Centauri Dreams
Imagining and Planning Interstellar Exploration
Photosynthesis: A New Angle into Fermi’s Paradox?
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 years. The tension between this and the Hubble constant values would persist, although Allan Sandage managed by the end of the 1950s to come up with an estimate for the universe of 13 billion years.
Fermi’s question gets more acute every time we come up with new information about how old our system is compared to the age of the galaxy. As we’ve discussed in these pages many times before, Charles Lineweaver’s work early in the 21st century demonstrated that we are newcomers compared to at least some of the stars in our vicinity. If that’s the case, then the idea of habitable planets being in existence several billion years before we showed up is plausible. And if we take ourselves as the measure (always dangerous, but we are the only datapoint), the idea of advanced extraterrestrial civilisations seems likely, assuming that these could find ways to avoid destroying themselves.
Image: The galaxy evolves. How many stars of the 400 billion now thought to exist here emerged at least a billion years before the Sun coalesced?
As always, though, we have to scout our assumptions. Just because it took what we now believe to be 4.6 billion years for Earth to produce intelligent life, why should that be the case everywhere else? An interesting new paper takes on that question by suggesting that no matter the size of their headstart, planets much older than our own may still be in the early stages of microbial life, without yet reaching the point of producing even primitive larger species.
The work of Chris Doughty (Northern Arizona University) and colleagues, the paper argues that we should be looking at what the team calls ‘plant energy,’ and stop focusing on time as an indicator of likely development. The hypothesis: “The biological evolution rate is a linear function of cumulative carbon fixed on a planet.” Note the word ‘fixed.’ What this describes is the process of taking carbon dioxide, an inorganic gas, and turning it into organic molecules like sugars. Photosynthesis does most of this work on Earth. It uses the energy derived from sunlight as the driver, with the carbon taken out of the atmosphere and oceans and put to use in biological systems.
Proposing a linear link between the amount of carbon fixed in this way and the rate of evolutionary development is a striking move. It’s even more so when considered as a tool for exoplanet research. The paper looks at the amount of carbon Earth has fixed over its lifetime and compares that to what other planets are likely to have fixed during their own lifetimes. 29 exoplanets are studied here, with only two of them surpassing Earth’s cumulative Net Primary Production (NPP), and therefore capable of developing multicellular and perhaps intelligent life. NPP refers to the carbon fixed by photosynthesis that ends up as new biomass.
Image: How we see plant photosynthetic pigments. The MESSENGER image of Earth on the left is very close to what can be seen by the human eye. For the image on the right, a red component was substituted that shows near infra-red colors. The vegetation in the Amazon basin produces the purplish-red color in the center of the image. The new paper proposes that cumulative fixed carbon is itself a marker that can be tied not only to life but to the pace of evolutionary change. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington, via JPL Photojournal).
The planets on Doughty’s list are chosen from the Habitable Worlds Catalog, which organizes NASA data based on factors such as radius, irradiation, temperature and age. The authors use stellar radiation, temperature and precipitation maps from several recent studies to calculate how Earth fixed carbon in different stages of biological evolution, and ask how long the examined planets would take to achieve the same amount of carbon.
From the paper:
Assuming Darwinian evolution, a baseline astrobiological assumption… each generation of life has a small potential for genetic change following either sexual or asexual reproduction. These genetic changes will either be successful or not depending on the environment, species competition or predation around the organism. We therefore hypothesize that Earth’s cumulative carbon fixed at certain periods has led to major evolutionary transitions such as the emergence of photosynthetic organisms, eukaryote and multicellular animals that fundamentally altered the Earth’s carbon cycle, accelerating it at certain points.
So we can think of the accumulated plant energy of an entire planet and acknowledge that planets with more plant growth as mediated by photosynthesis will tend to be warmer, wetter places than average. This gets interesting when we think about red dwarf planets, especially since these have enormous lifetimes and many are several billion years older than Earth. The authors make the case that these time factors provide no necessary advantage.
What counts is that life on a planet like TRAPPIST-1e, one of those studied here, would have lower rates of total photosynthesis because the surface receives correspondingly less light. Moreover, tidal lock on M-dwarf habitable planets would mean losing half their surface for photosynthesis. In this study, TRAPPIST-1e is found to have the capability of fixing no more than 21 percent of Earth’s carbon. An older world, but perhaps one with nothing more than microbial life.
We have interesting simulations of places like TRAPPIST-1e, climate maps that allow us to estimate how long it would take other planets to achieve the same amount of carbon fixed as we find on Earth. Of the 29 worlds considered potentially habitable by the authors, 27 are in fact orbiting red dwarf stars, and presumably tidally locked. Net Primary Production is calculated for each. The results are heavily weighted toward life at no more than microbial level:
If the biological evolutionary state is a function of cumulative carbon fixed and life began on each of the 29 exoplanets like it had on Earth, life on most of those 29 exoplanets would most likely be evolutionarily behind Earth (with two exceptions discussed below). The majority of our simulations led to most planets at the predicted microbial life stage with the exception of simulations using climates with 1 bar CO2. These very warm, wet planets accelerated NPP production which led about a third of the planets potentially ahead of Earth.
That sounds rather promising, but read on:
However, recent JWST observations showed no evidence of a thick carbon dioxide atmosphere on TRAPPIST-1c… or TRAPPIST-1e… therefore 1 bar CO2 may be unlikely on potentially habitable exoplanets. This raises the question of whether life can exist on an exoplanet with 1 bar CO2 in the atmosphere. CO2 concentrations in the early Earth may have been as high as 10 bar and up to ∼4,000 ppm CO2 in the atmosphere in the Cambrian (Royer, Reference Royer 2006), but 1 bar CO2 might not be conducive to land-based life.
The uncertainties here abound, as the authors are quick to acknowledge. We do not, in fact, know whether any of these planets actually have atmospheres in the first place. Nor, obviously, do we have any idea of their composition if they do exist. We have no knowledge about the presence of carbon at the surface, and also have to factor in the possibility of biological processes modifying the composition of any atmosphere present, just as Earth’s atmosphere was gradually transformed as the effects of photosynthesis began to be felt.
For that matter, can we assume that the life we are looking for uses carbon along the lines of life on Earth? If it does, this study predicts that most stars in our stellar neighborhood, despite sometimes being much older than Earth, are behind our planet when it comes to biological evolution. Two planets – GJ 1061c and K2-3d – do stand out as being of unusual observational interest for present and future space telescopes. Both are both larger and older than Earth.
This is useful information, given that our first thorough analyses of planets of Earth mass are going to occur with planets orbiting low mass stars. When we reach the point of instruments like Habitable Worlds Observatory that can image planets around G-class stars, the discouraging catalog analyzed in this paper may be replaced with a more positive one. If Doughty and team are right, however, we have an answer to the Fermi paradox and the time problem. Intelligent life has far fewer places on which to develop than we thought.
The paper is Doughty et al, Calculating potential cumulative carbon fixed and evolutionary stage for Earthlike planets in our solar neighborhood, International Journal of Astrobiology (2026). Published online by Cambridge University Press 22 September 2026. Full text.
Sakurai’s Object: A Stellar Rebirth
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 recorded a magnitude of 21, whereas when Sakurai tagged it, it had reached magnitude 11. The apparent eruption here was first thought to be the result of a nova, but that was discounted for spectral reasons.
Several years later the unusual brightening began to decline. That was evidently the result of loss of mass and subsequent condensation of stellar material, which wound up hiding the star behind a dusty screen. It now shows a spectrum similar to what is known as a Wolf-Rayet star. Sakurai’s Object appears, however, to be in the much less massive Wolf-Rayet class known as a [WR] star. A conventional Wolf-Rayet star is massive, stripped of its hydrogen by huge stellar winds that leave the underlying helium-burning layers exposed. The odd [WR] notation turns out to be needed because low-mass objects like these can mimic a Wolf-Rayet star, so it was necessary to show that this is a different kind of object and a much smaller kind at that, though with Wolf-Rayet features.
There are also sub-categories of [WR] including [WC] that don’t need to occupy us now, although the paper explains what they mean. What’s intriguing about Sakurai’s object is its pace. According to current calculations it’s now roughly 6 times hotter than it was 30 years ago, and is climbing back toward the white dwarf temperatures it had before the eruption that made it observable by Sakurai. Albert Zijlstra (Jodrell Bank Centre for Astrophysics, University of Manchester), describes its significance:
“Most stars evolve so slowly that major changes take place over timescales far longer than a human lifetime. As a result, we usually have to piece together snapshots of stellar evolution by comparing different stars at different stages of their lives. Sakurai’s Object offers something far rarer. It is one of the very few stars known to have changed dramatically within just a few decades, giving us the opportunity to watch stellar evolution unfold in real time. With our observations, we can test theories of how stars evolve and gain new insights into one of the shortest and least understood phases in the life of a dying star.”
Image: The rapid brightening of Sakurai’s object allows astronomers to study the final phases of the stellar evolution in only a few decades. The left and right panels show the brightening. The middle panel is an image obtained with the radio telescope ALMA, showing the material ejected after the star re-ignited. The material currently extends over a size similar to our entire solar system. Credit: Stefan Kimeswenger, University of Innsbruck; Peter van Hoof, Royal Observatory Belgium. The observatory also has a short video showing the brightening.
What we apparently have here is a star once similar to the Sun that had finished its nuclear burning and was in the process of turning into a dense white dwarf star about the size of the Earth. But an event known as a ‘very late thermal pulse’ seems to have occurred. This happens when helium deep inside the star reignites, forcing a rapid expansion along with the ejection of stellar materials, so that the star has, at least for the time being, been reinvigorated. Along with another star called V605 Aquilae, Sakurai’s Object is one of only two stars that have been directly observed going through this process.
Let me turn to the paper to home in on the matter of thermal pulses:
Depending on when the pulse occurs, it is classified as an AGB final thermal pulse (AFTP), a late thermal pulse (LTP; post-AGB), or a very late thermal pulse (VLTP; see M. M. Miller Bertolami 2024). In the most extreme case (VLTP), the star is already on the white-dwarf cooling track when the flash causes rapid expansion and cooling, accompanied by substantial mass ejection into the circumstellar environment. The star is thus “born again” and returns close to its former AGB position in the HR diagram. Subsequent evolution involves reheating, and possibly an additional cooling excursion, as the star evolves back towards the white-dwarf domain with a markedly altered surface composition (T. M. Lawlor & J. MacDonald 2003).
No wonder this was a hard object to observe. The ejected gas and dust following the 1996 outburst caused the star to became hidden to direct imaging. Low density gases are coming off the star even as the outflowing atmosphere, moving at e 500 kilometers per second, is optically thick. Much of the spectrum produced is nebular. The team compared data from the VLT with computer models originally developed to study the processes that power the atmospheres and winds of Wolf-Rayet stars. The emission lines studied in this paper are embedded in the stellar wind, as opposed to the ejecta and dust. Much of the credibility of the analysis depends upon separating these factors.
The analysis reveals a stellar temperature at the surface pegged at between 27,000 and 36,000 degrees Kelvin. Scientists will now be able to study the process of the reheating following the eruption that occurred thirty years ago. Early indications are that the process is occurring more slowly than some models had predicted, so that Sakurai’s Object becomes a useful laboratory, like V605 Aquilae, into stellar behavior in this extremely rare class of stars. At some point, Sakurai’s Object will return to its fate as a white dwarf, only now under close observation as we ponder massive changes in a very short order.
Griet Van de Steene (Royal Observatory of Belgium), a co-author of the paper adds:
“Sakurai’s Object evolved much more quickly than pre-existing models for stellar evolution predicted. This led to a new generation of models that we now need to test. Our measurements show that the star is reheating more gradually than some of these new models predicted. That gives us an important way of testing which theories best describe what happens when a dying star briefly springs back to life. As we continue to monitor the star over the coming years, we expect to learn much more about this remarkable phase of stellar evolution.”
The paper is Marcolino et al (2026). The emergence of a [WC] star in Sakurai’s object. Monthly Notices of the Royal Astronomical Society, 552(1), Article stag1533. Full text.
Disrupted Systems: Implications for Life
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 with a Mars lander.
Which gets me to today’s interesting take on binary stars. The binaries – HD 129171 and HD 129209 – are G-class, both having formed from the same molecular cloud. This is a common enough scenario, because binary systems are extremely common. In fact, about half of the stars in the Milky Way have a companion star, and thus are likely to share a common chemistry.
About 180 light years from the Sun (based on Gaia data) in Boötes, the system is proving unusually helpful. Using the UVES spectrograph on ESO’s Very Large Telescope (VLT) in Chile, an international effort led by Anne Rathsam at the University of São Paulo in Brazil is using this binary as a laboratory to study chemical differences between the stars that may be telling us something about planet formation and orbital evolution. What is driving the differences?
All this has a bearing on life, because for life to occur, conditions must exist for long enough to let the necessary processes go to work. And that may be a problem. HD 129171 turns out to be enriched in refractory elements, while its companion HD 129209 is not. Refractory elements condense at high temperatures, as opposed to volatiles, and the proportion of one to the other can be an interesting diagnostic tool, telling us something about the system’s history. A star depleted in refractories is likely one that has spawned planets, while one heavy in these elements has likely swallowed planets whole.
Rathsam’s work, available in a paper just published in Astronomy & Astrophysics, focuses on beryllium, whose abundance here is interesting because it is not produced in stellar interiors. Measured properly, its presence points to a star that consumed planetary material long after formation. Lithium, beryllium, and boron, in fact, share characteristics that make them exceptional in terms of chemical emergence in the galaxy. Jorge Luis Melendez Moreno (USP), who served as study advisor to Rathsam on this paper, explains:
“All other chemical elements originate from primordial nucleosynthesis [the formation of the first atomic nuclei in the minutes following the Big Bang] or stellar nucleosynthesis [the nuclear fusion process that occurs inside stars throughout their lifetimes]. But not beryllium and boron. They primarily arise through a process called ‘cosmic spallation,’ in which high-energy particles fragment heavier nuclei, such as carbon, nitrogen, and oxygen, producing lighter elements.”
Image: The binary system of HD 129171 and HD 129209. Credit: Digital Sky Survey/Aladin/Anne Rathsam.
Lithium has its own uses as a marker, but the USP researchers found that beryllium is the more reliable tool, with a longer lasting chemical signature. HD 129171’s surplus of refractory elements (including magnesium, silicon, calcium and titanium) compared to its companion HD 129209 is accompanied by lithium and beryllium excess as well. The authors see evidence for rocky material equivalent to more than eleven times the mass of the Earth. This would have been ingested in the star, raising interesting questions about planet dynamics.
The infall of entire planets into a host star can be explained in various ways, from gravitational perturbations from other planets on eccentric orbits or skewed inclinations, to interactions within the early circumstellar disk driving young planets onto migratory trajectories. Although I hadn’t seen this paper before, the authors cite a 2025 study by Soares and team (citation below) that draws on simulations to show that about half of the stars simulated should ingest planets, leaving a chemical signature in perhaps 20 percent of them.
Evidently we can imagine system disruptions as a common occurrence in the Milky Way. We might add to this the fact that planet configurations with giant planets in circular outer orbits and rocky planets on inner ones are not common. Our observational data so far tends to confirm this, although tracking outer Jupiter-class planets with our current detection methods is always problematic given their sparse transit signatures. Overall, though, the picture that is emerging is that systems similar to the Solar System seem rare. If many systems are going through upheavals through planet migration and ingestion into the host, stable orbits may be trickier than we’ve thought. Rathsam comments:
“In our planetary system, the planets have relatively stable, low-eccentricity orbits. However, if planetary engulfment is common, it suggests that many systems undergo violent dynamic phases.”
Implications?
“Life wouldn’t just need billions of years to emerge and evolve. The planet would also have to remain in a sufficiently stable orbit to survive significant gravitational perturbations.”
If you’re wondering about our own star, it’s light in refractory materials relative to volatiles, which at least one recent study sees as a sign of planet formation at an early era. What became rocky planets and planetesimals, in other words, was never accreted into our star. I give that citation below. This and subsequent work seems to peg the Sun as the center of a dynamically quiet system compared to many, but be aware that the debate on this matter continues.
How useful is beryllium as a marker in such an analysis? The authors argue that despite the fact that beryllium is eventually depleted in a stellar interior, it persists long enough to provide reliable information. From the paper (my italics):
Refractory elements offer an excellent way to distinguish between the planet engulfment or the proto-cloud inhomogeneity scenarios. Since they have high condensation temperatures (≳1000 K), they are the primary constituents of the rocky material in planetary systems – terrestrial planets and cores of gaseous planets. In case of engulfment by a Sun-like star, this material is accreted by the star and then dissolved and mixed in the convective envelope, increasing the stellar surface abundances after the event (Sandquist et al. 2002). This process, however, produces a metal-rich outer layer with an unstable mean molecular weight gradient, which triggers thermohaline mixing (Théado & Vauclair 2012; Sevilla et al. 2022). For fragile elements such as Li and Be, this thermohaline mixing induces depletion, as it can carry these elements below the convective zone, into their burning regions. Thus, the chemical enrichment caused by the engulfment disappears over time. Nevertheless, Sevilla et al. (2022) demonstrated through simulations that the Li engulfment signature in stars with masses close to solar can be detected for ≥1 Gyr.
As far as I can tell, it’s the treatment of beryllium as a marker of engulfment that gives this paper its significance, as heretofore it has been used primarily as a diagnostic for the mixing of elements in stellar interiors. More broadly speaking, though, any reminders of the factors that make our Solar System adaptable for life should help us in identifying systems where life is less likely. That’s worth keeping in mind as we move beyond easy assumptions about life’s ubiquity and dig into realities that may make it more unusual than we thought.
The paper is Rathsam et al. (2026). Planet engulfment in the chemically anomalous HD 129171/HD 129209 pair. Astronomy & Astrophysics, 710, A236 (full text). The interesting paper on beryllium’s persistence is Soares et al. (2025). Assessing the processes behind planet engulfment and its imprints. Astronomy & Astrophysics, 693, A47 (preprint). The paper on the composition of our Sun is Meléndez et al. (2009). The peculiar solar composition and its possible relation to planet formation. The Astrophysical Journal Letters, 704(1), L66–L70. Abstract.
Pandora: Tuning Up our Data on Exoplanet Atmospheres
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 because their low cost also gives them the option of higher tolerance of failure, making it possible to push the limits without great financial risk (the cost cap on this class of mission is $20 million). A tool like this can be tightly focused on specific targets without compromising larger instruments that are already besieged with obligations to existing observing programs. Word from the Pandora team is that science work begins with all instruments performing as expected.
Image: Artist’s concept of NASA’s Pandora mission, which will help scientists untangle the signals from exoplanets’ atmospheres and their stars. Credit: NASA GSFC/Conceptual Image Lab.
What makes Pandora so interesting is that it’s a multi-wavelength mission. Pandora’s telescope, an aluminum Cassegrain instrument 45 centimeters in diameter, feeds detectors that work in both visible light for long-baseline photometry as well as near-infrared (NIR) wavelengths. Starspots or other stellar activity can be separated from the near-infrared spectroscopy data on the planet’s clouds and atmospheric hazes. This is information that will inform subsequent work with telescopes like JWST and Roman as we refine our tools for removing noise in the data. A recent paper on Pandora makes the case:
Alongside the opportunities explored throughout this work, Pandora provides a unique opportunity to help overcome many hurdles inherent in observations with current instruments. Namely, multi-epoch observations of exoplanet atmospheres with JWST are often observed at different points in the stellar rotation, making them difficult to fit jointly (e.g., E. M. May et al. 2023). By providing information about the stellar activity and allowing for corrections at the data level, joint Pandora–JWST programs will unlock new insights into planets around active hosts. Additionally, these same insights will inform the presence of offsets between different instruments and epochs, which have been difficult to constrain thus far with JWST alone (e.g., A. L. Carter et al. 2024).
Pandora is going to give us useful data on stellar contamination in our transmission spectroscopy work. That means a clearer and more reliable look at the composition of exoplanet atmospheres. Stellar contamination should stand out, with a minimum of 10 transit observing sessions per target, each lasting about 24 hours. The plan is to accumulate, for each target, roughly 240 hours of pointing time, which should yield more than 120 hours of science data once Earth occultations and unavoidable gaps for downlinks, etc. are taken into account. An instrument like JWST can collect transmission spectroscopic data for exoplanets but only with relatively short observing sessions involving one or a small number of transits. The combined datasets of the two observatories will cleanly excise star signals from the data on planetary ones.
The finalized target list was published last January and contains 19 host stars, one of which is orbited by two of the target worlds. The stars range from M-dwarfs to K-class. 16 of these planets have been observed previously by JWST, which will allow the retrofitting of the Pandora measurements onto the JWST spectra. As far as I can tell, earlier provisional target lists included planets that didn’t make the final list, with the emphasis shifting toward larger warm Neptunes and Saturns. That makes sense given that these offer higher signal-to-noise ratios as we put these techniques to work together for the first time.
Image: This is Figure 1 from the paper. Caption: The absorption cross sections of common absorbers in exoplanet atmospheres considered in this work, shown at a pressure and temperature of 0.1 mbar and 1000 K. The wavelength coverage of Pandora’s NIR detector (NIRDA), JWST’s NIRCam F322W2 and F444W filters, and HST’s WFC3 instrument (for the G141 grism) are shown. Pandora/NIRDA covers absorption bands of H2O, CH4, NH3 and the wing of the K doublet, making it most sensitive to these absorbers. Credit: Rotman et al.
Using these methods, Pandora’s science observations should be more accurate and reliable than any planetary atmosphere readings ever taken before. The paper is Rotman et al., “NASA’s Pandora SmallSat Mission: Simulated Modeling and Retrieval of Near-Infrared Exoplanet Transmission Spectra,” accepted at The Astronomical Journal (preprint).
Fermi Explorer: Building the First Mission to Another Star?
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 time the craft would arrive, Centauri A and B would be a bit over 6 light years from the Sun as opposed to their current 4.365 light years. Trajectory analysis going this far into the future is going to be an interesting challenge.
I mention all this because a call to mount such a mission has now arisen. It bears the name Fermi Explorer, and according to its new website, its intention is to get a spacecraft with a 1 kilogram, 10X10X10 cm payload to the barycenter of the binary Centauri A and B system. In other words, the target is not either star itself but the common center of mass between the two as they orbit.
Some particulars: The mission should launch before the end of 2029 if the effort succeeds, and is intended to cost less than $15 million to design, build, launch and operate. Mission co-founder Philip Johnston is going to have his hands full.
As to departure, Fermi Explorer would take a year and a half moving out of Earth orbit. Then, using a series of Oberth maneuvers taking it to within 0.42 AU of the Sun, the craft would rely upon what the site calls a ‘perihelion pump,’, which involves multiple close solar flybys over 12 years to build the energy to achieve an escape trajectory that, after climbing out of the Sun’s gravity well, attains 23.64 km/sec. That’s a bit higher than Voyager 1’s 17 km/sec. Final Solar System departure would be, after a 2029 launch, around the year 2043. Ahead for the spacecraft would be an unpowered cruise of over 70,000 years.
What the craft will carry is not yet determined, although I notice the plan to put a copy of the Voyager Golden Record and similar materials onboard (I’m assuming this is to be done digitally). Ahead is a three-month period for solicitations for other items of cultural value. Likewise, scientific instruments will undergo their own period of solicitation. The emphasis is on flight-proven hardware with little research and development necessary. To quote from the website:
We will soon put the mission out for open tender to all the major satellite manufacturers, and we aim to open-source as much of the design as we can. The four primary objectives are considered non-negotiable. Everything else is negotiable. For example, the manufacturers can determine the power system, antenna strength, propulsion, mission profile, and whether to include gravity assists, etc. We anticipate that we can do the mission with around a 100-200 kg small solar-powered satellite with just electric propulsion, doing what we call a perihelion pump maneuver… We expect the mission will not have a large antenna for communication, and so we expect we will lose connectivity relatively quickly, and so much of the mission will be autonomous. It will be too small to track and will lose power once it leaves the solar system.
Can crowdfunding build an interstellar craft? The hope is clearly that enough people will become interested to help, with the site offering engraved names and physical objects in the payload itself, so the scientific payload, already tightly squeezed, will have a mass budget with even tighter constraints.
And with all the attention AI is getting in the press, note its use here. The website points to a key technical report called “Interstellar Precursor Mission to Alpha Centauri: Technical Feasibility Assessment,” dated July of 2026. Specifically, the report is said to be: “Prepared with PSI’s Autonomous Physics-Research Platform,” under which is stated “Physical Superintelligence’s agentic research system produced the analyses, simulations, and proof-grade verification in this report end-to-end under staged independent audit.” And again: “This report did not undergo comprehensive human peer review.”
This gets interesting. Writing for MIT Technology Review, Michelle Kim has a fine piece on the use of AI for Fermi Explorer that fills in the background. PSI is a research laboratory called Physical Superintelligence, and its AI system is what came up with the trajectory Fermi Explorer would follow. According to Kim, PSI’s AI went to work on the problem of getting a small spacecraft like this up to speed:
A week later, the AI system turned up a novel trajectory… It combined well-known orbital maneuvers in a way the Fermi team had not considered, according to a paper that has not been peer-reviewed. It suggested that the spacecraft could first slow down so its orbit swings in close to the sun—closer than Mercury. On each close pass, it would fire its engine so that the solar panels get four times the light, and a burst of thrust delivered at high speed would buy more energy than the same burst anywhere else. Because the engine would run only near the sun, the solar panels could stay small and the spacecraft light.
The Fermi Explorer site also links to a separate mission analysis which cross-references the PSI report and seems to agree with its results almost completely. I’m assuming human peer review is going to come into play if momentum for this mission builds. But watching the development of these models for physics and their tweaking along the way is a fascinating exercise.
Roman Space Telescope Launches Tomorrow
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 can tune in on Facebook, Instagram, Twitch, X, Discovery+, Amazon Prime, YouTube, or NASA+ (see https://www.nasa.gov/live/ for links and updates).
And as Jim reminds us: “As with any launch, timing can change because of weather or other conditions, so check NASA for the latest schedule. Fingers crossed!”
