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

What’s going on on the floor of Europa’s ocean? It’s hard to imagine a place like this, crushed under the pressure of 100 kilometers or more of water, utterly dark, although I have to say that James Cambias does wonders with an ice moon ocean in his novel A Darkling Sea (Tor, 2014). Science fiction aside, Europa Clipper is in queue for a 2024 launch, and we can anticipate a flurry of new studies that feed into plans for the mission’s scientific investigations. The latest of these puts Clipper on volcano watch. The work deploys computer modeling to show that volcanic activity seems to have occurred recently on Europa’s seafloor. The concept is that there may be enough internal heat to cause melting -- at least in spots -- of the rocky interior, which would produce the needed results. How this heating affects the moon is deduced from the 3D modeling of heat production and transfer in the paper, which was recently published in Geophysical Research Letters. The lead author is Marie...

On the matter of city lights as technosignatures, which we looked at on Friday, I want to follow up with Thomas Beatty's work on the issue in the context of an assortment of nearby stars. Beatty (University of Arizona, Tucson) assumes Earth-like planets examined via direct-imaging by LUVOIR, a future space telescope in planning, or HabEx, a different architecture for a likewise powerful instrument. What he's done is to take data from the Soumi National Polar-orbiting Partnership satellite to find the flux from city lights and the spectra of currently available lighting. He goes on to model the spectral energy distribution from such emissions as applied to exoplanet settings at various distances. Why look at city lights in the first place? Because they're another form of technosignature that may be within the realm of detection, and we'd like to find out what's possible and what any results would imply. In particular, Beatty reminds us, the National Academies' Exoplanet Science...

Our recent look at the possibility of technosignatures at Alpha Centauri is now supplemented with a new study on the detectability of artificial lights on Proxima Centauri b. The planet is in the habitable zone, roughly similar in mass to the Earth, and of course, it orbits the nearest star, making it a world we can hope to learn a great deal more about as new instruments come online. The James Webb Space Telescope is certainly one of these, but the new work also points to LUVOIR (Large UV/Optical/IR Surveyor), a multi-wavelength space-based observatory with possible launch in 2035. Authors Elisa Tabor (Stanford University) and Avi Loeb (Harvard) point out that a (presumably) tidally locked planet with a permanent nightside would need artificial lighting to support a technological culture. As we saw in Brian Lacki’s presentation at Breakthrough Discuss (see Alpha Centauri and the Search for Technosignatures), coincident epochs for civilizations developing around neighboring stars are...

Jim Benford's study of 'lurkers' -- possibly ancient probes that may have been placed here by extraterrestrial civilizations to monitor our planet's development -- breaks into two parts. The first, published Friday, considered stars passing near our Sun in the lifetime of the Solar System. Today Dr. Benford looks at the Drake Equation and sets about modifying it to include the lurker possibility. Along the way, he develops a quantitative way to compare conventional SETI with the strategy called SETA -- the search for extraterrestrial artifacts. Both articles draw on recently published work, the first in JBIS, the second in Astrobiology. The potential of SETA and the areas it offers advantages over traditional SETI argue for close observation of a number of targets close to home. by James Benford Introduction “To think in a disciplined way about what we may now be able to observe astronomically is a serious form of science.” –Freeman Dyson I propose a version of the Drake Equation for...

Jim Benford is continuing his research into the still nascent field known as SETA, the Search for Extraterrestrial Artifacts. A plasma physicist and CEO of Microwave Sciences, as well as a frequent Centauri Dreams contributor, Benford became intrigued with recent discoveries about Earth co-orbital objects -- there is even a known Earth Trojan -- and their possibilities in a SETI context. If we accept the possibility that an extraterrestrial civilization may at some point in Earth’s 4.5 billion year history have visited the Solar System, where might we find evidence of it? Two papers grew out of this, one in Astrobiology, the other in the Journal of the British Interplanetary Society (citations below). In the first of two posts here, Jim explains where his work has led him and goes through the thinking behind these recent contributions. by James Benford Part 1: How Many Alien Probes Could Have Come From Stars Passing By Earth? 1. Searching for Extraterrestrial Artifacts Alien...

Just how useful is oxygen as a biosignature? It’s a question we’ve examined before, always with the cautionary note that there are non-biological mechanisms for producing oxygen which could make any detected biosignature ambiguous. But let’s go deeper into this, thanks to a new paper on ‘oxygen false positives’ out of the University of California at Santa Cruz. The paper, produced by lead author Joshua Krissansen-Totton and team, offers scenarios that can place an oxygen detection in the broader context that would distinguish any such find as biological. Let’s begin with the fact that in addition to its obvious interest because of Earth’s history, photosynthesis involving oxygen requires the likely ubiquitous carbon dioxide and water we would expect on habitable zone planets. Helpfully, oxygen should be readily detectable on exoplanets because of its absorption features, which are prominent not only in visible light but in the near infrared and thermal infrared, if we include ozone....

Interesting news out of CNRS (the French National Center for Scientific Research) renews our attention to the mechanisms for supplying the early Earth with water and carbonaceous molecules. We've looked at comets as possible water sources for a world forming well inside the snow line, and asteroids as well. What the CNRS work reminds us is that micrometeorites also play a role. In fact, according to the paper just out in Earth and Planetary Science Letters, 5,200 tons of extraterrestrial materials -- dust particles from space -- reach the ground yearly. Image: From the paper's Figure 1, although not the complete figure. The relevant part of the caption: Fig. 1. Left: Location of the CONCORDIA station (Dome C, Antarctica). Centre: View of a trench at Dome C. Credit: Rojas et al. This conclusion comes from a study spanning almost twenty years, conducted by scientists in an international collaboration involving laboratories in France, the United States and the United Kingdom. CNRS...