by Paul Gilster | Mar 31, 2014 | Uncategorized
Reading Charles Adler’s Wizards, Aliens and Starships over the weekend, I’ve been thinking about starflight and cost. Subtitled ‘Physics and Math in Fantasy and Science Fiction,’ Adler’s book uses the genres as a way into sound science, and his chapters contain numerous references to writers like Poul Anderson, Larry Niven and Robert Heinlein. On the matter of speculative propulsion systems, he lingers over fusion and describes the work of Project Daedalus back in the 1970s, when an ad hoc team of volunteer scientists and engineers put together a serious starship study.
Like the vessels written about in the science fiction of that era and before, Daedalus was simply a mammoth craft — 53 million kilograms! — but that corresponded with what SF had been telling us all along. We would travel to the stars aboard vessels not so different from ocean liners, perhaps big enough to be livable on a daily basis, or at least big enough to pack thousands of humans into cryogenic containers for a trip under suspended animation. It’s a natural enough thought: Long journeys demand big vessels. Scenarios like this burn up plenty of energy, as Adler is quick to note:
…the implication of an interstellar probe [like Daedalus]…is that we possess an extremely energy-rich society. The cost of Project Daedalus was estimated at $10 trillion. Using the rule of thumb that prices for everything double every 20 years, the estimate comes in at about $40 trillion today, dwarfing the U.S. GDP. This amount of money is about equal to the GDP of the entire world. Energetics tell us why this is so: the total energy contained in the payload is about 10% of the total world energy usage for one year. This is too expensive for any current world civilization to undertake, and it may well be too expensive for any civilization to undertake under any circumstances.
Adler, a professor of physics at St. Mary’s College in Maryland, is a lively writer who is well versed in both science fiction and fantasy, making this an entertaining volume indeed. He doesn’t mention the ongoing Project Icarus study, but it will be interesting to see how the ensuing years have modified the original Daedalus concept to produce a less costly, more viable design. Even so, the assumption is that a fusion starship as designed today is going to be a large vehicle because it has to deliver enough of a payload to make the journey to the star worthwhile.
Realm of the Small
Enter Alan Mole. A retired engineer, Mole is an aerospace stress analyst who has worked at the University of Colorado Laboratory for Atmospheric and Space Physics, and as a contract engineer for Ball Aerospace, McDonnell Douglas, Pratt and Whitney, Thiokol-ATK and other firms. A recent issue of the Journal of the British Interplanetary Society contains his paper “One Kilogram Interstellar Colony Mission,” which reverses the big starship paradigm and looks to deliver a seriously effective payload at a sharply reduced cost. Mole is, he tells me, interested not only in physically possible ways to solve difficult problems, but also in making the solutions economically feasible.
Image: The Milky Way over Ontario. As we ponder a human future in the stars, can nanotech and biology breakthroughs show the way forward? Credit & Copyright: Kerry-Ann Lecky Hepburn.
The difficulty of the problem is hard to overstate. It was not some skeptical bystander but Anthony Martin himself, a major player in the Daedalus design effort, who noted the cost to the society that chose to build Daedalus: “It seems probable that a Solar System wide culture making use of all of its resources would easily be wealthy enough to afford such an undertaking.” But Alan Mole is not the first to point out that we are developing lower cost alternatives. If we can create a smaller payload and find a propulsion method that scales down to meet its requirements, we can start talking about an interstellar effort that would prove economically viable while offering choices for human expansion including interstellar colonization.
If Daedalus totalled 53 million kilograms, Mole thinks we should be looking at a single kilogram as sufficient for our colony probe. Making something like this even imaginable involves advances in artificial intelligence, computer memory, materials science, nanotechnology and biology that we can imagine continuing throughout the century, barring the kind of societal catastrophe that disrupts civilization itself. The kind of probe Mole envisions is a world in itself or, I should say, the seed of a world to come, for it uses technology to raise a human colony at destination:
Consider a one kg colony probe sent to a nearby extrasolar planet at about 0.1 c. It will land and nanobots will emerge to build ever larger robots and greenhouses etc. for colony infrastructure. The nanobots will be powered by batteries and recharged by solar cells, building larger arrays of these as work progresses. They will then hatch human embryos (millions per gram) or build humans directly from DNA formulas stored in memory (as was done for a simple bacterium in the artificial life experiments in 2010.) The probe will transmit no data to Earth but if the colony is successful it will eventually build transmitters and establish contact.
Charles Adler doesn’t suggest science fictional treatments of such ideas, but I know current authors must be working this turf, and I’d appreciate pointers from readers. I’m reminded of Robert Freitas’ ideas about self-reproducing probes, a concept I discussed in Centauri Dreams (the book) in the context of an earlier Freitas idea called REPRO, which involved probes on a Daedalus scale that built replicas of themselves and continued out into the galaxy. By reducing the probe to the size of a sewing needle, Freitas envisions sending just enough nanotechnology to turn assemblers loose at destination to build a station to take scientific measurements, report findings back to Earth and, eventually, move on to another star.
Alan Mole is likewise intrigued by the world of the small, but as the above quote demonstrates, he’s thinking in terms of biology as well. Tomorrow I want to explore the implications of Mole’s thinking, looking first at previous ideas for very small payloads from the likes of Freeman Dyson, Dan Goldin and Gregory Matloff. Then we’ll talk about the propulsion systems that could make such a concept work. For it may not be feasible to carry our propellant with us, opening the door for a variety of beamed energy concepts whose cost is far less onerous than the alternatives.
The paper we’ll be discussing for the next few days is Mole, “One Kilogram Interstellar Colony Mission, Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387.
by Paul Gilster | Mar 28, 2014 | Outer Solar System
The European Space Agency’s Rosetta spacecraft, having traveled for ten years, is on track for its close-up investigation of comet 67P/Churyumov–Gerasimenko to begin later this year. Three years ago we had the first actual image of the comet, a 13-hour exposure taken shortly before the craft entered a lengthy period of hibernation. On the 20th of January, Rosetta was ‘awakened’ and controllers are in the process of commissioning its onboard instruments. As part of the process, we have two ‘first-light’ images taken on March 20 and 21.
Image: Comet 67P/Churymov-Gerasimenko in the constellation Ophiuchus. This image was taken on 21 March by the OSIRIS Narrow Angle Camera. The comet is indicated by the small circle next to the bright globular star cluster M107. The image was taken from a distance of about 5 million kilometres to the comet. A wide-angle image was taken on 20 March. Credit & copyright: ESA © 2014 MPS for OSIRIS-Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
We’re seeing Rosetta from a distance of 5 million kilometers, from which vantage we see its light in less than a pixel through a series of 60 to 300 second exposures. Even so, the sense of exhilaration in the words of OSIRIS principal investigator Holger Sierks (Max-Planck-Institut für Sonnensystemforschung, Göttingen) is palpable:
“Finally seeing our target after a 10 year journey through space is an incredible feeling. These first images taken from such a huge distance show us that OSIRIS is ready for the upcoming adventure.”
Keep in mind the relevance of Rosetta’s mission not only to the evolution of the Solar System but also to future propulsion ideas. One area of interest is the interaction between the solar wind and cometary gases, needed information as we deepen our knowledge not only of the solar wind itself but how its stream of charged particles might be used in electric and magnetic sail concepts. The solar wind’s variability is one key issue about which we have much to learn.
Rosetta’s studies will be wide-ranging. The spacecraft flies with eleven science instruments onboard, fine-tuned to study everything from the comet’s surface geology to its internal structure and the dust and plasma that surround it. OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) has both a wide-angle and a narrow-angle camera involved in the capture of the early images, all part of six weeks of activity as all eleven instruments are checked out for arrival in August.
This ESA news release offers more, noting that on its current trajectory, the spacecraft would pass approximately 50,000 kilometers from the comet at a speed of 800 meters per second. It will be in May that a series of maneuvers are begun to reduce Rosetta’s velocity relative to the comet to 1 meter per second, with the aim of bringing it within 100 kilometers by the first week of August. The re-activation of OSIRIS now gives way to checks on the other instruments as we prepare for what ought to be a memorable encounter. The Philae lander is scheduled to attempt its landing in November.
by Paul Gilster | Mar 27, 2014 | Exoplanetary Science
When it comes to habitable planets, we focus naturally enough on stars like our own. But increasing attention has been paid to stars smaller and cooler than the Sun. M-class dwarfs have small but interesting habitable zones of their own and certain advantages when it comes to detecting terrestrial planets. K-class stars are also interesting, with a prominent candidate, Alpha Centauri B, existing in our stellar back yard. What we haven’t examined with the same intensity, though, are stars a bit more massive and hotter than the Sun, and new work suggests that this is a mistake.
Manfred Cuntz (University of Texas at Arlington), working with grad student Satoko Sato, has been leading work on F-class stars of the kind normally thought problematic for life because of their high levels of ultraviolet radiation. Along with researchers from the University of Guanajuato (Mexico), Cuntz and Sato suggest that we take a closer look at F stars, particularly considering that they offer a wider habitable zone where life-sustaining planets might flourish.
Cuntz thinks the case is a strong one:
“F-type stars are not hopeless. There is a gap in attention from the scientific community when it comes to knowledge about F-type stars and that is what our research is working to fill. It appears they may indeed be a good place to look for habitable planets.”
Image: The habitable zone as visualized around different types of star. Credit: NASA.
The team’s paper in the International Journal of Astrobiology makes this argument based on its studies of the damage that ultraviolet radiation can cause to the carbon-based macro-molecules necessary for life. Its estimates of the damage that would accrue to DNA on planets in F-class star systems covered calculations for F-type stars at various points in their evolution. Planets in the outermost regions of the habitable zone experience much lower levels of radiation. This UT-Arlington news release quotes the paper:
“Our study is a further contribution toward the exploration of the exobiological suitability of stars hotter and, by implication, more massive than the Sun…at least in the outer portions of F-star habitable zones, UV radiation should not be viewed as an insurmountable hindrance to the existence and evolution of life.”
F-type stars represent 3 percent of the stars in the Milky Way, as compared with G-class at about 7 percent and K-class at approximately 12. And then there are M-dwarfs, which may account for over 75 percent of all main sequence stars. In any event, the more we widen the prospects for astrobiology beyond stars like the Sun, the more we address the possibility of a galaxy suffused with life, even if we still have no direct evidence. Just as intriguing: If it turns out life is abundant, is intelligence abundant as well?
The paper is Sato et al., “Habitability around F-type Stars,” International Journal of Astrobiology, published online 25 March 2014 (abstract).
by Paul Gilster | Mar 26, 2014 | Uncategorized
Most Centauri Dreams readers are hardly going to be surprised by the idea that a large number of objects exist well outside the orbit of Pluto and, indeed, outside the Kuiper Belt itself. The search for unknown planets or even a brown dwarf that might perturb cometary orbits in the Oort Cloud has occupied us for some time, with the latest analysis of WISE findings showing that nothing larger than Jupiter exists out to a distance of 26,000 AU. Objects of Saturn size or larger are ruled out within 10,000 AU, according to the work of Kevin Luhman (Penn State) and team, whose study probed deeply into the Wide-field Infrared Survey Explorer’s results. For more on all this, see WISE: New Stars and Brown Dwarfs.
But the evidence for objects big enough to perturb the local neighborhood does persist, even if we have to scale down our expectations as to its size. A new paper in Nature reports the discovery of 2012 VP113, a dwarf planet that joins Sedna in orbiting entirely beyond the Kuiper Belt’s outer edge, which is normally defined at 50 AU. The object at perihelion does not approach closer than 80 AU, making it more distant than Sedna itself. The work of Scott Sheppard and Chadwick Trujillo (Carnegie Institution for Science, Washington), the paper goes on to suggest a larger inner Oort Cloud population and the possibility of perturbed orbits there. Are the orbits of objects like 2012 VP113 and Sedna telling us something about larger bodies in this region?
The researchers used the NOAO 4-meter telescope in Chile in conjunction with the Dark Energy Camera (DECam), a high-performance, wide-field CCD imager, a combination that offers a wide field of view in the search for faint objects in large areas of sky. They also used the Magellan 6.5-meter instrument at Las Campanas Observatory to help determine the orbit of the newfound object. As with Sedna, we find that the orbit of 2012 VP113 takes it well outside the Kuiper Belt. In fact, given that their orbits extend at aphelion out to hundreds of AU, it is only the fact that both are currently near their closest approach to the Sun that has made them detectable.
Image: Artist’s rendering of the Oort cloud and the Kuiper belt. Credit: NASA.
Sedna, it appears, is not unique, and we can continue to infer from this the existence of the so-called inner Oort Cloud, extending out to about 1500 AU, where numerous objects with sizes larger than 1000 kilometers may exist. Sheppard and Trujillo, basing their estimate on the amount of sky searched, believe that 900 objects in this category may be found there, with a total inner Oort Cloud population probably larger than both the Kuiper Belt and the main asteroid belt.
The problem of distance is such that most would not be visible with current technology. However, says Sheppard, “Some of these inner Oort cloud objects could rival the size of Mars or even Earth. The search for these distant… objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our solar system formed and evolved.”
2012 VP113’s orbit brings it to as close as 80 AU, outside Sedna’s perihelion. Interestingly, this finding indicates at least the possibility of a much larger planet, perhaps ten times the size of the Earth, orbiting in the inner Oort and influencing the orbits of both Sedna and the newfound object. The possibility remains that a ‘super-Earth’ or somewhat larger object at hundreds of AU, and thus well within the inner Oort, could be influencing the orbital configurations of objects like 2012 VP113 and Sedna. And based on Kevin Luhman’s WISE data studies, the existence of such a planet would not be inconsistent with what WISE is capable of telling us. If this unseen world is just several Earth masses in size, it’s going to be tricky to find, although locating more small objects being gravitationally influenced by it could eventually help us pin its orbit down.
Image: This is an orbit diagram for the outer solar system. The Sun and Terrestrial planets are at the center. The orbits of the four giant planets, Jupiter, Saturn, Uranus and Neptune, are shown by purple solid circles. The Kuiper Belt, including Pluto, is shown by the dotted light blue region just beyond the giant planets. Sedna’s orbit is shown in orange while 2012 VP113’s orbit is shown in red. Both objects are currently near their closest approach to the Sun (perihelion). They would be too faint to detect when in the outer parts of their orbits. Notice that both orbits have similar perihelion locations on the sky and both are far away from the giant planet and Kuiper Belt regions. Credit: Scott Sheppard / Carnegie Institution for Science.
Meanwhile, the inner edge of the Oort Cloud seems to be fairly well defined. From the paper:
Although our survey was sensitive to objects from 50 AU to beyond 300 AU, no objects were found with perihelion distances between 50 AU and 75 AU, where objects are brightest and easiest to detect. This was true for the original survey that found Sedna and the deeper follow-up survey… If the inner Oort cloud objects had a minimum perihelion of 50 AU and followed a size distribution like that of the large end of all known small-body reservoir distributions…, there would be only a 1% chance of finding 2012 VP113 and Sedna with perihelion greater than 75 AU and no objects with perihelion less than 75 AU. Therefore, we conclude that there are few (although probably not zero) inner Oort cloud objects in the 50-75 AU region. Some stellar encounter models that include the capture of extrasolar material predict a strong inner edge to the perihelion distribution of objects, which is consistent with our observations.
A few words about this: Sheppard and Trujillo distinguish between the inner Oort out to 1500 AU and an outer Oort Cloud, assuming that beyond 1500 AU objects are more subject to interstellar influences. One theory of inner Oort Cloud object formation is that Sedna and its ilk are captured extrasolar planetesimals lost in encounters with stars in the Sun’s birth cluster. Primordial close encounters with other stars may be implicated, but only further discovery of other inner Oort Cloud objects will provide the information needed to make this call about our system’s evolution.
The paper is Sheppard and Trujillo, “A Sedna-like body with a perihelion of 80 astronomical units,” Nature 507 (27 March, 2014), 471-474..
by Paul Gilster | Mar 25, 2014 | Exoplanetary Science
This morning I want to circle around to a story I had planned to write about a couple of weeks ago. One thing writing Centauri Dreams has taught me is that there is never a shortage of material, and I occasionally find myself trying to catch up with stories long planned. In this case, the imaging of an exoplanet around the star Beta Pictoris demands our attention because of the methods used, which involve charge-coupled devices and wavelengths close to visible light. The detection marks real progress in visible light imaging of exoplanets.
The work, which is slated to appear in The Astrophysical Journal, was conducted by researchers from the University of Arizona led by Laird Close. Charge-coupled devices (CCD) are the same kind of technology we find in digital camera imaging sensors, used here in a setting where we’d normally expect an infrared detector. But using infrared means viewing massive young planets hot enough to put out considerable heat. As the exoplanet hunt develops and we push the search for life in the cosmos, we’re after much trickier game, says Close:
“[W]e now are a small step closer to being able to image planets outside our solar system in visible light. Our ultimate goal is to be able to image what we call pale blue dots. After all, the Earth is blue. And that’s where you want to look for other planets: in reflected blue light.”
Image: An image of the exoplanet Beta Pictoris b taken with the Magellan Adaptive Optics VisAO camera. This image was made using a CCD camera, which is essentially the same technology as a digital camera. The planet is nearly 100,000 times fainter than its star, and orbits its star at roughly the same distance as Saturn from our Sun. (Image: Jared Males/UA).
Beyond young, hot planets, we’d like to image planets that have long since cooled, the kind of worlds where the passage of time has allowed for the development of life. Beta Pictoris b certainly does not fit that bill, but the technology points in the right direction. Now deployed at the Magellan 6.5-meter instrument in Chile, the system Close and team have developed — Magellan Adaptive Optics — can manipulate a deformable mirror so that its shape changes a thousand times a second in real time, overcoming atmospheric distortion. The team used the MagAO system in tandem with VisAO, a visible wavelength camera. The detection points toward future space-based observatories that can ‘drill down’ to the detection of cooler terrestrial worlds.
“[W]e were able to record the planet’s own glow because it is still young and hot enough so that its signal stood out against the noise introduced by atmospheric blurring,” added lead author Jared Males. “But when you go yet another 100,000 times fainter to spot much cooler and truly earthlike planets, we reach a situation in which the residual blurring from the atmosphere is too large and we may have to resort to a specialized space telescope instead.”
The imaged planet orbits at 9 AU from the host star, a bit closer than Saturn in our own Solar System, and appears 100,000 times fainter than the star. Males describes the image as having the highest contrast ever achieved on an exoplanet this close to its star. That the image was actually that of Beta Pictoris b, an object about twelve times the mass of Jupiter with an atmospheric temperature in the range of 1700 Kelvin, was confirmed using a second MagAO image taken in the infrared spectrum, where the giant world shines much more brightly.
So we’re a long way from directly imaging Earth-like planets around other stars, but tuning up our methods in visible light will eventually pay off with future space-based planet finders. The paper is Males et al., “Magellan Adaptive Optics ?rst-light observations of the exoplanet ? Pic b. I. Direct imaging in the far-red optical with MagAO+VisAO and in the near-IR with NICI,” accepted at The Astrophysical Journal (preprint). A University of Arizona news release is also available.