Centauri Dreams
Imagining and Planning Interstellar Exploration
The Infrastructure Problem [1]
Nick Nielsen today tackles an issue we’ve often discussed in these pages, the space-based infrastructure many of us assume necessary for deep space exploration. But infrastructures grow in complexity in relation to the demands placed upon them, and a starship would, as Nick notes, be the most complex machine ever constructed by human hands. Are there infrastructure options, including building such vehicles on Earth, and what sort of societies would the choice among them eventually produce? You’ll find more of Nielsen’s writing in his blogs Grand Strategy: The View from Oregon and Grand Strategy Annex. In addition to his continuing work for the space community, Nick is a contributing analyst with strategic consulting firm Wikistrat.
by J. N. Nielsen
Although we have spacecraft in orbit around Earth, as well as on the moon and other planets and their moons, and even spacecraft now in interstellar space, so that the products of human industry are to be found throughout our solar system and beyond, we have as yet no industrial infrastructure off the surface of the Earth, and this is important. I will try to explain how and why this is important, and why it will remain important, potentially shaping the structure of our civilization.
Made on Earth
All our spacecraft to date have been built on Earth where we possess an industrial infrastructure that makes this possible. The International Space Station, of course, was assembled in orbit from components built on the surface of the Earth and boosted into space on rockets. It has long been assumed, if we were to build a very large spacecraft (say, for a journey to Mars or beyond), that it would be constructed in much the same way: the components would be engineered on Earth and assembled in space. There is an obvious terrestrial analogy for this: we build our ships on land, where it is convenient to do the work, and then launch them only when the hull is seaworthy. Once the hull is in the water it is fitted out, and then come sea trials, but it would not be worth the trouble to try to build the hull of a ship in the water.
The analogy, however, seems misleading when applied to space. In space, we could build very large spacecraft in microgravity environments that would considerably ease the task of manipulating awkwardly large and heavy components. Also, large spacecraft never intended to enter into planetary atmospheres could be built in the vacuum of space with no concern for the aerodynamics that are crucial for a craft operating in a planetary atmosphere. The stresses of transiting a planetary atmosphere would be an unnecessary requirement for most deep-space vehicles. But what would it take to really build a spacecraft in space, in contradistinction to the assembly of completed modules in orbit?
Image: One take on building starships in space. This view of the Project Icarus orbital construction ring prototype design shows resupply from the Skylon single stage to orbit spacecraft now under development by Reaction Engines. Credit: Adrian Mann.
Even a “basic machine shop” in orbit would not come close to providing the kind of industrial infrastructure we have been building on the surface of the Earth for more than two hundred years now. Production processes ripple outward until they involve much of the planet’s industrial production capacity, a lesson that can be illustrated by Adam Smith’s famous example of the day-laborer’s woolen coat or by what Austrian economist Eugen Böhm von Bawerk called round-about production processes. [2] I suspect that many will argue that the advent of 3D printing is going to change everything, and that all you need to do is to boost a 3D printer into orbit and then you can produce anything that you might need in orbit. Well, not quite.
The Growth of Infrastructure
As civilization grows more complex, infrastructure becomes more complex, and more precursors are necessary to achieving the basic functionality assumed by the institutions of society. We see this in the increasing complexity of our cities. There was a time when cutting edge technology meant bringing water into a city with aqueducts and having underground sewers to carry away the waste. To the infrastructure of water supplies we have added fossil fuel supplies, electricity supplies, telecommunications lines, and now fiber optic cables for high speed internet access. (On the growing infrastructure of civilization cf. my post The Computational Infrastructure of Civilization.) All of these infrastructure requirements have been continually updated since their initial installation, so that, for example, the electricity grid is significantly more advanced today than when introduced.
For the lifeway of nomadic foragers, no infrastructure is necessary except for a knowledge of edible plants and available game. Since the geographical expansion of nomadic foragers is slow, change in requisite knowledge is also slow, as a moving band of foragers only very gradually sees the diminution of traditional dietary staples and only very gradually sees the emergence of unfamiliar plants and animals. Much greater infrastructure characterizes agrarian-ecclesiastical civilization, and much greater still industrial-technological civilization. The extraterrestrialization of industrial-technological civilization (yielding extraterrestrial-technological civilization) requires an order of magnitude of increase in infrastructure for the necessary maintenance of human life.
How to Build a Starship
The spacecraft requisite to the achievement of extraterrestrialization are today, and are likely to remain, the most complex and sophisticated machines ever built by human beings. To produce not only their components, but the machines required to produce the components, requires the entire advanced infrastructure that we now possess in our most developed centers of manufacturing. A useful analogy for understanding the industrial requirements for the production of spacecraft is to think of building the spacecraft of the future as we think today of building a nuclear-powered submarine. Like a nuclear submarine, an SSTO (single stage to orbit) spacecraft will be one of the most technically difficult and demanding engineering tasks ever attempted; it will involve parts suppliers from all over the world; it will involve millions of individual parts that each have to fitted in place by a human hand, and the assembly itself is likely to require many years of painstaking construction.
There is another sense in which spacecraft probably will be like nuclear submarines: a spacecraft is going to have significant power demands, and the most compact way to address this with our current technology is what we now do with your biggest submarines: nuclear power. The compact reactors on submarines (and aircraft carriers, which typically have two reactors for redundancy) have proved themselves to be safe and serviceable, and they can keep generating power for 25-30 years without refueling – possibly a sufficient period of time to make an interstellar journey. We can, of course, readily make use of solar power in space, though this is not compact and would not be suitable for a starship, which would be operating for extended periods of time far from the light of the sun or any other star.
I think it is clear that once we attain the ability to produce technologies commensurate to the challenge of a practicable starship, we are likely going to want to employ more than one propulsion technology, so that the drive system is highly hybridized. By “hybridized” I mean two or more forms of propulsion on a single spacecraft, and if these multiple forms of propulsion can share structures of the propulsion system, the more they do so the more truly “hybrid” the propulsion design. We may want to have one drive system for use in planetary atmospheres, another for orbital maneuvering, a third for interplanetary travel, and lastly a drive for interstellar travel. Later that list may need to be lengthened for a drive for intergalactic travel.
Hybrid propulsion systems are already in development, and these innovations could greatly improve the efficiency of chemical rockets. I have written many times about the Skylon spaceplane with its “combined cycle” SABRE engines that operate as conventional jet engines in the atmosphere, and which are able to transition to rocket propulsion for exoatmospheric operation. (Cf., e.g., Skylon spaceplane engine concept achieves key milestone, Key Tests for Skylon Spaceplane Project, Move to Open Sky for Skylon Spaceplace, and Addendum on Jet Propulsion Technology) This is a truly hybrid propulsion system, as the jet engine and chemical rocket share structures of the propulsion system, though it remains within the parameters of chemical rockets.
For faster travel to farther destinations, we will need hybrid propulsion systems of exotic technologies that do not exist today except in theory. A spacecraft with an Alcubierre drive and some basic form of chemical or nuclear or ion thrusters might be able to do the job, and this might well be the first step in building a starship that give us access to the galaxy in the way that we now have access to the surface of Earth. However, a spacecraft with an Alcubierre drive and a fusion or antimatter drive, or with Q-thrusters, would be much better. If, for example, you traveled to our closest cosmic neighbor, Alpha Centauri, you might want to travel the greater part of the distance with the Alcubierre drive, but once you get there you would probably want to make your passage between Proxima Centauri, Alpha Centauri A, and Alpha Centauri B with your fusion or antimatter drive, and you would definitely want to explore the planets of these stars with this “slower” drive. (And you probably wouldn’t want to use something like a Bussard ramjet for transit within a solar system.)
Two Responses to the Infrastructure Problem
A spacecraft mounting the kind of hybridized propulsion systems outlined above would represent an order of magnitude complexity even beyond the example of assembling a nuclear submarine. For the next few decades at least, and perhaps for longer, there will be no machine tools and no industrial plant in space. All the facilities we need to build a large and complex engineering project that is likely to occupy many years of painstaking effort, are earth-bound. Moreover, such technical assembly work would probably need to be performed by skilled craftsmen in a familiar environment conducive to careful and patient work. While there are significant advantages to constructing spacecraft in orbit, as noted above, the world’s most advanced industrial plant and best construction teams are on the earth and will be for some time, so that there remain compelling reasons for continuing to construct spacecraft on Earth, despite being at the bottom of a gravity well. This, in a nutshell, is the infrastructure problem.
There are two obvious responses to the infrastructure problem: (1) we accept the limitations of our industrial plant at face value and organize all space construction efforts around the assumption that spacecraft will be built on Earth, or (2) we begin the long task of constructing an industrial infrastructure off the surface of Earth. This latter approach may take as long as or longer than the building of our industrial infrastructure on Earth. While we have the advantage of higher technology and knowing what it is we want to produce, we also face the disadvantage of the harsh environment of space, and the need to initially boost from the surface of Earth everything not only required for industry, but also everything required for human life.
Almost certainly any human future in space will consist of some compromise between these two approaches, with the compromise tending either toward Earth-based industry or space-based industry. The model of extraterrestrialization that eventually prevails will not only be a matter of socioeconomic choice, but also a function of what is technological possible and what is technologically practicable. This latter requirement is insufficiently appreciated.
The Role of Contingency
The large-scale structure of human civilization, once it expands into space (provided we do not languish in permanent stagnation) will depend upon technological innovations that have not yet happened, and therefore the parameters of which are not yet known. That is to say, humanity as a spacefaring civilization is not indifferent to how we are able to travel in space, and how we are able to travel in space will be a result of the sciences we develop, the technologies that emerge from this science, and which among these technologies prove to be something that can be engineered into a practical vehicle, in terms of extraterrestrial transportation.
Just as we as a species are subject to contingencies related to the climatological conditions that shaped our evolution, the geography that has shaped our civilization, the gravity well of the Earth as a function of its mass that constrained our initial entry into space, and eventually the layout of our solar system as it will shape the initial spacefaring civilization that we can build in the vicinity of our own star, so too we are subject to contingencies that will arise out of our own actions (and inactions). These latter contingencies include the sciences we pursue, the technologies we develop, and the engineering of which we are capable. The human contingencies that determine the structure of our civilization in the future also include unknowns such as exactly which science, technology, and engineering projects get funding (cf. my recent post Why the Future Doesn’t Get Funded).
If it turns out that the science behind the Alcubierre drive concept is sound, and that this science can be the basis of a technology, and this technology can be engineered into a practicable starship, we may never construct an industrial infrastructure in space. It may prove to be easier to construct starships not as massive works slowly assembled in Earth orbit, but rather as relatively compact spacecraft constructed in the convenience of a hangar, which, once finished, can be rolled out onto the tarmac, fired up, and blasted into space, thence to activate its Alcubierre drive once in orbit in order to fly off to other worlds. If, in addition, habitable planets (or planets that can be made habitable) are not too rare in the Milky Way, and human beings prefer to spend their time planetside, the industrialization of space may never occur. In this scenario, space-based industry always remains marginal, even as we become a spacefaring civilization.
As it is, we already today seeing the beginnings of the gradual transition of our industrial infrastructure into something cleaner than the smoke-belching chimneys of the early industrial revolution. As this process continues, and we continue to improve the efficiency of solar cells, there may be little or no economic benefit for moving industry into space. We may pass a threshold, beyond which Earth-based industry can be made entirely benign, therefore obviating the need to move industry into space. But all of this hinges on unknowns of an eminently practical sort, and which we cannot predict until we have actual experience operating the technologies in question.
Space-Based Infrastructure and Planetary-Based Infrastructure
If the Alcubierre drive turns out to be impracticable, or even not practicable at technological levels of development obtainable in the next few hundred years, then the need to construct different kinds of spacecraft will be more pressing. The idea of building a sleek spacecraft in a hangar and blasting off to other worlds directly from Earth’s surface may be impossible. In this case, becoming a spacefaring species, and especially becoming a starfaring species, will likely mean the construction of enormous industrial works off the surface of the Earth, initially assembling large spacecraft in Earth orbit or beyond, but gradually providing more and more goods and services in space without having to boost them all from the ground, which means the industrialization of space.
The industrialization of space, in turn, would mean a very different kind of large-scale spacefaring civilization than a spacefaring civilization that had no need of the industrialization of space, as described in the examples above. A spacefaring civilization of primarily space-based industry would be distinct from a spacefaring civilization of primarily planetary-based industry. Distinct social, political, and economic institutions and imperatives would emerge from these distinct industrial infrastructures.
If, as Marx claimed, ideological superstructures follow from the economic infrastructure that the former emerge to justify, [3] then it is to be expected that space-based economic infrastructure will produce an ideological superstructure distinct from planetary-based economic infrastructure. In the distant future, when we have occasion to survey many different spacefaring civilizations, this may prove to be a fundamental distinction that divides them.
Notes
[1] At the Icarus Interstellar Starship Congress last year, a member of the audience asked a question of Kelvin Long in which the questioner used the phrase, “the infrastructure problem,” which strikes me as the perfect formulation for the topics I am covering today.
[2] On Adam Smith’s example of the day-laborer’s woolen coat cf. Smith’s The Wealth of Nations, the final paragraph of Book I, chapter 1; on round-about production processes in the work of Eugen Böhm von Bawerk, cf. Thesis 22 of my book Political Economy of Globalization.
[3] The locus classicus for this Marxian view is to be found in Marx’s A Contribution to The Critique of Political Economy, translated from the Second German Edition by N. I. Stone, Chicago: Charles H. Kerr & Company, 1911, Author’s Preface, pp. 11-12: “In the social production which men carry on they enter into definite relations that are indispensable and independent of their will, these relations of production correspond to a definite stage of development of their material powers of production. The sum total of these relations of production constitutes the economic structure of society — the real foundation, on which rise legal and political superstructures and to which correspond definite forms of social consciousness. The mode of production in material life determines the general character of social, political, and spiritual processes of life. It is not the consciousness of men that determines their existence, but, on the contrary, their social existence determines their consciousness.” Note that Marx usually refers to the “economic base” of a society rather than to its “economic infrastructure.”
55 Cancri A: Stable Orbital Solutions
We’re developing a model for the fascinating planetary system around the binary star 55 Cancri, a challenging task given the complexity of the inner system in particular. What we have here is a G-class star around which five planets are known to orbit and a distant M-dwarf at over 1000 AU. Have a look at the diagram below and you’ll see why the system, 39 light years away in the constellation Cancer, draws so much attention. It’s much more than the fact that direct measurements of the G-class star’s radius are possible at this distance, which have led to precise measurements of its mass, about the same as our Sun. It’s also the tightly packed configuration of the inner planets.
Image: An illustration of the orbital distances and relative sizes of the four innermost planets known to orbit the star 55 Cancri A (bottom) in comparison with planets in own inner Solar System (top). Both Jupiter and the Jupiter-mass planet 55 Cancri “d” are outside this picture, orbiting their host star with a distance of nearly 5 astronomical units (AU), where one AU is equal to the average distance between the Earth and the Sun. Credit: Center for Exoplanets and Habitable Worlds, Penn State University.
First discovered to be orbited by a giant planet in 1997, 55 Cancri A has been the subject of numerous studies in the years since. We have five planets in total, one a cold gas giant evidently similar to Jupiter and in a similar orbit and another, of particular interest, a ‘super-Earth’ in close proximity to the host star. This world, 55 Cancri e, was thought until 2011 to orbit the star in three days, but astronomers then determined that its complete orbit took less than 18 hours. The software developed by Penn State graduate student Benjamin Nelson and Eric Ford (Penn State Center for Astrostatistics) has pegged the mass of 55 Cancri e at eight Earth masses.
A quick note on nomenclature: The formal designation for the innermost world here should be 55 Cancri A e, with the other planets referred to accordingly. I’m following the just published paper on this work in referring to it as 55 Cancri e, without reference to the distant M-dwarf.
The transiting world is now known to have a radius twice that of Earth and a density about the same as our planet. Another glance at the diagram shows that this is a world far too hot for life as we know it, reaching temperatures in the range of 2300 Kelvin. The computations of Nelson and Ford draw the details of 55 Cancri e out of the motions of the giant planets 55 Cancri b and c, worlds that although orbiting outside the orbit of 55 Cancri e are still located closer to the star than Mercury is to our Sun. The new techniques help us understand how large planets like these can orbit so close to their star without collision or the expulsion of one of the two worlds.
The motion of the inner giant planets has to be accounted for to measure the detailed properties of the ‘super-Earth,’ and Ford notes that most previous work on this system had ignored their interactions. Nelson explains the significance of understanding the stability of their orbits:
“These two giant planets of 55 Cancri interact so strongly that we can detect changes in their orbits. These detections are exciting because they enable us to learn things about the orbits that are normally not observable. However, the rapid interactions between the planets also present a challenge since modeling the system requires time-consuming simulations for each model to determine the trajectories of the planets and therefore their likelihood of survival for billions of years without a catastrophic collision.”
1418 radial velocity observations from four observatories went into this work along with transit studies for 55 Cancri e, out of which orbital solutions stable for a minimum of 108 years emerge. The researchers evolved four- and five-planet models as they examined instabilities in the system, coupling their work with radial velocity observations to constrain the planet masses and orbital parameters that produce dynamically stable solutions. As the paper notes, “By combining a rigorous statistical analysis, dynamical model and improved observational constraints, we obtain the first set of five-planet models that are dynamically stable.” Another interesting finding: 55 Cancri d turns out to be “the closest Jupiter analog to date” in terms of orbital period and eccentricity.
The paper is Nelson et al., “The 55 Cancri Planetary System: Fully Self-Consistent N-body Constraints and a Dynamical Analysis,” Monthly Notices of the Royal Astronomical Society, published online 22 April 2014 (preprint). Also see this Penn State news release.
Envisioning Alien Worlds
How we conceive of distant worlds is important. After all, we want to be scientifically accurate even as we deal with subjects that fire the public imagination. Thinking about planets in the habitable zones of other suns invariably makes us think of ‘Earth 2.0’ and the prospect of green and blue planets filled with life. But each situation will be different, which is part of the great fascination of this quest. Billions and billions of worlds, each of them sui generis.
Science fiction has offered us glimpses of many worlds tantalizingly like the Earth but in some major respect different. Here, for example, is a prose description of a planet circling the star 82 Eridani, as envisioned by Stephen Baxter in his 2011 novel Ark. We are looking at it from the starship that has taken a band of colonists/refugees from a drowning Earth to what could be their new home:
A big strip of land stretching north to south across the equator was “the Belt,” a kind of elderly Norway with deep-cut fjords incising thousands of kilometers of coastline. The northern half of the Belt was currently ice-free, but its southern half, stretching into the realm of shadow, was icebound, and snow patches reached as far north as the equator. Sprawling across a good portion of the eastern hemisphere was the roughly circular continent they called “the Frisbee,” a mass of rust red broken by the intense blue of lakes and lined by eroded mountains. Its center was dominated by a huge structure, a mountain with a base hundreds of kilometers across, and a fractured caldera at the top. The mount was so like Olympus Mons on Mars that giving it the same name had been unavoidable, and it so dominated the overall profile of the continent, giving it an immense but shallow bulge, that the nickname “Frisbee” was a good fit. Then, to the west of the Belt, an archipelago sprawled, a widespread group of islands, some as large as Britain or New Zealand, that they called “the Scatter.” There was one more continent at the south pole, currently plunged in darkness and buried under hundreds of meters of winter snow, called “the Cap.” The world ocean itself had no name yet; the seas could be named when they were ready to go sailing on them…
Image: An artist’s concept of a habitable zone world, in this case Kepler-69c. This image is, of course, based on an actual Kepler discovery, though like Baxter’s science fictional description, it has to substitute imagination for detailed data. Credit: Ames Research Center/NASA, JPL-Caltech.
Baxter’s world is fascinating, a place the colonists assume is Earth 2.0 until they take a closer look. For one thing, there’s little tectonic activity here, so the kind of geological and biological cycling we take for granted on Earth has been, over the eons, sharply reduced. But the real showstopper is the planet’s obliquity, interesting to note in light of the University of Washington work on axial tilt that we looked at on Monday. This world around 82 Eridani shows an obliquity of ninety degrees — compare that to Earth’s 23.5 degrees. In other words, each part of the planet except for a band along the equator will suffer through months of perpetual darkness, then perpetual light.
Land and colonize such a world or press on for another? I won’t give away that decision, which Baxter handles in a believable and interesting way. But as we saw yesterday, there are models now emerging that show such a planet might make itself habitable by never developing truly global ice. In any case, imagine what life would be like on such a world, and ask yourself whether humans could adapt to it. The guess here is that they could, but the impetus for developing a migratory pattern of development would be profound.
The Kepler-186f Image
Spurring these thoughts was an email from Thomas Barclay, a research scientist working on the Kepler mission at NASA Ames. Tom writes the excellent Planet Hunter blog, which he used several days ago to explain How we designed the Kepler-186f artists concept image that I wrote about on Monday. I seldom post the same image several days running, but today is an exception since I want to relate that image to the entire issue of how we visualize alien planets. Here it is again:
As I mentioned on Monday, this view — created by Tim Pyle and Robert Hurt (JPL/Caltech) — is a splendid piece of work, but you’ll recall that I wondered whether it wasn’t a bit too realistic, given that the public audience contains many who would assume we actually have this level of detailed information about the planet. The flip side of that question is to note how much care went into the image and what decisions were made given that we really know little beyond the size of the planet, the size and temperature of the star, and the distance between planet and star.
What I hadn’t really noticed was the star, Kepler-186, itself. It’s a red dwarf, but as you look at the image, you see that it’s much brighter than we might expect. What we know about Kepler-186 is that its temperature is about 3800 Kelvin. Now if you go to work on the spectrum of various star types and study the response of the human eye — check What color are the stars? for more — you’ll find that in the absence of any atmosphere, Kepler-186 would be yellow/orange in color. Tom writes that the team chose to make it a bit more orange in this image that it would actually appear to the eye, to get across the fact that the star is not truly like our G-class Sun.
Now look at the planet itself, which shows continents that are yellow and oceans in blue/grey. The ice caps as well as the clouds have an orange hue. Why these choices? Let me quote Tom on this:
This star emits very little blue light which we represented by making the sea a dull grey/blue color. Ice and clouds Mie scatter light [see this Wikipedia entry on Mie scattering] which is fairly uniform across all wavelengths hence clouds and ice appear the same color as the star. Then we come to the color of the continents – we had fun with this one. When we were designing the image Elisa Quintana found an article by Nancy Kiang titled The Color of Plants on Other Worlds. Nancy is a scientist based at NASA Ames (she moved to Ames from GISS the week after we talked to her, small world heh!) who works with the Virtual Planetary Laboratory. We called her up and chatted about what colors plants might be on planets orbiting cool stars. While this is a very complex issue involving evolution of photosynthesis, she recommended a dark yellow/green color as a potential color for alien planet life on this world.
And reminding us how little we know about this planet, Tom goes on to note that the artists chose to depict the planet as a bit colder than Earth, realizing that we have no knowledge about its atmosphere, which will have a great deal to say about its temperature. This was an educated guess to show a planet with prominent ice caps and plant life in the equatorial regions. It’s based on the understandable analogy with the Earth, which has the water, continents and clouds we see in this image translated to a hypothetical planetary body around another star.
So am I being too fussy in talking about people getting the wrong idea from such images? Maybe so, in the sense that along with the excellent artwork, we have to be careful to get the message out about what we actually know about the world. I think Tom gets it right when he says “Hopefully this image provides a nice tool to explain what might be the same and what might be different between this planet and Earth.” Making those explanations is a job for those of us who try to communicate the findings of our exoplanet hunters to the general public, and it’s something we need to do well to separate the genuine excitement of the work from the frequent media hype.
Enter the ‘Anti-Transit’
Gravitational lensing is a technique rich enough to help us study not only distant galaxies but exoplanets around stars in our own Milky Way. As gravity warps space and time, light passing near a massive object takes the shortest route, from our perspective seeming to be bent by the gravitational field. Inside the Milky Way, such effects are referred to as ‘microlensing,’ capable of magnifying the light of a more distant object and sometimes revealing the presence of an unseen planet around the intervening star. Now we have a Kepler find with implications for binary stars.
Working with Eric Agol at the University of Washington, graduate student Ethan Kruse has discovered a ‘self-lensing’ white dwarf eclipsing binary system. He made the find while looking for transits in the Kepler data, the signatures of planets crossing in front of their stars as seen from Earth. KOI-3278 turned out to have an unusual signal, says Kruse:
“I found what essentially looked like an upside-down planet. What you normally expect is this dip in brightness, but what you see in this system is basically the exact opposite — it looks like an anti-transit.”
In other words, a transiting planet causes a dip in the overall light of the star that shows up in the well known lightcurves that have flagged the presence of so many Kepler planets. Kruse was seeing not a dip but a surge in brightness, the apparent result of movement within this binary star system. 2600 light years away in the constellation Lyra, KOI-3278 is now known to be made up of two stars with an orbital period of 88.18 days, one of them a white dwarf, separated by about 70 million kilometers. The brightness surge is the white dwarf’s lensing effect upon the star it passes in front of as we view the system. The lensing effect allows the mass of the white dwarf to be measured as roughly 63 percent the mass of our Sun.
Image: An image of the Sun used to simulate what the sun-like star in a self-lensing binary star system might look like. Credit: NASA.
It was about a year ago that Philip Muirhead (Caltech) and colleagues published their own findings, likewise based on Kepler data, of a white dwarf being orbited by an M-class dwarf that was, although larger, less massive than the white dwarf it circled. KOI-256 looked at first glance to show the signature of a gas giant planet eclipsing the red dwarf, but radial velocity follow-up studies using the Hale instrument at Palomar Observatory demonstrated that the intervening object was a white dwarf. The KOI-256 data showed the same brightening effects that Kruse found with KOI-3278, although the microlensing in the former was not nearly as powerful.
In both cases, refined mass measurements of the white dwarf have followed, as well as more accurate analysis of the mass and temperature of both stars. Kruse and Agol think the effect can be used in follow-up observations to reveal the white dwarf’s size, and have applied for time on the Hubble Space Telescope to study the system in greater detail. We may or may not find more systems like this in the Kepler data, but the KOI-3278 discovery gives us yet another way to use the extremely subtle effects of microlensing. In this case, the lensing is a repeatable phenomenon as the two stars orbit each other, not the case with most microlensing events.
The paper is Kruse and Agol, “KOI-3278: A Self-Lensing Binary Star System,” Science Vol. 344, No. 6181 (18 April 2014), pp. 275-277 (abstract). The KOI-256 paper is Muirhead et al., “Characterizing the Cool KOIs. V. KOI-256: A Mutually Eclipsing Post-Common Envelope Binary,” The Astrophysical Journal Vol. 767, No. 2 (2013), 111 (abstract).
Two Takes on Habitability
Last week’s announcement about Kepler-186f presented a world that is evidently in the outer reaches of its star’s habitable zone, with the usual caveats that we know all too little about this place to draw any conclusions about what is actually on its surface. Is it rocky, and does it have liquid water? Perhaps, but as Greg Laughlin (UC-Santa Cruz) points out on his systemic site, the widely circulated image of Kepler-186f was all but photographic in its clarity. Listen to Laughlin as he looks at the image:
I stared at it for a long time, tracing the outlines of the oceans and the continents, surface detail vivid in the mind’s eye. Yes, ice sheets hold the northern regions of Kepler-186f in an iron, frigid grip, but in the sunny equatorial archipelago, concerns of global warming are far away. Waves lap halcyon shores drenched in light like liquid gold.
He goes on to look at how the press has handled earlier stories on habitable planets, dating back to the Gliese 581c frenzy of 2007. And you can see the evolution in artist’s renderings of the various worlds under discussion, culminating in a Kepler-186f image that could indeed be misconstrued as a photograph by someone who didn’t realize the limits of our capabilities. Here’s the image again (credit: NASA Ames/SETI Institute/JPL-Caltech):
It’s beautiful work, and I ran it last Thursday along with my story on the new planet. But we have to be careful not to get too far ahead of ourselves. Yes, researchers tracking the exoplanet hunt understand that this is entirely conjectural, but upon reflection, I think we’re sending a signal to the general public that we’re more confident about what these worlds are like than is justified. In the case of Kepler-186f, the fact that a planet is close to Earth-sized does not render it Earth’s twin in any other meaningful way, especially given that the planet orbits a red dwarf and pulls in only about a quarter of the insolation that Earth receives.
The Benefits of Axial Tilt
What we do surmise about habitable zones keeps getting tweaked around the edges, and on a more theoretical plane, the work on planets with ’tilted’ orbits — this comes out of the University of Washington, Weber State and NASA — is intriguing because it pushes liquid water on the surface much further out than earlier habitable zone notions would allow. The paper, which appears in the April Astriobiology may, in fact, expand the habitable zone by ten to twenty percent, which would greatly increase the number of planets suitable for life.
We’re talking about planets whose axis has been tilted from their orbital plane thanks to gravitational interactions with other planets in the system. The contention here is that a fluctuating tilt in a planet’s orbit may enhance rather than diminish the chances for life, because glaciation becomes more difficult when polar regions melt thanks to the erratic spin. Says Rory Barnes (University of Washington), “…the rapid tilting of an exoplanet actually increases the likelihood that there might be liquid water on a planet’s surface.” From the paper:
We interpret our results to mean that planets with large and rapid obliquity oscillations are more likely to be habitable than those with negligible oscillations, such as the Earth. This perspective is at odds with the notion that the stability of the Earth’s obliquity is important to the development of life. While it still may be true that rapid oscillations can be detrimental, and certainly at some point obliquity cycles could be too large and rapid, our results clearly show that rapid obliquity evolution can be a boon for habitability. At the least, one should not rule out life on planets with rapid obliquity cycles.
Image: Tilted orbits such as those shown might make some planets wobble like a top that’s almost done spinning, an effect that could maintain liquid water on the surface, thus giving life a chance. Credit: NASA/GSFC.
One consequence is that future searches for living planets might be extended farther from the target star, given the deeper habitable zone available, a result with a bearing on how difficult it is to separate stellar and reflected planetary light. The researchers do point out in their conclusion that their simulations all began with planetary spin rates of 24 hours and obliquities of 23.5 degrees, clarifying the need for future work on a wider range of initial conditions. In particular, does a specific solar system ‘architecture’ always produce a particular obliquity cycle?
Interesting stuff, and bear in mind that it could have ramifications on another theory, that planets need a large, stabilizing moon to be suitable for life. The Earth’s axial tilt of 23.5 degrees would, in the absence of Luna, increase to the point where climate fluctuations became more extreme. This could be problematic for planets in orbits like ours, but at the outer edge of the habitable zone, in this view, those fluctuations could be precisely what is needed to prevent ice from becoming global, making the lack of a moon is a distinct plus. Large moons, then, may have a role to play in both directions, depending on the planet’s position in the habitable zone.
The paper is Armstrong et al., “Effects of Extreme Obliquity Variations on the Habitability of Exoplanets,” Astrobiology Vol. 14, Issue 4 (April 15, 2014), full text available. The University of Washington press release is here.
An Outward-Looking Grand Strategy
We use strategies to weigh the issues around us and maximize our chances for success. Can we create a strategy not just for a specific short-term goal but for the survival and growth of our entire species? In the essay that follows, Michael Michaud looks at the elements of such a vision, one that by necessity takes us out of our own biosphere and into the cosmos. As long-time Centauri Dreams readers know, Michaud is well suited to discussing the resolution of conflict and the attainment of goals. His lengthy career in the U.S. Foreign Service led to posts as Counselor for Science, Technology and Environment at U.S. embassies in Paris and Tokyo, and Director of the State Department’s Office of Advanced Technology. He has also been chairman of working groups at the International Academy of Astronautics on SETI issues, and is the author of the highly regarded Contact with Alien Civilizations: Our Hopes and Fears about Encountering Extraterrestrials (Springer, 2007).
By Michael A.G. Michaud
We are living amid four revolutions that draw human minds beyond the limits of the Earth.
* Astronomical exploration of the cosmos by ground-based instruments, orbiting observatories, and robotic spacecraft brings the rest of our solar system closer to us, so that we can more realistically consider living on or utilizing other worlds.
* Human spaceflight enables us to expand our presence and our field of action beyond the Earth. It changes the way we see our position in the cosmos, implying that we – and our prospects for the future — need not remain confined to our home planet.
* The search for extraterrestrial life and intelligence changes our perspective on the role of biology and sentience in the universe. Life may prove to be a widespread phenomenon, not unique to the Earth. Contact with another civilization might challenge us, or open up vast opportunities for our species.
* Proposals for extraterrestrial macroengineering , such as mining the Moon and the asteroids, building satellite solar power stations, and terraforming Mars, could enable us to expand our influence on matter and energy beyond the Earth, utilizing those resources to remove the limits to growth and open up new options for our species.
These revolutions broaden Earth-bound conceptions. They urge us to reach outward. They imply grand shared tasks for Humankind.
These revolutions also contrast us to an outside, heightening our awareness that we spring from a common origin and live in a common biosphere. They encourage us to think about the shared interests of humankind.
Synergy
Astronomy, planetary exploration, and human spaceflight are not mutually exclusive. Work in one field has stimulated new ideas – and sometimes new programs and more funding – in others.
Astronomy has been a powerful stimulus to thinking about spaceflight. It has given us a better understanding of potential destinations, and potential risks.
This can work both ways. Astronomy and planetary exploration would not have enjoyed the growth they experienced during after the beginning of the space age had it not been for the Moon landing program and the prospect of eventual human missions to Mars.
We find stimulus and response elsewhere too. The search for extraterrestrial life has been a major factor in gaining support for planetary exploration missions to Mars. The possible presence of oceans under the ice of outer planet moons is stimulating new interest. SETI, a search for evidence of alien technology, grew out of radio astronomy.
Ideas about bases on the Moon and Mars became more credible after human and robotic missions gave us geological information about lunar and planetary materials. Extraterrestrial macroengineering concepts such as mining or diverting asteroids help justify further exploration of our solar system.
Discovering planets around other stars has given new impetus to astrobiology, SETI and interstellar exploration by robotic probes.
Those who support the implementation of these grand ideas have learned to play politics, to lobby for their causes in national capitals and multinational organizations. Their efforts have concentrated on budget processes, encouraging a near term approach. Political persuasion has focused on funding specific projects.
Instead of seeing the competition for funding as a zero-sum game, we could make a more conscious effort to see connections and seek synergisms. To cite one example, ground-based astronomers have been surveying asteroids that cross or come near the orbit of the Earth. Unmanned missions to asteroids and comet nuclei might pave the way for human exploration. Those in turn could assist in developing mining operations, making those bodies part of the human resource base.
If separate advocacies worked together, the whole might be greater than the sum of its parts. What is missing is a unifying concept.
A Grand Extraplanetary Strategy
All of these fields of human endeavor are parts of an unarticulated grand strategy for our species.
At the most basic level, a strategy is simply a thoughtful way of dealing with one’s environment to improve one’s prospects for success. A grand strategy for the human species would be one designed to improve our ability to survive, to grow, to diversify, and to increase our influence on our environment and our future.
There are many elements to such a strategy, including the better management of our resources, reducing undesirable impacts on our biosphere, limiting conflict among humans, and maintaining the conviction that our future can be better than our past. Most conceptions constrain the design of such a strategy to the biosphere of our origin – a stage that many find unnecessarily narrow. The environment of a technological species is much larger than the planetary biosphere that gave it birth.
Here we may have the common purpose that underlies the four outward-looking revolutions of our time. Astronomy, planetary exploration, and SETI are reconnaissances of our larger environment. They are essential elements of any rational extraplanetary strategy for the human species; without them, we could not conduct intelligent operations beyond the Earth.
Human spaceflight is partly for reconnaissance and partly for operations, depending on the objectives of particular missions. Extraterrestrial mining and macaroengineering, including the building of large structures in space, clearly would be operations.
Whatever our differences about specific missions may be, we could share a broad vision of human activity beyond the Earth, placing astronomy, planetary spaceflight, SETI, and proposals for extraterrestrial macroengineering in a common context.
Hard times can produce new alliances. Instead of seeing other programs as rivals for funding, we could look for opportunities for each to help the others, designing missions to be synergistic wherever that is possible. For example, advocates of interstellar exploration by probes could more actively support the search for extrasolar planets and invite extrasolar planet seekers to reciprocate.
This approach will not lead to quick miracles in public funding. Governments and international organizations are unlikely to adopt a formal extraplanetary strategy, or even to agree that we should have one. But they might respond to tactical alliances among the revolutionaries.
Many differences may divide us, but we can share a unifying idea: that we are participating in the definition and implementation of a grand strategy for our species.
Armed with a shared vision, we can work quietly and persistently to see that the parts of such a grand strategy are put into place, supporting each other whenever possible. That will require patience, and an enlightened sense of self-interest.
Separately, we have worked wonders. Imagine what we could do together.
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This essay is based on three documents written more than thirty years ago. The author first presented a paper on this subject at the 1981 International Astronautical Congress in Rome. A more detailed discussion can be found in “Towards a Grand Strategy for the Species,” Earth-Oriented Applications of Space Technology, Vol. 2, No. 3-4 (1982), 213-219. A simpler, more popularized version entitled “Sharing the Grand Strategy” appeared in Space World, August 1984, 5-9.
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