by Paul Gilster | Feb 21, 2013 | Exoplanetary Science |
The planetary system around Kepler-37, some 210 light years from Earth in the constellation Lyra, had its place in the media spotlight yesterday, although it will surely be a brief one. But it’s heartening to see the quickening interest in exoplanets that each new discovery brings. Will the interest continue? In the Apollo days, public enthusiasm reached a frenzy as we moved toward the first lunar landings, then plummeted. What the media see as the big event in exoplanetary science is the discovery of a terrestrial world around a star like the Sun. Let’s hope there is no similar letdown afterwards.
After all, we’re getting close, and discoveries like those announced yesterday remind us that Kepler can find very small worlds indeed. Kepler-37b lays claim to being the smallest planet yet found around a star similar to the Sun, similar in this case meaning a G-class star with a radius about three-quarter’s of the Sun’s. The new planet is just a bit larger than our Moon, as the image below shows. The world is assumed to be rocky and, with a 13-day orbit, its surface temperature is probably in the range of 700 K.
Image: NASA’s Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra. The line-up above compares artist’s concepts of the planets in the Kepler-37 system to the moon and planets in the Solar System. The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth. Credit: NASA/Ames/JPL-Caltech.
As you can see from the image, we have three new worlds all told, all of them orbiting at a distance less than Mercury’s distance to the Sun. Kepler-37c orbits the star every 21 days, while Kepler-37d, probably a Neptune-class world, orbits every 40 days. A fourth candidate, identified as KOI-245.04 in the most recent Kepler planet catalog, is now disregarded, thought to be the result of random noise, starspot activity on Kepler-37, or instrumental artifacts.
Variable starlight can confuse transit detections, particularly of tiny worlds like Kepler-37b. Fortunately, Kepler-37 is both bright and quiet, allowing the methods of asteroseismology to be brought into play. The oscillations caused by sound waves generated beneath the stellar surface appear as a flickering of the star’s brightness. These measurements are tricky to observe in smaller stars, but making them allows the team to calculate the radius of Kepler-37 to a three percent accuracy. That, in turn, gives us accurate readings of the planetary radii in the system.
All of this is good news, for it implies that Kepler will be able to find Earth-sized planets in longer orbits around Sun-like stars. Once we begin finding them, is the public going to get exoplanet fatigue just as it lost interest in the Moon after Apollo? Astronomer John Johnson (Caltech) takes note of the possibility in this article in the Los Angeles Times:
“I don’t think anyone would have been taken seriously if they had said, before Kepler launched, that we’d find planets as small as Mercury,” he said. Mercury is slightly larger than Earth’s moon.
The telescope has revolutionized astronomers’ notions of our galaxy as a place that must be “teeming with rocky planets” that seem to be “a natural outgrowth of star formation,” he added.
Indeed, Kepler has been so prolific that many space enthusiasts have become blasé about exoplanet discoveries just as scientists are closing in on finding truly Earth-like worlds, Johnson said.
“Every one of these detections was unimaginable in 2008,” he said. “Every one of these is super-important.”
The paper is Barclay et al., “A sub-Mercury sized exoplanet,” published online in Nature 20 February 2013 (abstract).
by Paul Gilster | Feb 20, 2013 | Outer Solar System |
Yesterday we looked at the possibility of colonizing worlds much different from the Earth. Seen in one light, pushing out into the Kuiper Belt and building settlements there is part of a slow migration to the stars that may occur without necessarily being driven by that purpose. Seen in another, experimenting with human settlements in extreme environments is a way of exploiting the resources of nearby space, pushing the human presence out into the Oort Cloud. Either way, we can find places that, while not ‘habitable’ in the classic sense of liquid water at the surface, are nonetheless colonizable.
In his Tale of Two Worlds, novelist Karl Schroeder works on a definition of a colonizable world. It has to have an accessible surface, for one thing, meaning one we can work with — obviously a surface gravity of 4 g’s is going to be a problem. Much smaller worlds like Pluto, as we saw yesterday in Ken Roy’s work on possible colonies there, pose less of a challenge, as we can imagine strategies to produce one g for the inhabitants. Schroeder also notes there has to be a manageable flow of energy at the surface in which we can move heat around. That seems reasonable enough, although advanced technologies will have a wider zone than we have.
But I found Schroeder’s third point interesting. Here he’s drawing on a 1978 paper in Science called “The Age of Substitutibility,” by Harold Goeller and Alvin Weinberg (Oak Ridge National Laboratory), in which the authors describe the artificial mineral they call ‘demandite.’ It comes, as Schroeder notes, in two forms:
A molecule of industrial demandite would contain all the elements necessary for industrial manufacturing and construction, in the proportions that you’d get if you took, say, an average city and ground it up into a fine pulp. There’re about 20 elements in industrial demandite including carbon, iron, sodium, chlorine etc. Biological demandite, on the other hand, is made up almost entirely of just six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It’s called cellulose.)
The point is that the right elements have to be accessible on the object you’re trying to live on to make it colonizable. Now if you can find a place that meets the three criteria, surprising things can happen. Centauri B b looks to be a nightmarish place, probably tidally locked and roiling with lava on its day side, and almost certainly without a breathable atmosphere. But from the standpoint of colonizability, we can’t rule out the night side, and the fact that this (still unconfirmed) world has a surface gravity about the same as Earth’s also works in its favor.
From the Kuiper Belt Past Proxima
Ken Roy’s talk at Huntsville looked at places that seemed equally inhospitable, but which may have the necessary resources to provide an advanced human civilization with what it needs to create settlements there, whether as part of a deliberate interstellar migration or simple exploration. Yesterday I focused on Pluto, but of course the Kuiper Belt is stuffed with objects, hundreds of which may be Pluto-sized, while cometary bodies in the Oort Cloud are thought to number in the trillions, based on the study of long-period comets and their frequency.
Like Schroeder, Roy is interested in brown dwarf possibilities as well. The odds on our finding a brown dwarf closer than Proxima Centauri are dwindling, though I don’t think we can rule out a possible ultra-cool Y dwarf in this space (please correct me with any updated information). In any event, the WISE mission (Wide-field Infared Survey Explorer) has shown us that brown dwarfs are less common than we thought. WISE has discovered 200 brown dwarfs (including 13 Y dwarfs), 33 of which are within 26 light years of the Sun. Given that there are 211 stars in the same volume of space, we’ve found that there are about six stars for every brown dwarf.
If they’re not as abundant as we had thought, brown dwarfs may still become useful staging areas for far-future interstellar expeditions, for we know that some have accretion disks that indicate the possibility of planet formation. I’ve written before about brown dwarf habitable zones (see Brown Dwarfs and Habitability), but Roy’s point is that whether or not we find a world that’s habitable in the classic sense, we can still assume we’ll find the same kind of small, icy planets we see in our own Kuiper Belt, and the same technologies could exploit them.
Roy is one of those intrigued with the idea of ‘rogue’ planets that move through the interstellar deep far from any star. We know little about these worlds, but it’s assumed that great numbers of them are out there, doubtless the result of gravitational interactions in young solar systems that caused them to be ejected. Dorian Abbot and Eric Switzer (University of Chicago) call these ‘steppenwolf’ planets because they ‘exist like a lone wolf wandering over the galactic steppe.’
Image: A ‘steppenwolf’ planet moving between the stars. Credit: NASA/JPL-Caltech.
Louis Strigari (Stanford University) has estimated that as many as 105 objects larger than Pluto exist for every main sequence star. If that’s anywhere like the case, then rogue planets ranging between the size of Ceres and Jupiter should be out there in abundance, and we can hope to put some constraints on their numbers through future gravitational microlensing surveys and even exoplanet transit studies, which may catch a rogue planet’s transit. Some studies show that radiogenic heating from the planetary core could keep an ocean under crustal ice liquid for billions of years even out here, where there is no star to provide warmth.
Deep space is not without resources, as we’re learning every day. Roy told the audience in Huntsville that cometary objects from the Kuiper Belt to the Oort Cloud should offer CO2, ammonia, methane, oxygen, carbon and nitrogen, while we can exploit asteroids for silicates and metals. We can only imagine what resources might be available in unattached worlds moving between the stars. This is all work for a civilization that has built a thriving deep space infrastructure, but then, thinking about the future is what we do here.
by Paul Gilster | Feb 19, 2013 | Astrobiology and SETI |
Are habitable planets the best places to look for life? The question seems odd, because we’re assuming life has to have clement conditions to emerge and survive. But step beyond the question of life’s formation and the issue can be framed differently. Where beyond its birthplace might life migrate? In SETI terms, where might we look for the signature of a civilization advanced enough to move beyond its home world and expand between the stars?
A lot of ideas seem to be converging here. In Huntsville, Ken Roy (whose description at the recent interstellar conference was ‘an engineer living and working amidst the relics of the Manhattan Project in Oak Ridge, Tennessee’) described potential habitats stretching far out into the Solar System and beyond. Roy has been working for some time with Robert Kennedy and David Fields on colonization scenarios.
My own talk covered the kind of places where we might extract resources, ranging from icy dwarfs like Pluto to cometary objects and ‘rogue’ planets without any star. And science fiction author Karl Schroeder, in a recent blog post called A Tale of Two Worlds, also brought the topic up. Let me quote Schroeder, because I want to return to his post in a day or so:
…it’s important to bear in mind that habitability and colonizability are not the same thing. Nobody seems to be doing this; I can’t find any term but habitability used to describe the exoplanets we’re finding. Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there. So, the term applies to places that are vitally important for study; but it doesn’t necessarily apply to places we might want to go.
Both Schroeder and Roy are assuming not near-term projects but the kind of settlement and terraforming that draw on huge resources of energy. The premise, in other words, is that we’re talking about a culture that ranges freely through its own system, having mastered fusion or other technologies and being capable of large-scale building projects in space and on planetary or other surfaces. Grant that premise and then think about what kind of structures it might make sense to build when exploiting local resources and looking out toward the stars.
Pluto and the Ice Dwarfs
Pluto is a case in point. Here we have a surface that appears to be a shell of nitrogen ice covering water ice. When New Horizons gets to the Pluto/Charon binary in 2015, one thing to look for is an equatorial bulge that could have been left over from the early days of Pluto’s formation. No bulge makes the case for stretching of the ice shell over Pluto’s lifetime, strengthening the possibility some are noting that the ice dwarf could contain an ocean beneath about 165 kilometers of crust, an ocean that may be just as deep as the crust is thick (see The Case for Pluto’s Ocean for more).
As Roy told the crowd in Huntsville, icy worlds like Pluto are rich in volatiles, and of the tens, if not hundreds of thousands of Kuiper Belt objects out there between 30 and 50 AU, several hundred may be Pluto-size. Such worlds are doubtless common not just here in our own system but as rogue planets in interstellar space and perhaps circling brown dwarfs, those dim objects that blur the distinction between gas giants like Jupiter and true stars like Proxima Centauri.
Image: This artist’s conception of the ‘scattered disk’ object Sedna reminds us that even beyond the Kuiper Belt and as we move into the Oort Cloud, vast numbers of icy objects are thought to exist. Can we exploit these as we move outward toward another star?
Build a settlement on an ice dwarf in the outer system and you are not only creating space for living and doing science, but also building the technologies that will one day be used in interstellar colonization missions. But Roy noted that the science fictional image of a domed city in a harsh landscape just won’t work here. Induce Earth-class atmospheric pressure inside such a dome and even a small one (1000 feet in radius) would require a four-inch thick layer of steel to keep the dome intact. Moreover, ice dwarfs have but feeble gravity, creating medical issues from muscle atrophy to bone problems, loss of body mass, sleep disturbance and more. A better choice, then, is to move inward, creating the colony deep within the ice dwarf itself.
At 160 meters, the ceiling of a colony hollowed out within Pluto would be fully supported by the air pressure inside. Artificial light would be essential, of course, and we still have a gravity problem, for Pluto’s gravity is only 6.7 percent that of the Earth — a 200 pound person on Earth weighs but 14 pounds on Pluto. Roy suggests a rotating torus in this setting could provide living and working spaces at 1 Earth gravity. At 1 revolution per minute, a 1790-meter torus supported by maglev rails could accommodate, by Roy’s estimation, 10,000 people living in conditions that would more or less resemble the worldships so often imagined by science fiction writers.
We’re assuming technologies that can create large rotating structures in low-gravity environments, with the ability to move spacecraft at velocities of 0.001 c to build and supply the colony. We’re also assuming proven fusion power plants and considerable expertise in mining and construction. We would put these tools to work to extract local silicates and metals from the surface and, perhaps, rock from buried impactors. We would be working in an environment rich in H2O, but also in methanol, hydrogen cyanide, formaldehyde, ethanol, ethane and long-chain hydrocarbons, all within a salty ice mantle.
Interstellar Migration
Here’s long-haul migration to the stars presented as a series of steps at 0.001 c. Moving roughly 400 AU at a time between various objects in the outer system and, eventually, interstellar space, we spend 50 years at each to establish a colony and then build and crew another ship. The 4.2 light years to Proxima Centauri in this scenario demands 664 such jumps and reaches the star in 38,000 years, leaving a chain of colony worlds behind that are self-sustaining.
The technologies needed for this kind of expansion are well beyond us, but it is not inconceivable that more advanced cultures as they move up the Kardashev scale may have accomplished such things. Places that are habitable, as Karl Schroeder says, are not the same thing as places that are colonizable, and it’s also true that we have to be wary of imputing human motivation to hypothetical extraterrestrial civilizations. Their detectable artifacts, in other words, might extend between the stars far into the interstellar deep and so, in some remote futurity, might ours.
by Paul Gilster | Feb 18, 2013 | Asteroid and Comet Deflection |
We can hope that the celestial events of February 15, including the spectacular fireball over Chelyabinsk and the near-miss from asteroid 2012 DA14, have raised public consciousness about Earth’s neighbors in space. And indeed, this seems to be the case. Media outlets were flooded with articles, photos and video, and talk show hosts found themselves asking what could be done to prevent future impacts. Could all of this prompt a new surge of interest in space?
The scenario is exactly what Arthur C. Clarke wrote about in Rendezvous with Rama (1972), where what it takes for humanity to get serious about developing a protective system (and, by extension, about pushing its space program forward) is an impact. We can be grateful that the one we’ve just seen was far smaller than Clarke’s, as described in the first chapter of the novel:
At 0946 GMT on the morning of September 11 in the exceptionally beautiful summer of the year 2077, most of the inhabitants of Europe saw a dazzling fireball appear in the eastern sky. Within seconds it was brighter than the Sun, and as it moved across the heavens — at first in utter silence — it left behind it a churning column of dust and smoke.
Somewhere above Austria it began to disintegrate, producing a series of concussions so violent that more than a million people had their hearing permanently damaged. They were the lucky ones.
Clarke goes on to recount the impact in northern Italy, where Padua, Verona and Venice are destroyed by the combination of impact and tsunami. The deaths of 600,000 people and the great chunk torn out of human history create a resolution that this must not happen again, and out of this is born the system of radars that eventually finds the alien intruder dubbed Rama. Clarke’s book is about the encounter with this enigmatic vessel, but the asteroid-warning radars he imagines create the kind of warning grid we may eventually put in place.
The B612 Foundation has been making the case for asteroid detection and mitigation studies for some years now. Its Sentinel Space Telescope is scheduled for launch in 2018, with the aim of detecting over 90 percent of asteroids over 100 meters in diameter — these are the ones large enough to destroy an entire region of the planet if they were to hit us. Sentinel also aims to track more than 50 percent of near-Earth asteroids in the DA-14 category. With decades of warning, says CEO Ed Lu in this B612 news release, we can use existing technology to destroy or alter the trajectory of any such objects.
Chelyabinsk and 2012 DA14 also put the University of Hawaii at Manoa’s work on ATLAS into the news. The Asteroid Terrestrial-Impact Last Alert System — an ominous title, that — is to operate eight telescopes, each with a camera of up to 100 megapixels, on sites in the Hawaiian Islands. The goal here is to offer, according to this news release from the university’s Institute for Astronomy in Honolulu, a one-week warning for a 45-meter asteroid and a three-week warning for a 140-meter object. That’s enough time, according to astronomer John Tonry, “to evacuate the area of people, take measures to protect buildings and other infrastructure, and be alert to a tsunami danger generated by ocean impacts.”
But among the spate of asteroid warning news items that surged over the weekend, the project that caught my eye first was one called DE-STAR, the explanation of whose acronym is so tortuous that I will direct you to the University of California at Santa Barbara news release it appeared in. What UC-Santa Barbara researchers Philip Lubin and Gary Hughes are proposing is a system that could, over the course of a year, destroy asteroids ten times larger than 2012 DA14, using a massive phased array of lasers to break up or evaporate the object.
Says Hughes:
“This system is not some far-out idea from Star Trek. All the components of this system pretty much exist today. Maybe not quite at the scale that we’d need — scaling up would be the challenge — but the basic elements are all there and ready to go. We just need to put them into a larger system to be effective, and once the system is there, it can do so many things.”
DE-STAR is being described as a ‘directed energy orbital defense system,’ one that uses solar energy to feed its lasers. The researchers have calculated DE-STAR systems in various configurations, including a 100-meter DE-STAR 2 and a 10-kilometer DE-STAR 4, the latter capable of delivering the energy needed to obliterate a 500-meter asteroid in about a year.
Image: Concept drawing of the DE-STAR system engaging both an asteroid for evaporation or composition analysis, and simultaneously propelling an interplanetary spacecraft. Courtesy Philip M. Lubin.
And now we start getting into Bob Forward territory as Lubin and Hughes go on to describe a DE-STAR 6 that would function not only in asteroid defense but as the propulsion system of an interstellar spacecraft, beaming enough laser energy to the craft to get it up to a substantial percentage of the speed of light. An asteroid mitigation strategy that involved planetary safety, power generation and spacecraft propulsion is a tempting long-term goal, but a DE-STAR 2 about the size of the International Space Station could begin small-scale trajectory alterations on a variety of objects as we experiment with planet-defending techniques.
Meanwhile, many of us talked to Claudio Maccone at the Huntsville conference and learned of his plans to attend the IAA’s Planetary Defense Conference, coming up in Flagstaff on April 15-19. Claudio crosses the ocean all the time, as inveterate a conference-goer as I’ve ever seen, but who would have thought this year’s Planetary Defense meeting would become so highly visible? You can bet media coverage at Flagstaff will be considerably higher than in years past thanks to Chelyabinsk and 2012 DA14, making them unusually effective wake-up calls for our species.
by Paul Gilster | Feb 15, 2013 | Culture and Society |
If the title of this piece conjures up exotic images, that’s all to the good. In fact, I’m surprised that “Alpha Centauri Sunrise” hasn’t been the title of a science fiction story somewhere along the line, but a quick check shows no such reference. Thus when Robert Kennedy (The Ultimax Group) created a drink called the Alpha Centauri Sunrise at our recent conclave in Huntsville, he was breaking new ground. And maybe images of a double sunrise also came to mind, the view from an as yet undiscovered world where Centauri A is a bright flare in the morning sky while a still closer Centauri B begins to nudge up over the hills, flooding the scene with orange light.
And what happened to Proxima Centauri? It would not be a factor in a scene like that, its light so dim that it would not stand out from other stars in a completely dark sky. Only its proper motion would alert local astronomers to how close it was (roughly 15000 AU). But let’s drink to Proxima anyway. I promised the recipe for the Alpha Centauri Sunrise two weeks ago and it’s time to deliver, as a number of readers have reminded me. Here we have it, from the pen (or keyboard) of Robert Kennedy himself:
The Alpha Centauri Sunrise
Best served in a martini glass or a champagne flute to accentuate the color gradient.
Ingredients:
1 jigger Tennessee moonshine;
2 jiggers Red Bull (different cognate but Centauri sorta suggests a bull, plus one of the stars is reddish);
4-6 oz. orange juice;
½ tsp. grenadine (to make the red-to-yellow color gradient);
three little red berries (to represent the three suns of the triple star system: α Centauri A, α Centauri B, and Proxima Centauri.
If, after all these puns, your customer still doesn’t crack a smile, then instead of three little red berries, give him a big raspberry (literally or figuratively).
With an Alpha Centauri Sunrise in hand, you might want to recall some of the great science fiction venues where drinks like this might be served. Callahan’s Place is the creation of Spider Robinson (it’s immortalized in Callahan’s Crosstime Saloon), a place where time travelers make the occasional appearance and aliens from a variety of worlds might wander in at any time. Robinson devotees will recognize ‘Callahan’s Law’: “Shared pain is lessened, shared joy, increased – thus do we refute entropy.” And I would say that refuting entropy is a task worth accomplishing.
Callahan’s, of course, had forerunners, among them Gavagan’s Bar, which was the work of Fletcher Pratt and L. Sprague de Camp, depicted in a series of tall tales (most of them, I believe, written for John Campbell’s Unknown) and collected into a 1953 book. The one that comes most readily to my mind, though, is Arthur C. Clarke’s Tales from the White Hart, a 1957 collection that brought science fiction and pub culture to a triumphant peak. These stories are still lively today, and recall a time when the members of the British Interplanetary Society and science fiction fans met regularly at such venues.
Image: Alpha Centauri Sunrise creator Robert Kennedy with the finished product.
Of course there are wonderful movie and TV bars in science fiction, from the Mos Eisley Cantina on Tatooine (Star Wars) to Star Trek‘s Ten Forward, which is where I would have spent my time on the Enterprise whenever possible. But Britain’s pub culture gave birth not only to Clarke’s Harry Purvis, the raconteur who spun his tales, but also to the British Interplanetary Society’s later work on Project Daedalus, the fusion starship design. Much of their work took place in a pub called the Mason’s Arms, where propulsion concepts and target stars offered just as magical a look at reality as anything in the White Hart. Thus it’s written SF and the White Hart I come back to when thinking of starships and bars.
Harry Purvis could hardly have had better companions than I had in Huntsville. Looking toward next week, I’ll be tapping the ideas of one of these, Ken Roy (The Ultimax Group), whose thoughts on colonizing outer system and deep space objects dovetail beautifully into my own thinking on gradual expansion into the Oort Cloud. Ken is a frequent contributor with colleagues Robert Kennedy and David Fields in venues like JBIS and Acta Astronautica. We’ll soon be looking at an unusual take on terraforming and how it might transform human expansion.
Image: Robert Kennedy’s co-author Ken Roy (left) and ‘neighbor/fellow habitué of the Friday Night Dinner Club’ John Preston, with Alpha Centauri Sunrises in hand.
