Paul Gilster | Centauri Dreams

Exoplanets: Weeding Out False Positives

by Paul Gilster | Jun 12, 2012 | Exoplanetary Science | 10 Comments

The success of the Kepler mission in sifting through a field of more than 150,000 stars to locate transiting planets is undeniable, and the number of planets thus far discovered has been used to estimate how often planets occur around stars like the Sun. Now comes a paper to remind us that statistical analysis based on Kepler results assumes that most of the planet candidates are real and not false positives. Alexandre Santerne, a graduate student at the University of Aix-Marseille, has worked with a team of researchers to study the false positive rate for giant planets orbiting close to their star. 35 percent of these Kepler candidates may be impostors. The problem is that eclipsing binaries can mimic planetary transits, which is why scientists perform follow-up radial velocity studies or use transit timing variations (TTV) to confirm the existence of the planet. Another technique is to systematically exclude all possible false positive scenarios to a high level of confidence....

Brown Dwarfs Sparser than Expected

by Paul Gilster | Jun 11, 2012 | Deep Sky Astronomy & Telescopes | 33 Comments

Nobody has been anticipating the results from WISE -- the Wide-field Infrared Survey Explorer -- any more than I have. Speculations about the number of brown dwarfs in the galaxy have been all over the map, with some suggesting they might be as plentiful as M-dwarfs, which make up perhaps 80 percent of the stellar population. But the latest results from our infrared scan of the sky argue a much different result: Brown dwarfs turn out to be considerably more rare than stars, with an initial tally of the WISE data showing just one brown dwarf for every six stars. Thus Davy Kirkpatrick, a member of the WISE science team at NASA's Infrared Processing and Analysis Center at Caltech: "This is a really illuminating result. Now that we're finally seeing the solar neighborhood with keener, infrared vision, the little guys aren't as prevalent as we once thought." Ouch. The nice thing about a sky full of undiscovered brown dwarfs was that it might serve up interstellar destinations closer than...

Science, Fiction and the Sail

by Paul Gilster | Jun 8, 2012 | Sail Concepts | 5 Comments

Thinking about the poem "To Sail Beyond the Sun: A Luminous Collage," which I published excerpts from yesterday, I was reminded that if Ray Bradbury didn't spend a lot of time on solar sails, many of his compatriots did. Indeed, the early story of the solar sail is inseparable from science fiction. Astounding Science Fiction's John Campbell published the first serious look at solar sails for propulsion all the way back in May of 1951. The article's title, "Clipper Ships of Space," would be echoed by a highly influential paper by Gregory Matloff and Eugene Mallove called "Solar Sail Starships: The Clipper Ships of the Galaxy," which ran in the Journal of the British Interplanetary Society in 1981. The thirty years that passed between publication of the two articles saw the solar sail come into its own as a serious mission concept. Carl Wiley, who wrote the essay in Astounding, knew that many scientists and engineers were science fiction readers, but he was concerned enough about his...

On Ray Bradbury

by Paul Gilster | Jun 7, 2012 | Culture and Society | 25 Comments

Thinking of Ray Bradbury, as I suppose most of us were yesterday after learning of his death, I found my reminiscences of his work mixing with what was to have been today's topic, solar sails and their beamed sail counterparts. I've read almost all of Bradbury's work up through the 1960s and admittedly little after that, but he's a writer I return to often to try to recapture the early magic. I was going through his stories trying to think of one involving solar sails and I came up blank, but in a moment of pure serendipity, I realized that a book I mentioned yesterday held a little Bradbury gem that was all about sails and their implications for the human imagination. The book is Arthur C. Clarke's collection Project Solar Sail (Roc, 1990), which contains a poem Bradbury wrote with Jonathan V. Post called "To Sail Beyond the Sun: A Luminous Collage." Like so much of Bradbury's work, it uses language like witchcraft to pull you into the experience, and like so much of the later...

Big Sails, Challenging Dreams

by Paul Gilster | Jun 6, 2012 | Sail Concepts | 19 Comments

I've been thinking about solar sails these past few days, a topic that inevitably invokes Arthur Holly Compton, who first demonstrated that x-rays have particle-like properties. Compton's experiments in 1923 produced a body of work for which he would receive the Nobel Prize in Physics later that decade. Thanks to him we learned that while photons have no mass, they do have momentum, a useful fact for space exploration in that momentum can be transferred to a thin reflective sail, like the Japanese IKAROS that was successfully launched and tested in space in 2010. No question that the force is tiny -- a sail would have to be a square mile in area to feel just five pounds of force at the Earth's distance from the Sun. The beauty of the sail, of course, is that it can keep producing thrust as long as it's in sunlight. But how to increase the thrust? In an essay in his new book Going Interstellar (edited with Jack McDevitt and just out from Baen), Les Johnson notes that if we wanted to...

A Space Telescope on the Cheap

by Paul Gilster | Jun 5, 2012 | Deep Sky Astronomy & Telescopes | 16 Comments

Back in 1997, astronaut John Grunsfeld pulled off one of the great radio gags of all time by calling in to National Public Radio's 'Car Talk' program while orbiting the Earth aboard Atlantis in STS-81. He had called to complain about his vehicle's performance which, as he told the show's hosts -- known as 'Click and Clack, the Tappet Brothers' -- was driving him crazy. His troublesome ride would buck and rattle and run loud for four minutes, then get much quieter for another ten, and then the engine would quit. Odd behavior for any vehicle but the Space Shuttle, as Click and Clack eventually realized, and a memorable exploit for Grunsfeld's second Shuttle mission. Image: A bumpy ride to orbit -- liftoff of STS-81 on January 12, 1997. Credit: NASA. Grunsfeld is more commonly remembered as a repairman for the Hubble Space Telescope, a task he performed on three subsequent missions without the help of 'Car Talk.' Now the astronaut, with over 58 days in space and eight space-walks, is in...

HD 189733b: An Evaporating World?

by Paul Gilster | Jun 4, 2012 | Exoplanetary Science | 4 Comments

While we wait for the last transit of Venus of the century, it's worth remembering how tricky transit studies can be when we push them out to exoplanetary distances. You would think that catching a transit of a planet like Venus, closer to us than the Sun, would be simplicity itself, but the orbital planes of Venus and the Earth are not precisely enough aligned to allow for more than a pair of transits followed by over a century of waiting for the next. I've just received a copy of Mark Anderson's The Day the World Discovered the Sun (Da Capo Press, 2012) and will be writing about 18th Century transit studies and their impact in coming weeks. The transits Anderson writes about and the expeditions that ranged the globe to study them played a role in helping astronomers understand the dimensions of the Solar System. And you can see that if Venus is a challenge, tracking planets around other stars will push our technology to its limit. Nonetheless, we're getting quite good at teasing...

All Quiet Around Gliese 581

by Paul Gilster | Jun 1, 2012 | Exoplanetary Science | 31 Comments

When you're looking for signs of an extraterrestrial civilization, you can take two basic approaches. Think back to Frank Drake's initial SETI experiment at Green Bank in 1960, when because of limited resources and time he chose specific targets: Epsilon Eridani and Tau Ceti. The choice made sense at the time because both were nearby stars and SETI, fresh off the classic paper "Searching for Interstellar Communications" by Philip Morrison and Giuseppe Cocconi, was just beginning to define a methodology. Drake studied his targets near the 1.420 GHz frequency -- the 21 centimeter hydrogen line -- that the authors had suggested. Of course, sky surveys are also possible, of which SETI@home may be the most widely known. Here the idea is to make no assumptions whatever about the location of a SETI signal and observe the entire sky. SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is an attempt, for example, to analyze radio telescope data...

Is Our Civilization Detectable?

by Paul Gilster | May 31, 2012 | Astrobiology and SETI | 69 Comments

I haven't even finished the first line of this post and I'm already in a digressive mood. The mental sidetrack comes from yesterday's talk about the Square Kilometer Array, whose primary installations are now to be built in both South Africa and Australia. By observing an object through many instruments simultaneously, astronomers can use the technique called interferometry to combine incoming data and emulate a much larger instrument. The SKA's sensitivity promises to be high enough to allow the detection of possible leakage radiation from another civilization, which prompted me to recall a quote I had buried in my archives: "I know perfectly well that at this moment the whole universe is listening to us -- and that every word we say echoes to the remotest star." The words are those of Jean Giraudoux, a French writer and diplomat whose plays, written between the two world wars, gained him an international audience (Christopher Fry was among the admirers who adapted Giraudoux's work...

Thoughts on the Square Kilometer Array

by Paul Gilster | May 30, 2012 | Deep Sky Astronomy & Telescopes | 16 Comments

We now know that the vast collection of radio dishes and antennae that will become the Square Kilometer Array (SKA) will be built on two sites, with the majority of dishes in Phase 1 (beginning in 2016) being constructed in South Africa, and further dishes added in Australia as the project develops. The SKA is to be a radio telescope of unprecedented sensitivity capable of sky surveys at frequencies from 70 MHz to 10 GHz. A SKA news release notes that "All the dishes and the mid-frequency aperture arrays for Phase II of the SKA will be built in Southern Africa while the low-frequency aperture array antennas for Phase I and II will be built in Australia." Combining the signals from the project's dishes, mid-frequency aperture arrays and low-frequency aperture arrays will offer a telescope with a collecting area equivalent to a dish with an area of one square kilometer, a truly formidable observing platform. Phase 1 construction will involve about 10 percent of the array and will...

A Longer, Heavier Bombardment

by Paul Gilster | May 29, 2012 | Asteroid and Comet Deflection | 8 Comments

We know that the early Earth was a violent place, but just how violent? The so-called Late Heavy Bombardment is thought to have occurred from 4.1 billion to 3.8 billion years ago, likely the result of asteroids being destabilized in their orbits by shifts in the orbits of the outer planets. That model is self-limiting, with the unstable asteroids being depleted over time and the Late Heavy Bombardment winding down, and it matches the dating of rocks from the lunar basins that show vivid evidence of the battering both Earth and Moon took. But as I mentioned last week, the question of the length of the Late Heavy Bombardment is in play, with two papers in Nature suggesting that heavy impacts may have continued for a much longer time, perhaps half of the Earth's history. William Bottke (Southwest Research Institute) and team are suggesting that during this early period, the inner edge of the asteroid belt was just 1.7 AU from the Sun -- in a region called the E-belt, a largely extinct...

Impacts Spreading Life through the Cosmos?

by Paul Gilster | May 25, 2012 | Asteroid and Comet Deflection | 49 Comments

Still catching up after the recent series on antimatter propulsion, I want to move into some intriguing work on panspermia, the idea that life may spread throughout a Solar System, and perhaps from star to star, because of massive impacts on a planetary surface. Catching up with older stories means leaving some things unsaid about antimatter -- in particular, I want to return to the question of antimatter storage, which in my mind is far more significant a problem even than antimatter production. But there's time for that next week, and as I said yesterday, interesting stories keep accumulating and deserve our attention. Planetary Ejecta and Trapped Microorganisms What Tetsuya Hara (Kyoto Sangyo University) and colleagues put forth in a recent paper are their calculations about the ejection of life-bearing rocks and water into space from events like the possible 'dinosaur killer' asteroid impact some 65 million years ago, which involved an asteroid 10 kilometers in diameter. It's a...

Disruptive Planets and their Consequences

by Paul Gilster | May 24, 2012 | Uncategorized | 12 Comments

One of the joys of writing a site like Centauri Dreams is that I can choose my own topics and devote as much or as little time as I want to each. The downside is that when I'm covering something in greater depth, as with the four articles on antimatter that ran in the last six days, I invariably fall behind on other interesting work. That means a couple of days of catch-up, which is what we'll now see, starting with some thoughts on a possible planet beyond Neptune, a full-sized world as opposed to an ice dwarf like Pluto or Eris. This story is actually making the rounds right now, but it triggered thoughts on older exoplanet work I'll describe in a minute. It's inevitable that we call such a world Planet X, in my case because of my love for the wonderful Edgar Ulmer film The Man from Planet X (1951), in which a planet from the deeps wanders into the Solar System and all manner of trouble -- including the landing of an extraterrestrial on a foggy Scottish moor -- breaks out. Of...

Losing Our Cosmology

by Paul Gilster | May 23, 2012 | Deep Sky Astronomy & Telescopes | 26 Comments

Long-time Centauri Dreams readers know I love the idea of ‘deep time,’ an interest that cosmology provokes on a regular basis these days. Avi Loeb’s new work at Harvard tweaks these chords nicely as the theorist examines what we know and when we won’t be able to study it any longer. For an accelerating universe means that galaxies are moving outside our light horizon, to become forever unknown to us. Using tools like the Wilkinson Microwave Anisotropy Probe, we’ve been able to learn how density perturbations in the early universe, thought to have been caused by quantum fluctuations writ large by a period of cosmic inflation, emerged as the structures we see today. But are there limits to cosmological surveys? Start with that period of inflation after the Big Bang, which would have boosted the scale of things by more than 26 orders of magnitude, helping to account for the fact that the cosmic microwave background (CMB) appears so uniform in all directions. We can tease out the...

Toward a Beamed Core Drive

by Paul Gilster | May 22, 2012 | Antimatter | 14 Comments

If you didn't see this morning's spectacular launch of the SpaceX Falcon 9, be sure to check out the video (and it would be a good day to follow @elonmusk on Twitter, too). As we open the era of private launches to resupply the International Space Station, it's humbling to contrast how exhilarating this morning feels with the great distances we have to traverse before missions to another star become a serious possibility. We've been talking the last few days about the promise of antimatter, but while the potential for liberating massive amounts of energy is undeniable, the problems of achieving antimatter propulsion are huge. So we have to make a lot of leaps when speculating about what might happen. But let's assume just for the sake of argument that the problem analyzed yesterday -- how to produce antimatter in quantity -- is solved. What kind of antimatter engine would we build? If everything else were optimum, we'd surely try to master a beamed core drive, the pure product of the...

Antimatter: The Production Problem

by Paul Gilster | May 21, 2012 | Antimatter | 22 Comments

Antimatter is so tantalizing a prospect for propulsion that every time a new slant on using it appears, I try to figure out its implications for long-haul missions. But the news, however interesting, is inevitably balanced by the reality of production problems. There's no question that antimatter is potent stuff, with the potential for dealing out a thousand times the energy of a nuclear fission reaction. Use hydrogen as a working fluid heated up by antimatter and 10 milligrams of antimatter can give you the kick of 120 tonnes of conventional rocket fuel. If we could get the cost down to $10 million per milligram, antimatter propulsion would be less expensive than nuclear fission methods, depending on the efficiency of the design. But how to reduce the cost? Current estimates show that producing antimatter in today's accelerator laboratories runs the total up to $100 trillion per gram. But when I was researching my Centauri Dreams book, I spent some time going through the collection...

100 Year Starship Organization Launches

by Paul Gilster | May 18, 2012 | Culture and Society | 16 Comments

Today was to have been devoted to antimatter, continuing the discussion not only of how to produce the stuff on Earth or harvest it in nearby space, but how to create the kind of propulsion system that could tap its enormous energies. But the Dorothy Jemison Foundation for Excellence released its first public announcement about the 100 Year Starship yesterday, and I want to go right to that story given the interest that grew out of last year's starship symposium in Orlando. I'll get back to antimatter, then, and particularly the provocative work of Ronan Keane and Wei-Ming Zhang on magnetic nozzles for propulsion systems, on Monday. For today, though, let's talk about pushing out into the galaxy. The Tau Zero Foundation has a particular interest in the 100 Year Starship organization because our friends at Icarus Interstellar, who are re-thinking the 1970s Project Daedalus design, were partners in the winning proposal, which was called "An Inclusive, Audacious Journey Transforms Life...

Antimatter: Finding the Fuel

by Paul Gilster | May 17, 2012 | Antimatter | 30 Comments

In Stephen Baxter’s wonderful novel Ark (Roc, 2010), a team of scientists works desperately to come up with an interstellar spacecraft while epic floods threaten the Earth. The backdrop gives Baxter the chance to work through many of our current ideas about propulsion, from starships riding a wave of nuclear explosions (Orion) to antimatter possibilities and on into Alcubierre warp drive territory. I won’t give away the solution, but will say that it partly involves antimatter used in an unorthodox way, and because Baxter’s is a near-term Earth, there simply isn’t enough antimatter to go around. That means getting to Jupiter first to harvest it. Antimatter in space is an idea that James Bickford (Draper Laboratory) analyzed in a Phase II study for NASA’s Institute for Advanced Concepts, for he had realized that high-energy galactic cosmic rays interacting with the interstellar medium (and also with the upper atmospheres of planets in the Solar System) produce antimatter. In fact,...

Changing the Risk Paradigm

by Paul Gilster | May 16, 2012 | Asteroid and Comet Deflection | 17 Comments

As we continue to think about the implications of Planetary Resources and its plans for asteroid mining, I was interested to see exoplanet hunter Sara Seager (MIT) make a rousing case for the company's ideas and for commercial space ventures in general. Seager, who works with Planetary Resources as a science advisor, tells The Atlantic's Ross Andersen in a May 14 interview that one reason for optimism is the progress we're making with robotics. Mining operations currently being managed beneath the seas are being handled by robotics. Couple that with our ability to get to and orbit an asteroid as well as to scoop up surface materials and you have all the ingredients for a workable mining operation in a low-gravity environment. Seager explains that asteroids are attractive mining targets because unlike fully formed planets like the Earth, their heavier elements have not largely sunk inside through planetary differentiation in the early days of the planet's existence. Asteroids are...

A Near-Term Enterprise?

by Paul Gilster | May 15, 2012 | Missions | 28 Comments

It's too bad we don't already have a workable Enterprise, that vast near-term rendition of the Star Trek vehicle that a systems engineer named 'Dan' has been talking about on BuildTheEnterprise.org (a site which has been so heavily trafficked in the last 48 hours that it has proven almost inaccessible). What Dan has in mind is the design, down to the smallest level of detail, of a ship powered by three ion propulsion engines that tap on-board nuclear reactors to remain operational. It may not be an antimatter-powered Enterprise, but it's a faithful simulacrum, reflecting its creator's long-lasting interest in the ship that William Shatner once commanded. Dan thinks the new Enterprise could get us to Mars in 90 days, but getting nuclear reactors into low Earth orbit in the first place will be a challenge not only technically but politically, and shielding the crew will also involve a serious amount of mass that has to get lifted. One of the fascinations of this highly detailed site is...

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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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