Paul Gilster's Blog, page 230

Stranger Than Fiction

Just what does it take to make a habitable world? Keith Cooper is editor of Astronomy Now, the British monthly whose first editor was the fabled Patrick Moore. An accomplished writer on astronautics and astronomy as well as a Centauri Dreams regular, Keith has recently become editor of Principium, the newsletter of the Institute for Interstellar Studies, whose third issue has just appeared. In this essay, Keith looks at our changing views of habitable zones in light of recent work, and takes us to two famous science fictional worlds where extreme climates challenge life but do not preclude it. How such worlds emerge and how life might cope on them are questions as timely as the latest exoplanet findings.

by Keith Cooper

Literally overnight, two habitable planets – tau Ceti f and HD 85512b – were rendered barren and lifeless. What was the cause of this cataclysm? A nearby supernova? Asteroid impacts? On the contrary, it was something far more mundane.

A dozen light years away, scientists at Penn State University were re-analysing the extent to which habitable zones penetrate the space around stars; in other words, at what distance liquid water could potentially exist on a planetary surface assuming an Earth-like atmosphere. The basics for habitable zone theory had been worked out in part by, among others, Penn State’s James Kasting in decades previous. Building on his work, Ravi Kumar Kopparapu and Ramses Ramirez discovered that habitable zones are found further from their stars than had been envisaged (see Habitable Zones: A Moving Target for more).

The result was bad news for our two exoplanets. Suddenly, as the habitable zone shifted imperceptibly around them, they found themselves on the wrong side of the inner habitable zone boundary, too close to their respective stars. Consequently the Planetary Habitability Laboratory at the University of Puerto Rico, Arecibo, declared them uninhabitable. Too bad for any life-forms living there.

Despite only knowing the scarcest of details about these worlds – mass, radius, density, the amount of heating from their stars – these two worlds have been cast into the obsolescence in a manner that seems shockingly final. We know so little about these planets, how can we possibly say whether they are habitable or not, especially when the only standard we are holding them to is habitability for human beings?

Key Factors for Habitability

Determination of habitability is based on worlds not necessarily having exactly the same atmosphere as Earth, but at least having water and carbon dioxide, which are abundant and vital for life, Dr Abel Mendez of the Planetary Habitability Laboratory at the University of Puerto Rico, Arecibo, tells me. “The problem of the inner edge is that once you evaporate more water you get into a runaway greenhouse effect that will make the planet lose all its water,” he says.

There are other factors that play a part though. Just because a planet is inside a habitable zone doesn’t mean it is automatically habitable. The presence of an atmosphere, water, a global magnetic field, plate tectonics and a not too heavy impact rate are all factors. For those worlds close to the edges of the habitable zone, the margins are even narrower.

For example, habitability of planets on the edge could be largely dependent upon cloud cover, says Mendez, which can increase a planet’s albedo, or reflectivity, preventing heat from reaching the surface, but if there’s no way to see clouds on a planet many light years away, how can we just write off worlds like tau Ceti f and HD 85512b? Mendez admits nothing is for certain. “The intention of the habitable zone is to determine the limits [at which habitable planets can exist from their stars], but I will not call them hard limits yet due to uncertainties such as the effects of clouds.”

A constrained, limited view of habitability that says only Earth-like conditions will do limits the number of worlds we think would look friendly. And there’s nothing wrong with this approach – we know that a planet like Earth is suitable for life, so that is what we look for, whereas we don’t know yet whether life could exist on worlds like Europa or Titan, for example. It’s not that planetary scientists are ignoring other kinds of worlds, either. “Many groups are considering the more exotic possibilities, such as tidal habitable zones, habitable planets around white dwarfs, etc,” says Mendez. “The problem is that the habitability of such conditions are harder to observe or interpret than known biosignatures, and observational astronomers need to measure things, but we will get there.”

Science Fiction at the Boundaries

Until we do, however, we’re left to speculate with our imaginations and where is that not done best but in science fiction? So let’s take a look at a few imaginary worlds that are different to Earth but which could exist on the boundaries of the habitable zone and see how they stack up in comparison. Could reality really be as strange as fiction?

One common science fiction trope is the planet with the same climatic conditions over its entire globe, for example the desert planet, the ice planet, the jungle planet. In reality things are more complex – you can have what seems like all four seasons in one day on parts of the Earth. We don’t expect the same climate at the equator as at the poles. Meanwhile the change of seasons see cycles of weather, not just on our planet but on Mars, Saturn and Titan to name but three. What then do we make of our first two science fiction choices, the desert world Arrakis from Frank Herbert’s Dune, and the ice planet Hoth from The Empire Strikes Back?

Arrakis first. Dry as a bone, it has no surface water and no precipitation. What little atmospheric moisture there is is harvested by wind-traps and the water then ferried by canal to underground reservoirs in anticipation of using it as part of the terraforming of the planet. In the novels, however, the planet is mostly sand dunes, inhabited of course by the fearsome sandworms, except for at the pole where a large slab of bedrock ringed by mountains provides a more habitable zone.

Image: A sandworm rears up out of the desert of Arrakis on the March, 1965 cover of Analog. I can never resist the chance to display the artwork of the remarkable John Schoenherr. What memories…

So how did Arrakis end up like this? In Dune, Frank Herbert described the world as having salt flats, indicating that it once had lakes. The introduction of the non-indigenous sandworms, in their protoform as ‘sand trout’, saw them sequester all of the water. Arrakis, described as orbiting the star Canopus, changed from a fertile world to a desert planet.

We have our own desert planet in the Solar System in the form of Mars, skirting the outer edge of the habitable zone. While there are no sandworms on the red planet, liquid water dried up on the surface long ago and today only exists in frozen ice caps, sub-surface ice or possibly in aquifers deep underground. Indeed, what happened to Mars’ water, and the truth behind the climatic history of the planet, are still something of mystery, but we can hazard a best guess.

We know that Mars once had running water on its surface, in the form of rivers, lakes and even a northern sea. They existed billions of years ago. Today we see only their long-lasting consequences on the Martian terrain: river channels, floodplains, a surface chemistry forever altered by the presence of liquid water. The problem with Mars is that it is small, which results in a double whammy for the planet: its diminutive size means not only a smaller gravitational field but also a greater loss of heat from its core. As Mars’ interior began to cool, its molten core began to stiffen and the magnetic dynamo contained within began to stall. These two things conspired to allow the solar wind to strip Mars’ atmosphere, including its water vapour. (The European Space Agency’s Mars Express spacecraft has actually witnessed this stripping in action, watching Mars’ atmosphere lose oxygen at a rate ten times faster that Earth’s atmosphere; see Earth’s Magnetic Field Provides Vital Protection.

Move Mars closer in to the Sun and you could easily have a warmer Arrakis-type world. So desert worlds are feasible and you don’t require sandworms to create them either. But what about the other extreme, an ice planet like Hoth?

Life on the Outer Edge

Twice in Earth’s history – 2.5 billion years ago, and about 700,000 years ago – our planet completely froze over. Even the oceans were covered with a thick layer of ice, right down to the equator. Dubbed ‘Snowball Earth’, what causes such events is uncertain, but a significant reduction in atmospheric carbon dioxide (possibly as a result of increased silicate weathering in the warm and wet tropics as continents gathered there) or methane (destroyed through oxidisation, as a result of an oxygen influx into the atmosphere from the first oxygen-exhaling life-forms) would do the trick. Both carbon dioxide and methane are potent greenhouse gases; without them the planet cooled and must have teetered close to the edge of an abyss from which it would never recover.

Of course, it did recover. The freezing of the planet brought the carbon-silicate cycle to a halt. Water vapour froze out of the atmosphere, which meant that precipitation ground to a halt. Ice covered the land so there could be no weathering and ice topped the oceans, preventing carbonates from reaching the sea floor. The way out of this predicament for the planet was that there was still an input into the carbon-silicate system, namely carbon dioxide belched out by volcanoes. Gradually the atmosphere accumulated carbon dioxide, with no rain to wash it out. Temperatures rose and the Earth thawed, but the point is that ice planets can very easily happen, particularly if a world lacks plate tectonics to provide that carbon dioxide input that acts as part of a thermal blanket for the world. If there were a ‘slushy’ belt around the equator, which doesn’t quite freeze over, then some life may be able to survive, although it’s hard to imagine what ecology could flourish on a planet like Hoth to permit a food chain with the monstrous yeti-like wampas at the top. Ironically, if methane was the primary greenhouse force in early Earth’s atmosphere, and was destroyed by oxygen, then the discovery of another snowball planet around another star could potentially be a biosignature indicating the presence of oxygen-exhaling life on that world.

Hoth was a world covered in ice. What about planets covered in water, such as Solaris in Stanislaw Lem’s novel of the same name (ignoring the fact that this fictional planet’s global ocean was actually a living entity)? According to the United States Geological Survey seventy percent of Earth’s surface is covered in water and simulations depicting planet formation suggest that planets could easily acquire much more water than Earth did; indeed, Earth is actually quite dry. Perhaps water is delivered to planets by comets and asteroids, or perhaps these water-worlds are born further out, beyond the ‘snow line’ where water-ice is prevalent, before migrating inwards to hotter climes where their ice melts. There’s even observational evidence for water-worlds – in February 2012 Hubble Space Telescope observations of the 6.5 Earth-mass world GJ 1214b, some forty light years distant, show that starlight passing through its atmosphere is being absorbed at the characteristic wavelength of water vapour, enough to contribute a large fraction of the planet’s mass.

All of these worlds – desert, ice and ocean planets – could potentially be habitable to a point; even in Earth’s own snowball periods, life persevered. However their occurrence was before the arrival of complex life and it is doubtful such life would have survived the onset of such a catastrophic change in climate. More to the point, Mars was once wet and warm with a thicker atmosphere, even if it was only for a short while, while still existing outside of the habitable zone. Now it is a barren. On the other hand Earth was once a frozen wilderness despite being in the habitable zone, but is now resplendent with life.

While habitable zones are a starting point, it is clear they are not necessarily the final word on habitability and locating planets within their limits does not guarantee that they are going to be Earth-like, nor does it automatically correspond that planets outside of the habitable zone will be inhospitable. Furthermore, astronomers also suspect that life could exist in such exotic locales as planets in ten hour-orbits around white dwarfs, on tidally locked worlds around red dwarfs, on exomoons orbiting gas giants and even on rogue planets that wander interstellar space, kept warm by their own innate radioactivity. Surely if any of these types of planet are discovered to be habitable it will prove that reality can be far stranger than fiction.

SETI: The Artificial Transit Scenario

Among the many memorable things Freeman Dyson has said in a lifetime of research, one that stands out for me is relatively recent. “Look for what is detectable, not for what is probable.” This was Dyson speaking at a TED conference in Monterey, CA back in 2003, making the point that the universe continually surprises us, and by making too many assumptions about what we are looking for, we may miss unexpected things that can advance our understanding. Dyson has been thinking about this for a long time considering that it was way back in 1960 that he first suggested looking for the excess infrared radiation that might flag a distant Dyson sphere.

I would call this an unorthodox approach to SETI in its day except that when he first came up with it, Dyson didn’t have a SETI effort to consider. It was only in the same year that Cornell’s Frank Drake began SETI observations at Green Bank, and a scant year before that that Philip Morrison and Giuseppe Cocconi published the seminal paper “Searching for Interstellar Communications” in Nature. SETI in 1960 was a nascent field, but it would soon be focused on radio and, later, optical transmissions. Even so, Dyson’s thinking remains viable and unorthodox SETI efforts continue.

Image: Our Milky Way presents a field full of stars. How to search for signs of an extraterrestrial civilization among the countless targets? Looking for a Dyson sphere is unorthodox, but some scientists are suggesting this and other unusual ways of detecting the macro-engineering of distant civilizations. Image credit: NASA.

Luc Arnold (Aix Marseille Université) runs through the scholarship on what we might call ‘non-traditional’ forms of SETI in a new paper, noting that what he calls Dysonian SETI looks for signatures of macro-engineering projects in space. We’ve discussed many of these here before, delving particularly into the papers of Milan Ćirković and Robert Bradbury, but it’s worth recalling that others picked up on Dyson’s ideas earlier, including Carl Sagan and Russell Walker, who concluded as far back as 1966 that Dyson spheres should be detectable but would probably be hard to tell apart from natural objects having the same low temperatures.

In articles like Toward an Interstellar Archaeology, I’ve looked at Richard Carrigan’s searches for macro-engineering, and Luc Arnold reminds me in his new paper that Michael Harris has proposed methods of observing antimatter burning by advanced civilizations. Harris would go on in 2002 to use gamma ray observations in a first attempt to find such a signature. In fact, we can trace non-traditional SETI studies to authors as diverse as Ronald Bracewell, Michael Papagiannis and Robert Freitas, who along with several others Arnold references have followed Dyson’s lead in looking for what is detectable rather than what is probable.

Back to Arnold himself, who proposed in 2005 that transit studies like Kepler and CoRoT should be aware of the possibility of detecting an artificial signal. What the scientist has in mind is a planetary size object that orbits its star, constructed by a civilization as a celestial marker. The idea fits with something Jill Tarter said in 2001: “An advanced technology trying to attract the attention of an emerging technology, such as we are, might do so by producing signals that will be detected within the course of normal astronomical explorations of the cosmos.”

Transmission Methods and the Drake Equation

Arnold’s new paper compares radio wavelengths with laser transmissions and his own idea of artificial transits with respect to the factor L in the celebrated Drake Equation. L is generally considered to refer to the lifetime of a civilization, which obviously limits its ability to transmit a detectable signal. Working out the solid angle over which the transit could be ‘transmitted’ over one year, Arnold arrives at a figure of between 25,000 and 75,000 stars depending on stellar densities, and therefore uses a mean number of targets of 50,000 to set up comparisons between artificial transit ‘messaging’ and the more conventional radio and laser transmission options.

The idea is to examine efficiency as seen from the perspective of a transmitting civilization. A radio transmitter is the best choice for short-term messaging — a brief, highly targeted program of signaling — while lasers would require 102 times more energy. In terms of construction and maintenance, artificial transiting objects are more costly. They become interesting only for extremely long-term thinkers who are using the method to produce attention-getting signals where “…the transmitting time can be very long, possibly much longer than the lifetime on the civilization itself.”

Arnold notes that the shape of a transiting object shows up in the transit light curve, making the detection of an artificial planetary sized object a clear possibility. Weighing the costs and energy required to signal other stars, he concludes that if we make such a detection, it should be interpreted as the message of an old and perhaps defunct civilization. It would demonstrate at least that the lifetime of a technological civilization can be longer than several centuries.

It is also true that large artificial objects may be constructed for purposes other than communication. From the paper:

We may also argue that a civilization wanting to communicate with other beings also may want to leave a trace or an artifact in the galaxy that would survive much longer that the civilization itself. These two civilization behaviours seem not incompatible, but rather naturally linked and complementary, at least from an anthropocentric psychological point of view. But artificial planetary-sized objects may also be built for other technological purposes than communication, like energy gathering for example. Such macro-engineering achievements could be the result of natural technological evolution… making the will or desire of communication only an optional argument.

Arnold’s points are intriguing. SETI by radio and optical methods assumes we are looking for an active civilization. But lasers and radios fall silent when a civilization dies. Meanwhile, large artificial objects that transit their stars could remain indefinitely, markers of a culture that might have flourished billions of years ago and is now gone. The Dysonian approach of looking for macro-engineering thus offers the chance to do the kind of interstellar archaeology Richard Carrigan has championed through his exhaustive efforts. Turning up the signs of an artifact without any presumption of further communication still changes our view of the universe.

Who would construct a vast artificial occulter to send a signal to other stars? Several possibilities come to mind, including the idea that the occulting object might have been constructed for purposes other than being detected by another civilization. It is conceivable, though, that a dying culture would want to leave some trace of its existence. Because we are speculating on the motivations of extraterrestrials, we have no way of knowing. This is why Dyson’s idea of looking for what is detectable continues to resonate. Being surprised by the universe is part of our experience and there is no reason to expect that to change now.

The paper is Arnold, “Transmitting signals over interstellar distances: Three approaches compared in the context of the Drake equation,” accepted for publication in the International Journal of Astrobiology (preprint). Thanks to Antonio Tavani for the pointer to this paper.

Into Europa’s Ocean

Europa continues to fascinate us with the possibility of a global ocean some 100 kilometers deep, a vast body containing two to three times the volume of all the liquid water on Earth. The big question has always been how thick the icy crust over this ocean might be, and we’ve looked closely at Richard Greenberg’s analysis, which shows surface features he believes can only be explained by interactions between the surface and the water, making for a thin crust of ice. See Unmasking Europa: Of Ice and Controversy for more, and ponder the prospects of getting some kind of future probe through a thin ice layer to explore the potentially habitable domain below.

Possible interactions between the surface and the ice are considered in a new paper by Mike Brown (Caltech) and Kevin Hand (JPL), one that makes the case that there are two ways of thinking about Europa. One is to see the Jovian moon purely as an ice shell upon which the bombardment of electrons and ions have created a chemical cycle. The other is to see it as a geologically active world with an internal ocean that affects what happens on the surface.

Just how much, in other words, does the chemistry of the internal ocean affect what we see from our spacecraft and telescopes? Brown and Hand now believe they can identify a chemical exchange between the ocean and the surface that we can analyze to learn more about both.

Using data from the Keck instrument on Mauna Kea, the researchers have used adaptive optics and spectroscopy to go far beyond what the instruments on the Galileo probe were able to tell us about Europa’s surface. Turning up in their results is a magnesium sulfate salt called epsomite. Magnesium could not be found on the surface unless it came from the ocean below, meaning that ocean water does make it through onto the surface, while surface materials get into ocean water. Says Brown:

“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals. That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”

Image: Based on new evidence from Jupiter’s moon Europa, astronomers hypothesize that chloride salts bubble up from the icy moon’s global liquid ocean and reach the frozen surface where they are bombarded with sulfur from volcanoes on Jupiter’s innermost large moon, Io. The new findings propose answers to questions that have been debated since the days of NASA’s Voyager and Galileo missions. This illustration of Europa (foreground), Jupiter (right) and Io (middle) is an artist’s concept. Credit: NASA/JPL.

Because Europa is tidally locked to Jupiter, the same hemisphere always leads in its orbit around the planet, while the other always trails. The difference between the two is striking: While the leading hemisphere has a yellow tint, the trailing hemisphere is streaked with a red material that has been under study for many years. It is believed that volcanic sulfur from Io accumulates on Europa’s trailing hemisphere, existing there along with a substance other than water ice that Galileo could not identify. Keck’s OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS) turned out to be what was needed to map the distribution of water ice and home in on the other material.

It turns out that both hemispheres contain significant amounts of non-water ice, but on the trailing hemisphere Brown and Hand identified the spectral signature of magnesium sulfate. Interestingly, the magnesium sulfate does not itself appear to come from the ocean. Because it only appears on Europa’s trailing side, where Io’s sulfur is accumulating, the researchers surmise there is a magnesium-bearing mineral — probably magnesium chloride — everywhere on the moon that produces magnesium sulfate in the presence of sulfur. The same magnesium chloride might then make up the non-water ice detected on the leading hemisphere.

Europa’s ocean can be rich in sulfate or rich in chlorine, but Brown and Hand rule out a sulfate-rich ocean because magnesium sulfate only appears on the trailing hemisphere. This fits with other work Brown has done on Europa’s atmosphere, which identified atomic sodium and potassium as constituents. The researchers believe that sodium and potassium chlorides consistent with this atmosphere are the dominant salts on the surface of Europa. Their conclusion is that Europa’s is a chlorine-rich ocean with sodium and potassium present as chlorides. By this analysis it closely resembles Earth’s oceans. “If you could go swim down in the ocean of Europa and taste it, it would just taste like normal old salt,” Brown adds.

The paper is Brown and Hand, “Salts and radiation products on the surface of Europa,” in press at the Astrophysical Journal (preprint). More in this Keck Observatory news release.

A Framework for Interstellar Flight

Those of us who are fascinated with interstellar travel would love to see a probe to another star launched within our lifetime. But maybe we’re in the position of would be flyers in the 17th Century. They could see birds wheeling above them and speculate on how humans might create artificial wings, but powered flight was still centuries ahead. Let’s hope that’s not the case with interstellar flight, but in the absence of any way of knowing, let’s continue to attack the foundational problems one by one in hopes of building up the needed technologies.

Marc Millis, who ran NASA’s Breakthrough Propulsion Physics project at the end of the 20th Century, always points out in his talks that picking this or that propulsion technology as the ‘only’ way to get to the stars is grossly premature. In a recent interview with the Australian Broadcasting Corporation’s Antony Funnell, Millis joined physicist and science fiction writer Gregory Benford, Icarus Interstellar president Richard Obousy and astronomer and astrobiologist Ian Crawford in a discussion of the matter. Asked where we stood with nuclear fusion, Millis said this:

At this point it is really too soon to pick any favourites because…well, let me put it to you this way; in three different studies, one done by looking at the amount of energy available, one done by financing and one done by technology, all of them came in that there is still going to be about two centuries before we could do a serious interstellar flight. So even if you pulled off the technology for a fusion rocket, to develop the infrastructure to mine enough helium-3 to fuel it, it’s still going to take a very long time. In other words, you could make the technology but to have the amount of energy to put into it takes even longer than developing the technology.

We had much the same discussion at the 100 Year Starship symposium last year in Houston, where a backer of the project from the business world asked why an interstellar mission would be so expensive. The answer simply comes down to the amount of money it takes to create the energy needed to push a payload to the kind of speeds we’re talking about. Given all that, we continue to study everything from beam-driven sails to antimatter-induced fusion and the whole boatload of possibilities in between, hoping to find more efficient ways to drive the starship.

Image: High-intensity lasers produce particle/antiparticle pairs from the vacuum, in a concept introduced by Richard Obousy. Credit: Adrian Mann.

Timeframes Short and Long

People differ widely on time-frames — some people get positively passionate about them — but my own view is that working toward the interstellar goal is just as valuable for me if it happens three centuries from now than if it happens by 2100. I’m no seer and the few times I’ve tried to predict the future, I’ve been humbled by how surprisingly an ‘obvious’ outcome can change. I’m also reminded of what Richard Obousy often tells his own audiences, that humans tend to overestimate what they can do in the short run and underestimate what they can do over longer periods. So maybe interstellar flight is going to happen sooner than I think. Either way, I’ll keep on writing about the topic in hopes of encouraging research and public involvement.

Whenever interstellar flight comes, assuming it does, we’ll all do better by looking out for our planet in timeframes of centuries rather than years or even decades. Gregory Benford told Funnell that the reason we fall into short-term thinking traps is that we live in a tightly defined environment, one in which the great age of physical exploration on our planet is long past. Moving out into the Solar System and ultimately beyond it in search of resources may once again instill a longer-term view as we seek out elements like helium-3 that fusion reactors will demand.

New human societies should emerge from all that as we move toward the construction of an economy throughout the system. Let me quote Benford on this from the interview, in a section where he’s asked about the 100 Year Starship project and the choice of the time frame. A century may be a symbolic goal, but the act of choosing goals is itself part of the process.:

The expansion of the United States into the West began roughly around 1850 and within a century was accomplished, largely through railroads and use of coal for power. But it went on to new heights, we invented the aeroplane, and a century later we already had intercontinental air flight commonly available. It’s this kind of building upon a model that makes star flight a proper goal for the development of the inter-planetary economy that we believe is coming, and therefore sets a goal; 100 years from now let’s see if we can build a starship, and what does it look like, and is it manned or unmanned or robotic or does it have artificial intelligence aboard? Those are secondary issues. The main thing is let’s have a goal and let’s build toward it.

Thus the method: Create a concrete goal and discover a way to reach it. Benford told Funnell that prosperity grows out of these efforts because the structure is being built every step of the way. I’m also reminded here of the ‘horizon mission methodology’ that NASA has found useful in stimulating thinking in its conferences — John Anderson described this in a 1996 JBIS paper. The idea here is to present a problem that is at present impossible to solve. The team then sets about defining what breakthroughs will be needed if this problem is ever to be conquered.

The Dangers of Presumption

Defining the goal and setting the target is the beginning of the process. This is one reason for the original Project Daedalus, which set out to examine the question of whether an interstellar vessel was even possible. The reasoning was that if a culture at our own level of technological development could identify a conceivable way to reach another star, then future breakthroughs should make the job that much more realistic. No one seriously planned to send a 50,000 ton vehicle to Barnard’s Star, but the project proved, way back in the 1970s, that designs that did not violate known physics could be contemplated. Project Icarus now refines the Daedalus model.

Former astronaut Mae Jemison, who heads up the 100 Year Starship initiative, put the matter this way in her conversation with Funnell:

One of the biggest challenges is, again, to keep people from trying to design every step of the way right now, because we don’t know. And as soon as you start saying ‘I know the answer right now’, then you’re probably going to cut off other avenues. There is something that I would say when you talk about how daunting this is and whether or not people say that it’s not possible. It’s a term that I first heard associated with movies, and that term is ‘suspending disbelief’. At some point in time we have to do move forward by suspending disbelief.

Jemison is not talking about suspending disbelief in known physics, of course. What she’s saying is that setting the goal and collecting the wide range of options is how the process begins, and if we succumb to assumptions — from ‘interstellar flight is impossible’ to ‘there’s only one way to do it, my way’ — then we’re not honoring the need for lengthy and challenging research that’s ahead. Personally, I find this notion invigorating. We are beginning to realize through our exoplanet research that Earth-like planets may be out there in the billions. We now engage scientists and engineers in the great work of studying the options that may one day put a human-made payload into another solar system. Humans themselves may eventually make the journey if we are wise enough to make the foundations of this enterprise deep, strong and true.

Interstellar Ice Grains and Life’s Precursors

One of the first science fiction novels I ever read was The Black Cloud, by astrophysicist Fred Hoyle. I remember that one of my classmates had smuggled it into our grade school and soon we were passing it around covertly instead of reading whatever it was we had been assigned. In Hoyle’s novel, scientists discover that the cloud, which approaches the Solar System and decelerates, may be a life-form with which they can communicate. My young self was utterly absorbed by this book and I suspect it will hold up well to re-reading.

What brings The Black Cloud to mind is recent work using data from the Green Bank Telescope in West Virginia, where scientists have been studying an enormous gas cloud some 25,000 light years from Earth near the center of the Milky Way in the star forming region Sagittarius B2(N). This cloud is not, of course, behaving as entertainingly as Hoyle’s, but it’s offering up information about how interstellar molecules that are intermediate steps toward the final chemical processes that lead to biological molecules can form in space.

Although we’ve found interesting molecules in interstellar gas clouds before, the new work suggests that the chemical formation sequences for these molecules actually occurred on the surface of icy grains in interstellar space. One of the molecules is cyanomethanimine, which scientists believe is part of the process that produces adenine, one of four nucleobases forming the ‘rungs’ in the DNA lattice. The other is ethanamine, thought to play a similar role in the formation of alanine, one of twenty amino acids in the genetic code.

The biological interest is the suggestion that life’s building blocks are widely available, as noted in one of the two papers on this work:

One important goal of the field of astrobiology is the identification of chemical synthesis routes for the production of molecules important in the development of life that are consistent with the chemical inventory and physical conditions on newly formed planets. One mechanism for seeding planets with chemical precursors is delivery by outer solar system bodies, like comets or meteorites… These objects can be chemical reservoirs for the molecules produced in the interstellar medium during star and planet formation. The chemical inventory of these objects includes the molecules that are directly incorporated from the interstellar medium and molecules subsequently formed by chemical processing of the interstellar species…

What we’re after, then, is an understanding of the process by which interstellar molecules can undergo further change relevant to the formation of life. The paper continues:

This subsequent chemical processing can synthesize larger, more complex molecules that are more directly relevant to prebiotic chemistry from the simpler molecules that can be formed in the interstellar medium. The identification of molecules in the interstellar medium is a key step in understanding the chemical evolution from simple molecular species to molecules of biological relevance and radio astronomy has played the dominant role in identifying the chemical inventory of the interstellar medium…

Image (click to enlarge): The Green Bank Telescope and some of the molecules it has discovered. Credit: Bill Saxton, NRAO/AUI/NSF.

The region under study, Sgr B2(N), turns out to be incredibly rich for this kind of work. According to the scientists, about half of the 170 molecules that have been detected in space were first found in this region. The team was able to measure the characteristic radio emission signatures of the rotational states of cosmic chemicals, using radio emission studies of cyanomethanimine and ethanamine and comparing these to the data generated by the Green Bank Telescope. “Finding these molecules in an interstellar gas cloud means that important building blocks for DNA and amino acids can ‘seed’ newly-formed planets with the chemical precursors for life,” says Anthony Remijan, of the National Radio Astronomy Observatory (NRAO).

The papers are Loomis et al., “The Detection of Interstellar Ethanimine (CH3CHNH) from Observations taken during the GBT PRIMOS Survey,” accepted in Astrophysical Journal Letters (preprint) and Zaleski et al., “Detection of E-cyanomethanimine towards Sagittarius B2(N) in the Green Bank Telescope PRIMOS Survey,” also accepted at Astrophysical Journal Letters (preprint). See this NRAO news release for more.

Icarus Interstellar – A Grass Roots Community

One of the pleasures of conferences like the recent Huntsville gathering is the chance to meet up with old friends. Richard Obousy and I had been talking about his offering a review of Icarus Interstellar’s recent work for some time, and Huntsville gave us the chance to firm up the idea. The article below is the result, an examination of the Icarus team’s current structure and planning as they continue with the Project Icarus starship design and look toward other interstellar possibilities. The president and senior scientist for Icarus, Richard is a familiar face on Centauri Dreams. He did his doctoral work at Baylor University, studying the possibility that dark energy could be an artifact of Casimir energy in extra dimensions. He’s now engaged in planning the Icarus conference this summer, about which more shortly.

By Richard Obousy

Having served as President of Icarus Interstellar for 18 months now, I’ve been privileged to be knee deep in the evolving face of this exciting organization. I’ve been promising Paul an article since last September and I’ve realized that much of my procrastination has been founded on not quite knowing how and where to start.

Perhaps the easiest place to begin is to discuss very broadly our organizational structure, and to then talk about some of the elements of that structure to bring clarity to our activities. Icarus Interstellar is a 501(c)(3) US tax exempt non-profit organization with a mission statement to launch an interstellar probe by 2100. While this is certainly a bold objective, especially considering the arguably slow pace of current space exploration activities, I believe it’s important that we set our objectives high. Setting a date gives us something tangible and measurable to aim for, and we’re ever aware that the clock is ticking.

Icarus Interstellar is organized around four Committees, which serve as ‘bins’, for lack of a more endearing term, for certain projects and programs. In my mind, the nucleus of the organization is the Research Committee, which houses several exciting projects which I’ll summarize briefly here.

Project Icarus, Fusion Starship Engineering Study

Project Icarus is an engineering challenge and designer capability exercise to design an unmanned fusion based, interstellar starship capable of exploring a star system within 15 light-years. The total mission duration is limited to a maximum of 100 years from launch. This study started in September 2009 and is being conducted by an international team of volunteer physicists, engineers, and other suitably qualified people.

Research areas are divided into modules encompassing all of the spacecraft systems and problem scope, ranging from Astronomical Target, Primary Propulsion, Power Systems, Science, Communications, Computing, Vehicle Risk and Repair, Technological Maturity and Design Certification. The project is structured into a number of phases and follows a goal directed pathway outlined in the Project Icarus Project Program Document.

Project Icarus has a rotating Project Leader (PL), with the first PL being Kelvin Long, the Project’s Founder. Next, I served as PL, followed by Dr. Andreas Tziolas , Pat Galea and currently Rob Swinney. Project Icarus is responsible for approximately 2/3 of the organization’s 33 peer reviewed papers.

Some fascinating work is coming out of Project Icarus, and we’re pleased to be working with a team at Rutgers university, led by Dr. Haym Benaroya, who are performing thermal and vibration modeling (and ultimately experimentation) of the Daedalus reaction chamber, to help provide insights for Project Icarus. In addition, we have a team at the University of Huntsville, Alabama, who have access to powerful codes and are performing simulations of magnetic nozzles. Milos Stanic recently presented his, and partner Richard Hatcher’s, work at the International Astronomical Congress last year.

Project Forward, Beamed Propulsion Starship Study

Project Forward, led by Dr. Jim Benford, is a parallel study performed by members of Icarus Interstellar and affiliated organizations with expertise in the field of beamed propulsion. The study involves:

1) Analyzing past concepts to see if they are off-optimal, in terms of the recent cost-optimized model, so can be improved. Then quantify such improved sail system concepts.

2) Exploring properties of materials that are being used for solar sails or have been suggested for beam-powered sails to determine their practicality. In particular, studying their properties in several domains of EM (microwave, millimeter wave, laser) to find out what accelerations they are limited to due to heating in the beam.

3) Quantifying an alternate use of sails-deceleration of sail probes from a fusion-powered starship as it approaches stellar systems.

Project Hyperion, Human Interstellar Flight Study

Most studies of interstellar craft focus on vessels that are unmanned. This is because the task of starship construction is considered sufficiently challenging without the additional complexity of creating an environment where humans could survive for decades or even centuries.

Project Hyperion, led by Andreas Hein, tackles this specific challenge head on is performing a preliminary study that defines concepts for a crewed interstellar starship. Major areas of study include propulsion, environmental control, life support, social studies related to crewed multi-decadal/multi-century missions, habitat studies, communications, psychology of deep spaceflight, mission objectives, and the ethics of sending humans to the stars.

Like with all complex system developments, a major challenge is to merge the results from the domain-specific sub studies into a coherent system design. This is being accomplished by using up-to-date systems engineering approaches like concurrent engineering and model-based systems engineering.

Project Persephone, Living Architectures for Worldships

Project Persephone, led by TED Fellow Dr. Rachel Armstrong is considering the application of living technologies such a protocells and programmable smart chemistries, in the context of habitable starship architecture that can respond and evolve according to the needs of its inhabitants.

This project has direct relevance to the challenges of the 21-century where our megacities & urban environments will grow at astonishing rates. Yet the building industry, utilities and energy companies necessarily lag behind the physical demands of a growing city and where inflexible infrastructures become inadequate or inappropriate then urban decay sets in with crime, homelessness, waste & resource management issues, traffic congestion etc. A habitable long duration starship will need evolvable environments that not only use resources efficiently but can respond quickly to the needs of populations and bypass the current necessary time lags that are implicit in the current system – in identifying critical upgrades and then activating industrial supply and procurement chains – which are already playing catch-up by the time they are realized.

Project Bifrost. Emerging Nuclear Space Technologies Project

The Icarus NST Program led by Tabitha Smith has the long-term goals of tangible NST deliverables such as (1) The creation of RTGs, (2) Creation of Nuclear Engines (Thermal and/or Electric) and (3) Partnership with the US Government for Pulsed Nuclear Propulsion use for Starship.

The Helius Experiment, Experimental Starship Systems Research

The Helius Experiment, led by Rob Swinney, has the objective of conducting small scale experimental research on systems integral to the development of interstellar spacecraft. Some specific objectives are to develop engineering designs and small scale pulsed propulsion prototypes, optical systems used in beamed propulsion, radiators and other heat rejection methods simulating the rejection of megawatt power systems to be used for interstellar travel.

Project Tin Tin, Interstellar NanoSat Research and Development

Tin Tin, led by Dr. Andreas Tziolas, is conducting design, research and experimental studies relating to the use of nanosats for interstellar exploration, including modular interstellar systems testing. Project Tin Tin is a collaborative effort between the Kickstart program, Team Phoenicia, The British Interplanetary Society and Icarus Interstellar.

Small satellite technologies developed in response to the NASA Centennial Challenge and Google Lunar X-Prize have sent space mission research teams around the world back to the drawing board. One of the conclusions of a tangent study was the viability of an interstellar nanosat mission, which is currently under design as Icarus Interstellar’s first interstellar mission.

The TinTin baseline will consist of KickSat, CubeSat frames modified to include cameras (IR/spectrometer), a deep space science (dust, gas analyzer, magnetometer, etc) and deep space communication package.

X-Physics Propulsion & Power Project (XP4)

XP4, led by myself, is a group organized to explore deep future propulsion and energy generation concepts including, but not limited to, the manipulation of spacetime (warp drive/wormhole metrics) and the exploration of the quantum vacuum as a possible energy source.

Longshot II, Student Research Project

Longshot II, led by students Divya Shankar and Tiffany Frierson is a revisit of the 1987 Project Longshot unmanned interstellar probe mission conducted by NASA sponsored summer graduate students. Our Icarus Interstellar student designers are currently revisiting the project, correcting mistakes, incorporating omissions and updating the technology to the current state of the art.

Broader Activities

These ten project form the core of Icarus Interstellar. As a 100% volunteer organization we rely on the initiative and dedication of unpaid members so the productivity of the group typically rises and falls in relation to how busy people’s ‘days jobs’ are keeping them. With that said, I’ve been thrilled with the progress that each of these projects is making and amazed at just how much measurable work comes from a relatively small core of dedicated enthusiasts.

Another key committee within the organization is the Public Outreach Committee, which covers anything and everything relating to how Icarus Interstellar interacts with the world at large. This includes the development of our website with ongoing help from Student Designer Tiffany Frierson and Director Robert Freeland, the growth of our public blog, the creation of articles specifically written for high traffic media outlets – we’ve had a long and positive relationship with Discovery Space News for a number of years now for example. We’ve also dabbled in “interstellar art” and I’ve been working with a local Texas based artist in the creation of pieces specifically intended to be inspirational, with a strong interstellar theme.

The Public Outreach Committee is also responsible for the creation of video interviews with team members. These have been conducted by Hailey Bright and Sheila Kanani, who both conduct 5-15 minute interviews, quizzing team members as to their research and their role within the organization. I feel that these are important as they help to put a face to the names and allow people who are interested in our activities a glimpse at those of us involved directly in the programs.

I personally feel strongly about Icarus Interstellar placing strong emphasis on outreach. I taught physics for nearly seven years while working on my PhD, then at a local community college for a year after I finished graduate school. While I was often amazed at how bright some of my students were, I was also stunned at the general ignorance regarding the typical student’s understanding of our place in the universe, and a lack of awareness of how advanced we are (or not) technologically in the context of interstellar flight. The impression I received is that many students consider spaceflight routine and easy, when in fact it is far from it. I also found the distinction between science fiction and science fact blurred, in all too many students’ minds. Thus, I believe it important that we articulate the vision that many of us share relating to humanities exploration of the stars, and that we reliably convey the vast and undeniable challenges associated with this sort of endeavor.

Image: An artist’s conception of a possible Icarus design. Credit: Adrian Mann.

Another active area for Icarus Interstellar is the Fund Development Committee, led by Director Bill Cress. This committee explores ways in which we can generate funds to help the organization grow. Sadly, the field of interstellar flight is not the most resource rich of communities, so we are left to our own devices to figure out how to actually generate money. This is important for a range of things, starting at simple administrative matters like website hosting and basic accounting extending up to reimbursing team members for representing Icarus Interstellar at conferences. While the volunteer work from our team members is astounding, I’m not convinced that a 100% volunteer effort is sustainable for long periods. I’m also not convinced that relying on governments, or philanthropic organizations to generate resources for this endeavor is reliable, so I believe that it’s important nurture an entrepreneurial spirit in Icarus Interstellar.

One example of a recent program that has proved successful is the Icarus Interstellar pioneered by Director Robert Freeland. In this program, US based individuals can sign up for a special credit card with starship designs on the front of the card created by the interstellar art luminary Adrian Mann. Icarus Interstellar receives a 1-2% cash donation from Capital One Bank on everything spent on these cards, so given enough people that sign up for this program, a small but constant revenue stream is generated for the organization. I personally signed up for one of these cards the day the program went live, and make all my day to day purchases on it, paying it off in full at the end of the month. This is one of many examples where our community can embrace entrepreneurship to help move us forward to our common goal.

Lastly, we have the Educational Committee chaired by Vice President Andreas Tziolas. This committee focuses on all aspects relating to educating the next generation of starship engineers. Andreas has also been working on his “Starflight Academy” concept, detailing a series of technical courses that could be taught at university level. The hope is that if we can either launch this ourselves — or through a university as an affiliated program — then we can help garner interest in the field of ‘Interstellar Research” as a tangible subject that can be studied at an advanced level. Andreas’s ideas can be read about in the latest issue of JBIS (Vol 65, No 9/10) with his paper titled “Starflight Academy: Education in Interstellar Engineering”.

Icarus Interstellar is still a young organization, not quite two years old (though our flagship Project Icarus is two years older). In this short time we’ve gathered a lot of momentum, and are garnering interest from all corners of the globe. I frequently receive emails from people interested in getting involved with our efforts. I think that the biggest challenge we face over the coming months, and beyond, is to figure out how to best organize and direct the efforts of volunteers who wish to contribute. I’ve spent a lot of time figuring out how to task people with non-traditional backgrounds in a way that’s valuable both to them, and to the interstellar community. While there’s plenty of work to be done on the science and the engineering front, I think it’s important we learn how to welcome the interests of people who come from more varied backgrounds.

For example, some months ago I started working with a bright chap named Steve Summerford. Steve comes from an Urban Planning background, something you wouldn’t typically associated with starship engineering. However, I thought that there would be fantastic potential tasking Steve with work relating to designing interstellar colonies, and exploring facets of planning Worldships – huge and slow moving interstellar vessels designed to take many generations to reach their target. After just a few months work, Steve came up with a wonderful paper titled “Colonized Interstellar Vessel: Conceptual Master Planning“, with publication accepted for JBIS. He also adapted this paper into a popular science article called “What Would an Interstellar ‘Worldship’ Look Like?” which was published on Discovery Space News. The research proposes a new type of worldship design, which adds to the current worldship portfolio of the O’Neill cylinder, the Bernal Sphere, and the Stanford Torus. This type of research demonstrates that non-traditional “interstellar disciplines” – in this case Urban Planning, has much of substance to offer the community.

Another case of working with non-traditional disciplines is the example of Josh Reiger, a young man in his early 20s from San Antonio Texas. Joshua is a construction worker, with a strong passion for interstellar research and astronomy. While most may have simply ignored his email, or found an excuse not to engage with him, I felt that there had to be something that someone with a lot of passion could direct their efforts. After several back and forth emails I decided to get Joshua working on a wiki-style ‘how to’ guide for amateur astronomers interested in learning how to detect signatures of exoplanets. While this is no easy task, there is no reason why a well organized global team of volunteers cannot pool their resources and participate in this fascinating venture. Josh’s work is “in progress” however he’s already created for the Icarus blog a fairly extensive first pass which can be read on the article “Exoplanet Detection and the Amateur Astronomer“.

While I think it’s important to emphasize that most of the work performed by the Icarus Interstellar team to date does follow a typical physics/engineering theme, as can be seen from our publications page, I think these last two examples showcase my own personal ambition to find a way to galvanize as large a cross section of the planet as possible to help us move toward becoming an interstellar species. And, while we’re some way off, I believe that everyone can play a role, no matter how big or small. It’s just up to people like you and I, who read Centauri Dreams, to figure out creative ways to engage with the rest of the world.

This article is really just a glimpse at our multifaceted organization. I’m tempted to write more, but am cognizant of just how long this article is getting. Please drop me an email at info@icarusinterstellar.org if you’re interested in helping Icarus Interstellar in some way, shape, or form or would just like to learn more about us.

Mars Flyby: Daring to Venture

Existential risks, as discussed here yesterday, seem to be all around us, from the dangers of large impactors to technologies running out of control and super-volcanoes that can cripple our civilization. We humans tend to defer thinking on large-scale risks while tightly focusing on personal risk. Even the recent events near Chelyabinsk, while highlighting the potential danger of falling objects, also produced a lot of fatalistic commentary, on the lines of ‘if it’s going to happen, there’s nothing we can do about it.’ Some media outlets did better than others with this.

Risk to individuals is understandably more vivid. When Apollo 8 left Earth orbit for the Moon in 1968, the sense of danger was palpable. After all, these astronauts were leaving an orbital regime that we were beginning to understand and were, by the hour, widening the distance between themselves and our planet. But even Apollo 8 operated within a sequenced framework of events. Through Mercury to Gemini and Apollo, we were building technologies one step at a time that all led to a common goal. No one denied the dangers faced by every crew that eventually went to the Moon, but technologies were being tested and refined as the missions continued.

Inspiration Mars is proposing something that on balance feels different. As described in yesterday’s news conference (see Millionaire plans to send couple to Mars in 2018. Is that realistic? for more), the mission would be a flyby, using a free return trajectory rather than braking into Martian orbit. The trip would last 501 days and would be undertaken by a man and a woman, probably a middle-aged married couple. Jonathan Clark, formerly of NASA and now chief medical officer for Inspiration Mars, addresses the question of risk head-on: “The real issue here is understanding the risk in an informed capacity – the crew would understand that, the team supporting them would understand that.” Multi-millionaire Dennis Tito, a one-time space tourist who heads up Inspiration Mars, says the mission will launch in 2018.

Image: A manned Mars flyby may just be doable. But is the 2018 date pushing us too hard? Image credit: NASA/JPL.

We’ll hear still more about all this when the results of a mission-feasibility study are presented next weekend at the 2013 IEEE Aerospace Conference in Montana. Given the questions raised by pushing a schedule this tightly, there will be much to consider. Do we have time to create a reliable spacecraft that can offer not only 600 cubic feet of living space but another 600 for cargo, presumably a SpaceX Dragon capsule mated to a Bigelow inflatable module? Are we ready to expose a crew to interplanetary radiation hazards without further experience with the needed shielding strategies? And what of the heat shield and its ability to protect the crew during high-speed re-entry at velocities in the range of 50,000 kilometers per hour?

For that matter, what about Falcon Heavy, the launch vehicle discussed in the feasibility analysis Inspiration Mars has produced for the conference? This is a rocket that has yet to fly.

No, this doesn’t feel much like Apollo 8. It really feels closer to the early days of aviation, when attention converged on crossing the Atlantic non-stop and pilots like Rene Fonck, Richard Byrd, Charles Nungesser and Charles Lindbergh queued up for the attempt. As with Inspiration Mars, these were privately funded attempts, in this case designed to win the Orteig Prize ($25,000), though for the pilots involved it was the accomplishment more than the paycheck that mattered. Given the problems of engine reliability at the time, it took a breakthrough technology — the Wright J-5C Whirlwind engine — to get Lindbergh and subsequent flights across.

Inspiration Mars is looking to sell media rights and sponsorships as part of the fund-raising package for the upcoming mission, which is already being heavily backed by Tito. I’m wondering if there is a breakthrough technology equivalent to the J-5C to help this mission along, because everything I read about it makes it appear suicidal. The 2018 date is forced by a favorable alignment between Mars and the Earth that will not recur until 2031, so the haste is understandable. The idea is just the kind of daring, improbable stunt that fires the imagination and forces sudden changes in perspective, and of course I wish it well. But count me a serious skeptic on the question of whether this mission will be ready to fly on the appointed date.

And if it’s not? I like the realism in the concluding remarks of the feasibility study:

A manned Mars free-return mission is a useful precursor mission to other planned Mars missions. It will develop and demonstrate many critical technologies and capabilities needed for manned Mars orbit and landing missions. The technology and other capabilities needed for this mission are needed for any future manned Mars missions. Investments in pursuing this development now would not be wasted even if this mission were to miss its launch date.

Exactly so, and there would be much development in the interim. The study goes on:

Although the next opportunity after this mission wouldn’t be for about another 13 years, any subsequent manned Mars mission would benefit from the ECLSS [Environmental Control and Life Support System], TPS [Thermal Protection System], and other preparation done for this mission. In fact, often by developing technology early lessons are learned that can reduce overall program costs. Working on this mission will also be a means to train the skilled workforce needed for the future manned Mars missions.

These are all good reasons for proceeding, leaving the 2018 date as a high-risk, long-shot option. While Inspiration Mars talks to potential partners in the aerospace industry and moves ahead with an eye on adapting near-Earth technologies for the mission, a whiff of the old space race is in the air. “If we don’t fly in 2018, the next low-hanging fruit is in ’31. We’d better have our crew trained to recognize other flags,” Tito is saying. “They’re going to be out there.”

In 1968, faced with a deadline within the decade, NASA had to make a decision on risk that was monumental — Dennis Tito reminded us at the news conference that Apollo 8 came only a year after the first test launch of the Saturn 5. Can 2018 become as tangible a deadline as 1970 was for a nation obsessed with a Moon landing before that year? If so, the technologies just might be ready, and someone is going to have to make a white-knuckle decision about the lives of two astronauts. If Inspiration Mars can get us to that point, that decision won’t come easy, but whoever makes it may want to keep the words of Seneca in mind: “It is not because things are difficult that we dare not venture. It is because we dare not venture that they are difficult.”

Bostrom: From Extinction to Transcendence

At the top of my list of people I’d someday like to have a long conversation with is Nick Bostrom, a philosopher and director of Oxford’s Future of Humanity Institute. As Centauri Dreams readers will likely know, Bostrom has been thinking about the issue of human extinction for a long time, his ideas playing interestingly against questions not only about our own past but about our future possibilities if we can leave the Solar System. And as Ross Andersen demonstrates in Omens, a superb feature on Bostrom’s ideas in Aeon Magazine, this is one philosopher whose notions may make even the most optimistic futurist think twice.

I suppose there is such a thing as a ‘philosophical mind.’ How else to explain someone who, at the age of 16, runs across an anthology of 19th Century German philosophy and finds himself utterly at home in the world of Schopenhauer and Nietzsche? Not one but three undergraduate degrees at the University of Gothenburg in Sweden followed. Now Bostrom applies his philosophical background, along with training in mathematics, to questions that are literally larger than life. As Andersen reminds us, ninety-nine percent of all species that have lived on our planet are now extinct, including more than five tool-using hominids. Extinctions paved the way for the emergence of new species, but for the species du jour, survival is the imperative.

Image: Philosopher Nick Bostrom at a 2006 summit at Stanford University. Credit: Wikimedia Commons.

Colonizing Waves or Individual Explorers?

You’ll want to read Andersen’s essay in its entirety (helpfully, there’s a Kindle download link) to see how Bostrom sizes up existential risks like asteroid impacts and supervolcanoes. One of the latter, the Toba super-eruption about 70,000 years ago, seems to have pumped enough ash into the atmosphere to destroy the food chain of our distant ancestors, leaving a scant few thousand alive to move into and populate the rest of the planet. We do seem to be a resilient species. Bostrom likes the long view, which means he sees a 100,000 year hiatus as humans bounce back from a possible future catastrophe as little more than a pause in cosmic time. That perspective has interesting consequences, as Andersen notes:

It might not take that long. The history of our species demonstrates that small groups of humans can multiply rapidly, spreading over enormous volumes of territory in quick, colonising spasms. There is research suggesting that both the Polynesian archipelago and the New World — each a forbidding frontier in its own way — were settled by less than 100 human beings.

This is a point worth remembering as we contemplate the possibility of interstellar flight. We sometimes think of enormous colonies of humans moving to nearby stars, but early human settlements may be the result of tiny groups who, for reasons we can only guess at, decide to cross these fantastic distances. Maybe rather than a planned program of expansion, our species will see sudden departures of groups heading out for adventure or ideology, small bands who leave the problems of Earth behind and create entirely new societies outside of any central planning or control. Meanwhile, the great bulk of humans choose to stay at home.

Andersen’s essay is so rich that I will, for today at least, pass over his discussions with Bostrom about artificial intelligence and the dangers it represents — you should read this in its entirety. Let’s focus in on the Fermi paradox and why Bostrom hopes that the Curiosity rover finds no signs of life on Mars. For the consensus at Bostrom’s Future of Humanity Institute, shared by several of the thinkers there, is that the Milky Way could be colonized in a million years or less, leading to the question of why we don’t see this happening.

Filters Past and Future

Are we looking at an omen of the human future? Robin Hanson, another familiar name to Centauri Dreams readers, works with Bostrom at the Institute. He tells Andersen that there appears to be some kind of filter that keeps civilizations from developing to the point where they build starships and fill the galaxy. The filter would exist somewhere between inert matter and cosmic transcendence, and thus could be somewhere in our past or in our future.

In other words, what if we have somehow survived a filter that keeps life from developing on most planets? Or perhaps it’s a filter that acts to screen out intelligent life-forms, and we have somehow made our way through it. If the ‘great filter’ is in our past, then we can hope to expand into a cosmos that may be largely devoid of intelligent life. If it is in our future, then we can’t predict what it will be, but the ominous silence of the stars bodes ill for our survival.

But let Andersen tell it, in one of his conversations with Bostrom:

That’s why Bostrom hopes the Curiosity rover fails. ‘Any discovery of life that didn’t originate on Earth makes it less likely the great filter is in our past, and more likely it’s in our future,’ he told me. If life is a cosmic fluke, then we’ve already beaten the odds, and our future is undetermined — the galaxy is there for the taking. If we discover that life arises everywhere, we lose a prime suspect in our hunt for the great filter. The more advanced life we find, the worse the implications. If Curiosity spots a vertebrate fossil embedded in Martian rock, it would mean that a Cambrian explosion occurred twice in the same solar system. It would give us reason to suspect that nature is very good at knitting atoms into complex animal life, but very bad at nurturing star-hopping civilisations. It would make it less likely that humans have already slipped through the trap whose jaws keep our skies lifeless. It would be an omen.

This essay will take up half an hour of your day, but I suspect that, like me, you’ll go back and read it again, reflecting on its themes for days to come. Are there questions of philosophy that are more urgent than others? Ponder a moral issue that is much in play at the Future of Humanity Institute, the idea that existential threats to our species may outweigh our obligations to serve those who are suffering today. “The casualties of human extinction,” Andersen writes, “ would include not only the corpses of the final generation, but also all of our potential descendants, a number that could reach into the trillions.”

In my view, that’s an argument for, among other things, a robust space program going forward, one that is capable of securing our planet from impact threats and establishing off-world colonies that would survive any other forms of planetary catastrophe, from runaway artificial intelligence to the weaponization of microbes. It’s also an argument for taking the kind of long-term perspective so lacking in modern culture, the case for which has never been made more clearly than in this elegant and illuminating essay.

Life Around Dying Stars

Where is the best place to look for life? At first glance, a red dwarf would seem to be the ideal choice because a transiting terrestrial-class world in the habitable zone of a red dwarf is going to block a larger part of the star’s light than a similarly sized world orbiting a larger star. Red dwarfs pose their own problems for life, including the possibility of tidal lock and severe flares, but in terms of detectability, they seem made to order for planet hunters with transit methods in mind.

But white dwarfs turn out to be interesting targets in their own right, and in at least one significant way may offer even more advantages. So says a new paper by Avi Loeb (Harvard-Smithsonian Center for Astrophysics) and Don Maoz (Tel Aviv University), who point out that a habitable planet orbiting a white dwarf would have to be close to its star indeed, perhaps as close as 1.5 million kilometers. As with a red dwarf, a transit here will block a large fraction of the star’s light — astronomers speak of a large ‘transit depth’ — and should therefore be readily detectable.

But there is more to the story. Loeb and Maoz are interested in not just detecting such a world but studying its atmosphere. We’ve already been able to examine the atmosphere of the gas giant HD 209458 using Hubble data, so the method is known to work. Astronomers make spectroscopic observations of the unobstructed light of the star and compare these to measurements of the star during a planetary transit. It’s tricky work, and getting it down to the scale of smaller planets will require future instruments like the James Webb Space Telescope.

JWST, in fact, should be able to make atmospheric measurements down to planets of just a few Earth masses in the habitable zone of red dwarfs, but the paper points out how many hours of total exposure time will be necessary and how many conditions will need to be right for this to happen. But Loeb and Maoz argue that the signature of water vapor and perhaps oxygen will be detectable by the Webb instrument in just a few hours if found on a planet around a white dwarf. The researchers simulated a JWST observation of an Earth-like planet’s transit across such a star and found that the atmospheric ‘transmission signal’ is much more detectable than around any main-sequence stars, with oxygen in particular being a feasible catch for the JWST.

Image: A new study finds that we could detect oxygen in the atmosphere of a habitable planet orbiting a white dwarf (as shown in this artist’s illustration) much more easily than for an Earth-like planet orbiting a Sun-like star. Here the ghostly blue ring is a planetary nebula – hydrogen gas the star ejected as it evolved from a red giant to a white dwarf. Credit: David A. Aguilar (CfA).

But can planets form around white dwarfs, which are, after all, the remnants of red giants? Recent work has shown that stars like these can have long-lasting habitable zones, and studies of the photospheric metals in these stars have led to estimates that between 15 and 30 percent could host planets. A small planet within a few AU of its star would not survive the red giant phase, so we are talking about planets that migrated in from a much wider orbit after the white dwarf had formed. And even assuming such, we still have issues of water loss:

Barnes & Heller (2012) and Nordhaus & Spiegel (2012) have emphasized that the tidal heating of the planet, until it had achieved full circularization and synchronization, would lead to full loss of any water and volatiles present. We note, however, that the young Earth was also a hot and dry place, but volatiles and water were then delivered to it by a barrage of comets. The comet impact rate then decreased to its present low level, greatly lowering the biological damage of such impacts. It is not implausible that such post-formation volatile delivery also could take place on an earth-like planet in a WD’s habitable zone, perhaps driven by the same scattering process that drove the planet itself to migrate inward after the formation of the WD.

All this leaves us with the question of finding white dwarfs with transits to study. The authors call for sampling some 500 white dwarfs within approximately 40 parsecs, a study that should be feasible with the European Space Agency’s Gaia observatory, scheduled for launch later this year. These targets would then be monitored with small telescopes in search of transits. “Earth-mass planets in the habitable zones of WDs,” write the authors, “may offer the best prospects for detecting bio-signatures within the coming decade.”

The paper is Loeb and Maoz, “Detecting bio-markers in habitable-zone earths transiting white dwarfs,” accepted for publication in Monthly Notices of the Royal Astronomical Society (preprint).

Looking Back from Deep Space

It’s reasonable to call the two Voyager spacecraft our first interstellar probes, in the sense that they are approaching the heliopause and are still transmitting data. Long before controllers shut them down — which should occur somewhere in the 2020s — Voyager 1 will have left the Solar System and we’ll have data on what happens when the solar wind gives way to the stellar winds from beyond. A case could be made for the Pioneer craft as interstellar probes as well, but while Pioneer 10 has reached a distance of 107 AU, the Pioneers are no longer transmitting data. Voyager 1 is now 123.45 AU out, for a round-trip light time of 34 hours, 15 minutes.

But does leaving the Solar System mean we’ve truly entered interstellar space? An entertaining piece called Postcards from the edge, published in early February by The Economist, notes that much depends on how we define ‘interstellar.’ Gravity, says its author, defines the universe at the largest scales, and if we’re talking about gravity, Voyager is still deeply in the grip of the Sun. In fact, Voyager 1 would have to travel another 14,000 years to reach the roughly 50,000 AU distance where the Sun’s gravity would cease to be a factor.

Image: Voyager 1’s cameras were turned back on in early 1990 to take pictures of our Solar System. The spacecraft took some 60 pictures of the Sun and 6 of the planets; the 60 frames were combined to make the mosaic seen above. The six individual shots were taken when Voyager 1 was more than 4 billion miles from Earth. Earth appears framed in brightness due to the amount of light scattered while taking the picture with Earth so close to the Sun. Credit: NASA/Caltech.

Over the weekend I’ve enjoyed playing around with deep space scenarios and thinking about what the sky might look like from Voyager 1. When I was growing up, some accounts I read of the outer Solar System implied that the Sun would be nothing more than another star from a place like Pluto. That turns out to be incorrect, as Phil Plait pointed out in a 2012 post. Working with Pluto’s average distance from the Sun — 39 AU — Plait found that the Sun would still be 250 times brighter on Pluto than the full Moon appears on Earth. Factor in the eccentricity of Pluto’s orbit and the actual numbers move from 150 to 450 times as bright as the full Moon.

So let’s ask this: How far would our Voyagers have to be from the Earth before the Sun began to look like just another star? It turns out we’d have to go a long way. From 400 AU, a distance at which we’re definitely in the local interstellar medium, the Sun still shows an apparent magnitude of -13.7, which makes it the brightest star in the sky (Sirius comes in at -1.46). This information comes from Mike Gruntman (USC), who worked it out in a paper studying what kind of instrumentation we’d like to have aboard a probe expressly designed for interstellar space.

The Sun obviously still dominates Voyager 1’s sky. According to Gruntman’s figures, a probe would have to reach a distance of 100,000 AU — 1.61 light years — before the Sun would finally be perceived as just another bright star. In these terms, the Voyagers are close to home indeed, but work continues on longer-range spacecraft. The ‘pale blue dot’ image showing our Earth as just an inconsequential blob of light is justly famous. Maybe the next perspective changer will be a glimpse of our system from beyond the heliosphere. From the paper:

As our first interstellar spacecraft leaves the solar system, a ‘‘look back’’ would provide us with an unusual view of our home stellar system, a view from the outside. A view back will provide a unique opportunity for a global study of the heliosphere, a vast essentially 3-D region governed by the sun. This view back would also be a glimpse of what a truly interstellar mission of the distant future would encounter in approaching a target star. A combination of obtaining images from two vantage points, one from the outside of a stellar system and one from inside, would allow the characterization of an astrosphere.

In Centauri Skies

Thinking about the brightness of the Sun in Voyager’s sky brings up the question of how other stars look from space. But first, how bright would the Sun be if it were seen from the distance of Alpha Centauri? We have to distinguish between apparent magnitude (as seen by an observer on Earth) and absolute magnitude, which measures intrinsic brightness. The Sun’s apparent magnitude in our sky is -26.8. And we learn thanks to the good folks at Cornell University that seen at Alpha Centauri distance, the Sun’s apparent magnitude becomes +0.34. By contrast, Centauri A’s apparent magnitude in our sky is -0.01; Centauri B’s is 1.33.

And in case you’re wondering, from a planet orbiting Centauri B at 1 AU, the apparent magnitude of Centauri A ranges from -21.9 to -19.4, changing as Centauri A and B orbit around each other. During this 80-year period their separation varies from 11 to 35 AU. Jean-Louis Trudel (University of Ottawa) and Edward Guinan (Villanova University) worked the apparent magnitude figures out for science fiction writer Robert Sawyer, as presented here. From a planet orbiting Centauri A at 1 AU, the apparent magnitude of Centauri B ranges from -18.1 to -20.6.

We’ve learned that descriptions of the Sun as ‘just another star’ from distances of mere hundreds of AUs aren’t correct. Maybe the ‘just another star’ idea fits better in our neighboring stellar system, for Proxima Centauri would be anything but prominent in the night skies of Centauri A and B. Astronomers there would surely notice it sooner or later, because Proxima’s proper motion would tell them it was close. But this M5-class red dwarf would be a nondescript 5th magnitude star otherwise. From Earth, with an apparent magnitude of 11, Proxima is visible only in telescopes.

The paper by Mike Gruntman that I reference above is, “Instrumentation for Interstellar Exploration,” Advances in Space Research 34 (2004), pp. 204-212 (available online).