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Musings on White Dwarfs and Planetary Survival

by Paul Gilster | Oct 7, 2026 | Exoplanetary Science | 5 Comments

A research team at the University of Warwick (UK) has turned up what may be a planet orbiting a white dwarf. That’s an interesting find given the lifetime of white dwarfs after the parent star has lost its outer envelope. Any life on such a world would have several billion years to work with (see White Dwarfs and Habitable Planets for more), although this planet is far too young for that. But this find has other implications. If confirmed, it would be the first planet thought to have formed through accretion of materials left over from the death of the red giant. It would be evidence of a second generation, a planet-hosting period that begins after the red giant phase is over. The star is HS 0209+0832, a young and hot white dwarf maybe five million years beyond the red giant phase. The original discovery came in 1999 by way of the Hubble Space Telescope, although the data had remained little studied in the archives since then. It took examination by doctoral candidate Jamie Williams...

Photosynthesis: A New Angle into Fermi’s Paradox?

by Paul Gilster | Oct 2, 2026 | Exoplanetary Science | 39 Comments

One of the things that gives the Fermi paradox its punch is the age of the galaxy. Back in 1950 when Fermi uttered his famous ‘Where is everybody?’ question, ideas about how old the Milky Way was were all over the map. Working with Hubble’s constant as understood at the time, the entire universe looked to be no more than 2 billion years old, a problem given what we were learning about the age of the Earth itself based on radioactive dating. So workarounds were needed, and they included the then widely supported steady-state theory, which saw a universe without beginning or end. Then too, the problem of the age of the galaxy could not be satisfactorily worked out because we had no good methods to gauge the age of individual stars. A book could be written about the evolution of our thinking on both age problems, but for now, let’s say that Fermi asked his question about extraterrestrials at a time when values for the age of the galaxy were generally set at between 3 and 5 billion...

Sakurai’s Object: A Stellar Rebirth

by Paul Gilster | Sep 24, 2026 | Deep Sky Astronomy & Telescopes | 28 Comments

Given how long stars live in comparison to human lifetimes, I always do a double-take at science fiction tales of starships dropping in to study a nova just as it’s about to go off. I suppose we have to assume the starship civilization has found a way to time such matters. There’s a Star Trek: The Next Generation episode that involves rescuing a planetary population from a star that’s about to explode (“A Fury Scorned”), but of all the nova arrivals, I like Samuel Delany’s 1968 novel Nova the best. Here, in order to harvest a rare element dubbed ‘Illyrion,’ the exact moment of the explosion has to be known and exploited through a mind-bending run through the debris. Today’s paper doesn’t involve a nova, but it does involve a star that is doing things on a very short timeframe indeed. The star is known as Sakurai’s Object (V4334 Sagittarii). Japanese amateur Yukio Sakurai observed the object in 1996, noting how it appeared to be brightening. A 1976 detection of the progenitor star had...

Disrupted Systems: Implications for Life

by Paul Gilster | Sep 16, 2026 | Exoplanetary Science | 14 Comments

Anthropocentric thinking is a persistent problem when we’re talking about extraterrestrial civilizations. Some of our most cherished notions can be invoked so effortlessly as to defy the imagination. The Copernican idea that life must exist elsewhere because elsewhere is bound to be more or less like here has had a long lifetime in SETI studies. It seems like the most basic common sense. And yet, as we’ll see once again today, scientific results continue to make it apparent that the fact that we are here does not mean that they are there. Finding stellar systems more or less like our own continues to be difficult. I’m not going full ‘rare Earth’ here but acknowledging that our circumstances may be unusual enough to tamp down estimates of the number of life-supporting planets. For that matter, our lack of knowledge about abiogenesis itself makes the case that we cannot necessarily expect it around other suns. On this matter, at least, we should be able to gather data soon, perhaps...

Pandora: Tuning Up our Data on Exoplanet Atmospheres

by Paul Gilster | Sep 9, 2026 | Uncategorized | 13 Comments

Launching a flagship-class mission like the Roman Space Telescope is always exciting, but with Roman in space, let’s also keep an eye on Pandora, a smaller though fascinating NASA mission (through its Astrophysics Pioneers program) that is now beginning its own work in exoplanet science. 20 exoplanets are targeted here, the idea being to work with data from transits to characterize their atmospheres via transmission spectroscopy, but with an additional twist. Elisa Quintana,(NASA GSFC) is principal investigator: "Pandora’s data will help close a major gap in our knowledge about planets and their host stars because, right now, we can’t be entirely sure how the star’s light affects measurements of what makes up exoplanet atmospheres. We designed the Pandora spacecraft and its in-depth observing program to better understand this vexing issue.” Launched January 11 of this year, Pandora is now beginning observations of its target stars. It’s in that category of smallsats that fascinate me...

Fermi Explorer: Building the First Mission to Another Star?

by Paul Gilster | Sep 2, 2026 | Missions | 49 Comments

The question of when to launch an interstellar mission has occupied us many times in the past. Specifically, how long do we wait so that travel times are reduced to something like the lifetime of a researcher working on the project? But there is another approach to all this. Someone is going to launch an interstellar mission that will be the first human effort to send a payload to another star. It’s all about intentionality and the choice of targets. A symbolic act? Sure, but don’t write the idea off. We can learn a lot from symbolic acts, and if we only have, at our current level of technology, the ability to reach Voyager-like speeds, we can still work on issues like equipment lifetimes, self-healing technologies, navigational issues and more. We can also work to refine existing AI tools to achieve the most efficient design. If we give ourselves 80,000 years to reach Alpha Centauri, we have to contend with the fact that the system is constantly moving. On this timeframe, by the...

Roman Space Telescope Launches Tomorrow

by Paul Gilster | Aug 29, 2026 | Exoplanetary Science | 18 Comments

We’ll have a lot to talk about when observations from the Nancy Grace Roman Space Telescope start coming in. But first we’ve got to get it out to its halo orbit around the L2 Sun-Earth Lagrange point. With the Sun, Earth and Moon permanently blocked out, the seeing should be good from this vantage some 1.5 million kilometers out. Just now I’ve had a note from Jim Benford reminding me that launch is currently scheduled for tomorrow, August 30, at 0726 ET (1126 UTC). The additional good news is that Jim’s son Dominic will be one of two hosts of the live coverage from NASA. I remember meeting Dominic some years back at Goddard Space Flight Center, where I had the chance to see the JWST telescope being prepared to go through its vibration testing. Dominic has spent more than a decade working on the Roman telescope, so the honor of working the NASA live coverage is well deserved. The photo below shows him during preparations for the Sunday coverage, which starts at 0620 ET (1020 UTC). You...

A ‘Time Variable’ Feature on Pluto?

by Paul Gilster | Aug 25, 2026 | Uncategorized | 15 Comments

With New Horizons now 63 AU out, it’s time to ponder that record hibernation period that the spacecraft just went through. Over 10 months long, this one had the same goal as previous such periods, to hold down operating costs but also give a break to onboard instrumentation in hopes of augmenting mission lifetime. As a kid, I often thought how cool it would be to be involved with a distant spacecraft. For some reason I always visualized this as being here on Earth while working with a craft beyond the Solar System. So maybe I was dreaming more of being a flight controller than an astronaut. I hadn’t realized until reading Alan Stern’s recent update that while hibernation means there are no commands and responses going back and forth, the craft does continue active data gathering from its Solar Wind at Pluto (SWAP) plasma detector and the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument. The Student Dust Counter is also in operation. Since awaking early...

The Limits of Understanding Between Species, and the Issue for Interstellar Communication

by Paul Gilster | Aug 14, 2026 | Astrobiology and SETI | 32 Comments

We've yet to find any evidence of intelligent life beyond Earth, a puzzling failure given the widespread belief that where habitable planets exist, life will somehow emerge. If we do receive a signal, though, would we be able to understand it? We've made some progress in piecing together animal communications here on Earth, but figuring out what the whistles and clicks of sea creatures mean remains a work in progress. In today's essay, associate editor Alex Tolley goes to work on key questions: Is mathematics truly a universal language? Does language change how we experience the world, and if so, what aspects of an alien culture will we actually be able to understand? The questions are daunting and now coming into public discourse in the realm of AI. Alex's thoughts on that phenomenon and how we might interact with a machine civilization are only part of the interest here. by Alex Tolley Introduction Discussions about alien communication usually focus on the technology of message...

The Ones Who Look Outward

by Paul Gilster | Aug 6, 2026 | Astrobiology and SETI | 36 Comments

Thinking about a great filter through which a civilization must pass before its survival is assured usually leads to catastrophic scenarios, such as planetary suicide by nuclear war, or climate holocaust (assuming the filter lies ahead of us and not behind). But filters may be more subtle and tied in with epistemology. How does intelligence view its place in the universe and thereby engage with other beings? In today’s essay, Ian Brownlie looks at the matter from the standpoint of how knowledge is acquired and transmitted. Based in New Zealand (near Hawke’s Bay on the North Island), Ian is an Electrical Engineer who works with commissioning high voltage complex power systems. The survival and evolution of technology may be a harder step than we think. by Ian Brownlie, BE(E&E) Intelligence has appeared on Earth in many forms. Science-like inquiry has appeared more than once. But sustained, cumulative science appears to be different. It survives across generations, sharpens its own...

Detection of a Habitable Zone Planet with an Atmosphere

by Paul Gilster | Jul 29, 2026 | Exoplanetary Science | 21 Comments

If we couldn’t figure out what to call CD-35 2722B b, which I assume is the correct way to refer to the planet-sized object in this red dwarf / brown dwarf/ gas giant system, another planet has a bit of a definitional problem as well. LHS 1140 b is an interesting super-Earth orbiting a red dwarf in Cetus in its habitable zone. Some 49 light years out, this planet is almost 6 times Earth’s mass and boasts a radius 1.7 times larger. Receiving 42 percent of the stellar radiation that Earth does, its surface temperatures allow the presence of liquid water. But exactly what kind of planet is this? Is it an airless, rocky world, an ocean planet, or even a mini-Neptune? We can probably rule out the latter because its mass would be low for that category, and we can also, contrary to some press reports, not consider it in any way, shape or form ‘Earth-like.’ But thanks to new work out of Harvard and the Carnegie Institution for Science, we can now declare that it does have an atmosphere. This...

Moon or Planet? The Awkward Case of CD-35 2722B

by Paul Gilster | Jul 23, 2026 | Uncategorized | 17 Comments

Problems of definition will long be with us as we take ever closer looks at exoplanets. But they’re suddenly on everyone’s mind because of the detection of what some are calling an ‘exomoon’ in the system CD-35 2722, found in the constellation Columba. The primary in this system is an M-dwarf thought to be 50–200 million years old. I imagine there is no shortage of flare activity on this star, although the paper doesn’t get into that. The interesting finding in this work just published in Nature is expressed in its title: “Planetary-Mass Exosatellite Detected Around a Star’s Substellar Companion.” Image: This illustration shows the system around the star CD-35 2722, with the newly found moon-like object at the centre. The star –– the point source to the left –– has about half the mass of our Sun, and it is orbited by a brown dwarf, the reddish-brown object seen here in the foreground (right). The brown dwarf has about 37 times the mass of Jupiter: too massive to be a planet, but not...

New Propulsion Systems for Deep Space Smallsats

by Paul Gilster | Jul 17, 2026 | Advanced Rocketry | 4 Comments

Building the infrastructure we will need for interstellar exploration requires an imaginative look at today’s technologies as applied to distant targets. Indeed, we can leverage the scientific interest in, say, an orbit around each of the ice giants to explore launch capabilities through beamed energy, but we will also need to consider how we can use economical smallsats to provide stationkeeping nodes in such studies. Advances in miniaturization and the growing sophistication of CubeSats all point in the same direction. We can exploit our early flybys by fleshing out an observational smallsat matrix around targets at system’s edge to form a robust data and communications network. The thing that is going to vitalize the development of small satellite packages is a new kind of propulsion system of the sort recently developed at MIT. The problem is easily stated: A small spacecraft – think suitcase size or less – has to maximize payload while ensuring flexibility in adjusting...

What the Comments Taught Me: A Reply on Self-Replicating Probes

by Paul Gilster | Jul 13, 2026 | Astrobiology and SETI | 23 Comments

Self-replicating probes continue to be a controversial subject, just as they were when Frank Tipler up the ante on Michael Hart by invoking them as a way of further tightening the tension of the Fermi Paradox. After all, Tipler had discovered an economic edge. Any civilization that wants to colonize the galaxy is going to expend vast resources, but if self-replication is available, that culture need only create the first probe, and let subsequent ones harvest resources as needed. Self-replication or not, the galaxy gets filled up in only a fraction of the current age of the Milky Way, but the economic stimulus provides yet another tightening of the Fermi knot. I hadn't thought about all of this in connection with actual probe designs, but Peter Marinko's article on the matter clearly touched a nerve, judging from the messages I've been getting about it. When Peter wrote recently with his thoughts on reader reactions, I asked him for permission to run it as a regular post rather than...

A Metallurgist’s Doubts About Self-Replicating Probes

by Paul Gilster | Jul 10, 2026 | Astrobiology and SETI | 26 Comments

Frank Tipler jolted the astrophysics community in 1980 when he introduced self-replicating interstellar probes into discussion of the Fermi Paradox. The mathematical model of self-replication came from John von Neumann, and was codified in 1966 (after von Neumann's death) by Arthur Burks in Theory of Self-Reproducing Automata (1966). SF fans will also know of Fred Saberhagen's berserker novels and short stories (the first appeared in 1963). I've found an even earlier SF reference but will leave that for a future post. Right now I want to introduce Peter Marinko, who today weighs in on self-replication and the problems therein. Based in Uppsala, Sweden Peter holds an M.Sc. in metallurgy and has a career background in industrial process engineering. He has studied SETI under Erik Zackrisson at Uppsala University, and his current work explores the thermodynamics of technological civilizations — including a manuscript on high-exergy technospheres and the longevity of detectable...

New Horizons: Pushing Toward the ‘Termination Shock’

by Paul Gilster | Jul 3, 2026 | Missions | 11 Comments

Mission planning for any future star probe will adjust not only for conditions in the interstellar medium but also the Solar System’s outer reaches. Let’s confine ourselves for now to conditions in the outer heliosphere. Currently we have precisely one spacecraft operating here. New Horizons has only reached 65 AU from the Sun, while Voyager 1 exited the heliopause in 2012 at 121 AU, and Voyager 2 crossed in 2018 at about 119 AU. New Horizons won’t have sufficient power to keep taking data as it makes its own crossing in the 2040s, but from its current position in the Kuiper Belt we can look back at what the spacecraft has reported so far about the solar wind and the local interstellar medium. New Horizons’ Solar Wind Around Pluto (SWAP) instrument is the key here, examining how the solar wind slows as we leave the inner system behind. A new study from Southwest Research Institute (SwRI) points out what happens as this stream of hot ionized hydrogen and helium nuclei fills the...

The Intergalactic Fermi Problem

by Paul Gilster | Jun 24, 2026 | Astrobiology and SETI | 88 Comments

The headwaters of the Fermi Paradox channel directly through Michael Hart and Frank Tipler, and it’s a testament to the power of their arguments that this remains true today. It was Hart who in "An Explanation for the Absence of Extraterrestrials on Earth" (published in the Quarterly Journal of the Royal Astronomical Society in 1975) pointed out something blindingly obvious once stated. Moving at one-tenth of the speed of light, a civilization could send its probes throughout the galaxy in as little as 650,000 years. Hart set an upper limit on this at 2 million years, but either way the point resounded in the astrophysics community because these are tiny time spans compared to the age of the universe. Hart even factored in a pause after each leap to a new star to found a ‘colony,’ or whatever such a probe would do there. Our Sun being a relatively youthful 4.6 billion years old, that was a vast amount of time for earlier civilizations to have mastered technologies opening up trips to...

HD 39474: A Brown Dwarf Shapes a Planetary System

by Paul Gilster | Jun 19, 2026 | Uncategorized | 14 Comments

With well over 6,000 exoplanets now confirmed and a continuing flow of data containing new detections, it has been clear for some time that our own Solar System’s model is hardly a template. I enjoy dipping into the bewildering variety of new systems and pondering the contingencies that have led to their architecture. Science fiction is an intensely visual genre, so I naturally try to imagine the more extreme systems. But more than most, today’s catch at HD 39474, an F-class star in Pictor some 360 light years out, is just begging for a gifted SF writer to go to work on it. Here we have, in addition to the central star, a long-period transiting brown dwarf with a planetary system, coplanar and aligned with the brown dwarf, packed inside its orbit. HD 39474 is also, at least for now, known as TOI-201, TOI standing for TESS Object of Interest, an indication that while the Transiting Exoplanet Survey Satellite’s photometry has found what looks like a planetary transit, that result has...

The Physics of Interstellar Travel

by Paul Gilster | Jun 11, 2026 | Research Tools | 36 Comments

Coryn Bailer-Jones’ The Physics of Interstellar Travel fills a need which has become apparent only in the last twenty years. Indeed, going back to the turn of the century, one would find the idea of traveling to another star discussed only in relatively isolated pockets, often presented at the tail end of conferences devoted to other astronautical topics. Papers, though, were being written at an increased rate, building on early work begun in the 1950s through the efforts of luminaries such as Les Shepherd and Eugen Sänger and continuing into the era of Robert Forward. By the year 2000, a number of mission designs had been created, still very much on the back burner but of high interest to specialists. In today’s landscape, interstellar travel has become a vibrant topic. The wave of interest that energized the field incorporated high-visibility projects like NASA’s 100 Year Starship and in 2016, the emergence of the Breakthrough Starshot Initiative, which focused directly on the...

Observations on ‘The Search for Technosignatures: A Review of Possibilities’

by Paul Gilster | Jun 5, 2026 | Astrobiology and SETI | 27 Comments

I don't usually post comments at the top of the site, but I'm making an exception here for a couple of reasons. The recent paper I reviewed by Clément Vidal and colleagues covering technosignatures and strategies for detection is a significant work, the kind of consolidation of resources the field needs as the original radio and optical-oriented SETI expands into new realms. We now have options calibrated for intelligence via archival and observational detection of megastructures, planetary or stellar engineering, or other projects far beyond our own level of technology. Dean Zierman's thoughts on the Vidal paper open a number of issues and highlight assumptions we'll always need to examine. Dean is a telecommunications expert specializing in radio frequency communications, one who has been deployed to over 150 disasters and dangerous events including earthquakes, hurricanes, tsunamis and the 9/11 attacks on the United States. He has served as a subject matter expert on...

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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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