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Gl 581: The Case for Habitable Planets

by Paul Gilster | Aug 2, 2012 | Exoplanetary Science | 20 Comments

Not long ago, while making a presentation about possible destinations for an interstellar probe, I called Gl 581d the most likely candidate for habitability yet discovered among nearby stars. I knew the planet was problematic, perhaps too far on the outer edge of the habitable zone to be a realistic candidate, although this seems to depend on a variety of factors including atmospheric modeling. But what I had really been pondering in deciding whether or not to include Gl 581d in the talk was whether its purported sister world, Gl 581g, should be brought into play. Steven Vogt (UC-Santa Cruz) and colleagues were getting ready to distribute their new paper making a further case for a super-Earth in the habitable zone, one that seemed to be ideally placed for liquid water to exist on the surface. Bring that into the discussion? I decided against it, because the controversy over this world continues and Centauri Dreams seems a better venue than a short public talk to get into the...

Habitable Worlds around White Dwarf Stars?

by Paul Gilster | Aug 1, 2012 | Astrobiology and SETI | 33 Comments

Not all that long ago we assumed habitable planets needed a star like our Sun to thrive, but that view has continued to evolve. M-class red dwarfs may account for as many as 80 percent of the stars in our galaxy, making habitable worlds potentially more numerous around them than anywhere. And let's extend our notion of habitability to what Luca Fossati (The Open University, UK) and colleagues call a Continuous Habitable Zone (CHZ). Now things really get interesting, for a red dwarf evolves slowly, so planets could have a CHZ with surface water for billions of years. But what about white dwarfs? Stellar evolution seems to rule out habitable worlds around them because we normally think of stars entering their red giant phase and destroying their inner planets enroute to becoming a white dwarf. But can a new planetary system emerge from the wreckage? We've already found planets orbiting close to the exposed core of a red giant (KOI 55.01 and KOI 55.02), showing that the end of main...

Communication with Extraterrestrial Intelligence

by Paul Gilster | Jul 31, 2012 | Astrobiology and SETI | 64 Comments

By Larry Klaes One result of the biennial Astrobiology Science Conference (AbSciCon) held the last week of April in 2010 was to gather SETI specialists from around the world to look at everything from search strategies and signal processing to the best ways of creating an interstellar message. Tau Zero's Larry Klaes has been reading the collected papers from the meeting's SETI sessions, which have inspired him to ponder SETI's place in the scheme of things and how our reaction to the search tells us something about who we are and who we are becoming. Readers with a long memory may recall that the first major conference on interstellar communications, held in Soviet Armenia in 1971, produced a volume of proceedings titled Communication with Extraterrestrial Intelligence, a title editor Douglas Vakoch deliberately echoes in the current work, partly as a nod to the field's past and partly as a measure of how far it has come. I love anthologies. There is nothing like having a collection...

On Cosmic Isolation

by Paul Gilster | Jul 30, 2012 | Astrobiology and SETI | 31 Comments

Michael Chorost is a science writer whose research interests grow directly out of his personal experience. You may have already read about his struggle with hearing loss -- a problem he has dealt with since childhood -- in his book Rebuilt: How Becoming Part Computer Made Me More Human (Houghton Mifflin, 2005). It's natural to find Chorost writing often on things like cochlear implants and neurotechnology, but intriguing to find that he is also a SETI advocate, and one who believes his hearing issues have a bearing on a field he has studied passionately all his life. In fact, the book he plans next, which follows on 2011's World Wide Mind (Free Press) will be a SETI title. So what's the connection between deafness and hunting for signs of an extraterrestrial civilization? Chorost sees it as a matter of isolation and communication, as he notes in a recent entry on the Psychology Today site. Is the entire human race subject to deafness? It is in the sense that we have no idea whether...

Defending the Interstellar Vision

by Paul Gilster | Jul 27, 2012 | Culture and Society | 51 Comments

An interstellar movement has been brewing for the past sixty or so years among physicists and engineers who have taken a serious look at what it would take to get to the stars. Their work is not based on wishes but on physics, and while they are aware of the intractable distances to reach even the nearest star (4.2 years at the speed of light itself), they have continued to study how to send spacecraft on such epic journeys. Organizations have emerged -- DARPA's 100 Year Starship, Icarus Interstellar, the Tau Zero Foundation -- whose members call to mind physicist Robert Forward's injunction: "Travel to the stars is difficult but not impossible." Centauri Dreams readers know all this, but at least on the basis of Adam Frank's op-ed Alone in the Void, many readers of The New York Times do not. A professor of physics and astronomy himself (University of Rochester), Frank is well versed in the problems of distance and time and understands how difficult it will be to send humans to the...

Al Jackson: A Laser Ramjet Reminiscence

by Paul Gilster | Jul 26, 2012 | Advanced Rocketry | 11 Comments

by A. A. Jackson It’s always good when you can go to the source, which I am delighted to do with this reminiscence by Al Jackson, whose laser-powered ramjet (and laser-powered interstellar rocket) ideas we’ve been looking at for the past few days. Al recalls discovering the work of Eugen Sänger back around 1960 and beginning the study of interstellar propulsion ideas, a passion he continues to this day. His 1975 doctorate from the University of Texas at Austin followed his work for NASA during the heyday of Apollo as astronaut trainer on the Lunar Module Simulator. Here he thinks back to the genesis of his interest in astronautics and reflects on the factors that led to his combining the Bussard ramjet concept with the developing idea of beamed energy. I don’t think I had ever planned to write a technical paper about interstellar flight. However, as an SF reader I had been entranced by the idea since the early 1950?s. I was already a space cadet! When I got to university in 1959 and...

Rocketry on a Beam of Light

by Paul Gilster | Jul 25, 2012 | Advanced Rocketry | 7 Comments

The year after Al Jackson, working with Daniel Whitmire, published his concept of a laser-powered interstellar ramjet, the duo returned in the pages of JBIS with a spinoff design. The issue was obvious: Central to Robert Bussard's ramjet design was the idea that the spacecraft would carry no fuel, but collect reaction mass from the interstellar medium. There were a number of reasons why this was problematic, including the drag of the ram scoop and the problem of lighting proton/proton fusion. So Jackson and Whitmire decided to look at a space-based laser powering up a starship that carried its own reaction mass onboard. It turned out that John Bloomer had looked at supplying a spacecraft through an external laser energy source as far back as 1967, though in his case the craft would use the laser energy it received to run an electrical propulsion system (the Bloomer citation is given at the end of this article). Jackson wanted to think in terms of relativistic interstellar flight, and...

A Laser-Powered Interstellar Ramjet

by Paul Gilster | Jul 24, 2012 | Advanced Rocketry | 8 Comments

Many of the interstellar concepts I write about in these pages take on a life of their own. After the initial brainstorming, the idea gets widely enough disseminated that other scientists take it on, looking to modify and improve on the original concept. That's been true in the case of solar sails and the more recently devised 'lightsails,' which use beamed energy from a laser or microwave source to drive the vehicle. We continue to study magnetic sails -- 'magsails' -- and various nuclear options like the inertial confinement fusion that powered Daedalus and perhaps Icarus. Sometimes insights arise when ideas are grafted onto each other to create a hybrid solution. The idea I want to examine today, a hybrid design combining a Bussard-style interstellar ramjet with laser beaming -- exemplifies this mix and match process. Working with Daniel Whitmire, A. A. Jackson, a frequent commenter and contributor here on Centauri Dreams, pondered the various issues the Bussard ramjet had run...

A Closer Look at Medusa

by Paul Gilster | Jul 23, 2012 | Advanced Rocketry | 13 Comments

I see that 'Zarmina' is back in the news. The informal designation refers to Gliese 581 g, an exoplanet candidate announced by the Lick-Carnegie team in an effort led by Steven Vogt (UC-Santa Cruz). First you see it, then you don't -- Gl 581 g has been controversial from the start, and is now the subject of a new analysis describing a 32-day orbit, a super-Earth in the habitable zone. More on the analysis later in the week, because my purpose today is to keep digging into the options for getting to a place like this once we're sure it really does exist. Gl 581 is just over 20 light years from the Sun in the constellation Libra, a red dwarf whose planetary system is one of the nearest yet detected. Among the options for propulsion in a future interstellar probe is Medusa, the brain-child of Los Alamos physicist (now retired) Johndale Solem. As examined here on Friday, Medusa is a nuclear-pulse system, like Orion in that it relies on the explosion of a series of atomic bombs to propel...

Medusa: Nuclear Pulse Propulsion and the Sail

by Paul Gilster | Jul 20, 2012 | Sail Concepts | 21 Comments

Hybrid propulsion technologies have emerged naturally as we look at ways to reach the stars. They're the result of trying to extract maximum performance from each option, and it sometimes turns out that putting two ideas together works better than either by itself. Next week we'll be looking at one such concept, A. A. Jackson's idea of combining the Bussard ramjet with laser beaming in ways that turn out to be surprisingly effective. Today I want to start the hybrid discussion - already about a week late because of competing news -- by talking about Johndale Solem's 'Medusa,' a combination of sail technologies with nuclear pulse propulsion. Solem's work evidently draws on the ideas of Ted Cotter at Los Alamos in the 1970s, which evolved into what George Dyson has described as a 'rotating-cable pusher.' Think back to the Orion concept, with its immense pusher-plate and shock absorbers that would withstand the explosion of nuclear devices behind the plate, propelling the vehicle...

Proximity Hunt: Exoplanets Around Nearby Stars

by Paul Gilster | Jul 19, 2012 | Exoplanetary Science | 15 Comments

Finding new worlds with Kepler is an absorbing occupation, but the one thing missing from most exoplanet news is proximity. While we continue to search for planets around the Alpha Centauri stars, the closest candidate I know about is the gas giant thought to orbit Epsilon Eridani, some 10.5 light years out. If you're looking for potential habitability, you have to extend all the way out to Gliese 581 (almost twice the distance), where planets are plentiful and there is at least the chance (GL 581d) that one skirts the edge of the habitable zone. There are probably many planets closer than 20 light years, but we don't have the tools in space to find them easily. Kepler, you'll recall, studies a field of stars in Cygnus, Lyra and Draco, the goal being to develop a statistical approximation of the prevalence of Earth-sized planets in the galaxy. Looking out along the Orion arm, Kepler is watching stars anywhere from 600 to 3000 light years away. In fact, fewer than 1 percent of the...

Resolving the Pioneer Anomaly

by Paul Gilster | Jul 18, 2012 | Exotic Physics | 24 Comments

Anomalies are always fascinating because they cause us to re-examine our standard explanation for things. But in the case of the so-called 'Pioneer anomaly,' the Jet Propulsion Laboratory's Slava Turyshev, working with a group of scientists led by JPL's John Anderson, needed an explanation for practical reasons. The possibility that there was new physics to be detected had the scientists wondering about a deep space mission to investigate the matter, but missions are expensive and the case for a genuine Pioneer effect had to be strengthened or else put to rest. All of this led Turyshev to begin a multi-year data-gathering mission of his own, scouring records related to Pioneer wherever they might be found to see if what was happening to the spacecraft could be explained. The effect was tiny enough that it was originally dismissed as the result of leftover propellant in the fuel lines, but that explanation wouldn't wash. Something was causing the two Pioneers to decelerate back toward...

Remembering Ary Sternfeld

by Paul Gilster | Jul 17, 2012 | Culture and Society | 9 Comments

Galileo Galilei makes a brief appearance in the news this morning with word that several copies of his books, including two examples of the Sidereus Nuncius, have turned out to be forgeries. The latter, whose title is usually translated as Starry Messenger, was the first scientific presentation on observations made with a telescope, and contains Galileo's early work on the Moon and the moons of Jupiter, among other things. One Marino Massimo De Caro, currently under arrest for massive thefts from the Girolamini Library in Naples, may have had connections with the forgeries, which are worrisome news for those of us who like to poke around in ancient manuscripts and for anyone interested in the history of science. News of the manuscripts also puts me in mind of a paper by Danielle Briot (Observatoire de Paris), which uses Galileo in quite a different context. Briot became interested in the life and work of Ary Sternfeld (1905-1980), a prolific writer on science and a researcher who may...

Detecting Exoplanet Oceans

by Paul Gilster | Jul 16, 2012 | Exoplanetary Science | 19 Comments

Is the discovery of oceans on planets orbiting distant stars within our reach? Finding such an ocean would be of immense interest from an astrobiological perspective because water on the surface is the traditional marker for a habitable zone. Astrobiology Magazine has just written up work by Nicholas Cowan (Northwestern University) and colleagues, who have been looking at the ways we might detect such oceans. The researchers are thinking ahead to a time when we have an actual image of a terrestrial world to look at, even if that image is little more than the 'pale blue dot' Voyager saw in its famous portrait of the Solar System. When we have identified that 'dot,' we can do a lot with it by studying the way its light varies as it orbits its star. Let's assume we deploy a starshade and use it in conjunction with the James Webb Space Telescope to block the light of the star and reveal the faint signature of the planet. A disk tens of meters wide with petal-like extensions, the...

Pluto: Moons, Debris and New Horizons

by Paul Gilster | Jul 13, 2012 | Outer Solar System | 15 Comments

When I was a boy, I became fascinated early on with the outer planets. The further out, the better as far as I was concerned, and as you might imagine, I had a special fascination with Pluto. In the summer, I used to haunt the library in the nearby suburb of Kirkwood (in St. Louis, where I grew up), working my way through all the books on astronomy and space I could find. Because I was reading all of them, I would encounter older volumes, some pre-dating the discovery of Pluto, and more recent tomes with details about the planet I didn't know. It didn't matter; I just kept reading. What was fun about all this was that I kept expecting to find something new each time I opened a book, and was sometimes rewarded with a fact that brought this distant realm into perspective. The news that Hubble has now found a fifth moon orbiting Pluto awakens that same sense of satisfaction, for as we keep tuning up our observing skills, we're learning much about the outer system that surprises us. The...

Interstellar Flight Goes Mainstream

by Paul Gilster | Jul 12, 2012 | Culture and Society | 6 Comments

Paging back through Kelvin Long’s book Deep Space Propulsion (Springer, 2011) last night, I was reminded that Freeman Dyson had written about his disillusionment with nuclear pulse propulsion methods long after Project Orion was terminated. The passage is in his autobiographical account Disturbing the Universe (Basic, 1981), which caught Long’s attention and led him to reprint it. Here’s a snippet of Dyson’s reflections: Sometimes I am asked by friends who shared the joys and sorrows of Orion whether I would revise the project if by some miracle the necessary funds were suddenly to become available. The answer is an emphatic no... By its very nature, the Orion ship is a filthy creature and leaves its radioactive mess behind it wherever it goes... Many things that were acceptable in 1958 are no longer acceptable today. My own standards have changed, too. History has passed Orion by. There will be no going back. Long speculates that Dyson may simply have been referring to Orion as an...

An Interstellar Provocation

by Paul Gilster | Jul 11, 2012 | Culture and Society | 12 Comments

It had never occurred to me that there was something the Graf Zeppelin and the Saturn V had in common. Nonetheless, a re-reading of Freeman Dyson's paper "Interstellar Transport" confirms the obvious connection: Like the great airships of the 1930s, the Saturn V was huge and carried a payload that was absurdly small. Dyson, writing in 1968 fresh off the end of Project Orion, the rise of Apollo, and the triumph of chemical propulsion, had thought at one time that the US could bypass the Saturn V and its ilk, offering a fast track to the planets at a fraction of Apollo's cost. The Atmospheric Test Ban Treaty of 1963 was a major factor in putting an end to that speculation. I mentioned yesterday that I thought Dyson set about to be deliberately provocative in this piece, that he hoped to reach people who would have been unaware that interstellar distances could conceivably be crossed (thus his choice of Physics Today as his venue). To do that, he had to show that even reaching the Moon...

Beginnings of the Interstellar Idea

by Paul Gilster | Jul 10, 2012 | Culture and Society | 45 Comments

My time off last week really was refreshing, although it coincided with the same heat wave that has kept the Eastern US under duress for many days now, especially dangerous for those who lost power because of severe storms. Fortunately, I used part of my time to fly to San Jose to participate in Steve Durst's Galaxy Forum (sponsored by the International Lunar Observatory Association), where I spoke on destinations in the outer Solar System and beyond as we make our first tentative steps into the galaxy. It was a good gathering, with lively talk from Seth Shostak, Jon Lomberg, Tony Cardoza (who signs people up to travel on future flights with Virgin Galactic), and Durst himself. It was also a pleasure to meet Centauri Dreams regular Alex Tolley. Blissfully, the temperatures never got out of the low 70s, with a refreshing breeze that made walking around downtown a pleasure. Miles, my older son, lives near San Francisco and the trip was also a wonderful chance to reconnect. I can recall...

Revealing The New Universe and a Shared Cosmology

by Paul Gilster | Jul 9, 2012 | Culture and Society, Deep Sky Astronomy & Telescopes | 34 Comments

By Larry Klaes Larry Klaes, a frequent Centauri Dreams contributor and commenter, here looks at a new book that explores humanity's place in the cosmos. Is there a way to rise above our differences of outlook and perspective to embrace a common view of the universe? The stakes are high, for technology's swift pace puts the tools of exploration as well as destruction in our hands. C.P. Snow explored the gulf between science and literature 50 years ago, but as Larry notes, the division may be broader still as we confront the possibility of intelligent life other than ourselves. Just about anyone who has even taken the time to go outside on a clear night and stare up at the starry firmament over their head (assuming it is also largely free of the relatively recent artificial impediment called light pollution) has often been moved in rather profound ways by the sight, whether they are astronomically inclined or not. This feeling can be summed up, I think, by this quote from the artist...

Summer Comes to Green Town

by Paul Gilster | Jul 2, 2012 | Culture and Society | 21 Comments

Summer in Green Town, Illinois back in 1928 opened like this: "It was a quiet morning, the town covered over with darkness and at ease in bed. Summer gathered in the weather, the wind had the proper touch, the breathing of the world was long and warm and slow. You had only to rise, lean from your window, and know that this indeed was the first real time of freedom and living, this was the first morning of summer." Thus the beginning of Ray Bradbury's Dandelion Wine, which I re-read not long after the author's death. With catastrophic fires in the American west and triple-digit heat along the Atlantic seaboard, summer has indeed come, and so has a brief summer holiday for Centauri Dreams. Although I won't have months ahead of me the way Bradbury's character Douglas Spaulding did, I am looking forward to a week off. This site is now approaching its eighth anniversary and I'm ready for a break, one that will give me time to catch up on reading, do necessary work around the house, and...

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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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