Can an Interstellar Generation Ship Maintain a Population on a 250-year Trip to a Habitable Exoplanet?

I grew up on generation ship stories. I'm thinking of tales like Heinlein's Orphans of the Sky, Aldiss' Non-Stop, and (from my collection of old science fiction magazines) Don Wilcox's "The Voyage that Lasted 600 Years." The latter, from 1940, may have been the first generation ship story ever written. The idea grows out of the realization that travel to the stars may take centuries, even millennia, and that one way to envision it is to take large crews who live out their lives on the journey, their descendants becoming the ones who will walk on a new world. The problems are immense, and as Alex Tolley reminds us in today's essay, we may not be fully considering some of the most obvious issues, especially closed life support systems. Project Hyperion is a game attempt to design a generation ship, zestfully tangling with the issues involved. The Initiative for Interstellar Studies is pushing the limits with this one. Read on. by Alex Tolley "Space," it says, "is big. Really big. You...

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The Ethics of Spreading Life in the Cosmos

We keep trying to extend our reach into the heavens, but the idea of panspermia is that the heavens are actually responsible for us. Which is to say, that at least the precursor materials that allow life to emerge came from elsewhere, and did not originate on Earth. Over a hundred years ago Swedish scientist Svante Arrhenius suggested that the pressure of starlight could push bacterial spores between planets and we can extend the notion to interstellar journeys of hardy microbes as well, blasted out of planetary surfaces by such things as meteor impacts and flung into outbound trajectories. Panspermia notions inevitably get into the question of deep time given the distances involved. The German physician Hermann Richter (1808-1876) had something interesting to say about this, evidently motivated by his irritation with Charles Darwin, who had made no speculations on the origin of the life he studied. Richter believed in a universe that was eternal, and indeed thought that life itself...

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Why Do Super-Earths and Mini-Neptunes Form Where They Do?

Exactly how astrophysicists model entire stellar systems through computer simulations has always struck me as something akin to magic. Of course, the same thought applies to any computational methods that involve interactions between huge numbers of objects, from molecular dynamics to plasma physics. My amazement is the result of my own inability to work within any programming language whatsoever. The work I’m looking at this morning investigates planet formation within protoplanetary disks. It reminds me again just how complex so-called N-body simulations have to be. Two scientists from Rice University – Sho Shibata and Andre Izidoro – have been investigating how super-Earths and mini-Neptunes form. That means simulating the formation of planets by studying the gravitational interactions of a vast number of objects. N-body simulations can predict the results of such interactions in systems as complex as protoplanetary disks, and can model formation scenarios from the collisions of...

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Deep Space and the Art of the Map

NASA’s recently launched SPHEREx space telescope will map the entire celestial sky four times in two years, creating a 3D map of over 450 million galaxies. We can hope for new data on the composition of interstellar dust, among other things, so the mission has certain astrobiological implications. But today I’m focusing on the idea of maps of stars as created from our vantage here on Earth. How best to make maps of a 3D volume of stars? I’ve recently been in touch with Kevin Wall, who under the business name Astrocartics Lab has created the Astrocartics and Interstellar Surveyor maps he continues to refine. He explains the background of his interest in the subject in today’s essay while delving into the principles behind his work. by Kevin Wall The most imposing aspect of the universe we live in is that it is 3-dimensional. The star charts of the constellations that we are most familiar with show the 2-dimensional positions of stars fixed on the dome of the sky. We do not, however,...

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Are Supernovae Implicated in Mass Extinctions?

As we’ve been examining the connections between nearby stars lately and the possibility of their exchanging materials like comets and asteroids with their neighbors, the effects of more distant events seem a natural segue. A new paper in Monthly Notices of the Royal Astronomical Society makes the case that at least two mass extinction events in our planet’s history were forced by nearby supernova explosions. Yet another science fiction foray turned into an astrophysical investigation. One SF treatment of the idea is Richard Cowper’s Twilight of Briareus a central theme of which is the transformation of Earth through just such an explosion. Published by Gollancz in 1974, the novel is a wild tale of alien intervention in Earth’s affairs triggered by the explosion of the star Briareus Delta, some 130 light years out, and it holds up well today. Cowper is the pseudonym for John Middleton Murry Jr., an author I’ve tracked since this novel came out and whose work I occasionally reread....

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Quantifying the Centauri Stream

The timescales we talk about on Centauri Dreams always catch up with me in amusing ways. As in a new paper out of Western University (London, Ontario), in which astrophysicists Cole Gregg and Paul Wiegert discuss the movement of materials from Alpha Centauri into interstellar space (and thence to our system) in ‘the near term,’ by which they mean the last 100 million years. Well, it helps to keep our perspective, and astronomy certainly demands that. Time is deep indeed (geologists, of course, know this too). I always note Paul Wiegert’s work because he and Matt Holman (now at the Harvard-Smithsonian Center for Astrophysics) caught my eye back in the 1990s with seminal studies of Alpha Centauri and the stable orbits that could occur there around Centauri A and B (citation below). That, in fact, was the first time that I realized that a rocky planet could actually be in the habitable zone around each of those stars, something I had previously thought impossible. And in turn, that...

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Spaceline: A Design for a Lunar Space Elevator

The space elevator concept has been in the public eye since the publication of Arthur C. Clarke's The Fountains of Paradise in 1979. Its pedigree among scientists is older still. With obvious benefits in terms of moving people and materials into space, elevators seize the imagination because of their scale and the engineering they would require. But we needn't confine space elevators to Earth. As Alex Tolley explains in today's essay, a new idea being discussed in the literature explores anchoring one end of the elevator to the Moon. Balanced by Earth's gravity (and extending all the way into the domain of geosynchronous satellites), such an elevator opens the possibility of moving water and materials between Earth and a lunar colony, though the engineering proves as tricky as that needed for a system anchored on Earth. Is it even possible given the orbital characteristics of the Moon? Read on. by Alex Tolley Image: Space elevator connecting the moon to a space habitat. Credit:...

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A New Class of Interstellar Object?

Peculiar things always get our attention, calling to mind the adage that scientific discovery revolves around the person who notices something no one else has and says “That’s odd.” The thought is usually ascribed to Asimov, but there is evidently no solid attribution. Whoever said it in whatever context, “that’s odd” is a better term than “Eureka!” to describe a new insight into nature. So often we learn not all at once but by nudges and hunches. This may be the case with the odd objects turned up by the Japanese infrared satellite AKARI in 2021. Looking toward the Scutum-Centaurus Arm along the galactic plane, the observatory found deep absorption bands of the kind produced by interstellar dust and ice. No surprise that a spectral analysis revealed water, carbon dioxide, carbon monoxide and organic molecules, given that interstellar ices in star-forming regions are rich in these chemicals, but the ‘odd’ bit is that these two objects are a long way from any such regions. Image:...

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Shaping the Sail: Metamaterials and the Manipulation of Light

Experimenting on beamed energy and sailcraft is no easy matter, as I hope the previous post made clear. Although useful laboratory experiments have been run, the challenges involved in testing for sail stability under a beam and sail deployment are hard to surmount in Earth’s gravity well. They’re also demanding in terms of equipment, for we need both the appropriate lasers and vacuum chambers that can approximate the conditions the sail will be subjected to in space. But this space is being explored now more than ever before. Jim Benford has pointed me to an excellent bibliography on lightsail studies at Caltech that I recommend to anyone interested in following this further. When I said we were in the early days of sail experimentation, I was drawing your attention to the fact that we’re only now learning how to produce and manipulate the metamaterials – structures that have electromagnetic properties beyond those we find in naturally occurring materials – that may be our best...

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Experimenting on an Interstellar Sail

The idea of beaming a propulsive force to a sail in space is now sixty years old, if we take Robert Forward’s first publications on it into account. The gigantic mass ratios necessary to build a rocket that could reach interstellar distances were the driver of Forward’s imagination, as he realized in 1962 that the only way to make an interstellar spacecraft was to separate the energy source and the reaction mass from the vehicle. Robert Bussard knew that as well, which is why in more or less the same timeframe we got his paper on the interstellar ramjet. It would scoop up hydrogen between the stars and subject it to fusion. But the Bussard ramjet had to light fusion onboard, whereas a sail propelled by a laser beam – a lightsail – operated without a heavy engine. The idea worked on paper but demanded a laser of sufficient size (Forward calculated over 10 kilometers) to make it a concept for the far future. His solution demanded very large lasers in close solar orbits, and thus an...

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Ernst Öpik and the Interstellar Idea

Some names seem to carry a certain magic, at least when we’re young. I think back to all the hours I used to haunt St. Louis-area libraries when I was growing up. I would go to the astronomy section and start checking out books until over time I had read the bulk of what was available there. Fred Hoyle’s name was magic because he wrote The Black Cloud, one of the first science fiction novels I ever read. So naturally I followed his work on how stars produce elements and on the steady state theory with great interest. Willy Ley’s name was magic because he worked with Chesley Bonestell (another magic name) producing The Conquest of Space in 1949, and then the fabulous Rockets, Missiles, and Space Travel in 1957, a truly energizing read. Not to mention the fact that he had a science column in what I thought at the time was the best of the science fiction magazines, the ever-engaging Galaxy. It still stuns me that Ley died less than a month before Apollo 11 landed on the Moon. My list...

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SETI’s Hard Steps (and How to Resolve Them)

The idea of life achieving a series of plateaus, each of which is a long and perilous slog, has serious implications for SETI. It was Brandon Carter, now at the Laboratoire Univers et Théories in Meudon, France, who proposed the notion of such ‘hard steps’ back in the early 1980s. Follow-up work by a number of authors, especially Frank Tipler and John Barrow (The Anthropic Cosmological Principle) has refined the concept and added to the steps Carter conceived. Since then, the idea that life might take a substantial amount of the lifetime of a star to emerge has bedeviled those who want to see a universe filled with technological civilizations. Each ‘hard step’ is unlikely in itself, and our existence depends upon our planet’s having achieved all of them. Carter was motivated by the timing of our emergence, which we can round off at 4.6 billion years after the formation of our planet. He reasoned that the upper limit for habitability at Earth’s surface is on the order of 5.6 billion...

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Pandora: Exoplanet Atmospheres via Smallsat

I’ve been digging into NASA’s Small Spacecraft Strategic Plan out of continuing interest in missions that take advantage of miniaturization to do things once consigned to large-scale craft. And I was intrigued to learn about the small spacecraft deployed on Apollo 15 and 16, two units developed by TRW in a series called Particles and Fields Subsatellites. Each weighed 35 kilograms and was powered by six solar panels and rechargeable batteries. The midget satellites were deployed from the Apollo Command and Service Module via a spring-loaded container giving the units a four foot-per-second velocity. Apollo 15’s operated for six months before an electronics failure ended the venture. The Apollo 16 subsatellite crashed on the lunar surface 34 days into its mission after completing 424 orbits. Here I thought I knew Apollo history backwards and forwards and I had never run into anything about these craft. It turns out that smallsats – usually cited as spacecraft with weight up to 180...

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A Three-Dimensional Look at an Exoplanet Atmosphere

Some 900 light years away in the constellation Puppis, the planet WASP-121b is proving an interesting test case as we probe ever deeper into exoplanetary atmospheres. As has been the case with so many early atmosphere studies, WASP-121b, also known as Tylos, is a hot-Jupiter, with a year lasting about thirty Earth hours, in a vise-like tidal lock that leaves one side always facing the star, the other away. What we gain in two new studies of this world is an unprecedented map of the atmosphere’s structure. At stake here is a 3D look into what goes on as differing air flows move from one side of the planet to the other. A jet stream moves material around its equator, but there is a separate flow at lower altitudes that pumps gas from the hottest regions to the dark side. “This kind of climate has never been seen before on any planet,” says Julia Victoria Seidel (European Southern Observatory), lead author of a paper that appears today in Nature. Seidel points out that we have nothing...

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What Would Surprise You?

Someone asked me the other day what it would take to surprise me. In other words, given the deluge of data coming in from all kinds of observatories, what one bit of news would set me back on my heels? That took some reflection. Would it surprise me, my interlocutor persisted, if SETI fails to find another civilization in my lifetime? The answer to that is no, because I approach SETI without expectations. My guess is that intelligence in the universe is rare, but it’s only a hunch. How could it be anything else? So no, continuing silence via SETI does not surprise me. And while a confirmed signal would be fascinating news, I can’t say it would truly surprise me either. I can work out scenarios where civilizations much older than ours do become known. Some surprises, of course, are bigger than others. Volcanoes on Io were a surprise back in the Voyager days, and geysers on Enceladus were not exactly expected, but I’m talking here about an all but metaphysical surprise. And I think I...

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Pondering Life in an Alien Ocean

No one ever said Europa Clipper would be able to detect life beneath the ice, but as we look at the first imagery from the spacecraft’s star-tracking cameras, it’s helpful to keep the scope of the mission in mind. We’re after some critical information here, such as the thickness of the ice shell, the interactions between shell and underlying ocean, the composition of that ocean. All of these should give us a better idea of whether this tiny world really can be a home for life. Image: This mosaic of a star field was made from three images captured Dec. 4, 2024, by star tracker cameras aboard NASA's Europa Clipper spacecraft. The pair of star trackers (formally known as the stellar reference units) captured and transmitted Europa Clipper's first imagery of space. The picture, composed of three shots, shows tiny pinpricks of light from stars 150 to 300 light-years away. The starfield represents only about 0.1% of the full sky around the spacecraft, but by mapping the stars in just that...

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Putting AI to Work on Technosignatures

As a quick follow-up to yesterday’s article on quantifying technosignature data, I want to mention the SETI Institute’s invitation for applicants to the Davie Postdoctoral Fellowship in Artificial Intelligence for Astronomy. The Institute’s Vishal Gajjar and his collaborators both in the US and at IIT Tirupati in India will be working with the chosen candidate to focus on neural networks optimized for processing image data, so-called ‘CNN architectures’ that can uncover unusual signals in massive datasets. “Machine learning is transforming the way we search for exoplanets, allowing us to uncover hidden patterns in vast datasets,” says Gajjar. “This fellowship will accelerate the development of advanced AI tools to detect not just conventional planets, but also exotic and unconventional transit signatures including potential technosignatures.” As AI matures, the exploration of datasets is a critical matter as these results from missions like TESS and Kepler are packed with both...

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Quantifying the Chances of a Technosignature

It’s one thing to talk about technology as we humans know it, but applying it to hypothetical extraterrestrials is another matter. We have to paint with a broad brush here. Thus Jason Wright’s explanation of technosignatures as conceived by SETI scientists. The Penn State astronomer and astrophysicist defines technology in that context as “the physical manifestations of deliberate engineering.” That’s saying that a technology produces something that is in principle observable. Whether or not our current detection methods are adequate to the task is another matter. Image: Artist’s concept of an interesting radio signal from galactic center. But the spectrum of possible technosignature detections is broad indeed, extending far beyond radio. Credit: UCLA SETI Group/Yuri Beletsky, Carnegie Las Campanas Observatory. A technosignature need not be the sign of industrial or scientific activity. Consider: In a new paper in The Astronomical Journal, Sofia Sheikh (SETI Institute) and colleagues...

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A Fast Radio Burst in a Dead Elliptical Galaxy

Work is healing, so let’s get back to it. I’m enthralled with what we’re discovering as we steadily build our catalog of fast radio bursts (FRB), close to 100 of which have now been associated with a galaxy. These are transient radio pulses of short duration (down to a fraction of a millisecond, though some last several seconds), the first being found in 2007 by Duncan Lorimer, an astronomer at West Virginia University. Sometimes FRBs repeat, although many do not, and one is known to repeat on a regular basis. What kind of astrophysical processes might be driving such a phenomenon? The leading candidate appears to be supernovae in a state of core collapse, producing vast amounts of energy as stars more massive than the Sun end their lives. Out of such catastrophic events a type of neutron star called a magnetar may be produced, its powerful magnetic field pumping out X-ray and gamma ray radiation. Young, massive stars and regions of active star formation are implicated under this...

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Centauri Dreams to Resume Soon

I'd like to thank all of you who wrote comments and emails about the recent pause in Centauri Dreams. My beautiful wife Eloise passed away on January 17. It was as peaceful a death as can be imagined, and I am so pleased to say that she was able to stay at home until the end. As she had battled Alzheimer's for eleven gallant years, death was simply a bridge that now had to be crossed. As she did with everything else in her life, she did it with class. This is to let you know that I will be getting Centauri Dreams back into action again in about three weeks. When I began the site in 2004, my primary goal was to teach myself as much as I could about the topics we address by writing about them, which is how I've always tended to learn things. I've always welcomed comments that informed me, caught my errors and extended the discussion into new realms. No one could work with a better audience than the readers I've been privileged to address, and for this I am profoundly grateful.

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Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it.

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