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Moving Stars: The Shkadov Thruster

by Paul Gilster | Nov 26, 2013 | Astrobiology and SETI | 25 Comments

Although I didn’t write about the so-called ‘Shkadov thruster’ yesterday, it has been on my mind as one mega-engineering project that an advanced civilization might attempt. The most recent post was all about moving entire stars to travel the galaxy, with reference to Gregory Benford and Larry Niven’s Bowl of Heaven (Tor, 2012), where humans encounter an object that extends and modifies Shkadov’s ideas in mind-boggling ways. I also turned to a recent Keith Cooper article on Fritz Zwicky, who speculated on how inducing asymmetrical flares on the Sun could put the whole Solar System into new motion, putting our star under our directional control. The physicist Leonid Shkadov described a Shkadov thruster in a 1987 paper called “Possibility of Controlling Solar System Motion in the Galaxy” (reference at the end). Imagine an enormous mirror constructed in space so as to reflect a fraction of the star’s radiation pressure. You wind up with an asymmetrical force that exerts a thrust upon...

The Star as Starship

by Paul Gilster | Nov 25, 2013 | Missions | 23 Comments

Moving entire stars rather than building spaceships would have certain benefits as a way of traveling through the galaxy. After all, it would mean taking your local environment with you on a millennial journey. Some have suggested it might therefore be an observable sign of highly advanced civilizations at work. But how would you move a star in the first place? In Bowl of Heaven (Tor, 2012), Gregory Benford and Larry Niven conceive of a vast bowl -- think of one-half of a Dyson sphere -- wrapped around a star whose energies are directed into a propulsive plasma jet that, over aeons, moves the structure forward. Thus this snippet of dialogue, said aboard a starship by the humans who discover the alien artifact: "...You caught how the jet bulges out near the star." More hand waving. "Looks to me like the magnetic fields in it are getting control, slimming it down into a slowly expanding straw…" "A wok with a neon jet shooting out the back...and living room on the inside, more...

Leafing Through Early Interstellar Ideas

by Paul Gilster | Nov 22, 2013 | Culture and Society | 21 Comments

Although John Jacob Astor IV did many things in his life -- as a businessman, builder, Spanish American War veteran and financier -- his place in history was secured with his death on the Titanic in 1912. His was actually one of the three hundred or so bodies that were later recovered out of over 1500 who died, and he is buried in Trinity Church Cemetery in New York City. Less well known is the fact that Astor was a writer who, in 1894, produced a science fiction novel called A Journey to Other Worlds in which people travel to the outer planets. I've been digging around in this curious novel and discovered an interstellar reference that was entirely new to me. Using a form of repulsive energy called 'apergy,' variants of which were much in vogue in the scientific romances of this era (think H. G. Wells' The First Men in the Moon, which uses gravity-negating 'cavorite'), Astor's crew sets out on the Callisto to explore Jupiter and Saturn, where various adventures ensue. Along the way,...

Ancient Brown Dwarfs Discovered

by Paul Gilster | Nov 21, 2013 | Deep Sky Astronomy & Telescopes | 8 Comments

How many brown dwarfs should we expect in the Milky Way? I can recall estimates that there could be as many brown dwarfs as main sequence stars back when people started speculating about this, but we have to go by the data, and what we have so far tells another tale. The WISE (Wide-field Infrared Survey Explorer) mission can only come up with one brown dwarf for every six stars, leading Davy Kirkpatrick (Caltech), who is part of the WISE science team, to say "Now that we're finally seeing the solar neighborhood with keener, infrared vision, the little guys aren't as prevalent as we once thought" (see Brown Dwarfs Sparser than Expected). Image: Brown dwarfs in relation to the Sun and planets. Credit: NASA/WISE mission. This is true, at least, in the Sun's vicinity, where WISE identifies about 200 brown dwarfs, with 33 measured within 26 light years. In the latter volume, some 211 other stars can be found. If we extrapolated this to the entire galaxy, we would get about 33 billion...

Hacking Humanity to the Stars: The DIY Space Program

by Paul Gilster | Nov 20, 2013 | Culture and Society | 23 Comments

Among the numerous groups now emerging with an eye toward space exploration, SpaceGAMBIT has been the one I knew the least about. It was a pleasure, then, to hear from Alex Cureton-Griffiths, who is UK Project Lead for SpaceGAMBIT. Alex was more than happy to offer this description of SpaceGAMBIT and its plans for the future. He tells me he spends his time traveling and talking to people about our future in space and how they can get involved. In his spare time he "hunts for good coffee and hacks on steam-powered satellite thrusters for fun." Alex, I buy coffee green and roast my own beans. If you're a coffee guy, we need to talk, man. by Alex Cureton-Griffiths When I mention to people that I'm trying to help build humanity into a spacefaring species, I usually get the same reaction: " I don't believe it - that's so cool!" I'm with them all the way on the second part of that reaction - it really is amazingly cool. It's the first part that gets me - the "I don't believe it" part. For...

Space Weathering: The Mars Connection

by Paul Gilster | Nov 19, 2013 | Outer Solar System | 8 Comments

I don't usually have much to say about Mars, for this site's focus is on deep space -- the outer Solar System and beyond. But with both the Mangalyaan and MAVEN Mars missions in progress, I'll take this opportunity to mention new work out of MIT that deals with the effect of Mars on asteroids. The topic is 'space weathering,' the result of impacts from high energy particles and more. Richard Binzel and colleague Francesca DeMeo have been looking at disruption to asteroid surfaces, finding that close planetary encounters can explain an unusual fact: The surfaces of most asteroids appear redder than the remnants of asteroids that have crashed as meteorites to Earth. Back in 2010, Binzel established what he sees as the basic mechanism. Main belt asteroids, orbiting between Mars and Jupiter, are exposed to cosmic radiation that changes the chemical nature of their surfaces. But take an asteroid out of the main belt and give it a close pass by the Earth and 'asteroid quakes' will occur,...

Two Ways to the Stars

by Paul Gilster | Nov 18, 2013 | Missions | 43 Comments

I often cite Robert Forward's various statements to the effect that "Travel to the stars is difficult but not impossible." Forward's numerous papers drove the point home by examining star travel through the lens of known physics, conceiving of ways that an advanced civilization capable of the engineering could build an interstellar infrastructure. But while Forward was early in this game, so were Iosif S. Shklovskii and Carl Sagan. A Russian astronomer, Shklovskii had written a book's whose Russian title translates roughly as 'Universe, Life, Intelligence' in 1962. Four years later, Sagan would join Shklovskii as co-author and the two would tackle the original book afresh, adding new material that reflected on and expanded the 1962 version's ideas. The result was the volume now called Intelligent Life in the Universe. I sometimes recommend books that are essential parts of a deep space library, and this is surely one, significant not only for its historical treatment of starflight...

The Inner System Viewed from Saturn

by Paul Gilster | Nov 15, 2013 | Outer Solar System | 13 Comments

With the Cassini mission continuing through 2017, we'll doubtless have many fine views of Saturn to come, but the images below merit special attention, enough so that I decided to close the week with them. We're looking at an annotated, panoramic mosaic made by processing 141 wide-angle images, sweeping across 651,591 kilometers. That covers the planet, its inner ring system and all its rings out to the E ring. Moreover, the view presented here is in natural color, so we see the color as it would be seen by human eyes rather than as distorted during observations at other wavelengths. You may remember the 'Wave at Saturn' campaign from last summer, when the word went out that Cassini would be snapping a view of the Earth from Saturn space. In the mosaic (click the image to zoom in) we can see the Earth as a blue dot to the lower right of Saturn, but Venus is visible too to the upper left, and Mars shows up as the faint red dot above and to the left of Venus. A close look will reveal...

What a Strange Asteroid Can Tell Us

by Paul Gilster | Nov 14, 2013 | Asteroid and Comet Deflection | 4 Comments

The Pan-STARRS survey telescope in Hawaii has reminded us how much we still have to learn about asteroids. We saw yesterday that the Chelyabinsk impactor could be studied through physical evidence as well as the ample photographic records made by witnesses on the ground. But P/2013 P5, discovered by Pan-STARRS and then the object of Hubble scrutiny, is in the main belt between Mars and Jupiter, and rather than appearing as a mere point source, the object shows six comet-like tails that have confounded all those who have looked at it. "It's hard to believe we're looking at an asteroid," said lead investigator David Jewitt, a professor in the UCLA Department of Earth and Space Sciences and the UCLA Department of Physics and Astronomy. "We were dumbfounded when we saw it. Amazingly, its tail structures change dramatically in just 13 days as it belches out dust." Image: This NASA Hubble Space Telescope set of images reveals a never-before-seen set of six comet-like tails radiating from a...

Piecing Together the Chelyabinsk Event

by Paul Gilster | Nov 13, 2013 | Asteroid and Comet Deflection | 13 Comments

We’re still trying to learn how frequently asteroid events like the spectacular fireball over Chelyabinsk occur. The Chelyabinsk object was the largest to fall to Earth since the Tunguska explosion in 1908, which leveled thousands of acres of forest in Siberia. This BBC story discusses Peter Brown (University of Western Ontario) and colleagues’ recent paper in Nature and goes on to quote Brown as saying that a few days’ to a week’s warning would have been valuable so that we would have been prepared for what happened near the Siberian city. True enough, but what’s significant here is that the Brown team studied 20 years of data from sensors positioned around the world to estimate the frequency of such events. The upshot: About sixty asteroids up to 20 meters in size entered Earth’s atmosphere during this period, a significantly higher number than was previously assumed. Brown’s team reports we’ve been underestimating the strike rate of asteroids between 10 and 20 meters in size by...

SETI, METI… and Assessing Risk like Adults

by Paul Gilster | Nov 12, 2013 | Astrobiology and SETI | 99 Comments

David Brin is a familiar name to science fiction readers worldwide, the award-winning author of the highly regarded 'uplift' novels that include Startide Rising (1983), The Uplift War (1987) and Brightness Reef (1995). Among his numerous other titles are The Postman (1985), Kiln People (2002) and Existence (2012). But Brin is also known as a futurist whose scientific work ranges over topics in astronautics and astronomy to forms of dispute resolution and the role of neoteny in human evolution. His Ph.D in Physics from the University of California at San Diego followed a masters in optics and an undergraduate degree in astrophysics from Caltech. He was a postdoctoral fellow at the California Space Institute and the Jet Propulsion Laboratory. Brin has served on advisory committees dealing with subjects as diverse as national defense, space exploration, SETI and nanotechnology, future/prediction and philanthropy. His essay The Great Silence (available here) is but one of his many...

James Benford: Comments on METI

by Paul Gilster | Nov 11, 2013 | Astrobiology and SETI | 22 Comments

Pardon this extended introduction to Jim Benford's response to Nick Nielsen's Friday essay, but it comes at a serendipitous time. Jim's recent online work has reminded me that we in the interstellar community need to work to see that as many resources as possible are made available online. In the absence of specialized bibliographies, useful information can be hard to find in more general indices. And it's always dismaying to read an intriguing abstract only to realize that the paper itself is behind a pricey firewall. Access to academic libraries certainly helps, but online databases still vary in what they make available, which is why I always check the home pages of the authors of a given paper to see if they have posted a copy of their work themselves. Scientists can do much to get the word out, as Jim's new site attests. You'll find it at http://jamesbenford.com/. Over the weekend, after Nick had discussed METI (Messaging to Extraterrestrial Intelligence) on Friday, I resorted...

SETI, METI, and Existential Risk

by Paul Gilster | Nov 8, 2013 | Astrobiology and SETI | 49 Comments

To broadcast or not to broadcast? The debate over sending intentional signals to other stars continues to simmer even as various messages are sent, with no international policy in place to govern them. Writer Nick Nielsen looks at METI afresh today, placing it in the context of existential risk and pondering the implications of what David Brin has dubbed the 'Great Silence.' If risk aversion is our primary goal, do we open ourselves to a future of permanent stagnation? Or is announcing ourselves to the universe something we have any real control over, given the ability of an advanced civilization to detect our presence whether we send messages or not? Mr. Nielsen, a contributing analyst with online strategic consulting firm Wikistrat, wonders whether our counterparts around other stars aren't wrestling with the same issues. by J. N. Nielsen At the Icarus Interstellar Starship Congress in Dallas last August I had the good fortune to be present for James Benford's talk about METI,...

Towards a Vessel Pattern Language

by Paul Gilster | Nov 7, 2013 | Culture and Society | 9 Comments

Today Heath Rezabek continues his investigation of the Vessel proposal, a strategy for preserving the cultural and biological heritage of our species. Based in Austin TX, librarian and futurist Rezabek is concerned with existential risk and ways to manage it. His work has yielded lively discussions in the comments section here, as has that of his collaborator Nick Nielsen, from whom we'll hear tomorrow. In this essay, Heath moves on to question not only the various forms a Vessel might take, but where and how it could be built. Your thoughts are solicited not only in comments but also through the online survey whose address is given at the end. Previous essays in this series are Deep Time: The Nature of Existential Risk (on the mitigation of Xrisk through long-term archival and learning labs) and Visualizing Vessel (on visualization, design fiction, science fiction prototyping and their application to the Vessel proposal). by Heath Rezabek Comments and discussion in the previous...

Looking Ahead to TESS

by Paul Gilster | Nov 6, 2013 | Exoplanetary Science | 2 Comments

Thinking about the Kepler results now under discussion in these pages, one thing that stands out is that for most of the Kepler planets, we have no idea of their density. A transit can tell you about the size of the planet crossing in front of its star, but following up the detection with ground-based telescopes is crucial, because radial velocity studies can put some boundaries on its mass. With both size and mass in hand, you can determine the density, and that tells us whether a detected world is rocky like the Earth or a water world or an ice giant like Neptune. In a recent interview with Popular Mechanics, David Latham (Harvard-Smithsonian Center for Astrophysics) described TESS, the Transiting Exoplanet Survey Satellite, and its role in the planet hunt beyond Kepler. With so many space observatories either cancelled (Space Interferometry Mission) or on indefinite hold (Terrestrial Planet Finder), it's heartening to have this mission in the pipeline. And because TESS is going to...

Earth-Sized Planets in Habitable Zone Common

by Paul Gilster | Nov 5, 2013 | Exoplanetary Science | 72 Comments

The widely circulated Kepler results, announced yesterday, tell us that over twenty percent of Sun-like stars in the Milky Way have Earth-sized planets in the habitable zone, where liquid water could exist on the surface. Work out the math and it turns out that the nearest Sun-like star with a planet like ours in the habitable zone is probably on the order of twelve light years away, an energizing thought for those of us who ponder future technology and interstellar probes. Imagine: One in five Sun-like stars with a planet the size of Earth in the zone where liquid water can exist. Image: Analysis of four years of precision measurements from Kepler shows that 22±8% of Sun-like stars have Earth-sized planets in the habitable zone. If these planets are as prevalent locally as they are in the Kepler field, then the distance to the nearest one is around 12 light-years.zone. Credit: Petigura/UC Berkeley, Howard/UH-Manoa, Marcy/UC Berkeley. But how did we get here? Kepler, which was...

Views of Proxima Centauri

by Paul Gilster | Nov 4, 2013 | Deep Sky Astronomy & Telescopes | 10 Comments

I haven't yet read Stephen Baxter's new novel Proxima, but because of my admiration for his previous books, it's at the top of my reading list. Judging from the Amazon description, Proxima gets into issues that for me make red dwarfs utterly compelling. What would a habitable planet look like around such a star, tidally locked so that its sun never moved in the sky? What would it be like to move around this world, going from a warm substellar point toward twilight and then a frigid night on the dark side? Given that this M-class red dwarf is 18,000 times fainter than the Sun, you wouldn't expect it to make much of an impression in photographs. The one above (credit: European Southern Observatory) is instructive because it puts the entire Alpha Centauri system in context. At top left we have Centauri A and B, which are bright enough to merge together and appear as a single bright object. At the lower right is the arrow indicating Proxima Centauri, so faint as to be barely visible....

Les Johnson: Big Projects and Deep Time

by Paul Gilster | Nov 1, 2013 | Culture and Society | 13 Comments

Not long ago I pulled a wonderful 1950 film out of my collection for a long-overdue viewing. I remember 711 Ocean Drive from late night television airings, and when it popped up a few years back on a local cable channel, I made a recording. Edmund O'Brien and Joanne Dru are the key players in this gritty tale about an electronics expert who gets drawn into big-time crime, and the ending, which takes place at the Hoover Dam straddling the Nevada/Arizona border, is simply terrific, with O'Brien taking the fall after his shady dealings have been exposed. Image: On the run at the Hoover Dam in Joseph Newman's 711 Ocean Drive. Titanic forces, vast engineering, gunplay in the desert, all artfully directed by Joseph M. Newman -- what more could you want? And now, thanks to Les Johnson, I connect Hoover Dam not only with a film noir classic but with long-term thinking and starflight. Johnson, speaking in his role as a science writer with deep connections to science fiction, told the recent...

Kepler-78b: Rocky World in Unusual Orbit

by Paul Gilster | Oct 31, 2013 | Exoplanetary Science | 26 Comments

When I was first learning about astronomy by reading every book I could find on the subject -- I spent a lot of time at the library in my youth -- I was fascinated to hear stories of a planet closer to the Sun than Mercury. The French scientist Urbain Le Verrier pondered the existence of such a world in the 19th Century, wondering if it wouldn't explain peculiarities in Mercury's orbit. When an amateur astronomer named Edmond Modeste Lescarbault claimed he had observed a transit of such a planet in 1859, Le Verrier's investigation satisfied him that the detection was legitimate. He went on to announce the discovery of the planet he dubbed Vulcan in Paris in 1860. Despite a string of other observing claims later in the century, the existence of Vulcan is now discounted, although the possibility of asteroids in tight solar orbits hasn't been ruled out. As for Mercury, it fell to Einstein to demonstrate that apparent anomalies in its orbit could be explained by his theory of General...

HD 21997: Challenge to Planet Formation Theories

by Paul Gilster | Oct 30, 2013 | Exoplanetary Science | 1 Comment

HD 21997 is a star in the southern constellation Fornax (the Furnace) that is yielding some surprising data about how planetary systems form. About 235 light years from Earth, the star is 1.8 times the mass of the Sun and is thought to be about thirty million years old. Observations by an international team using ESA’s Herschel Space Observatory and the Atacama Large Millimeter/sub-millimeter Array (ALMA) in Chile show a ring of material around the star that contains not only a good deal of gas but also the dust produced by the collision of planetesimals. Image: ALMA images of the disk around HD 21997. The left image shows the emission of cold dust grains, situated in a ring around the central star. The middle image displays the emission from carbon monoxide, and shows that gas can also be found closer to the star than dust. The right image depicts the velocity of the gas. The red-colored parts of the disk move away from us, while the blue-colored parts move towards us, indicating...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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