Supernova at Twilight

by Paul Gilster on April 6, 2016

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In his novel The Twilight of Briareus (John Day, 1974), Richard Cowper, who in reality was John Middleton Murry, Jr., wrote about a fictitious star called Delta Briareus that goes supernova (true, there is no constellation called Briareus, but bear with me). Because it is only 130 light years out, the supernova showers the Earth with radiation, with consequences that are in some cases obvious, in others imaginative in the extreme. It’s a good read, one that at least one critic, Brian Stableford, has compared to J. G. Ballard’s early disaster novels.

The novel contrasts an earthy domesticity with the celestial display that soon shatters it. It’s worth quoting a patch of the book:

It so happened that I, in common, no doubt, with several million others — was among the first in England to observe that ‘majestic effulgence’ within seconds of its arrival. At about twenty past nine on the Tuesday evening I switched off the telly and suggested to Laura that we could do worse than saunter down to The Three Foxes for some fresh air and a gin and tonic. Ten minutes later we were strolling pubwards when she suddenly gripped my arm and yelped: ‘Hey, look at that!’

We stood stock still and gaped up into the heavens.

‘It’s a magnesium flare,’ I said. ‘They used to drop them during the war. There must be some sort of RAF exercise.’

‘Well, why isn’t it moving then?’

‘It is. Only slowly. They have parachutes.’

‘But it’s so bright!’ exclaimed Laura. ‘Look at the shadows it’s given us!’

She was quite right. There on the road beside us were two distinct silhouettes. I contemplated them for a moment and then looked up again. The flare was still there, completely outshining every other thing in the sky with its eye-aching bluish-white brilliance.

And there we are, a supernova in progress, with results no one at this point in the tale can imagine. Cowper, who also wrote as Colin Murry, is a personal favorite. His short story collection Out There Where the Big Ships Go (Pocket Books, 1980) is a good introduction.

Image: The cover of the US paperback of The Twilight of Briareus, the edition I read when it came out.

Supernovae in the Pliocene?

Putting humans under the torch of a supernova makes for exciting fiction, but new work from an international team of researchers now suggests a very real supernova — and probably a series of them — exploded in the Pliocene epoch and later, with evidence of radioactive debris indicating a window between 3.2 to 1.7 million years ago. That would place these events at the boundary between the Pliocene and the Pleistocene (the latter beginning 2.58 million years ago and ending 11,700 years ago).

“We were very surprised that there was debris clearly spread across 1.5 million years,” said team leader Anton Wallner (Australian National University). “It suggests there were a series of supernovae, one after another. It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.”

We’re talking about supernovae no more than 300 light years away, which would make them comparable in brightness to the Moon, and certainly visible during daylight hours. Appearing in Nature, the work argues that iron-60 found in sediment and crust samples from the Pacific, Atlantic and Indian Oceans show Earth’s exposure to cosmic ray bombardment, but at levels that would have been too weak to cause major biological damage, much less extinctions.

The team searched for interstellar dust by examining 120 samples of the ocean floor spanning the past eleven million years. All iron had to be extracted from the ocean cores, work performed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany and the University of Tokyo, and the minute amounts of iron-60 had to be separated from terrestrial isotopes using the Heavy Ion Accelerator at ANU. The decay of the radioactive isotopes beryllium-10 and aluminum-26 was used to determine the age of the cores.

Iron-60 itself has a half-life of 2.6 million years, unlike the stable iron-56, and as Wallner explains, is ‘a million-billion times less abundant than the iron that exists naturally on Earth.’ Interestingly, fallout shows up not only in the 3.2 to 1.7 million year window, but also at about 8 million years back. The researchers suggest that the supernovae responsible were probably found in a star cluster that has subsequently moved away from the Earth.

A Writer’s Choice

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What would the much closer supernova of the fictional Delta Briareus do to the Earth? In The Twilight of Briareus, the effect is largely meteorological. At first.

The loss of ‘Tiros’ and the rest of the observation satellites hamstrung the world’s long-range weather forecasters, but there was still sufficient evidence of cataclysmic upheaval in the upper atmosphere for a hundred assorted professors to chill humanity’s blood with their doom-laden warnings. These ranged from an ice age at one end of the scale to a slow roasting at the other. The best we could hope for, apparently, was a period of tempests of unprecedented severity. We listened, felt appropriately chastened, and then cheered up again, either from endemic atrophy of the imagination or for no better reason than that the human psyche cannot exist for long on a diet of undiluted pessimism.

There is a compelling lyricism in Cowper’s fiction that eschews irony; in that sense he’s at odds with many of his contemporaries. What an interesting man. He gave up writing of any kind in 1986 and put his effort into painting and antiques, a kind of escape that makes him more akin to William Morris and his circle than, say, Anthony Burgess or Martin Amis (the latter detested his work). I’ve always been taken with Cowper’s elegance, and wonder what he would have done with ancient supernovae blossoming over one of his finely wrought landscapes. If only we knew. Cowper was devastated by the death of his wife Ruth, and died shortly after her in 2002.

Today’s paper is Wallner et al., “Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe,” Nature 532 (07 April 2016), 69–72 (abstract). See also Breitschwerdt et al., “The locations of recent supernovae near the Sun from modelling 60Fe transport,” Nature 532 (07 April 2016), 73–76 (abstract). From the latter:

The Local Bubble of hot, diffuse plasma, in which the Solar System is embedded, originated from 14 to 20 supernovae within a moving group, whose surviving members are now in the Scorpius–Centaurus stellar association7, 8. Here we report calculations of the most probable trajectories and masses of the supernova progenitors, and hence their explosion times and sites.

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SETI: A New Kind of ‘Water Hole’

by Paul Gilster on April 5, 2016

Some of you may recall an episode of Star Trek: The Next Generation in which the inhabitants of a planet called Aldea use a planetary defense system that includes a cloaking device. The episode, “When the Bough Breaks,” at one point shows the view from the Enterprise’s screens as the entire planet swims into view. My vague recollection of that show was triggered by the paper we looked at yesterday, in which David Kipping and Alex Teachey discuss transit light curves and the ability of a civilization to alter them.

After all, if an extraterrestrial culture would prefer not to be seen, a natural thought would be to conceal its transits from worlds that should be able to detect them along the plane of the ecliptic. Light curves could be manipulated by lasers, and as we saw yesterday, the method could serve either to enhance a transit, thus creating a form of METI signaling, or to conceal one. In the latter case, the civilization would want to create a change in brightness that would essentially cancel out the transit light curve. It’s not exactly a ‘cloaking device,’ but it ought to work.

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Image: The Next-Generation Transit Survey (NGTS) telescopes operating at ESO Paranal, Chile. Transit observations have SETI implications we are only beginning to explore. Credit: ESO/ G. Lambert.

A Galaxy of Xenophobes?

As I said yesterday, I’m not here to reignite the METI debate as much as to acknowledge that what an alien culture might do is unknown. Rather than asking whether any civilization should try to conceal itself, let’s simply ask what it could do if it made the attempt.

The idea has a brief history, with Eric Korpela (UC-Berkeley) and Shauna Sallmen (University of Wisconsin-La Crosse) suggesting in 2015 that ETI could effectively hide a planetary signature through the use of orbiting mirrors. This would, like the geometric masks envisioned by Luc Arnold, require engineering on a huge scale, and would also demand elaborate tuning for each target. Kipping and Teachey argue for a more affordable alternative using a directed laser beam:

In our scheme… the advanced civilization emits a laser directed towards the other planetary system at precisely the instant when the other system would be able to observe a transit. The power profile of the laser would need to be the inverse of the expected transit profile, leading to a nullified flat line eliminating the transit signature.

Screenshot from 2016-04-05 09:24:41

Image: Top: The unaltered light curve of the Earth transiting the Sun, as viewed by different broadband optical photometers (offset by 5 ppm). Middle: The power profile of a 600 nm laser array designed to cloak the Earth. An array of lasers producing a peak power of ∼ 30 MW over 13 hours nullifies the transit. Bottom: Residual light curve, as seen by the different photometers. Credit: David Kipping/Alex Teachey.

The Kepler mission has produced the vast majority of recent exoplanet discoveries, and we have upcoming transit surveys in the works including TESS (Transiting Exoplanet Survey Satellite), PLATO (PLAnetary Transits and Oscillations of stars) and NGTS (Next-Generation Transit Survey). If a civilization wanted to shield itself from this kind of broadband optical survey, a monochromatic optical laser should do the trick. The paper estimates that the Earth could be ‘cloaked’ — hidden from view from a particular star system by having its transit nullified — with a 600 nm laser array emitting a peak power of ~30 MW over 13 hours.

The power requirements are interesting because they are relatively low for a specific target, but the paper adds the obvious point that if we are trying to cloak a planet from a large number of targets, we would require larger power production. Nonetheless, we routinely use much larger numbers when talking about laser lightsails in the configurations that could enable interstellar flight. Kipping and Teachey point out that for a culture that develops those kinds of technologies, cloaking could become a secondary function of the laser arrays used primarily for propulsion.

Chromatic cloaking (across all wavelengths) could be achieved by using a large number of beams (although with an order of magnitude higher energy cost), while tunable (‘supercontinuum’) lasers may emerge that can simulate any spectrum. But even with these capabilities, is cloaking an entire planet the most efficient choice for a civilization trying to hide itself? Perhaps a better course from the standpoint of economics and efficiency is to cloak the biosignatures that announce life’s presence. Let me quote from the paper on this:

It is straightforward to use a chromatic laser array to cancel out the absorption features in the planet’s transmission spectrum, assuming laser emission can be produced at any desired wavelength. Indeed, the presence of an atmosphere could be cloaked altogether if the effective height changes of the planet as a function of wavelength are canceled out by lasers. The planet might then resemble a dead world totally devoid of any atmosphere and appear almost certainly hostile to life. Not only would this approach require a significantly smaller power output, it would also have the benefit of producing self-consistent observations insomuch as the presence of the planet might still be inferred by other means (i.e. through radial velocity analysis).

What SETI Can Learn

Kipping and Teachey refer to these methods as a ‘biocloak,’ and suggest that cloaking can be selective indeed, perhaps focusing on the absorption features of molecular hydrogen and ozone. In this case we are dealing with peak laser power of just ∼160 kW per transit. But the authors are clear about the limitations of these methods. Radial velocity methods can find a planet otherwise hidden by a chromatic transit cloak, and given technologies not so far advanced over what we have today, direct imaging can reveal atmospheric features of a planet even when a ‘biocloak’ is in place. “For these reasons” write the authors, “perhaps the most effective use of laser enabled transit distortion would be for broadcasting rather than cloaking.”

And it was on that note that I began yesterday’s look at these possibilities. If we have based fifty years-plus of SETI on the notion that another civilization may choose to contact us, we have to acknowledge what Kipping and Teachey make clear: There are ways to alter transit signatures that make it obvious we are dealing with an advanced technology. And you can make the argument, as the authors do, that transits offer a different kind of ‘water hole’ for SETI, comparable in its own way to the ‘water hole’ frequencies we monitor in radio SETI.

Thus while the cloaking aspects of this paper have received the most attention, I think the SETI implications are its strongest takeaway. It is a very short step from existing optical SETI to archival searches of transit signatures already in our files. Knowing what these signatures would look like is a step forward as we continue to probe for civilizations around nearby stars.

Addendum: This email from Dr. Kipping, excerpted below, further explains the authors’ thinking about cloaking possibilities:

…we never intended to solve cloaking from all detection methods in one paper (that would be a tall order to demand of any research paper). Rather, we started with the simplest and most successful technique, transits, and showed that it is energetically and technologically quite feasible for even our current level of technology to build an effective cloak. Whilst we acknowledge that there are ways to defeat the proposed cloak (e.g. polarization of laser beams, direct imaging), we see these as problems which are likely to be solved by more advanced civilizations than ourselves, or indeed in future work (by humans!). What we are trying to do on the cloaking side is stimulate a conversation- that it is surprisingly easy to hide planets. Given that many notable scientists are opposed to METI, it is not unreasonable that other civilizations may choose to do this. The scenario could be that they would have long ago observed the Earth as an inhabited planet, and then turned on a cloak as a insurance policy, buying them time to reveal their presence when they choose to, rather than our increasingly penetrating telescopes finding them before they wish.

The paper is Kipping and Teachey, “A Cloaking Device for Transiting Planets,” accepted at Monthly Notices of the Royal Astronomical Society (preprint), The Korpela and Sallmen paper is “Modeling Indications of Technology in Planetary Transit Light Curves – Dark Side Illumination,” Astrophysical Journal Vol. 809, No. 2 (abstract).

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A Transit Signature for SETI?

by Paul Gilster on April 4, 2016

David Kipping and Alex Teachey have a new paper out on the possibility of ‘cloaking’ a planetary signature. The researchers, both at Columbia University, make the case that any civilization anxious to conceal its existence — for whatever reason — would surely become aware that all stars lying along its ecliptic plane would see transits of the home world, just as its own scientists pursued transit studies of planets around other stars. And it turns out there are ways to make sure this signal is masked by adjusting the shape of the planet’s transit light curves.

Now this is a fascinating scenario as presented by the head of the Hunt for Exomoons with Kepler, whose business it is to know about the slightest of variations in light curves because they may contain information about exomoons or rings. Thus Kipping is a natural to look into the artificial manipulation of light curves, a study with definite SETI implications. Because methods like these work in two directions — a civilization that does want to communicate could also alter its light curve in ways that would be unambiguously artificial. Today I want to focus on the latter idea, reserving cloaking methods for tomorrow’s post.

This veers into the METI debate, but that’s not my purpose. Messaging to Extraterrestrial Intelligence is highly controversial, triggering arguments in these pages for the last decade. But let’s hold METI at one remove. The paper, delightfully titled “A Cloaking Device for Transiting Planets,” allows us to imagine how the manipulation of transit signatures could change a distant planet’s visibility. We may well decide not to brighten the Earth’s visibility through intentional transmissions, while understanding that an extraterrestrial culture might choose differently. Knowing what is possible by way of cloaking or enhancing a planetary signature, then, gives us plenty of food for thought for SETI as we consider what might turn up in our data.

Modifying the Light Curve

Here’s the notion in a nutshell, as drawn from the paper.

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Image: Figure 1. Illustration (not to scale) of the transit cloaking/broadcasting device. A laser beam (orange) is fired from the night side of inhabited planet (blue) towards a target star whilst the planet appears to transit the star, as seen from the receiver. In the case of the Earth, the planet could be cloaked by generating an inverse transit-like signal of peak power 60 MW. Credit: Kipping and Teachey.

Controlled laser emissions are the key, effectively distorting the shape of a transit light curve. Just how this could be done is something we’ll discuss in the next post. But to begin, let’s think about how visible we are to any advanced civilization studying us. Forget about our radio and television signature, which is infinitesimal, and focus instead on the things we are doing right now to study other stars. I often write about transmission spectroscopy, which is how we search for the constituent molecules in a planetary atmosphere. The transiting planet, as it moves in front of its host star (as seen by our instruments) is bathed in the star’s light, its atmosphere providing a particular ‘overlay’ to the star’s spectrum.

We’ll use the method to look for biosignatures as we refine it for smaller and smaller worlds, but we’ve already seen how successfully we can examine the atmospheres of ‘hot Jupiters’ like HD 189733b. A sufficiently capable civilization able to see our world transiting should be able to pick up the cluster of biosignatures that would identify the Earth as a living world. There have been proposals to look for atmospheric pollutants produced by industrial activity as a part of future SETI practice, and such activity could indeed become visible, though the idea of widespread pollution lasting for millennia seems a stretch. Understanding the damage it caused, surely the culture in question would either solve its pollution problems or else succumb to them.

Let’s not forget the recent flurry of interest in the unusual star KIC 8462852. Here we’re looking at what could well be a natural phenomenon in the form of clouds of comets, but could possibly be evidence of artificial megastructures throwing highly distinctive light curves. We have much work ahead on KIC 8462852, so I only bring it up to suggest that there are many ways an intelligent species might make itself visible whether its intent was to do so or not.

Turning Transits into ‘Broadcasts’

Scientists as diverse as Ronald Bracewell, Richard Carrigan, Michael Papagiannis and Robert Freitas have studied the possibilities of such detections, with Carrigan most prominently identified with the search for Dyson spheres, swarms of energy collectors that surround a star to feed its colossal energies to a growing Type II civilization. And back in 2005, Luc Arnold (now at Aix Marseille Université) suggested that a civilization wanting to be known could resort to deliberate signaling by building a particular kind of geometric megastructure, one that when viewed in a transit would all but shout, through its distinctive light curve, that it was artificial.

Kipping and Teachey are, as you would imagine, well aware of Arnold’s work, and argue that lasers offer far more practical methods. From the paper:

Whilst any number of artificial transit profiles can be created with lasers, one ideally seeks a profile which is both energy efficient and unambiguously artificial. Producing upward spikes in-transit might seem like an obvious suggestion, but star spot crossings produce these forms with complex and information rich signatures (e.g. see Beky et al. 2014). Here, we argue that cloaking the ingress/egress of a transit, but leaving the main transit undistorted, would be a highly effective strategy since no known natural phenomenon is likely to produce such an effect.

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Image: Figure 6 from the paper, highlighting broadcasting rather than cloaking. Top: The power profile of a laser array designed to broadcast the Earth. An array of lasers producing a peak power of ∼ 20 MW for approximately 15 minutes nullifies the transit ingress and egress. Bottom: The resulting light curves as viewed by different broadband optical photometers. The observed impact parameter would be complex infinity, for which a normal light curve fit would be unable to explain and thus indicating the presence of artificial transit manipulation.

A monochromatic laser emission could be spotted in a transit survey (and could be searched for in Kepler data), with follow-up spectroscopy confirming the artificial nature of the transmission. Kipping and Teachey also note what James and Dominic Benford recently pointed out in their paper on SETI efforts at KIC 8462852 — a beamed signal of whatever kind could carry information, so that in addition to identifying the presence of a technological culture, the beam could attempt more detailed communication (see SETI: Power Beaming in Context).

I’ve focused in on broadcasting via transit light curve alteration because, as the paper argues, it is the most efficient use of these techniques as compared to cloaking, which I’ll describe tomorrow. I’m trying to stay out of the METI weeds here — this is not an argument in favor of identifying the Earth to ETI. Rather, it is an argument that other civilizations may use such methods, and thus this paper shows us a signature we should add to our catalog.

And it has this further implication: If a civilization did choose to broadcast its existence through these methods, it would probably choose the shortest period planet in its solar system to carry the message. The choice is obvious, as the paper notes, for this produces “a higher duty cycle of distorted events,” making the detection all the more obvious. “We therefore suggest that any survey in archival data should not be limited to rocky planets in the habitable-zone of their host star.” An excellent reminder not to succumb to easy assumptions!

Tomorrow I’ll return to the Kipping and Teachey paper with a look at cloaking possibilities. The paper is “A Cloaking Device for Transiting Planets,” accepted by Monthly Notices of the Royal Astronomical Society (preprint).

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John Ford Fishback and the Leonora Christine

by Paul Gilster on April 1, 2016

Like the Marie Celeste, the Leonora Christine is a storied vessel, at least among science fiction readers. In his 1967 story “To Outlive Eternity,” expanded into the novel Tau Zero in 1970, Poul Anderson described the starship Leonora Christine’s stunning journey as, unable to shut down its runaway engines, it moved ever closer to the speed of light. Just how a real Leonora Christine might cope with the stresses of a ramjet’s flight into the interstellar deep is the subject of Al Jackson’s latest, which draws on memories not only of Robert Bussard, who invented the interstellar ramscoop concept, but a young scientist named John Ford Fishback.

by A. A. Jackson

Project Pluto – a program to develop nuclear-powered ramjet engines – must have been on Robert Bussard’s mind one morning at breakfast at Los Alamos. Bussard was a project scientist-engineer on the nuclear thermal rocket program Rover — Bussard and his coauthor DeLauer have the two definitive monographs on nuclear propulsion [1,2]. He said many times that the idea of the hydrogen scooping fusion ramjet came to him that morning. This was sometime in 1958 or 1959 and the SLAM (Supersonic Low Altitude Missile) would have been well known to him. SLAM was an nuclear ramjet, a fearsome thing, sometimes called the Flying Crowbar. Finding a solution to the mass ratio problem for interstellar flight was also something on Bussard’s mind. Thus was born the Interstellar Ramjet, published in 1960 [3].

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Image: Al Jackson delivering a plenary talk at the recent Tennessee Valley Interstellar Workshop. Credit: Joey O’Loughlin.

Most here at Centauri Dreams know that the interstellar ramjet scoops hydrogen from the interstellar medium and uses this as both a fuel and energy source by way of fusion reactor. The sun does proton fusion using gravity as the agent of confinement and compressional heating. However, doing fusion in a ‘non-gravitational’ magnetic fusion reactor makes the process very difficult [3,4]. That is, the proton and Deuterium burning is quite severe to realize on a ‘small scale’. Dan Whitmire attacked this problem by proposing the use of a carbon catalyst using the CNO cycle [4]. The CNO cycle is about 9 orders of magnitude faster than proton-proton fusion. It would still require temperatures and number densities way beyond any technology known at this time.

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Bussard noted a number of problems such as losses from bremsstrahlung and synchrotron radiation. He also noted scooping with a material scoop would create a problem with erosion, hinting that magnetic fields might be used, and noting that drag would have to be accounted for.

About 8 years after Bussard’s paper, an undergraduate at MIT, John Ford Fishback, took up the problems Bussard had mentioned. He wrote this up for his Bachelor’s thesis under the supervision of Philip Morrison. The thesis was published in Astronautica Acta [5] in 1969.

Image: Physicist Robert W. Bussard.

Fishback did three remarkable things in his only journal paper: finding an expression for the ‘scoop’ magnetic field, computing the stress on the magnetic scoop sources, and working out the equations of motion of the ramjet with radiation losses. These calculations were done using a special relativistic formulation.

Fishback’s most important finding is noticing that when capturing ionized hydrogen to funnel into the fusion reactor, there is a large momentum flow of the interstellar medium which must be balanced by the scooping and confining magnetic fields. Using very general arguments, Fishback showed that sources (magnetic coils and their support) of the magnetic field determine an upper limit on how fast a ramjet can travel. The convenient measure of starship speed is the Lorentz factor

Jackson_equation

where v is the starship velocity and c the speed of light. It comes from the physical properties of the field sources, in particular the shear stress.

At the time, Fishback modeled the upper limit using diamond, because of its shear stress properties, and found that one could only accelerate until the Lorentz factor reaches about 2000 [5,6]. Tony Martin expanded on Fishback’s study [6, 7] in 1971, correcting some numbers and elaborating on Fishback’s modeling. Since that time, Graphene has been discovered and it has a shear stress that allows a limiting Lorentz factor of about 6000. This in turn implies a range of over 6000 light years when under 1 g acceleration. It does not mean the final range is 6000 light years, but one must travel at a reduced acceleration and then constant speed, which means a longer ship proper time.

This is bad news for the Leonora Christine of Poul Anderson’s Tau Zero [8].The range can probably be pushed to 10,000 light years, but accelerating at 1 g for 50 years would bust the Lenora Christine’s coils! That is, unless some magic material is found to take the stress loading at a Lorentz factor 1019, there is no way to circumnavigate the universe. And with the new accelerating universe, the story of Tau Zero becomes still more complicated.

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Image: The interstellar ramscoop as envisioned by artist Adrian Mann.

What became of John Ford Fishback? I went to a lecture in California at Stanford in 1979 by Phillip Morrison. After the lecture I asked Morrison what had happened to Fishback. Morrison sadly told me that Fishback had gone to the University of California at Berkeley to work on his doctorate, but had committed suicide.

1. Bussard, R. W.; DeLauer, R.D. (1958). Nuclear Rocket Propulsion. McGraw-Hill.

2. Bussard, R.W.; DeLauer, R. D. (1965). Fundamentals of Nuclear Flight. McGraw-Hill.

3. Bussard, R.W., “Galactic Matter and Interstellar Flight”, Acta Astronatica, VI, pp. 179-195, 1960.

4. Whitmire, Daniel P. , “Relativistic Spaceflight and the Catalytic Nuclear Ramjet”, Acta Astronautica, 2 (5-6): 497–509, 1975.

5. Fishback, J. F., “Relativistic interstellar spaceflight,” Astronautica Acta, 15 25–35, 1969.

6. Anthony R. Martin; “Structural limitations on interstellar spaceflight,” Astronautica Acta, 16, 353-357 , 1971.

7. Anthony R. Martin, “Magnetic intake limitations on interstellar ramjets,” Astronautica Acta, 18, 1-10 , 1973

8. Anderson, Poul (2006), Tau Zero, Gollancz. ISBN 1407239139.

Table 1. Cut-Offs and Range for Ramjet accelerating at 1g. Interstellar medium 1/cm-3 using the p-p fusion reaction.

Structural Material𝛔/𝛒
dyn cm-2/gcm-3
1010
𝛄𝛃c
Proton
Range
LY
Aluminum.0628.612.6
Stainless Steel.26136.27.5
Silica3.3173.6120
Copper4.366051000
Diamond15.221103550
Graphene600.06628.06418.0

Addendum: While he was working on this article and corresponding with me, Al shared the story with Greg Benford, who had further thoughts on John Ford Fishback, as below:

greg-300x224

Good article. I can add a touch: I was interested in this, after Edward Teller pointed out to me Fishback’s 1969 paper in Astronaut. Acta. I discussed it with Teller and did some calculations (just exploratory, never published). The idea seemed extreme but enlivened my discussions of the paper with Poul Anderson, who lived in Orinda near my Walnut Creek home and whom I saw often.

Someone told me Fishback was at Berkeley and I called him, agreed to meet. I had a one-day-per-week agreement with the Livermore Lab, where I was just turning from being a postdoc for Teller into a staff physicist — I spent Wednesdays at the Lab in Berkeley. So I met him at an Indian restaurant–a rail-thin smoker, nervous, ascerbic. “I wanted to show that we could reach the stars, really do it, with the right engineering,” he said, approximately. His anxiety was clear, but not its cause.

I found him an odd duck but was shocked when a bit later I heard he had killed himself.

When I mentioned it to Poul, he found it contrasting that a man who wanted the stars would cut off his own personal hopes. We often discussed Tau Zero, Poul once remarking that he wished he had taken more time to polish and expand the novel, since it already looked as though it might be the most remembered of his works–and indeed, seems so. He said he had written it in a few months and needed the money–its 1967 serialization in Galaxy helped, but it was tough going as a full-time pro writer then. Plus he had a word limit on the hardcover.

Poul used his Nordic background in the novel, as he liked to do. From Wikipedia:

“Incidental to the main themes is the political situation on the Earth from which the protagonists set out: a future where the nations of the world entrusted Sweden with overseeing disarmament and found themselves living under the rule of the Swedish Empire. This sub-theme reflects the great interest which Anderson, an American of Danish origin, took in Scandinavian history and culture. In later parts of the book, characters compare their desperate situation to that of semi-mythical characters of Scandinavian legend, with the relevant poetry occasionally quoted.”

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SETI Looks at Red Dwarfs

by Paul Gilster on March 31, 2016

When it comes to astrobiology, what we don’t know dwarfs what we do. After all, despite all conjecture, we have yet to find proof that life exists anywhere else in the universe. SETI offers its own imponderables, adding on to the question of life’s emergence. How often does intelligence arise, and if it does, how often does it produce civilizations capable of using technology? Even more to the point, how long do such civilizations last if they do appear?

We keep asking the questions out of the conviction that one day we’ll start retrieving data, perhaps in the form of a signal from another star. It’s because of the lifetime-of-a-civilization question that I’m interested in a SETI search focused on red dwarf stars. True, M-dwarfs have a lot going against them, as Centauri Dreams readers know. A habitable planet around an M-dwarf may be tidally locked, which could be a showstopper except that some scientists believe global weather patterns may make at least part of such planets habitable.

Flare activity is always an issue on younger M-dwarfs, though it’s possible to conceive of this as an evolutionary spur, and we can’t rule out life’s ability to adapt to extreme circumstances. But despite all these unanswered issues, my interest in these stars draws primarily from two main points. First, they are the most common stars in the galaxy, comprising perhaps as much as 80 percent of the total. That gives us a huge number of candidates for life and potential civilization.

And while we can’t say how long civilizations live, not being sure if we ourselves will survive, we can take heart from the idea that if enough of them come into being, at least a few may get past whatever culture-shredding ‘filter’ they encounter to move into a serene maturity. Here red dwarfs truly stand out, because they live so much longer than any other stars. Every red dwarf that has formed in the universe is still there, and we can expect such stars to live for trillions — not billions — of years.

I like the odds, but I’m also trying to imagine what a civilization would look like a billion years after the emergence of tool-making. Or five billion. If a culture can survive for aeons, it will have mastered issues of conflict that plague us daily and much else besides. Surely a mature species long past emotional and technological infancy would want to know about its neighbors. Would such a culture reach out to others, if only to exchange notes? Or would it have moved into realms of philosophy and thought that make all this irrelevant?

We’re deep in imponderables here, but all we can do is look and listen. Thus I was pleased to see that the SETI Institute is initiating a search using the Allen Telescope Array that targets red dwarf stars. As the Institute’s news release explains, we now believe that somewhere from one-sixth to one-half of red dwarfs have planets in their habitable zones, which is a percentage that may be comparable to stars like the Sun, and for all we know at this point, may exceed it.

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“Significantly, three-fourths of all stars are red dwarfs,” notes SETI Institute astronomer Seth Shostak. “That means that if you observe a finite set of them – say the nearest twenty thousand – then on average they will be at only half the distance of the nearest twenty thousand Sun-like stars.”

That, of course, means that we have a larger population of stars whose potential signal to us would be stronger. The SETI Institute is drawing on a target list of 20,000 M-dwarfs compiled by Boston University astronomer Andrew West, one that will incorporate new data as it is collected by missions like TESS, the Transiting Exoplanet Survey Satellite, slated for launch next year. Using the ATA’s 42 antennae, the red dwarf survey will take two years to complete, working in several frequency bands between 1 and 10 GHz. Says Institute scientist Gerry Harp:

“Roughly half of those bands will be at so-called ‘magic frequencies’ – places on the radio dial that are directly related to basic mathematical constants. It’s reasonable to speculate that extraterrestrials trying to attract attention might generate signals at such special frequencies.”

My assumption is that as resources become available (never an easy matter), SETI will search broadly through the various stellar types — we can’t know what we’ll find until we look. But it’s heartening to find a SETI attempt specifically turning to a category of star that has generally received little attention. It may well be that a race that is deep into philosophical maturity will have moved beyond beaming signals to other stars. It may, for all we know, have moved beyond biology! But let’s keep up the search and learn as much as we can about the small red stars that pepper the cosmos and may, if in any way habitable, hold clues about life’s emergence.

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TVIW 2016: Worldship Track

by Paul Gilster on March 30, 2016

Our second report from the recent Tennessee Valley Interstellar Workshop is the work of Cassidy Cobbs and Michel Lamontagne, with an emphasis on the worldship track. Cassidy has an MS from Vanderbilt, where she studied ecology and evolution. She currently works at Memorial Sloan Kettering Cancer Center, doing traditional and next-generation gene and genome sequencing. Her interest in space travel/engineering was enhanced by attending Advanced Space Academy in Huntsville at age 14. Michel Lamontagne is a French-Canadian mechanical engineer, practicing in the fields of heat transfer and ventilation, with a passion for space. An active member of Icarus Interstellar, he tells me he has “been designing spaceships since he was 12 years old, and waiting for reality to catch up!” Photos throughout are from New York photojournalist Joey O’Loughlin, and are used with permission.

By Cassidy Cobbs and Michel Lamontagne

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This year’s Tennessee Valley Interstellar Workshop (TVIW-2016) was held in Chattanooga, Tennessee from February 28 to March 2. Attendance was good, reaching the limits determined by the organization committee. Everything seemed to run smoothly, although one can imagine the usual frantic behind the scenes activity required to create that illusion!

Image: Co-author Michel Lamontagne.

The Life Systems Engineering for the Worldship track was very productive, engaging in active work sessions and managing to start interesting lines of inquiry into some the questions of the biological, social, and heat transfer facets of the worldship concept.

In our first working track session, we split into two groups, designated “Biotic” and “Abiotic” to brainstorm on some of the unanswered questions of Worldship theory and design.

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Image: Abigail Sheriff (left), a graduate of the International Space University, and Cassidy Cobbs, co-leader of the Worldship track.

We began populating a whimsical list of included and excluded species, sure to generate heated debate — for example, the entire Australian continent was excluded on account of being too deadly!

We also came up with a number of unexplored questions, including three concerns that we would explore in depth in our Day 2 session: The agricultural framework of a Worldship; how to establish and maintain indefinitely carbon, nitrogen, phosphorus, and oxygen cycling; and how to adapt Earth-normal light, water, and heat cycles to a (much smaller) Worldship.

Cameron Smith (Portland State University) added his ongoing reflections about the human societal aspects of the worldship to the discussions, and provided fascinating parallels with early villages and paleolithic societies, where proto-cities housed small stable communities for periods similar to those expected for a worldship trip.

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Image: Biomedical engineer Leigh Boros in the Worldship track. Credit: Joey O’Loughlin.

In our second session, the track split into three groups to look at a few of the questions generated the day before.

Our first group decided to explore some of the changes in heat transfer regimes from living on a sphere with the heat from the outside to living in a cylinder with heat from the inside. We didn’t have the time to work out if we could make it rain in the worldship using only convection cycles, but we agreed that rain would be needed and decided to address the problem in follow-up work sessions on the Internet.

Group two looked at resource cycling, and began to develop the calculations necessary to determine how much of elements such as nitrogen, phosphorus, and oxygen would be needed on board the ship at launch to maintain those natural cycles.

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Image: Oz Monroe (left) and Miles Gilster (right), framing Greg Matloff in the background. Credit: Joey O’Loughlin.

The final group explored a potential framework for agri- and aquaculture, creating a list of diverse livestock and crops that would fulfill the nutritional and cultural needs of the humans on board. They also began to think about issues of crop rotation, soil health, and water requirements and to calculate what percentage of land would need to be allocated to agriculture.

The Worldship track was proud to host a new generation of designers, with Hannah Sparkes (age 15) and Ashleigh Hughes (age 17) joining with researchers Anton Smirnov (28) and Andrew Kirkpatrick (26) to ensure that analysis of interstellar worldship engineering has a future.

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Image: A poster for the worldship track, as prepared by Michel Lamontagne.

For the plenary events, the subjects covered in the papers and talks ranged widely, as usual for TVIW, from starwisps to space wars. Philip Lubin (UC-Santa Barbara) invited the crowd to do the math for his incarnation of the laser-powered sail, one that recently garnered a lot of media attention with a ‘30 minutes to Mars’ thought experiment, although the Mars journey is actually only one element of what Lubin sees as a complete Roadmap to the Stars.

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Image: A scene from the Space Mining track. Edwin Etheridge (left) discusses specifics with Matt Ernst. Credit: Joey O’Loughlin.

The Moon vs asteroid mining debate politely raged on, with proponents on both sides and an entire track devoted to exploring detailed mineral processing methods. Melting Lunar basalts to create large caverns for rotating habitats, both in system and at interstellar destinations, was also the subject of an interesting talk by Ken Roy. Meanwhile, the sheer immensity of asteroid resources was highlighted by John Lewis in his keynote address.

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Image: Keynote speaker John S. Lewis (author of Mining the Sky). Credit: Joey O’Loughlin.

Jim Benford proposed beam leakage from propulsion systems as a new SETI venue, inspired in part by the KIC 8462852 light anomalies uncovered in the Kepler planet finder data.

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Image: Jim Benford discussing beamed propulsion issues in a SETI context. Credit: Joey O’Loughlin.

Al Jackson revisited and augmented his seminal Interstellar Laser Powered Interstellar Ramjet design, applying graphene to increase performance and setting the ultimate physical limits of the technology. Creating antimatter from space vacuum fluctuations using high energy lasers, as a part of an advanced antimatter drive, while respecting classical conservation of energy, was the subject of the exotic physics talk by Gerald Cleaver.

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Image: Stefan Zeidler (left), newest member of the board of the Initiative for Interstellar Studies, with i4IS founder Kelvin Long and Bill Cress. Credit: Joey O’Loughlin.

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Of a Mountain on Titan

by Paul Gilster on March 29, 2016

If Saturn’s inner moons are, as we discussed yesterday, as ‘young’ as the Cretaceous, then we have much to think about in terms of possible astrobiology there. But Titan is unaffected by the model put forward by Drs. Ćuk, Dones and Nesvorný, being beyond the range of these complex interactions. Huge, possessed of fascinating weather patterns within a dense atmosphere, Titan probably dates back to Saturn’s earliest days, in some ways a frigid ‘early Earth’ analog.

When my son Miles was a boy, we drove through the Appalachians on a journey that eventually took us into Canada. Somewhere in the Shenandoah Valley he commented on how insignificant the mountains seemed compared to what he was used to out west, where the Rockies dominate the sky. True enough, but of course the Smokies and the Cumberlands have their own tale to tell. Once monumental, they’ve fallen prey to wind and rain, ancient relics of once grander peaks.

The latest work on Titan from Cassini data now reveals something about similar erosion on Titan, where we have rain, lakes and seas, not to mention rivers cutting their way through the landscape. But Jani Radebaugh (Brigham Young University, Utah), who works with the Cassini radar team, notes that erosion on Titan is actually a much slower process than on Earth, thanks to Titan’s being ten times Earth’s distance from the Sun. There is just that much less energy to drive these processes in the thick atmosphere. See this JPL news release for more.

With Titan we have to think in terms of analogies. On Earth it’s water that freezes, thaws, vaporizes, providing a hydrological cycle that works its seasonal magic in terms of weather change. On Titan it’s methane that performs a similar function. Meanwhile, Titan’s water ice behaves much more like rock on Earth, an icy crust overlaying what is likely to be an ocean of liquid water — here the analogy is with Earth’s upper mantle. In both cases, these inner layers accommodate slow changes as mountains form and ranges begin to settle.

Radebaugh’s team used Cassini’s radar instrument to study the ridges known as the Mithrim Montes, among which is found the moon’s tallest peak, some 3337 meters high. “It’s not only the highest point we’ve found so far on Titan, but we think it’s the highest point we’re likely to find,” says Stephen Wall (JPL), deputy lead of the Cassini radar team. The results were presented at the 47th Lunar and Planetary Science Conference in Texas.

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Image: The trio of ridges on Titan known as Mithrim Montes is home to the hazy Saturnian moon’s tallest peak. The mountain, which has an elevation of 3,337 meters, is located midway along the lower of the three ridges shown in this radar image from NASA’s Cassini spacecraft. Credit: NASA/JPL-Caltech/ASI.

The view above was acquired on the T-43 flyby back on May 12, 2008 at an incidence angle of about 34 degrees. Remember that this is a radar image, which uses reflections scattered off the moon’s surface to see through the thick, opaque atmosphere. Dark areas indicate regions that are relatively smooth or otherwise absorb radar waves, while bright regions are rougher materials that scatter the beam. A ‘speckle’ pattern is an artifact of the technique — in this image, ‘despeckling’ methods were used to reduce the noise and produce clearer views.

Titan’s mountains don’t reach the heights we see in some of Earth’s ranges, but researchers hadn’t expected they would because the water-ice bedrock is softer than Earth’s rock. But it is significant that we find tall mountains here, an indication of active forces shaping the surface that are perhaps Titan’s response to tidal forces from Saturn, or perhaps cooling of the crust. Finding such ‘active zones’ in the crust tells us something about Titan’s history.

“As explorers, we’re motivated to find the highest or deepest places, partly because it’s exciting,” adds Radebaugh. “But Titan’s extremes also tell us important things about forces affecting its evolution. There is lot of value in examining the topography of Titan in a broad, global sense, since it tells us about forces acting on the surface from below as well as above.”

Titan’s highest mountains all seem to be close to the equator, with other peaks of a similar height being found within the Mithrim Montes (for Tolkien cognoscenti, the Mountains of Mithrim ran northwest from the Ered Engrin, dividing Dor-lómin from Mithrim, and that is as far as I go with Tolkien today). Other peaks are known in the Xanadu region. Learning more about the forces that formed them is now a priority for researchers probing Titan’s mysteries.

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Saturn’s Moons: A Question of Age

by Paul Gilster on March 28, 2016

Some years back at a Princeton conference I had the pleasure of hearing Richard Gott discussing the age of Saturn’s rings. Gott is the author of, in addition to much else, Time Travel in Einstein’s Universe (Houghton Mifflin, 2001). I admit the question of Saturn’s rings had never occurred to me, my assumption being that the rings formed not long after the formation of the planet. But of course there is no reason why this should be, and a number of reasons why it should not. How long, for instance, does it take moons to collide with each other, contributing debris to a growing ring system? And are such collisions the only way a ring system can form?

With all this in mind, I was interested in a new paper that a number of readers referenced in emails. Lead author Matija Ćuk (SETI Institute), working with Luke Dones and David Nesvorný (both at SwRI), offers up the possibility that the inner moons of Saturn and possibly the rings were actually formed much later than we would expect. In fact, they may be positively recent in astronomical terms, having formed during or not so long after the era of the dinosaurs.

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Image: The new paper finds that Saturn’s moon Rhea and all other moons and rings closer to Saturn may be only 100 million years old. Outer satellites (not pictured here), including Saturn’s largest moon Titan, are probably as old as the planet itself. Credit: NASA/JPL.

The work involves the moon Rhea and all the other moons and rings closer in to Saturn. The outer satellites, including Titan, are still thought to be as old as the planet itself. But using numerical simulations, the trio explored the tidal effects that should be causing the inner moons of Saturn to spiral out to larger orbital radii. Each of the moons would experience different growth in its orbit, which would occasionally produce orbital resonances. Such effects, in a system crowded with moons, can cause orbits to diverge from their original plane.

The team’s simulations homed in on a hypothetical 3:2 resonance in the past between the moons Tethys and Dione, along with a 5:3 resonance crossing between Dione and Rhea. Remember what happens in such a resonance: A moon’s orbital period becomes a fraction — one-half, or two-thirds, for example — of another moon’s orbital period. The paper notes that the current Tethys/Dione and Dione/Rhea orbital period ratios are just above 2/3 and 3/5. Does this mean these resonances were crossed at some point in the past?

Perhaps not, for interestingly, the 3:2 resonance crossing should have led to an excitation in the orbital inclinations of both Tethys and Dione, something that is not observed in their current orbits. The 5:3 resonance between Dione and Rhea, according to the authors, probably did happen, to be followed by a previously unknown Tethys-Dione resonance. The combination can explain the current inclinations of both Tethys and Rhea. Quoting from the paper:

We can therefore state that Tethys and Dione evolved tidally by only a modest amount over their lifetimes, which is only about a quarter of the tidal evolution envisaged in Murray & Dermott (1999). There are two possible interpretations: either tidal evolution of Saturn’s moons has been very slow, or Saturn’s mid-sized moons are significantly younger than the Solar System. While both interpretations are consistent with the lack of the past Tethys-Dione resonance, we favor the idea that the moons are young, possibly as young as 100 Myr… The Trojan moons of Tethys and Dione that share their inclinations must have formed even more recently, after their passage through the secular resonance.

The inclination of the orbits of the moons in question, in other words, should have been altered more than they have been by gravitational interactions, an indication that orbital resonances have been few. And that, the authors conclude, is evidence they must have formed recently. That leads directly to the question of how the inner moons formed. Says Ćuk:

“Our best guess is that Saturn had a similar collection of moons before, but their orbits were disturbed by a special kind of orbital resonance involving Saturn’s motion around the Sun. Eventually, the orbits of neighboring moons crossed, and these objects collided. From this rubble, the present set of moons and rings formed.”

All this has implications for our view of Enceladus, which experiences intense tidal heating that is incompatible with a slowly evolving system. The presence of an internal ocean gives high astrobiological interest to this moon, but according to these researchers, Enceladus, Mimas and the rings could have formed at the same epoch as Dione and Rhea or be even younger (the authors intend to explore the tidal evolution of Mimas and Enceladus in future work). Would an Enceladus as young as the Cretaceous Period on Earth have had time to develop life? It’s a question we can clarify with future missions designed to fly through the Enceladus plume.

The paper is Ćuk et al., “Dynamical Evidence for a Late Formation of Saturn’s Moons,” to be published by The Astrophysical Journal (preprint). A SETI Institute news release is also available.

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Thirteen to Centaurus

by Paul Gilster on March 25, 2016

J. G. Ballard (1930-2009) emerged as one of the leading figures in 20th Century science fiction. His fascination with inner as opposed to ‘outer’ space infused his characters and landscapes with a touch of the surreal, taking the fiction of the space age into deeply psychological realms. Christopher Phoenix here looks at the question of centuries-long journeys to the stars, with reference to a Ballard story in which a crew copes with isolation on what appears to be an interstellar mission. What we learn about ship and crew informs the broader discussion: If it takes more than a single generation to make an interstellar crossing, what can we do to keep our crew functional? And is there such a thing as happiness under these constraints?

By Christopher Phoenix

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A few months back, Centauri Dreams ran Gregory Benford’s review of Kim Stanley Robinson’s novel Aurora. After reading that review and the discussion that followed, I began thinking about fiction that explores how starflight might fail. I hope that we will reach the stars someday, but it is always interesting to step back and explore the reasons why interstellar flight might not be an inevitable part of our future.

Perhaps due to science fiction’s roots in the pulp magazines of the 20s and 30s, many SF stories show an unwavering faith in humanity’s ability to overcome any obstacle. In most science fiction, it is a foregone conclusion that humanity will reach the stars. Space opera stories expect that the reader will accept the existence of a human interstellar civilization from the very first pages. Stories that dispute this assumption are much rarer.

One such story is James G. Ballard’s “Thirteen to Centaurus”. This short story takes place within a mysterious habitat known only as “The Station” by its thirteen-person crew. For generations, they have lived within the confines of the Station’s three decks. At the beginning of the story, one of the teenage members of the crew, a boy named Abel, suffers recurring nightmares of a burning disk. The only person who can tell him the meaning of these visions is Dr. Francis, the Station’s doctor, who lives alone on another deck.

Dr. Francis tells Abel that the Station is actually a starship traveling to Alpha Centauri and explains that the burning disk is a repressed genetic memory of the Sun he has never seen. When Abel asks Dr. Francis when they will arrive, he explains that the Station is a multi-generational spaceship. None of the current generation will live to see planetfall. Dr. Francis tells Abel that the rest of the crew cannot know this truth, as otherwise they will never be happy in their confined artificial world.

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Soon, however, the story takes another twist. It turns out that Dr. Francis is lying, and the Station is in fact an Earth-bound experiment designed to test whether humans can survive a century-long flight to Alpha Centauri. In truth, Dr. Francis is one of the researchers posing as a member of the crew, sent to secretly observe them from among their midst. The Station’s planners believed that humans could not survive such a trip knowing that they are condemned to live their whole lives in a confined spacecraft. Generations of crew will never see the Earth where they came from or live long enough to reach their destination. To solve this problem, the researchers use hypnotic suggestion to eradicate memories of Earth and make the crew accept the Station as the only world that exists.

Image: Science fiction writer J. G. Ballard.

As the story continues, we see Dr. Francis leave the habitat to meet with his colleagues. To his horror, his superiors tell him that the project must be shut down due to lack of public support. They ask Dr. Francis how to transition the crew from their isolated life in the station to the outside world. Hoping to convince them to continue the simulation, Dr. Francis insists that the crew cannot survive having their worldview shattered in this way. The only way to humanely end the project is to stop the crew from having children and wait for the current generation to die out. His superiors are so desperate to end the project that they agree to take this extreme course of action.

As the experiment is gradually shut down, Abel begins to ask Dr. Francis awkward questions about the Station. Dr. Francis’s clumsy attempts to hide the true nature of the Station only seed Abel’s mind with further doubts. In a more disturbing turn, Abel begins showing an unhealthy interest in performing psychological experiments of his own devising on the other members of the crew and even Dr. Francis himself.

Unwilling to accept the termination of the project, Dr. Francis finally decides to seal himself inside the dome to complete the imaginary trip to Centaurus with the crew, knowing that no one will dare enter the habitat to remove him. Once within the habitat, however, he realizes just how monotonous the crew’s life really is. Unfortunately, he dares not leave, since entering the habitat without permission carries a mandatory 20 year prison sentence. At this point, Abel takes the opportunity to turn the tables on Dr. Francis, forcing him to participate in his psychological experiments as a subject. Abel has begun to run the Station like a minor tyrant.

In the end, Dr. Francis finds a hole in the outer dome through which the previous captain and Abel have observed supplies being brought into the habitat. He realizes that the captain knew the truth and choose to stay in the dome. Before he died, he told Abel, and Abel has chosen to feign ignorance and stay within the station so that he can be the de facto ruler of this tiny world.

Trapped in a Tin Can

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Ballard questions whether humans can adapt to life in a multi-generational starship. In his story, the designers of the Station believe that people would find their life in such a ship so limited compared to life on a planet that they could never be happy. Their solution is to eradicate the crew’s awareness of any other possible existence. This one idea drives much of the design of the Station.

The Station’s planners attempt to achieve this goal by using hypnosis and subliminal suggestion. The crew only believe themselves to be happy because they are conditioned to do so. Subliminal messages have been embedded in educational tapes that the crew are required to listen to at regular intervals. The message that there is no life beyond the Station is constantly reinforced by these tapes. In addition to this regular conditioning, every aspect of the crew’s’ life is scheduled and controlled. They have no freedom of thought or action. Since they are supposed to believe that there is no life beyond the Station, the crew has no access to the books, art, and culture of Earth. Even though this sort of highly effective “mind control” doesn’t really exist outside of science fiction, Ballard presents a stark view of what life could be like in a multi-generational starship. Even if this scheme could work, it would only be at great psychological cost to generations of crew.

Image: “Thirteen to Centaurus” can be found in, among other places, The Complete Stories of J. G. Ballard (Norton, 2010).

Ballard is not alone in his opinion. If you mention multigenerational spaceflight, many people will tell you that it is incredibly unfair to condemn generations of people to life aboard a ship in interstellar space. The idea that it will be impossible to be truly happy in an artificial world that you cannot escape drives much of the criticism of multi-generational spaceflight. Ballard has clearly touched on a tender nerve.

In the story, however, Dr. Francis finds that not all is as it seems. After sealing himself in the simulator, he discovers that the late captain and the teenage Abel both knew that they were in a habitat on Earth, and yet they chose to remain. For Abel, staying in the habitat gives him the opportunity to dominate the other members of the crew and force them to participate in his psychological experiments.

Here, Ballard raises another disturbing question. In an enclosed habitat, might one ambitious individual or small elite group seek to control the rest of the crew? Aboard a starship in interstellar space, there would be no external checks on oppressive leadership, or any way to escape it. Because of this, choosing the right form of governance would be vital for a generation ship. Unfortunately for the inhabitants of the Station, the researchers put all their trust in their mind-control methods. They did not have any means to check someone, like Abel, who broke beyond their mental blocks.

This story reminds us that we must plan for the social and psychological factors of multi-generational trips as carefully as we do for the purely mechanical ones such as life support, radiation shielding, and propulsion systems.

Losing Enthusiasm

In Ballard’s story, the people running the century-long simulation decide to shut the project down midway. When the project was started, humanity was attempting to colonize the Moon and Mars. The public was enthusiastic about space travel, and many people believed that they would eventually build interstellar ships. So, it was decided to test social conditions on such a trip even before the technology to build a starship or a self-sustaining habitat was available.

When the story takes place, the Lunar and Martian colonies have failed. The public is no longer interested in space travel. Furthermore, they have begun to question the ethics of sealing generations of people in the simulator and observing their every move. Almost everyone wants to end the project.

Ballard suggests that humans will have difficulty maintaining focus and enthusiasm long enough to complete a prolonged effort like developing interstellar travel, which could take centuries. A case can be made for this argument by just looking at our history. Even though we reached the Moon, politicians chose to cancel the Apollo program. In the years that have followed, the numerous plans to return to the Moon and/or go to Mars have been not been carried out. Astronauts have not even ventured beyond low-Earth orbit since the Apollo missions.

Currently we don’t have a replacement for the space shuttle, or a coherent plan of what to do to follow up on our current space probe missions and the ISS. It often seems that ambitious plans to explore space are more likely to fail because of lack of political support than technological obstacles. Human civilization will need to develop a much longer planning horizon than we currently have to maintain the political will needed to develop interstellar travel.

Our lessons come from the journey, not the destination…

Ballard raises many interesting issues in this story. However, despite the melancholy ending of “Thirteen to Centaurus”, I’m still quite optimistic about the future of multigenerational space travel. Personally, I believe that it’s possible for humans to be happy aboard a generation ship in deep space, even knowing that they will not live to see their destination.

When a group of people set out on an interstellar journey that only their descendants will complete, the ship will become their home as well as the home of the generations between launch and planetfall. Therefore, I propose it is more important to plan for the interstellar journey than to fixate on the destination. We must plan the voyage so that the people who are born, live, and die on the spaceship have the opportunity to live full lives.

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Image: Ballard’s work occasionally made it to other media, most notably in the 1987 Spielberg film Empire of the Sun. This is a shot from a TV adaptation of “Thirteen to Centaurus,” as presented on Out of the Unknown, a BBC science fiction anthology series broadcast between 1966 and 1971. Starring were Donald Houston, John Abineri, Robert James and Noel Johnston.

The common objection to multi-generational spaceflight is that the crew will not be happy with their lives aboard the ship, or that they will even “go mad” from the psychological strain. Why should the crew go mad on a generation ship? Ballard’s story suggests two main reasons. One is lack of space and forced lifelong contact with only a few people, and no way to escape someone you do not wish to know. The other is a feeling of deprivation from being born on a starship, not on a planet of your own.

The first problem can be solved by simply sending a more reasonably sized crew. In Ballard’s story, the Station’s population is a scant thirteen, not nearly enough! So far, most population size studies for starships have focused on genetic factors or maintaining specialized skill sets, not on social or psychological needs. I’ll make a stab and say that a crew size of at least a few hundred people, similar to a typical Medieval village, will provide ample choice in human contacts.

Earlier, I touched upon the issue of leadership. Since there will be no possible external checks on dictatorial behavior within an isolated starship, we must choose the right form of governance at the beginning of the trip and place what safeguards we can to avoid abuses of power. While a certain amount of centralized authority will be necessary to respond to emergencies, the people responsible for the day-to-day life of the crew should not be autocratic or oppressive. The leadership must be flexible enough to accept any changes that will become necessary during the course of the trip. This suggests the traditional military-style command structure used on all crewed spaceflights since the Cold War will not work for multigenerational spaceflight.

But what about lack of space? In “Thirteen to Centaurus”, the crew was confined to only three decks. I don’t think any crew could thrive, or even survive, in such cramped conditions. We must provide the crew with sufficient space. I am of the opinion that a sufficiently spacious ship-style interior could work for people who have adapted to life in space habitats. Garden spaces can be incorporated into the interior design, creating a more naturalistic environment, unlike the harsh mechanized interiors described in many science fiction stories. But it is also possible to create a starship large enough to contain an open Earth-like landscape.

The largest generation ship concepts are designed like traveling O’Niell colonies. Such “world-ships” can contain an Earth-like landscape on their interior, including an artificial sun, creating an environment almost like an inside-out planet in miniature. The main problem with such a scheme is constructing and launching such a gigantic structure, but such a craft can offer an Earth-like existence during a long flight.

But will the crew feel deprived living their entire lives away from any planet, as the researchers in Ballard’s story believe? I think Ballard misses the mark here. We neither choose nor tend to question the environment we are born into. The crew of an interstellar ship would accept their environment as normal, just as countless people throughout history have accepted their unique environment on Earth as “normal”.

To modern first-world people, the idea of living and dying within a relatively small area like a generation ship seems impossible, but the amount of mobility available to us is unusual compared to the lifestyles of earlier people. It is even possible that people who have lived their entire lives in space will think of living on a planet as something strange or even unpleasant. They may wonder how we put up with weather we don’t control, or a constant gravitational acceleration we can’t modify to our preference just by going to another deck. On the other hand, things we see as strange and maybe even frightening, like relying for our very survival on ship systems continuing to function, will be accepted as normal by them.

Only time will tell if human civilization can muster the energy and will to send starships to the potentially habitable exoplanets we discover around nearby stars. But if we do, I firmly believe that people will be able to live happily aboard those ships. Even though these voyages will realistically take centuries to complete, humans possess the flexibility and resilience to adapt to life in almost any environment. Certainly, the culture aboard such a ship would not be anything like modern life on Earth, but that does not mean that such a culture could not be as complex and fulfilling as any throughout human history.

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Planets in the Process of Formation

by Paul Gilster on March 24, 2016

Back in 2014, astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to produce high-resolution images of the planet-forming disk around the Sun-like star HL Tau, about 450 light years away in the constellation Taurus. The images were striking, showing bright and dark rings with gaps, suggesting a protoplanetary disk. Scientists believed the gaps in the disk were caused by planets sweeping out their orbits.

All this was apparent confirmation of planet formation theories, but also a bit of a surprise given the age of the star, a scant million years, making this a young system indeed. Here is the ALMA image, along with the caption that ran with the original release of the story from NRAO.

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Image: The young star HL Tau and its protoplanetary disk. This image of planet formation reveals multiple rings and gaps that herald the presence of emerging planets as they sweep their orbits clear of dust and gas. Credit: ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF).

Now we have further work on HL Tau, this time based on data from the Very Large Array (VLA). As opposed to the ALMA work, which showed details in the outer portions of the disk only, the VLA findings, working at longer wavelengths, get us into the inner portions of the disk. At these wavelengths (7.0 mm), the dust emission from the inner disk can be penetrated.

What we see is what this NRAO news release calls ‘a distinct clump of dust’ in the inner disk region, one that contains from 3 to 8 times the mass of the Earth. The researchers believe they are looking at the earliest stage in the formation of protoplanets, seen in the image below for the first time. Not a ‘planet,’ mind you, but a ‘clump of dust.’

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Image: ALMA image of HL Tau at left; VLA image, showing clump of dust, at right.
Credit: Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF.

“This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation,” said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). “This is quite different from the case of star formation, where, in different objects, we have seen stars in different stages of their life cycle. With planets, we haven’t been so fortunate, so getting a look at this very early stage in planet formation is extremely valuable,” he added.

The inner region of the disk, thought to contain grains as large as one centimeter in diameter, is where Earth-like planets would be likely to form as aggregations of dust accumulate and draw in material, eventually gathering the mass to form the planetesimals that become planets. The paper on the VLA work argues that we are looking not at planets that have already formed in gaps in the dusty disk, but at the very earliest stages of future planet formation:

We propose a scenario in which the HL Tau disk may have not formed planets yet, but rather is in an initial stage of planet formation. Instead of being caused by (proto)planets, the dense rings could have been formed by an alternative mechanism. Our 7.0 mm data suggest that the inner rings are very dense and massive, and then, they can be gravitationally unstable and fragment. It is then possible that the formation of these rings result in the formation of dense clumps within them like the one possibly detected in our 7.0 mm image. These clumps are very likely to grow in mass by accreting from their surroundings, and then they possibly represent the earliest stages of protoplanets. In this scenario, the concentric holes observed by ALMA and VLA would not be interpreted as a consequence of the presence of massive (proto)planets. Instead, planets may be just starting to form in the bright dense rings of the HL Tau disk.

The following image pulls the ALMA and VLA work together.

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Image: Combined ALMA/VLA image of HL Tau. Credit: Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF.

The paper is Gonzalez et al., “The VLA view of the HL Tau Disk – Disk Mass, Grain Evolution, and Early Planet Formation,” accepted by Astrophysical Journal Letters (preprint).

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