by Paul Gilster | Apr 16, 2013 | Astrobiology and SETI |
Dyson spheres — technology wrapped around an entire star to maximize energy use — would be unimaginably big. But the idea of maximizing the light from a central star certainly makes sense. Imagine a sphere with a radius at the distance of Earth’s orbit. Now you’ve got a surface area more than 100 million times what’s available on our planet, a sensational venue for science fiction if nothing else. And you’re certainly changing the energy equation — our total power consumption today is the equivalent of about 0.01 percent of the sunlight falling on Earth, according to a new article in New Scientist. Keep energy demand growing at 1 percent per year and in a single millennium we’ll need more energy than strikes the surface of the planet.
Moving power generation into space is certainly something that would motivate a civilization a good deal more advanced than our own, and using abundant asteroid material, it could spread power generation entirely around the star. Stephen Battersby, who wrote Alien Megaprojects: The Hunt Has Begun, doubts they would create a single shell because it would be gravitationally unstable. But a Dyson ‘swarm’ is more plausible, with hordes of large power stations moving on independent orbits around the star. Dyson, who likes to talk about what is observable rather than what’s probable, thinks we could spot such a project through its waste heat in the infrared.
This wouldn’t be an easy catch because there are astronomical configurations — a young star in an envelope of gas and dust, for example — that radiate in the infrared in much the same way. But this, says Battersby, can be resolved:
…the infrared spectrum of these objects should be a giveaway. Silicate minerals in dust produce a distinctive broad peak in the spectrum, and molecules in a warm gas would produce bright or dark spectral lines at specific wavelengths. By contrast, waste heat from a sphere should have a smooth, featureless thermal spectrum. “We would be hoping that the spectrum looks boring,” says Matt Povich at the California State Polytechnic University in Pomona. “The more boring the better.”
Image: A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Since the Infrared Astronomical Satellite mission of 1983, we have added greatly to our databases of infrared objects. Will new searches help us locate a source with a clearly artificial signature? Image credit: NASA/JPL-Caltech/UCLA.
And that brings us to Vyacheslav Ivanovich Slysh, a Russian radio astronomer known for the so-called ‘Slysh formula,’ which helps determine the size of sources of synchrotron radiation, an important contribution to the study of active galactic nuclei. Known as well for his work on maser emission in star-forming regions, Slysh turned his attention in 1985 to a survey of infrared data in the hunt for Dyson objects, whether spheres or swarms. Battersby mentions Slysh only in passing, but the Russian work on what I usually refer to as ‘interstellar archaeology’ in these pages is quite interesting. In 2000, Slysh’s work was followed by M. Y. Timofeev, collaborating with Nikolai Kardashev, both efforts using data from the Infrared Astronomical Satellite.
Centauri Dreams readers will know to associate the search for extraterrestrial artifacts with Richard Carrigan, a scientist emeritus in the Accelerator Division at the Fermi National Accelerator Laboratory whose most recent search dates from 2009. Here’s what Carrigan says about the Slysh and Timofeev efforts in his Dyson Sphere Search History. Here he has just referred to a search by Jun Jugaku and Shiro Nishimura, looking for ‘partial’ Dyson spheres:
Slysh and Timofeev at al. have used the IRAS database for a different approach. Slysh investigates the flux at the maximum of a Dyson Sphere spectrum. He estimates that all Dyson Spheres with temperatures from 50 to 400 ºK within 1 kpc of the sun should have been detected. The Timofeev search looked at a population of IRAS sources in the 110-120 and 280-290?ºK temperature range as established by Kardashev and others and did Planck blackbody fits to the four IRAS bands. They fitted by minimizing to a Planck distribution. (Note that no Planck spectrum correction is made on the four measured fluxes from the filters.) Slysh identified one possible Dyson Sphere candidate, G357.3-1.3. The Timofeev at al. search identified 10 or so candidates but ruled out most of them, often on the basis of associations.
That figure of 1 kiloparsec (kpc) from the Sun identified with Slysh is chosen for a reason. In 1966, Carl Sagan and Russell Walker published a paper in The Astrophysical Journal on “The Infrared Detectability of Dyson Civilizations.” Their analysis showed that a search out to 1000 parsecs should be possible even with the technology of the day, but noted the problem of confusing a possible Dyson signature with natural phenomena. Carrigan’s 2009 search also used the IRAS data of 250,000 infrared sources (it covers 96 percent of the sky), looking for both full and partial Dyson spheres in the blackbody temperature region from 100 K to 600 K. Carrigan’s limits don’t go out as far. He says that IRAS’ Low Resolution Spectrometer was sensitive enough to find Dyson spheres out to 300 parsecs. That would encompass roughly a million solar-type stars.
Image: Richard Carrigan, who told New Scientist for its recent article: “I wanted to get into the mode of the British Museum, to go and look for artifacts.”
I’ve mentioned enough papers to begin a small bibliography, which I’ll list here, but go to Carrigan’s site for other references. I bring all this up for two reasons. First, new searches for extraterrestrial artifacts are in the works, about which more tomorrow. The other reason is that this work isn’t highly visible, but the change it represents from more conventional radio and optical SETI methods is profound. The change speaks not so much to the failure of earlier SETI to produce a result as to our growing understanding that civilizations substantially more advanced than our own — if they exist — could work with engineering on mind-boggling scales. Such engineering should be detectable, and we’ll look at new efforts to find it tomorrow.
The Slysh paper is “A Search in the Infrared to Microwave for Astroengineering Activity,” in The Search for Extraterrestrial Life: Recent Developments, M. D. Papagiannis (Editor), Reidel Pub. Co., Boston, Massachusetts, 1985, p. 315. Timofeev and Kardashev wrote “A Search of the IRAS Database for Evidence of Dyson Spheres,” Acta Astronautica 46 (2000), p. 655. The Sagan and Walker paper is “The Infrared Delectability of Dyson Civilizations,” Astrophysical Journal 144 (3), (1966), p. 1216. And Richard Carrigan’s 2009 study is “The IRAS-based Whole-Sky Upper Limit on Dyson Spheres,” Astrophysical Journal 698 (2009), pp. 2075-2086, available online.
by Paul Gilster | Apr 15, 2013 | Outer Solar System |
Last week’s post about the chemistry of Europa’s ocean is nicely complemented by new work on the moon’s interior by Brad Dalton (JPL) and colleagues. Like JPL’s Kevin Hand, who has been looking at the role of hydrogen peroxide in possible subsurface life there, Dalton is in the hunt for ways to learn more about the composition of Europa’s ocean. Both scientists have been using data from the Galileo mission, refining its results to produce new insights.
Usefully, the surface chemistry on Europa is affected by the charged particles continually striking the tiny world. That allows us to get a read on which parts of Europa would be the best targets for future spacecraft missions, for Dalton’s work helps us find the places where charged particles have had the smallest impact. It’s there — on parts of the leading hemisphere in Europa’s orbit — that material from within the ocean is most likely to be found in pristine condition, with the least chemical processing by incoming charged electrons and ions.
Here’s the mechanism: Europa keeps the same side toward Jupiter as it moves around the planet in its orbit. At the same time, Jupiter’s magnetic field is tugging ions of sulfur and oxygen from Io along the same path, as well as charged energetic particles that move much faster than Europa’s 3.6-day orbit. What happens is that the trailing hemisphere of Europa winds up with more sulfuric acid, apparently the result of sulfur ions bombarding the surface. Dalton’s team takes those earlier Galileo observations further by looking at five different parts of the surface.
Image: This graphic of Jupiter’s moon Europa maps a relationship between the amount of energy deposited onto the moon from charged-particle bombardment and the chemical contents of ice deposits on the surface in five areas of the moon (labeled A through E). Energetic ions and electrons tied to Jupiter’s powerful magnetic field smack into Europa as the field sweeps around Jupiter. The magnetic field travels around Jupiter even faster than Europa orbits the planet. Most of the energetic particles hitting Europa strike the moon’s “trailing hemisphere,” the half facing away from the direction Europa travels in its orbit. The “leading hemisphere,” facing in the direction of travel, receives fewer of the charged particles. Credit: NASA/JPL-Caltech/Univ. of Ariz./JHUAPL/Univ. of Colo.
Hydrated sulfuric acid and hydrated sulfate salts can be distinguished from water ice by the spectra gathered by Galileo’s Near-Infrared Mapping Spectrometer. Dalton and team are looking at the reflected light from frozen material on the surface, and comparing what they see with their models of what the particle bombardment from Jupiter and Io should produce. It turns out that sulfuric acid varies from undetectable levels near the center of the leading hemisphere to more than half of the surface materials near the center of the trailing hemisphere. The amount of electrons and sulfur ions hitting the surface shows a close correlation with this result.
So whatever chemical compounds may originally have erupted from the interior onto the surface, they’re most likely to be found unchanged on the leading edge. Says Dalton:
“The darkest material, on the trailing hemisphere, is probably the result of externally-driven chemical processing, with little of the original oceanic material intact. While investigating the products of surface chemistry driven by charged particles is still interesting from a scientific standpoint, there is a strong push within the community to characterize the contents of the ocean and determine whether it could support life. These kinds of places just might be the windows that allow us to do that.”
Europa is going to be a tough environment to work in given its high radiation environment. But work in it we must, because although oceans are also possible on Ganymede and Callisto, it’s Europa that seems to have thinnest crust, making it more likely that oceanic materials are preserved in frozen form on the surface there. To continue the investigation of Europan landing sites for future probes, another recent paper by Edward Sittler (University of Maryland) and team on plasma ion measurements near Europa makes that case that we need a 3-D model of the interactions between moon and magnetosphere to develop a global view of the electric and magnetic fields and the associated plasma environment our probes will have to work in.
The paper is Dalton et al., “Exogenic controls on sulfuric acid hydrate production at the surface of Europa,” Planetary and Space Science, Volume 77 (March 2013), pp. 45-63 (abstract). The Sittler paper is “Plasma Ion Composition Measurements for Europa,” available online at Planetary and Space Science 13 March 2013 (abstract).
by Paul Gilster | Apr 12, 2013 | Culture and Society |
No stranger to these pages, Richard Obousy is president and senior scientist for Icarus Interstellar, which among other things is engaged in the ambitious redesign of Project Daedalus. But the organization has more on its plate than a fusion-powered starship. From worldships to lightsails, Icarus Interstellar is probing the possibilities both near-term and far, all of which will be discussed at an upcoming gathering of the interstellar community that Richard now describes.
by Richard Obousy
Starship Congress is the interstellar summit that Icarus Interstellar is hosting this summer in Dallas, August 15-18. As an event, Starship Congress will play host and give voice to a wide variety of interstellar organizations and distinguished proponents from the interstellar community. Registration for Starship Congress is now open on Icarus Interstellar’s website. A call-for-papers has been made with selected presenter’s papers to be published in a special Starship Congress-dedicated issue of the Journal of the British Interplanetary Society.
The event is split into three days, with each day advancing progressively in terms of its focus on the future of science and technology.
Day 1—Interstellar Now
Day 1 will examine what we can do today and for the next twenty years. The aim is getting the interstellar community to think about critical building blocks needing to be addressed in the near term in order to establish the correct social, economic and technological conditions leading to the building and launch of a starship before the end of the century.
Day 2—Interstellar This Lifetime
DAY 2 will be focused on semi-realistic targets for what we may see accomplished from 20-to-50 years from now. Likely areas of discussion will be technologies that are presently considered to be at low-technology readiness level (TRL). On the propulsion side of things this will include fusion and antimatter rockets. There will also be discussions on the human exploration and colonization of our own solar system as a plausible next-step on way to becoming an interstellar civilization.
Day 3—Interstellar Future
DAY 3 will be focused on topics that are deemed speculative by today’s standards. Warp drives, wormholes, the extraction of energy from the quantum vacuum, are examples of the kinds of talks and discussions that are planned. In addition, papers and presentations are anticipated on ‘mega-engineering’ projects such as space elevators and terraforming. The consideration of social aspects of long distance space exploration will be talked about. (For example, how do closed communities evolve in space, and how do we ensure the protection of minorities on such a mission while limiting religious extremism?) Similarly, another interesting topic can be the degree of autonomy an interstellar crew have from the population that funded their mission.
Speaking for myself, as president of Icarus Interstellar I’m deeply cognizant of the relatively low interest there is globally in putting money into space exploration, and therefore the questionable assertion that we’ll be ‘going interstellar’ anytime soon. As an example, the annual budget of the US Department of Defense is about equal to the sum total of money NASA has ever spent since its inception in 1958. However, I’m also mindful of the unpredictable effects of disruptive technologies and the profound social and technological advancements humanity has seen in the last century. So Icarus will stick to its ambition of launching an expansive campaign of interstellar exploration and colonization to commence by the end of the century.
Idealistic? Undoubtedly. Possible? Yes.
by Paul Gilster | Apr 11, 2013 | Exoplanetary Science |
We’ve looked at a couple of exoplanet issues this week that bear further comment. The first is that different detection methods can be usefully combined to cover different scenarios. If radial velocity works best with larger planets closer to their star, direct imaging takes us deep into the outer planetary system. We saw yesterday how both imaging and radial velocity could be used to probe subgiant stars. We routinely use RV as a check on transiting planet candidates. And gravitational microlensing can find planets at a wide range of separation from their primary.
I think microlensing has plenty to teach us, though I’m sensitive to the criticism voiced in comments here that we’re dealing with non-repeating events when we have a microlensing detection. Centauri Dreams reader coolstar has also noted that distance may be a factor, questioning whether some of the resources by way of telescope hardware that we’re putting into microlensing studies wouldn’t be better employed looking at nearby worlds. After all, a new paper by Timothy Morton and Jonathan Swift makes the case that small planets around M-dwarfs are even more plentiful than recent studies reported here have shown. Maybe we should be putting more of an effort into finding these through transit studies?
If different detection methods each have their uses, radically different classes of telescope can likewise probe for planets. John Johnson (Caltech) heads up Project Minerva, a telescope array dedicated to Earth-like planets around nearby stars. The plan is to use small-aperture robotic telescopes atop Palomar Mountain to perform photometry and high-resolution spectroscopy, making it, according to Caltech’s site on the project, “the first U.S. observatory dedicated to exoplanetary science capable of both precise radial velocimetry and transit studies.” Following an initial design review, the project has now seen delivery of the enclosure for its telescopes.
Image: Minerva’s hardware. Minerva will be an array of small-aperture robotic telescopes to be built atop Palomar Mountain outfitted for both photometry and high-resolution spectroscopy. It will be the first U.S. observatory dedicated to exoplanetary science capable of both precise radial velocimetry and transit studies. The multi-telescope concept will be implemented to either observe separate targets or a single target with a larger effective aperture. The flexibility of the observatory will maximize scientific potential and also provide ample opportunities for education and public outreach. The design and implementation of MINERVA will be carried out by postdoctoral and student researchers at Caltech. Credit: Caltech/John Johnson.
TESS, the Transiting Exoplanet Survey Satellite, stands as a logical follow-on to the Kepler mission because it takes the hunt to nearby stars even as Kepler’s candidate totals push on toward 3000. But as we wait for new instruments to come online, including the upcoming James Webb Space Telescope and ground-based systems like the European Extremely Large Telescope, it’s great to see grad students like Johnson’s Exolab crew coming up with solutions like Minerva. It’s an inexpensive effort that could gain real traction, and as Johnson told one reporter, “If we lived in an ideal world, we wouldn’t do Minerva because we’d have money from our funding agencies.” But then, who ever said it was an ideal world?
Minerva had a poster devoted to it at the most recent meeting of the American Astronomical Society. The plan is to use an array of four instruments, each with a 0.7-meter mirror, that will over a period of three years scan stars within about 75 light years of the Earth. To get a look at it, see Unblinking Baby Telescopes Will Hunt Exoplanets for Cheap, a recent piece that explains the project this way:
The Minerva telescopes will look for a slight wobble that indicates a planet is tugging gravitationally on those stars. Using this data, [graduate student Kristina] Hogstrom said that her team expects to find around a dozen new local planets, most of them two to three times the size of Earth and a few of them orbiting in the habitable zone where liquid water could exist. The project will also find Earth-sized planets and perhaps smaller, but these will likely orbit too close to their parent star to host life.
What I like about this, and I can see why Centauri Dreams readers find it interesting, is that it’s a dedicated exoplanet project that, Kepler-like, stares at a designated number of stars. The article quotes Johnson as saying that astronomers aren’t really in planet ‘hunting’ mode these days so much as engaged in routine planet ‘gathering,’ which tells you how far we’ve come in this remarkable enterprise in the few short years since 1995, when the announcement of the first planet discovered orbiting a main sequence star was made by Michel Mayor and Didier Queloz, to be quickly confirmed by Geoff Marcy and Paul Butler.
So here we are with off-the-shelf hardware and a custom-built spectrometer, running up a tab of about $3.5 million as compared to the $600 million that the relatively cheap space-based Kepler cost. We’re probably less than a year away from the datastream beginning to flow at the Minerva site. Modest funding and limited resources used imaginatively in arrays of small dedicated telescopes may be forced upon us by circumstance, but we’re learning that good science can flow from such projects and private institutions can find ways to fund them.
by Paul Gilster | Apr 10, 2013 | Exoplanetary Science |
Our exoplanet detection methods have their limits. Radial velocity studies work great in the inner regions of planetary systems, but become more challenging as we move away from the star. Direct imaging is the reverse — we’re most likely to see a distant planet if it’s both large and well separated from the primary. Clearly we need to take the best data from each available method to characterize a planetary system. But direct images are rare and some stars — A-class in particular — are tricky for RV studies because of jitter and other problems. If you want to get in close to an intermediate mass star to look for planets or a debris disk, the way to do it seems to be to study ‘retired’ stars sitting on the subgiant branch of the Hertzsprung-Russell diagram.
These are stars that have slowed or stopped fusing hydrogen in their cores. Core contraction raises the star’s temperature enough to fuse hydrogen in a shell surrounding the core and the star begins to swell up toward giant status. A team led by Amy Bonsor (Institute de Planétologie et d’Astrophysique de Grenoble) has been looking at ? Coronae Borealis (? CrB), also known as HD 142091, using data from the Herschel space telescope in the far infrared. ? CrB turns out to be unique, offering an example of a debris disc around a subgiant and “…a rare example of an intermediate mass star, where both planets and planetesimal belts have been detected.”
That brief quote from the paper on this work goes on to note that the planets and debris disk here can tell us something about planet formation around such stars. There is much we need to learn — some studies have found that more giant planets tend to form around higher mass stars than lower ones, and we’d like to tune up planet formation models in this area. ? Coronae Borealis is a star of about 1.8 solar masses at a distance of 100 light years, some 2.5 billion years old. Previous radial velocity work has revealed one giant planet of about two Jupiter masses orbiting at a distance similar to the asteroid belt in our Solar System. The paper presents Keck measurements offering evidence for a second companion whose mass is unclear.
Image: Kappa Coronae Borealis, based on Herschel PACS observations at 100 ?m. North is up and east is left. The star is in the centre of the frame (not visible in this graphic) with an excess of infrared emission detected around it, interpreted as a dusty debris disc containing asteroids and/or comets. The inclination of the planetary system is constrained at an angle of 60º from face-on. Credit: ESA/Bonsor et al (2013).
These observations yield several possible configurations for the debris disk and planets, with the interesting possibility that the disk may be divided into two narrow belts (centered at 40 AU and 165 AU respectively) with the outermost planet being in actuality a brown dwarf. Another model has a single continuous dust belt extending from 20 to 220 AU, with a planet sculpting the inner edge of the disk. A third possibility: The disk is being stirred by two planets so that the rate of dust production in the disk peaks at roughly 80 AU from the star. Says Bonsor: “It is a mysterious and intriguing system: is there a planet or even two planets sculpting one wide disc, or does the star have a brown dwarf companion that has split the disc in two?”
From the paper:
As the ?rst example of a planetary system orbiting a subgiant, a more detailed population study is required to determine whether or not ? CrB is unusual, nonetheless, this work suggests that ? CrB did not su?er any dynamical instability that cleared out its planetary system, similar to the Late Heavy Bombardment. As the ?rst example of a > 1.4M? star, with a giant planet interior to 8AU, where there is also resolved imaging of a debris disc, ? CrB provides a good example system from which to further our understanding of planetary systems around intermediate mass stars.
The paper is Bonsor et al., “Spatially Resolved Images of Dust Belt(s) Around the Planet-hosting Subgiant ? CrB,” accepted for publication in Monthly Notices of the Royal Astronomical Society (preprint). More in this ESA news release.
