by Paul Gilster | Mar 17, 2022 | Culture and Society |
Just a quick note for today as I finish up tomorrow’s long post. But I did want you to be aware of this new title, Extraterrestrial Intelligence: Academic and Societal Implications, which has connections with recent topics and will again tomorrow, when we discuss a new paper from Jason Wright and SETI colleagues on technosignatures. As with the recent biography of John von Neumann, I haven’t had the chance to read this yet, but it’s certainly going on the list. The book is out of Cambridge Scholars Publishing. Here’s the publisher’s description:
What are the implications for human society, and for our institutions of higher learning, of the discovery of a sophisticated extraterrestrial intelligence (ETI) operating on and around Earth? This book explores this timely question from a multidisciplinary perspective. It considers scientific, philosophical, theological, and interdisciplinary ways of thinking about the question, and it represents all viewpoints on how likely it is that an ETI is already operating here on Earth. The book’s contributors represent a wide range of academic disciplines in their formal training and later vocations, and, upon reflection on the book’s topic, they articulate a diverse range of insights into how ETI will impact humankind. It is safe to say that any contact or communication with ETI will not merely be a game changer for human society, but will also be a paradigm changer. This means that it makes sense for human beings to prepare themselves now for this important transition.
Important indeed, but how demoralizing to see another title at a stiff tariff: £63.99 (that’s about $84 US). I will spare you my thoughts on the academic side of publishing, and in the meantime see if I can get a review copy, as I assume most Centauri Dreams readers aren’t going to want to pony up this amount for a book they know little about (although if you live near a good academic library, this one should turn up there).
by Paul Gilster | Mar 15, 2022 | Exoplanetary Science |
Why is it so difficult to detect planets around Alpha Centauri? Proxima Centauri is one thing; we’ve found interesting worlds there, though this small, dim star has been a tough target, examined through decades of steadily improving equipment. But Centauri A and B, the G-class and K-class central binary here, have proven impenetrable. Given that we’ve found over 4500 planets around other stars, why the problem here?
Proximity turns out to be a challenge in itself. Centauri A and B are in an orbit around a common barycenter, angled such that the light from one will contaminate the search around the other. It’s a 79-year orbit, with the distance between A and B varying from 35.6 AU to 11.2. You can think of them as, at their furthest, separated by the Sun’s distance from Pluto (roughly), and at their closest, by about the distance to Saturn.
The good news is that we have a window from 2022 to 2035 in which, even as our observing tools continue to improve, the parameters of that orbit as seen from Earth will separate Centauri A and B enough to allow astronomers to overcome light contamination. I think we can be quite optimistic about what we’ll find within the decade, assuming there are indeed planets here. I suspect we will find planets around each, but whether we find something in the habitable zone is anyone’s guess.
Image: This is Figure 1 from today’s paper. Caption: (a) Trajectories of ?-Cen A (red) and B (blue) around their barycenter (cross). The two stars are positioned at their approximate present-day separation. The Hill spheres (dashed circles) and HZs (nested green circles) of A and B are drawn to scale at periapsis. (b) The apparent trajectory of B centered on A, with indications of their apparent separation on the sky over the period from CE 2020 to 2050. The part of trajectory in yellow indicates the coming observational window (CE 2022–2035) when the apparent separation between A and B is larger than 6 and the search for planets around A or B can be conducted without suffering significant contamination from the respective companion star. Credit: Wang et al.
If we don’t yet have a planet detection around the binary Centauri stars, we continue to explore the possibilities even as the search continues. Thus a new paper from Haiyang Wang (ETH Zurich), who along with colleagues at the university has been modeling the kind of rocky planet in the habitable zone that we hope to find there. The idea is to create the benchmarks that predict what this world should look like.
The numerical modeling involved examines the composition of the hypothetical world, drawing on what we do know, based on spectroscopic measurements, of the chemical composition of Centauri A and B. Here there is a great deal of information to work with, especially on so-called refractory elements, the iron, magnesium and silicon that go into rock formation. Centauri A and B are among the Gaia “benchmark stars” for which stellar properties have been carefully calibrated, and up to 22 elements have been found in high-quality spectra, so we know a lot about their chemical makeup.
But a key issue remains. While rocky planets are known to have rock and metal chemical compositions similar to that of their host stars, there is no necessary correspondence when it comes to the readily vaporized volatile elements. The authors suggest that this is because the process of planetary formation and evolution quickly does away with key telltale volatiles.
The researchers thus develop their own ‘devolatilization model’ to project the possible composition of a supposed habitable zone planet around Centauri A and B, linking stellar composition with both volatile and refractory elements. The model grew out of Wang’s work with Charley Lineweaver and Trevor Ireland at the Australian National University in Canberra, and it continues at Wang’s current venue at ETH. This is fundamentally new ground that extends our notions of exoplanet composition.
Wang and team call their imagined world ‘a-Cen-Earth,’ delving into its internal structure, mineralogy and atmospheric composition, all factors in evolution and habitability. The findings reveal a planet that is geochemically similar to Earth, with a silicate mantle, although carbon-bearing species like graphite and diamond are enhanced. Water storage in the interior is roughly the same as Earth, but the deduced world has a somewhat larger iron core mixed with a possible lack of plate tectonics. Indeed, “…the planet may be in a Venus-like stagnant-lid regime, with sluggish mantle convection and planetary resurfacing, over most of its geological history.”
As to the atmosphere of the hypothetical world that grows out of Wang’s model, its early era shows an envelope rich in carbon dioxide, methane and water, which harks back to the Earth’s atmosphere in the Archean era, between 4 and 2.5 billion years ago. That gives life a promising start if we assume abiogenesis occurring in a similar environment.
Image: ? Centauri A (left) and ? Centauri B viewed by the Hubble Space Telescope. At a distance of 4.3 light-?years, the ? Centauri group (which includes also the red dwarf ? Centauri C) is the nearest star system to Earth. Credit: ESA/Hubble & NASA.
How far can we take a model like this? We may soon have data to measure it against, but it’s worth remembering what the paper’s authors point out. After noting that planets around the “Sun-like” Centauri A and B cannot be extrapolated from the already known planets around the red dwarf Proxima Centauri, they go on to say:
Second, although ? Cen A and B are “Sun-like” stars, their metallicities are ?72% higher than the solar metallicity (Figure 3). How this difference would affect the condensation/evaporation process, and thus the devolatilization scale, is the subject of ongoing work (Wang et al. 2020b).
That’s a big caveat and a useful pointer to the needed clarification that further work on the matter should bring – metallicity is obviously significant. The paper adds:
Third, we ignore any potential effect of the “binarity” of the stars on their surrounding planetary bulk chemistry during planet formation, even though we highlight that, dynamically, the planetary orbits in the HZ around either companion are stable. Finally, we have yet to explore a larger parameter space, e.g., in mass and radius, but have only benchmarked our analysis with an Earth-sized planet, which would otherwise have an impact on the interior modeling…
So we’re in early days with planet modeling using these methods, which are being examined and extended through the team’s collaborations at Switzerland’s National Centre of Competence in Research PlanetS. Note too that the authors do not inject any catastrophic impact into their model of the sort that could affect both a planet’s mantle and/or its atmosphere, with dramatic consequences for the outcome. We know from the Earth’s experience in the Late Heavy Bombardment that this can be a factor.
With all this in mind, it’s fascinating to see the lines of observation and theory converging on the Alpha Centauri binary pair. Finding a habitable zone planet around Proxima Centauri was exhilarating. How much more so to go beyond the many imponderables of red dwarf planet habitability to two stars much more like our Sun, each of which might have a planet in its habitable zone? The Alpha Centauri triple system may turn out to be a bonanza, showing us both red dwarf and Sun-like planetary outcomes in a single system that just happens to be the closest to us.
The paper is Wang et al,, “A Model Earth-sized Planet in the Habitable Zone of ? Centauri A/B,” The Astrophysical Journal Vol. 927, No. 2 (10 March 2022). Abstract/Full Text. Preprint also available.
by Paul Gilster | Mar 10, 2022 | Culture and Society |
We can’t know whether there is a probe from another civilization – a von Neumann probe of the sort we discussed in the previous post – in our own Solar System unless we look for it. Even then, though, we have no guarantee that such a probe can be found. The Solar System is a vast place, and even if we home in on the more obvious targets, such as the Moon, and near-Earth objects in stable orbits, a well hidden artifact a billion or so years old, likely designed not to draw attention to itself, is a tricky catch.
As with any discussion of extraterrestrial civilizations, we’re left to ponder the possibilities and the likelihoods, acknowledging how little we know about whether life itself is widely found. One question opens up another. Abiogenesis may be spectacularly rare, or it may be commonplace. What we eventually find in the ice moons of the outer system should offer us some clues, but widespread life doesn’t itself translate into intelligent, tool-making life. But for today, let’s assume intelligent toolmakers and long-lived societies, and ponder what their motives might be.
Let’s also acknowledge the obvious. In looking at motivations, we can only peer through a human lens. The actions of extraterrestrial civilizations, and certainly their outlook on existence itself, would be opaque to us. They would possibly act in ways we consider inexplicable, for reasons that defy the logic we apply to human decisions. But today’s post is a romp into the conjectural, and it’s a reflection of the fact that being human, we want to know more about these things and have to start somewhere.
Motivations of the Probe Builders
Greg Matloff suggests in his paper on von Neumann probes that one reason a civilization might fill the galaxy with these devices is the possibly universal wish to transcend death. A walk through the Roman ruins scattered around what was once the province of Gaul gave weight to the concept when my wife and I prowled round the south of France some years back. Humans, at least, want to put down a marker. They want to be remembered, and their imprint upon a landscape can be unforgettable.
But in von Neumann terms, I have trouble with this one. I stood next to a Roman wall near Saint-Rémy-de-Provence on a late summer day and felt the poignancy of all artifacts worn by time, but the Romans were decidedly mortal. They knew death was a horizon bounding a short life, and could transcend it only through propitiations to their gods and monuments to their prowess. A civilization that is truly long-lived, defined not by centuries but aeons, may have less regard for personal aggrandizement and even less sense of a coming demise. Life might seem to stretch indefinitely before it.
Image: Some of the ruins of the Roman settlement at Glanum in Saint-Rémy-de-Provence, recovered through excavations beginning in 1921. Walking here caused me to reflect on how potent memorials and monuments would be to a species that had all but transcended death. Would the impulse to build them be enhanced, or would it gradually disappear?
Probes as a means of species reproduction, another Matloff suggestion, ring more true to me, and I would suggest this may flag a biological universal, the drive to preserve the species despite the death of the individual. Here we’re in familiar science fiction terrain in which biological material is preserved by machines and flung to the stars, to be activated upon arrival and raised to awareness by artificial intelligence. Or we could go further – Matloff does – to say that biological materials may prove unnecessary, with computer uploads of the minds of the builders taking their place, another SF trope.
I can go with that as a satisfactory motivator, and it’s enough to make me want to at least try to find what Jim Benford calls ‘lurkers’ in our own corner of the galaxy. Another motivator that deeply satisfies me because it’s so universal among humankind is simple curiosity. A long-lived, perhaps immortal civilization that wants to explore can send von Neumann probes everywhere possible in the hope of learning everything it can about the universe. Encyclopedia Galactica? Why not? Imputing any human motive to an extraterrestrial civilization is dangerous, of course, but we have little else to go on. And centuries of human researchers and librarians attest to the power of this one.
Would such probes be configured to establish communication with any societies that arise on the planets under observation? This is the Bracewell probe notion that extends von Neumann self-reproduction to include this much more immediate form of SETI, with potential knowledge stored at planetary distances. Obviously, 2001: A Space Odyssey comes to mind as we recall the mysterious monoliths found on the early Earth and, much later, on the Moon, and the changes to humanity they portend.
But are long-lived civilizations necessarily friendly? Fred Saberhagen’s ‘berserker’ probes key off the Germanic and particularly Norse freelance bodyguards and specialized troops that became fixtures at the courts of royalty in early medieval times (the word is from the Old Norse word meaning ‘bearskin’). These were not guys you wanted to mess with, and associations with their attire of bear and wolfskins seem to have contributed to the legend of werewolves. Old Norse records show that they were prominent at the court of Norway’s king Harald I Fairhair (reigned 872–930).
Because they made violence into a way of life, we should hope not to find the kind of probe that would be named after them, which might be sent out to eliminate competition. Thus Saberhagen’s portrayal of berserker probes sterilizing planets just as advanced life begins to appear. The fact that we have not yet been sterilized may be due to the possibility that such a probe does not yet consider us ‘advanced,’ but more likely implies we have no berserker probes nearby. Let’s hope to keep it that way.
Or what about the spread of life itself? If abiogenesis does turn out to be unusually rare, it’s possible that any civilization with the power to do so would decide to seed the cosmos with life. In this case, we’re not sending uploaded intelligence or biological beings in embryonic form in our probes, but rather the most basic lifeforms that can proliferate on any planets offering the right conditions for their development. Perhaps there becomes an imperative – written about, for example, by Michael Mautner and Matloff himself – to spread life as a way to transform the cosmos. Milan ?irkovi? continues to explore the implications of just such an effort.
In an interesting post in Sentient Developments, Canadian futurist George Dvorsky points out that self-reproduction has more than an outward-looking component. Supposing a civilization interested in building a megastructure – a Dyson sphere, let’s say – decides to harness self-reproduction to supply the needed ‘worker’ devices that would mine the local stellar system and create the object in question.
At a truly cosmic level, Matloff speculates, self-replicating probes might be deployed to build megastructures that could alter the course of cosmic evolution. We’re in Stapledon territory now, freely mixing philosophy and wonder. We’re also in the arena claimed by Frank Tipler in his The Physics of Immortality (Doubleday, 1994).
We’ll want to search the Earth Trojan asteroids and co-orbitals for any indication of extraterrestrial probes, though it’s also true that the abundant resources of the Kuiper Belt might make operations there attractive to this kind of intelligence. One of the biggest questions has to do with the size of such probes. Here I’ll quote Matloff:
In a search for active or quiescent von Neumann probes in the solar system, human science would contend with great uncertainty regarding the size of such objects. Some science fiction authors contend that these devices might be the size of small planetary satellites (see for example L. Johnson, Mission to Methone and A. Reynolds, Pushing Ice). On the other hand, Haqq-Misra and Kopparapu (2012) believe that they may be in the 1-10 m size range of contemporary human space probes and these might be observable.
But there may be a limit to von Neumann probe detection. If they can be nano-miniaturized as suggested by Tipler (1994), the solar system might swarm with them and detection efforts would likely fail.
I remember having a long phone conversation two decades ago with Robert Freitas on this very point. Freitas had originally come up with a self-reproducing probe concept at the macro-scale called REPRO, but went on to delve into the implications of nano-technology. He made Matloff’s point in our discussion: If probe technologies operate at this scale, the surface of planet Earth itself could be home to an observing network about which we would have no awareness. Self-reproductive probes will be hard to rule out, but looking where we can to screen for the obvious makes sense.
The paper is Matloff, “Von Neumann probes: rationale, propulsion, interstellar transfer timing,” International Journal of Astrobiology, published online by Cambridge University Press 28 February 2022 (abstract).
by Paul Gilster | Mar 8, 2022 | Astrobiology and SETI |
Before getting into the paper I want to discuss today, I want to mention the new biography of John von Neumann by Ananyo Bhattacharya. I make no comment on The Man from the Future (W. W. Norton & Company, 2022) yet because while I have a copy, I haven’t had time to read it. But be aware that it’s out there – it’s getting good reviews, and given the impact of this remarkable figure on everything from programmable computers to game theory and the interstellar dispersion of civilizations, it’s a book you’ll at least want to stick on your reference list.
I figure anyone who masters calculus by the age of eight, as von Neumann is reputed to have done, is going to turn out to make a substantial contribution somewhere. I’m also interested in how polymaths function, moving with what seems effortless ease through diverse fields of study and somehow leaving their mark on each. What a contrast to our age of micro-specialization, where relentless drilling down into a single topic – and this seems true of most academic disciplines – is the mode of choice.
Image: John von Neumann, shown here with technology that might have been more to his taste, the 18,000 vacuum-tube strong ENIAC. One can only wonder what the sybaritic mathematician would have made of quantum computing. If only he were here to tell us.
It’s a good time for this book to come out, because von Neumann isn’t exactly in the spotlight these days. In a review in Science, Dov Greenbaum and Mark Gerstein note that he seems to have dropped out of public view:
In 2022…von Neumann could be the smartest person most people have never heard of. To wit, Google Trends shows that his online popularity last year was almost an order of magnitude less than that of Alan Turing, a contemporary in computing; Erwin Schrödinger, a predecessor in quantum mechanics; and Stephen Wolfram, a successor in the world of automata.
All fame is fleeting, but it’s also mutable, and the Bhattacharya biography should go some distance in pumping up von Neumann’s recognition. But let’s talk interstellar, where his name comes up today because Greg Matloff has just published a new paper dealing with what we now call ‘von Neumann probes.’ By this we simply mean probes that are self-replicating, a notion that originated with von Neumann and has now gone on to wide-ranging study. Throw self-replication and interstellar probes together and you generate various notions about how long it takes to populate the entire galaxy, as found in the work of, for example, Frank Tipler, Michael Hart and others.
Most of those exploring this space have been what Milan ?irkovi? calls ‘contact pessimists,’ who point out that if von Neumann probes could visit all stars with habitable planets in an entire galaxy, and do this within a small fraction of the galaxy’s age, their existence should be obvious. A more subtle school of thought holds that 1) dispersion need not be uniform and 2) a von Neumann probe may already be in our own Solar System, much less others, for we have only begun to explore deep space.
We can imagine these probes as having the built-in intelligence to make the interstellar crossing, which could be on the order of tens of thousands of years or more given that no biological crews need be involved. Around a target star, such a probe uses local resources – mining a native asteroid system, perhaps – to produce a new probe that, in turn, moves on to the next nearest star, or whatever target it chooses. Robert Freitas has considered self-replication in terms of nanotechnology, in which the size of the probe may be reduced to something as tiny as a needle packed with assemblers.
I come back to the question of biological crews, for without them (or perhaps given probes that carry biological materials that can be activated at destination), the von Neumann probes are free of the massive constraints of species lifespans. Miniaturize a probe to nanotechnological levels and a space-based solar-pumped laser array can push it up to relativistic velocities, possibly using materials like graphene or some kind of future metamaterial at levels of thickness no more than a single atom. But Matloff believes a 20-nm aluminum sail performing an Oberth maneuver (close pass by the Sun followed by a propulsive burn to maximize the gravity slingshot) could reach speeds in the range of 300 kilometers per second. That translates to one light year every 1,000 years.
Either way, we have a method to move human technologies out into the galaxy once our engineering is up to the challenge – the physics behind the project do not preclude this. So let’s imagine that we or some other civilization reach a stage in which we can build von Neumann probes and set them on their journeys. Matloff develops a conservative estimate of the expansion rate of a civilization using such probes.
Because of the vast canvas of time we have to work with given the age of our galaxy, we can afford to be quite conservative in our assumptions. Suppose that to minimize transit times, we say that civilizations doing this send out probes only when another star makes a close approach to the parent probe’s planetary system. Remember, the goal here is the eventual placement of probes galaxy-wide. We give up on all notions of probes reaching destinations within the lifetime of those who build them, even the lifetime of their civilization!
This gets intriguing, based on current data. The second data release of the Gaia space observatory tells us that a star like the Sun will pass within one light year of the Sun every half million years or so. This is, Matloff notes, a pretty conservative figure, for Gaia underestimates the number of low-mass red dwarfs that might also serve. Working the math, we come up with an estimated rate of expansion, granting that some stellar systems will not be suitable. After 500,000 years, we have but two occupied stellar systems. After 18 million years, we have 68.7 billion systems. Says Matloff:
This approach is only an approximation; not all stellar systems will be suitable for occupation by von Neumann probes, and some close stellar encounters will be repeated. But it does indicate that not many long-lived space-faring civilizations that deploy von Neumann probes are required to occupy the galaxy. Even if the slowest interstellar propulsion technique presented above — unpowered giant planet gravity assists — is the one selected by ET, the required galactic occupation time is not substantially increased.
Ah, the joys of exponential growth. I’m reminded of George Gamow’s treatment of such growth in his delightful One Two Three… Infinity, first published in 1947. With probes generating new probes and continuing to push outward, it becomes clear that it would not take a great number of spacefaring civilizations to occupy the entire galaxy even using nothing more than sundiver maneuvers or even gravity assists around gas giant planets to serve as the propulsion technique. Obviously, the process quickens if we reach relativistic speeds with nanotech probes that can exploit the resources they find. The process is fast enough that it’s inevitable to ask where such probes might be located if they are already here.
But first, why would a civilization choose to mount a campaign to spread through the galaxy using such probes? In the next post, we’ll consider a range of possible motivations.
The paper is Matloff, “Von Neumann probes: rationale, propulsion, interstellar transfer timing,” International Journal of Astrobiology, published online by Cambridge University Press 28 February 2022 (abstract).
by Paul Gilster | Mar 4, 2022 | Exoplanetary Science |
I always keep an eye on the Phase I and Phase II studies in the pipeline at the NASA Innovative Advanced Concepts (NIAC) program. The goal is to support ideas in their early stages, with the 2022 awards going out to 17 different researchers to the tune of a combined $5.1 million. Of these, 12 are Phase I studies, which deliver $175,000 for a nine-month period, while the five Phase II awards go to $600,000 over two years. We looked at one of the Phase I studies, Jason Benkoski’s solar-thermal engine and shield concept, in the last post. Today we go hunting exoplanets with a starshade.
This particular iteration of the starshade concept is called Hybrid Observatory for Earth-like Exoplanets (HOEE), as proposed by John Mather (NASA GSFC). Here the idea is to leverage the resources of the huge ground-based telescopes that should define the next generation of such instruments – the Giant Magellan Telescope, the Extremely Large Telescope, etc. – by using a starshade to block the glare of the host star, thus uncovering images of exoplanets. Remember that at visible wavelengths, our Sun is 10 billion times brighter than the Earth. The telescope/starshade collaboration would produce what Mather believes will be the most powerful planet finder yet designed.
Image: Three views of a starshade. Credit: NASA / Exoplanet Exploration Program.
Removing the overwhelming light of a star can be done in more than one way, and we’ve seen that an internal coronagraph will be used, for example, with the Nancy Grace Roman Space Telescope. It’s what NASA describes as “a system of masks, prisms, detectors and even self-flexing mirrors” that is being built at the Jet Propulsion Laboratory for the mission.
In conjunction with a space telescope, a starshade operates as a separate spacecraft, a large, flat shade positioned tens of thousands of kilometers away. Starshades have heretofore been studied in this configuration, so the innovation in Mather’s idea is to align the starshade with instruments on the ground. His team believes that we could detect oxygen and water on an Earth-class planet using a 1-hour spectrum out to a distance of 7 parsecs (roughly 23 light years. In an ASTRO2020 white paper, Mather described a system like this using a different orbit for each target star, with the orbit being a highly eccentric ellipse. Thrust is obviously a key component for adjusting the starshade’s position for operations.
From the white paper:
An orbiting starshade would enable ground-based telescopes to observe reflected light from Earth-like exoplanets around sun-like stars. With visible-band adaptive optics, angular resolution of a few milliarcseconds, and collecting areas far larger than anything currently feasible for space telescopes, this combination has the potential to open new areas of exoplanet science. An exo-Earth at 5 pc would be 50 resolution elements away from its star, making detection unambiguous, even in the presence of very bright exo-zodiacal clouds. Earth-like oxygen and water bands near 700 nm could be recognized despite terrestrial interference…
And what a positioning challenge this is in order to maximize angular resolution, sensitivity and contrast, with the starshade matching position and velocity with the telescope from an orbit with apogee greater than ~ 185,000 km, thus casting a shadow of the star, while leaving the light of its planets to reach the instrument below. In addition to the active propulsion to maintain the alignment, the concept relies on adaptive optics that will in any case be used in these ground instruments to cope with atmospheric distortion. Thus low-resolution spectroscopy becomes capable of analyzing light that is actually reflected from Earth-like planets.
Mather’s team wants to cut the 100-meter starshade mass by a factor of 10 to support about 400 kg of thin membranes making up the shade. Thus the concept of an ultra-lightweight design that would be assembled – or perhaps built entirely – in space. It’s worthwhile to remember that the starshade concept in orbit is a new entry in a field that has seen study at NASA GSFC as well as JPL’s Team X, with suitability considered for various missions including HabEx, WFIRST, JWST, New Worlds Explorer, UMBRAS and THEIA. The Mather plan is to create a larger, more maneuverable starshade, as it will indeed have to be to make possible the alignments with ground observatories contemplated in the study.
It’s an exciting prospect, but as Mather’s NIAC synopsis notes, the starshade is not one we could build today. From the synopsis:
The HOEE depends on two major innovations: a ground-space hybrid observatory, and an extremely large telescope on the ground. The tall pole requiring design and demonstration is the mechanical concept of the starshade itself. It must satisfy conflicting requirements for size and mass, shape accuracy and stability, and rigidity during or after thruster firing. Low mass is essential for observing many different target stars. If it can be assembled or constructed after launch, it need not be built to survive launch. We believe all requirements can be met, given sufficient effort. The HOEE is the most powerful exoplanet observatory yet proposed.
Image: Graphic depiction of Hybrid Observatory for Earth-like Exoplanets (HOEE). Credit: John Mather.
Centauri Dreams readers will know that Ashley Baldwin has covered starshade development extensively in these pages. His WFIRST: The Starshade Option is probably the best place to start for those who want to delve further into the matter, although the archives contain further materials. Also see my Progress on Starshade Alignment, Stability.
For more, see Peretz et al., “Exoplanet imaging performance envelopes for starshade-based missions,” Journal of Astronomical Telescopes, Instruments, and Systems 7(2), 021215 (2021). Abstract. And for an overview: Arenberg et al., “Special Section on Starshades: Overview and a Dialogue,” Journal of Astronomical Telescopes, Instruments, and Systems 7(2), 021201 (2021). Abstract.
