by Paul Gilster | Jan 24, 2012 | Astrobiology and SETI |
Yesterday’s post looked at SETI and its assumptions, using the lens of a new paper on how the discipline might be enlarged. The paper’s authors, Robert Bradbury, Milan ?irkovi? and George Dvorsky, are not looking to supplant older SETI methods, but rather to broaden their scope by bringing into play what we are learning about astrobiology and artificial intelligence. It is perilous, obviously, to speculate on how an alien civilization might behave, yet to some extent we’re forced to do it in choosing SETI targets, and that being the case, why not add into the mix methods that go beyond our current radio and optical searches, methods that may have a better chance of success?
The Engima of Contact
A key to extending SETI’s reach is to question the very idea of contact. One assumption many of SETI’s pioneers had in common was that there was an inherent need to communicate with other species, and that this need would take the form of intentional radio beacons or optical messages. What Bradbury, ?irkovi? and Dvorsky are calling ‘Dysonian SETI’ makes no such assumption, and actually gains strength from the fact that it does not. Acknowledging that we have not yet found an undisputed detection signature, Dysonian SETI says that intention is not necessary. A civilization may be detectable through its artifacts. A Dyson sphere, for example, should show an infrared signature that is distinguishable from the normal spectra of stars.
Once in place, a Dyson shell should be durable enough to potentially outlive its creators, ‘Ingrafted in eternal monuments/Of Glory,’ to cite the verses from Lucretius the authors use to illustrate their point. Thus we get around a significant problem noted by many SETI writers — the ‘window of opportunity’ for radio SETI is short, a mere flicker in the span of our own civilization, much less the span of our planet’s existence. Even if you posit a stunningly optimistic figure of 106 technologically advanced civilizations in the galaxy, it is clear that these cultures will exist at different levels of development. What are the odds that two will be at precisely that stage of technical evolution to enable back and forth radio communications?
Image: NGC 6744, a spiral galaxy some 30 million light-years away in the southern constellation of Pavo (The Peacock), as captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope. If tens of thousands of civilizations co-exist in such a galaxy, how many will be close enough to each other in terms of technological development to make radio or optical contact likely? Credit: ESO.
Dysonian SETI would surmount this problem because enormous astro-engineering projects could exist as archaeological survivals no matter what the fate of their parent civilization. The idea seems plausible and does not foreclose the ongoing SETI effort in radio and optical wavelengths. But the authors point out that our assumptions about artifacts themselves also need to be adjusted. If civilizations move toward a ‘singularity’ in which artificial intelligence leads to a kind of postbiological evolution, then searching for Dyson spheres takes a twist.
Why? Because so far we have assumed a Dyson shell roughly the size of Earth’s orbit, one with a working temperature that would sustain our kind of biological life on the surface of the shell. These parameters hardly fit the needs of postbiological intelligence. From the paper:
…from a postbiological perspective, this looks to be quite wasteful, since computers operating at room temperature (or somewhat lower) are limited by a higher kT ln 2 Brillouin limit, compared to those in contact with heat reservoir on lower temperature T…
I think what the authors are referring to above is also called the Landauer limit, which defines the minimum amount of energy needed to alter one bit of information — here k is the Boltzmann constant while T is the temperature of the circuit (K) and ln 2 is the natural log of 2. In any case, cooler is better. The paper continues:
Although it is not realistic to expect that efficiency can be increased by cooling to the cosmological limit of 3 K in the realistic model of the Galaxy, still it is considerable difference in practical observational terms whether one expects a Dyson shell to be close to a blackbody at 50 K, as contrasted to a blackbody at 300 K. This lowering of the external shell temperature is also in agreement with the study of Badescu and Cathcart… on the efficiency of extracting work from the stellar radiation energy. In this sense, the Dysonian approach needs to be even more radical than the published intuitions of Dyson himself.
Beyond the Dyson Shell
Widening the theoretical background of ongoing searches (the authors point to SETI@Home as one example of widely distributed processing) means taking such new perspectives into consideration, and the paper goes on to flag other possible signatures of an extraterrestrial civilization:
- Unusual chemical signatures in stellar spectra, which could indicate a technological culture trying to be noticed by distant astronomers
- Gamma-ray signatures created by antimatter burning in the activities of an extraterrestrial civilization
- Recognizable transits of large artificial objects
- Analysis of extragalactic astronomical data, which could reveal the presence of large-scale structures and Kardashev Type III astro-engineering
Interestingly enough, all of the above have been the subject of initial studies, and the bibliography of the paper (see yesterday’s citation) is laden with these and other references. These investigations have been regarded as little more than curiosities, but the impact of the discovery of clearly artificial objects would have such a quickening effect on human self-awareness that they are clearly worth the limited funds thus far spent on them.
Widening the Search Space
A Dysonian SETI would evolve along the lines suggested by Freeman Dyson himself when discussing the supposed willingness of alien civilizations to communicate with each other, and their implied benevolence when it comes to greeting new members to the ‘galactic club.’ Dyson would have none of it, saying “…I do not wish to presume any spirit of benevolence or community of interest among alien societies.” Why indeed do so, when a search for Dysonian artifacts like Dyson shells would make no such assumptions, while allowing us to bring to bear what we are learning about nanotechnology, artificial intelligence and astrobiology?
Why not widen the search space, then, adding to the already impressive and groundbreaking work of SETI’s pioneers by bringing into play recent findings like those of Charles Lineweaver, whose work shows that Earth-like planets in the habitable zone of the galaxy (itself a relatively new concept) are on average 1.8 billion years older than our planet? Assume civilizations not just millions but potentially a billion or more years older than our own and you play down the importance of contact (it is hard to imagine the advantages of such to the alien culture) but leave open the prospect of discovering the works they have built and possibly left behind.
Let me close with another quote from this vigorous paper re SETI old and new:
…the two approaches are at present compatible and should be pursued in parallel at least until there is better theoretical insight into the preconditions for emergence of technological civilizations in the Galaxy. The ability to extract information from the interstellar environment increases dramatically with each passing year. As the resolution of the data increases, so does the ability to process and infer its nature. This process will deeply challenge conceptions of the Universe and what we think we know about it. It will also challenge the way in which we see ourselves and our potential as an intelligent civilization.
by Paul Gilster | Jan 23, 2012 | Astrobiology and SETI |
Have you ever given any thought to intergalactic SETI? On the face of it, the idea seems absurd — we have been doing SETI in one form or another since the days of Project Ozma and without result. If we can’t pick up radio signals from nearby stars that tell us of extraterrestrial civilizations, how could we expect to do so at distances like M31’s 2.573 million light years, not to mention even the closest galaxies beyond? Herein lies a tale, for what intergalactic SETI exposes us to is the baldness of our assumptions about the overall SETI attempt, that it is most likely to succeed using radio wavelengths, and that it may open up two-way communications with extraterrestrials. It’s the nature of these assumptions that we need to explore today.
The Visibility of a Galactic Culture
Let’s suppose, for example, that Nikolai Kardashev’s thoughts about types of civilizations are compelling enough to put to the test. A Kardashev Type III civilization is one that is able to exploit the energy resources not just of its home star but of its entire galaxy. So unimaginably beyond our present capabilities is a Kardashev Type III that we scarcely know how to describe it, but it is within the realm of reason that signs of astro-engineering on this scale might be detectable in at least nearby galaxies if such a civilization had gone to work on them. And indeed, James Annis has made such a study, concluding that neither our Milky Way nor M31 or M33, our two large, neighboring galaxies, has been transformed by the work of a Type III civilization.
Image: M33, the Triangulum Galaxy. We’ve only begun to investigate whether nearby galaxies like this one might show signs of astro-engineering on a gigantic scale. Civilizations a billion years or more older than our own might be capable of feats detectable from great distance. Credit: Adam Block/NOAO/AURA/NSF.
It should hardly be necessary to point out how preliminary such results are, and how rare such studies have been. What’s striking about Annis (and related work by Richard Carrigan and P.S. Wesson) is that these scientists are pursuing ideas that are well outside the SETI mainstream. There is a new paradigm here, one that operates without any notion of ‘contact’ and subsequent exchange of ideas between civilizations. It is a search for artifacts, for artificial structure and signs of engineering. It is all about discovery. And just as we can have no two-way conversation with Mycenaean Greece as we dig for information about the era of Agammemnon, we may with this stellar archaeology discover something just as unreachable but likewise well worth the study.
Toward a Dysonian SETI
In a recent paper, Robert Bradbury, Milan ?irkovi? (Astronomical Observatory, Belgrade) and George Dvorsky (Institute for Ethics and Emerging Technologies) consider whether intergalactic SETI may be an example of what they call a ‘Dysonian’ approach to SETI, one that is a ‘middle ground’ between the traditional radio-centric view (with contact implications) and the hostile reaction of SETI detractors who see no value in the enterprise whatsoever and think the money better spent elsewhere. The nod to Freeman Dyson is based on the latter’s conjecture that a truly developed society would surmount the limits of planetary living space and energy by building a Dyson shell, capturing most or all of the energy from the star near which it lived.
A Dyson sphere immediately changes the terms of SETI because it is in principle detectable, but unlike nearby radio signals (either from a beacon or as unintentional ‘leakage’ from a civilization’s activities), a Dyson shell might be spotted at great astronomical distances through its infrared signature. Carl Sagan was one of the first to pick up on the idea and ponder its implications. Dyson was much in favor of attacking the question in a disciplined way, using our astronomical tools, as he once wrote, “…to transpose the dreams of a frustrated engineer into a framework of respectable astronomy.” And here again, we have seen attempts, especially by the aforementioned Richard Carrigan, to study infrared data for signs of such Dyson constructs.
The new direction in SETI that the three authors of the new paper champion is one that employs a broader set of tools. Rather than limiting itself to radio dishes or dedicated optical facilities, it broadens our workspace for extraterrestrial civilizations to include astronomical data that can be gathered in tandem with other research projects, scanning a far wider and deeper field. In the authors’ view, Dysonian SETI also takes into account new developments in astrobiology and even extends into computer science and the possibility of post-biological intelligence. They advocate a Dysonian SETI drawing on four basic strategies to supplement older methods:
- The search for technological products, artifacts, and signatures of advanced technological civilizations.
- The study of postbiological and artificially super-intelligent evolutionary trajectories, as well as other relevant fields of future studies.
- The expansion of admissible SETI target spectrum.
- The achievement of tighter interdisciplinary contact with related astrobiological subfields (studies of Galactic habitability, biogenesis, etc.) as well as related magisteria (computer science, artificial life, evolutionary biology, philosophy of mind, etc.)
The expansion of SETI into these areas would not replace ongoing SETI methods but would significantly expand the overall process in line with the great goal of learning whether other intelligent beings share the galaxy and the nearby universe with us. The paper offers more fruitful speculation than I can fit into a single entry, so we’ll be looking at these ideas over the course of the next few days. If there really is a Great Silence, to use David Brin’s phrase, these authors argue it’s one that we can only ponder usefully if we broaden our search toward the potentially observable achievements of cultures far more advanced than our own. That study has only recently begun.
The paper is Bradbury, ?irkovi? and Dvorsky, “Dysonian Approach to SETI: A Fruitful Middle Ground?” JBIS Vol. 64 (2011), pp. 156-165.
by Paul Gilster | Jan 20, 2012 | Asteroid and Comet Deflection |
The Dawn spacecraft, orbiting Vesta since July of last year, reached its lowest altitude orbit in December, now averaging 210 kilometers from the asteroid’s surface. Ceres is Dawn’s next stop, but that journey won’t begin until the close-in work at Vesta is complete, with the craft in its low altitude mapping orbit for at least ten weeks and then another period at higher altitudes before Dawn leaves Vesta in late July. The spacecraft’s Gamma Ray and Neutron Detector (GRaND) instrument is already telling us much about the giant asteroid’s surface composition.
In fact, the five weeks of mapping at low-altitude have provided the first look at global-scale variations on Vesta. GRaND measures the abundance of elements found in planetary surfaces, and while its investigations are still in the early stages of analysis, it’s clear that Vesta’s surface varies widely as opposed to the mostly uniform composition of smaller asteroids. We know that Vesta developed a core, mantle and crust, making it something closer to a planet than an asteroid. We’ll learn a great deal more as the low-altitude mapping continues and new results arrive.
Meanwhile, have a look at this close-in Dawn image, showing a crater with smaller craters on its edge, with rough textures in the crater wall (far right) that may indicate underlying bedrock. The image shows an area in the Rheasilvia basin in the south polar region, obtained with Dawn’s framing camera on December 18, 2011 — the distance to the surface here is 272 kilometers.
Image: An area in Vesta’s south polar region, centered around 58.3 south latitude and 283.7 degrees east longitude. Acquired during the LAMO (Low Altitude Mapping Orbit) phase of the mission, the image has a resolution of about 25 meters per pixel. Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA.
Ion Propulsion’s Slow Push
Let’s keep an eye not just on Dawn’s science results but on the performance of its thrusters as we continue to shake out ion propulsion and tweak its capabilities with missions to the outer system. The spacecraft’s thrusters apply more than 1000 volts to accelerate charged particles (ions) that are expelled out the back at speeds up to 40 kilometers/second. Xenon is used in these thrusters because it is a relatively massive atom, offering higher thrust than other possible propellants. Even so, the acceleration is tiny, underlining the fact that ion propulsion is effective not just in its efficiency but also in its cumulative acceleration over long periods.
As the Dawn team reminds us, the force of an ion thruster on the spacecraft is comparable to the weight of a single sheet of paper. But their enormous fuel efficiency means that the thrusters can continue this tiny push not just for days but for years, allowing the effects to build. Dawn chief engineer Marc Rayman has fittingly called ion thrusting ‘acceleration with patience.’ In a 2006 report on the mission, Rayman summarized the advantages of this kind of propulsion:
All else being equal, for the same amount of propellant, a spacecraft equipped with ion propulsion can achieve 10 times the speed of a craft outfitted with normal propulsion, or a spacecraft with ion propulsion can carry far less propellant to accomplish the same job as a spacecraft using more standard propulsion. This translates into a capability for NASA to undertake extremely ambitious missions such as Dawn.
The rate at which xenon is flowed through the thruster is very low. At the highest throttle level, the system uses only about 3.25 milligrams/second, so 24 hours of continuous thrusting would expend only 10 ounces of xenon. Because the xenon is used so frugally, the corresponding thrust is very gentle. The main engine on some interplanetary spacecraft may provide about 10,000 times greater thrust but, of course, such systems are so fuel-hungry that their ultimate speed is more limited.
Dawn uses a solar array to power up the ion propulsion system. At maximum throttle, Rayman notes, the acceleration is equivalent to about 7 meters/second/day, so a full day of thrusting can change the spacecraft’s speed by something like 24 kilometers per hour. By mission”s end, the spacecraft will have accumulated over five years of total thrust time, with an effective change in speed of 11 kilometers per second. Slow but steady gets you to your target, and Dawn’s mission planners have noted that using conventional chemical propulsion, the extra mass would have put the mission well beyond budget, yet another plus for frugal ion technologies.
by Paul Gilster | Jan 19, 2012 | Deep Sky Astronomy & Telescopes |
Imagine what we could do if we could attain speeds of 640 kilometers per second. That’s the velocity of a comet recently tracked just before passing across the face of the Sun and apparently disintegrating in the low solar corona. I’m just musing here, but it’s always fun to muse about such things. 640 kilometers per second drops the Alpha Centauri trip from 74,600 years-plus (Voyager-class speeds) to less than 2000 years. A long journey, to be sure, but moving in the right direction, and in any case, these are speeds that would allow exploration deep into the outer system. We’re a long way from such capabilities, but they’re a rational goal.
But back to the comet. The object was discovered on July 4, 2011 and designated C/2011 N3 (SOHO), the latter a reference to the ESA/NASA Solar and Heliospheric Observatory, whose Large Angle and Spectrometric Coronagraph made the catch. On July 6, NASA’s Solar Dynamics Observatory was able to pick up the comet some 0.2 solar radii off the Sun, where it was tracked for a mere 20 minutes before evaporating some 100,000 kilometers above the solar surface. The Extreme-Ultraviolet Imager aboard one of NASA’s Solar-Terrestrial Relations Observatories (STEREO) was also able to observe the comet, allowing researchers to get a good read on its makeup, as the lead author of the paper on this work, Karel Schrijver (Lockheed Martin Solar and Astrophysics Laboratory), points out:
“This unprecedented passage of a comet through the solar atmosphere in view of our AIA cameras [the Atmospheric Imaging Assembly aboard the SDO] presented us with a remarkable opportunity. As we witnessed this comet evaporate as it traversed a known amount of space over a specific period of time, we were able to work backward to estimate its mass just before it reached the Sun. We’ve been able to bracket its size as between 150 and 300 feet long, with a greater likelihood that it lies at the upper end of that range. And it most likely weighed in at as much as 70,000 tons, giving it about the weight of an aircraft carrier, when it first became visible to AIA.”
Image: Although it’s not C/2011 N3, this Sungrazer was also destroyed, its fiery fate recorded by the SOHO spacecraft’s Large Angle Spectrometric Coronagraph (LASCO) on December 23, 1996. LASCO uses an occulting disk, partially visible at the lower right, to block out the otherwise overwhelming solar disk allowing it to image the inner 5 million miles of the relatively faint corona. The comet is seen as its coma enters the bright equatorial solar wind region (oriented vertically). Spots and blemishes on the image are background stars and camera streaks caused by charged particles. Credit: LASCO, SOHO Consortium, NRL, ESA, NASA.
In addition to the image above, images of the ‘string of pearls’ comet Shoemaker-Levy 9 breaking apart before impact with Jupiter in 1994 inevitably come to mind, especially when we learn that C/2011 N3 likewise broke into a series of large chunks ranging up to 45 meters in size as it began to disintegrate. The comet’s coma — the envelope of ice, dust and gas surrounding its nucleus — is thought to have been some 1300 kilometers across, with a cometary tail approximately 16,000 kilometers long. The breakup of the comet was further flagged by pulsations in the brightness of the tail, a phenomenon Schrijver’s team was able to put to good use:
“I think the light pulses in the tail were one of the most interesting things we witnessed,” said Schrijver. “The comet’s tail gets brighter by as much as four times every minute or two. The comet seems first to put a lot of material into that tail, then less, and then the pattern repeats. Only because of these pulses can we measure how fast the tail falls behind the comet as its gases collide with those in the Sun’s atmosphere. And that, in turn, helps us measure the comet’s weight.”
A cometary demise is a spectacular event, but it turns out that the SOHO spacecraft has observed more than 2000 comets as they approached the Sun. The so-called Kreutz Sungrazers are comets whose orbits take them within one to two solar radii of the photosphere every 500 to 1000 years. This is the largest known group of comets, one which is thought to have resulted from the breakup of a massive progenitor body several thousand years ago. The smaller Kreutz group comets rarely survive perihelion. While the SOHO observatory now tracking a Sun-grazing comet on an average of once every three days, those that make it into the solar corona should be useful tools for extending our knowledge of cometary properties.
The paper is Schrijver et al., “Destruction of Sun-Grazing Comet C/2011 N3 (SOHO) Within the Low Solar Corona,” Science Vol. 335 no. 6066 pp. 324-328 (20 January 2012). Abstract available.
by Paul Gilster | Jan 18, 2012 | Advanced Rocketry |
NASA’s Innovative Advanced Concepts program has issued a second call for proposals, following the selection of its first round of Phase I concepts in 2011. NIAC (formerly the NASA Institute for Advanced Concepts) ran from 1998 to 2007 in the capable hands of Robert Cassanova, who is now external council chair for the new organization. After a four year interregnum, the program returned in 2011 with the goal of funding “early studies of visionary, long term concepts – aerospace architectures, systems, or missions (not focused technologies).” The 2011 effort resulted in funding for 30 advanced technology proposals, each of them receiving $100,000 for one year of study.
The new call for proposals continues the NIAC theme of looking for ideas that are both innovative and visionary, while remaining at an early stage of development, considered as being ten years or more from actual use on a mission. Approximately fifteen proposals are likely to win funding in the 2012 selection, with short proposals of no more than two pages in length accepted until February 9. Authors of the concepts that make the first cut will then be notified to submit a full proposal due on April 16. According to the NASA news release, the solicitation is “open to all U.S. citizens and researchers working in the United States, including NASA civil servants.”
I remember paging through reports and presentations from the first NIAC when working on my Centauri Dreams book — those reports are still available online and make for a compelling set of ideas, from antimatter collection strategies to micro-scale laser sails for deep space exploration. The new NIAC’s Phase I studies are equally provocative, and you might want to look through NIAC head Jay Falker’s presentation at the 2011 meeting to see not only an overview of the program but a set of posters explaining each of the Phase I studies chosen.
James Gilland (Ohio Aerospace Institute), for example, looks at ambient plasma wave propulsion, noting that an environment of magnetic fields and plasmas is associated not only with many planets but the Sun itself. Because plasmas with magnetic fields can support a variety of waves that can transmit energy and/or pressure, Gilland sees an opening for propulsion. Quoting the precis:
This? concept? simply? uses ?an? on?board? power? supply and? antenna? on? a? vehicle? that? operates ?in ?the? existing? plasma.? The? spacecraft ?beams? plasma? waves? in? one? direction? with? the? antenna,? to? generate? momentum? that? could? propel? the? vehicle ?in ?the? other? direction,? without? using? any? propellant? on ?the? space?ship. ?Such? a? system? could? maneuver? in ?the? plasma? environment? for? as ?long? as ?its? power? supply ?lasts,? without? refueling.? One? particular ?wave? to? consider ?is? the? Alfven? wave,? which? propagates ?in? magnetized? plasmas? and? has? been? observed? occurring ?naturally ?in? space.
Steven Howe (Universities Space Research Association), who devised the ingenious ‘antimatter sail’ concept that was analyzed in Phase I and II studies for the first NIAC, considers production methods for Pu-238, thus keeping Radioisotope Thermoelectric Generators (RTGs) in the game at a time when Pu-238 supplies are scarce. John Slough (MSNW LLC) looks at ‘a small scale, low cost path to fusion-based propulsion’ by using propellant to compress and heat a magnetized plasma to fusion conditions. Grover Swartzlander (Rochester Institute of Technology) explores so-called ‘optical lift’ and its potential to enhance solar sail missions.
Image: John Slough’s Phase I study, a ‘small scale, low cost path’ to fusion?based propulsion. It is accomplished by employing the propellant to compress and heat a magnetized plasma to fusion conditions, and thereby channel the fusion energy released into heating only the propellant. Passage of the hot propellant through a magnetic nozzle rapidly converts this thermal energy into both directed (propulsive) energy and electrical energy. Credit: John Slough/NIAC.
I won’t go through all of these Phase I ideas here, as they’re available in Falker’s excellent presentation, and you can also see some of them discussed in Enabling the future: NASA call for exploration revolution via NIAC concepts, an article on the NASASpaceflight.com site. NASA’s 2012 solicitation page for NIAC is here. Ahead for NIAC is the 2012 Spring Symposium, planned for March 27-29 at the Westin Hotel in Pasadena, CA, where current NIAC fellows will give presentations about their Phase I research. Public attendance at the meeting is encouraged.
