from another star – as opposed to picking up, say, leakage radiation – will we be able to decipher it? We can’t know in advance, but it's a reasonable assumption that any civilization wanting to communicate will have strategies in place to ease the process. In today's essay, Brian McConnell begins a discussion on SETI and interstellar messaging that will continue in coming weeks. The limits of our understanding are emphasized by the problem of qualia; in other words, how do different species express inner experience? But we begin with studies of other Earth species before moving on to data types and possible observables. A communication systems engineer and expert in translation technology, Brian is the author of The Alien Communication Handbook -- So We Received A Signal, Now What?, recently published by Springer Nature under their Astronomer’s Bookshelf imprint, and available through Amazon, Springer and other booksellers. by Brian McConnell...

I always knew where I stood with Alexander Zaitsev. In the period 2008-2011, he was a frequent visitor on Centauri Dreams, drawn initially by an article I wrote about SETI, and in particular whether it would be wise to go beyond listening for ETI and send out directed broadcasts to interesting nearby stars. At that time, I was straddling the middle on METI -- Messaging to Extraterrestrial Intelligence -- but Dr. Zaitsev found plenty of discussion here on both sides, and he joined in forcefully. Image: Alexander Leonidovich Zaitsev, METI advocate and radio astronomer, whose messages to the cosmos include the 1999 and 2003 'Cosmic Calls' from Evpatoria. Credit: Seth Shostak. The Russian astronomer, who died last week, knew where he stood, and he knew where you should stand as well. As my own views on intentional broadcasts moved toward caution in future posts, he and I would have the occasional email exchange. He was always courteous but sometimes exasperated. When I was in his good...

If self-reproducing probes have ever been turned loose in the Milky Way, they may well have spread throughout the galaxy. Our planet is 4.6 billion years old, but the galaxy's age is 13 billion, offering plenty of time for this spread. A number of papers have explored the concept, including work by Frank Tipler, who in 1980 argued that even at the speed of current spacecraft, the galaxy could be completely explored within 300 million years. Because we had found no evidence of such probes, Tipler concluded that extraterrestrial technological civilizations did not exist. Robert Freitas also explored the consequences of self-reproducing probes in that same year, reaching similar conclusions about how quickly they would spread, although not buying Tipler's ultimate conclusion. It's interesting that Freitas went to work on looking for evidence, reasoning that halo orbits around the Lagrangian points might be one place to search. He was, to my knowledge, the first to use the term SETA --...

I’m looking at a paper just accepted at The Astrophysical Journal on the subject of panspermia, the notion that life may be distributed through the galaxy by everything from interstellar dust to comets and debris from planetary impacts. We have no hard data on this -- no one knows whether panspermia actually occurs from one planet to another, much less from one stellar system to another star. But we can investigate possibilities based on what we know of everything from the hardiness of organisms to the probabilities of ejecta moving on an interstellar trajectory. In “Panspermia in a Milky Way-like Galaxy,” lead author Raphael Gobat (Pontificia Universidad Católica de Valparaíso, Chile) and colleagues draw together current approaches to the question and develop a modeling technique based on our assumptions about galactic habitability and simulations of galaxy structure. Panspermia is an ancient concept. Indeed, the word first emerges in the work of Anaxagoras (born ca. 500–480 BC) and...

Extraterrestrial civilizations, if they exist, would pose a unique challenge in comprehension. With nothing in common other than what we know of physics and mathematics, we might conceivably exchange information. But could we communicate our cultural values and principles to them, or hope to understand theirs? It was Ludwig Wittgenstein who said "If a lion could speak, we couldn't understand him." True? One perspective on this is to look not into space but into time. Traditional SETI is a search through space and only indirectly, through speed of light factors, a search through time. But new forms of SETI that look for technosignatures -- and this includes searching our own Solar System for signs of technology like an ancient probe, as Jim Benford has championed -- open up the chronological perspective in a grand way. Now we are looking for conceivably ancient signs of a civilization that may have perished long before our Sun first shone. A Dyson shell, gathering most of the light...

If we were to find a civilization at Proxima Centauri, the nearest star, it would either be a coincidence of staggering proportions -- two technological cultures just happening to thrive around neighboring stars -- or an indication that intelligent life is all but ubiquitous in the galaxy. ‘Ubiquitous’ could itself mean different things: Many civilizations, scattered in their myriads amongst the stars, or a single, ancient civilization that had spread widely through the galaxy. If a coincidence, add in the time factor and things get stranger still. For only the tiniest fraction of our planet’s existence has been impinged upon by a tool-making species, and who knows what the lifetime of a civilization is? Unless civilizations can live for eons, how could two of them be found around stars so close? Thus the possibility that BLC1 -- Breakthrough Listen Candidate 1 -- was a valid technosignature at Proxima Centauri was greeted with a huge degree of skepticism within the SETI community...

If you could send out a fleet of small lightsails, accelerated to perhaps 20 percent of the speed of light, you could put something of human manufacture into the Alpha Centauri triple star system within about 20 years. So goes, of course, the thinking of Breakthrough Starshot, which continues to investigate whether such a proposal is practicable. As the feasibility study continues, we'll learn whether the scientists involved have been able to resolve some of the key issues, including especially data return and the need for power onboard to make it happen. The concept of beam-driven sails for acceleration to interstellar speeds goes back to Robert Forward (see Jim Benford's excellent A Photon Beam Propulsion Timeline in these pages) and has been examined for several decades by, among others, Geoffrey Landis, Gregory Matloff, Benford himself (working with brother Greg) in laboratory experiments at JPL, Leik Myrabo, and Chaouki Abdallah and team at the University of New Mexico. At the...

I try to keep my ear to the ground (rather than my eye to the sky) when it comes to SETI. What I mean is that there are enough scientists working SETI issues that it's a challenge to know who is doing what. I try to track ongoing discussions even when, as at a conference, people keep ducking into and out of audibility. Hence the possibility of overlap in SETI efforts and, as Jason Wright points out in a discussion on his AstroWright site, the circulation of the same ideas without moving the ball forward. This is hardly a new phenomenon, as a look back at my own grad school experience in a much different area reveals. I was a medievalist with an ear for language, and I was always struck by how compartmentalized we tended to be when discussing medieval linguistics. At that time, northern European tongues like Gothic, Old Icelandic, Anglo-Saxon and Old Saxon formed a scholarly thicket I happily wandered through, but in the absence of computerized resources back in the day, the Gothic...

Vladimir Airapetian, senior astrophysicist in the Heliophysics Division at NASA’s Goddard Space Flight Center, has a somewhat unusual ambition. Most attention related to finding a ‘second Earth’ revolves around locating a world not only similar to ours in its characteristics but also similarly situated in terms of its host star’s evolution. In other words, a rocky world scorched by its star’s transition to red giant status isn’t a true analogue of our own, but a glimpse of what it will be at another stage. What Airapetian has in mind, though, is going in the other direction. His projected Earth analogue is one that mimics what our planet was in its early days, not all that long after the birth of its stellar system. It’s an ambition that points to learning where we came from, and thus what we might expect when we see a system like ours evolving around other stars. It has led to a search for a star like the Sun in its infancy. Says Airapetian: “It’s my dream to find a rocky exoplanet...

If we ever find life on a planet orbiting a white dwarf star, it will be life that has emerged only after the red giant phase has passed and the white dwarf has emerged as a stellar relic. That's the conclusion of a study being discussed today at the National Astronomy Meeting of Britain's Royal Astronomical Society, which convened online due to COVID concerns. The work is also recently published in Monthly Notices of the Royal Astronomical Society. At issue is the damage caused by powerful stellar winds that occur as a star makes the transition from red giant to white dwarf stage. This is the scenario that awaits our own Sun, which should swell to red giant status in roughly five billion years, eventually becoming a dense white dwarf about the size of the Earth. We've speculated in these pages about life surviving this phase of stellar evolution, but the study, in the hands of Dimitri Veras (Warwick University) concludes that this is all but impossible. We know that the Earth is...

I sometimes rely on nudges from my software to remind me of directions I've been meaning to take in a Centauri Dreams article. Seeing that Caleb Scharf has a new book out (The Ascent of Information), I was setting about ordering it when I noticed how many notes I had on my hard disk related to Scharf's work, a reminder of how provocative I find his writings. That took me back to a 2018 article called The Selfish Dataome, and also to the recent article The Origin of Technosignatures, which appeared a few days ago in Scientific American. Scharf (Columbia University) has the habit of asking questions no one else seems to have thought of. So let's kick this around a bit. The notion of a 'dataome' is about external things that a species generates. Scharf defines it as: a deeper way to quantify intelligent life, based on the external information that a species generates, utilizes, propagates and encodes in what we call technology—everything from cave paintings and books to flash...

Although we've been focusing lately on photosynthesis, radiolysis -- the dissociation of molecules by ionizing radiation -- can produce food and energy for life below the surface and in deep oceans. Our interest in surface conditions thus needs to be complemented by the investigation of what may lie within, as Alex Tolley explains in today's essay. Indeed, biospheres in a planet's crust could withstand even the destruction of all surface life. The possible range of microorganisms well beyond the conventional habitable zone defined by liquid water is wide, and while detecting it will be challenging, we may be able to investigate the possibilities in our own system with landers, looking to a day when interstellar probes are possible to explore exoplanet interiors. by Alex Tolley "There may be only one garden of Eden here for large life forms such as ourselves. But living beings small enough to populate tiny pore spaces may well exist within several - and perhaps many-other planetary...

Most autotrophic organisms on Earth use photosynthesis to work their magic. Indeed, photosynthesis accounts for about 99 percent of Earth's entire biomass (a figure likely to change as we learn more about what lies beneath the surface). The process allows organic matter to be synthesized from inorganic elements, drawing on solar radiation as the energy source, and providing the oxygen levels needed to drive complex, multicellular life. Does photosynthesis occur in other star systems? We know that it emerged early on Earth, and can trace its development back to the Great Oxidation Event in the range of 2.4 billion years ago, although its origins are still under scrutiny. In a new paper, lead author Giovanni Covone (University of Naples) and colleagues examine the conditions needed for oxygen-based photosynthesis to develop on an Earth-like planet not just at Earth’s level of stellar flux but throughout the classical habitable zone. The key to the study is stellar radiation as received...

Six decades of SETI have yet to produce a detection. Are there strategies we have missed? In today’s essay, Michael Hippke takes us into the realm of quantum communication, explaining how phenomena like ‘squeezed light’ can flag an artificial signal with no ambiguity. Quantum coherence, he argues, can be maintained over interstellar distances, and quantum methods offer advantages in efficiency and security that are compelling. Moreover, techniques exist with commercially available equipment to search for such communications. Hippke is a familiar face on Centauri Dreams, having explored topics from the unusual dimming of Boyajian’s Star to the detection of exomoons using what is known as the orbital sampling effect. He is best known for his Transit Least Squares (TLS) exoplanet detection method, which is now in wide use and has accounted for the discovery of ~ 100 new worlds. An astrophysics researcher at Sonneberg Observatory and visiting scholar for Breakthrough Listen at...

When the question of technosignatures at Alpha Centauri came up at the recent Breakthrough Discuss conference, the natural response was to question the likelihood of a civilization emerging around the nearest stars to our own. We kicked that around in Alpha Centauri and the Search for Technosignatures, focusing on ideas presented by Brian Lacki (UC-Berkeley) at the meeting. But as we saw in that discussion, we don't have to assume that abiogenesis has to occur in order to find a technosignature around any particular star. Ask Jason Wright (Penn State) and colleagues Jonathan Carroll-Nellenback and Adam Frank (University of Rochester) as well as Caleb Scharf (Columbia University), whose analysis of galaxies in transition has now produced a fine visual aid. Described in a short paper in Research Notes of the AAS, the simulation makes a major point: If civilizations last long enough to produce star-crossing technologies, then technosignatures may be widespread, found in venues across...

Put a rocky, Earth-sized planet in the habitable zone of a Sun-like star, and good things should happen. At least, that seems to be the consensus, and since there are evidently billions of such planets in the galaxy, the chances for complex life seem overwhelmingly favorable. But in today's essay, Centauri Dreams associate editor Alex Tolley looks at a new paper that questions the notion, examining the numerous issues that can affect planetary outcomes. Just how long does a planetary surface remain habitable? Alex not only weighs the paper's arguments but runs the code that author Toby Tyrrell used as he examined temperature feedbacks in his work. Read on for what may be a gut-check for astrobiological optimists. by Alex Tolley