By Larry Klaes 'The Gasbags of Jupiter' sounds for all the world like the title of an early 1930s novel that would have run in a venue like Science Wonder Stories. In fact, as Larry Klaes tells us below, the idea grew out of Carl Sagan's speculations about free-floating life-forms that might populate the atmospheres of gas giant planets like Jupiter. Cornell physicist Edwin Salpeter had much to do with the evolution of that concept, helping Sagan produce a paper that was a classic of informed imagination (and one that led to numerous science fiction treatments as the idea gained currency). Larry's celebration of Salpeter's life gives a nod to that paper but also notes his deep involvement in the study of the most distant celestial objects. On March 14, the Department of Astronomy at Cornell University will commemorate the life of one of their most prestigious faculty members: Edwin E. Salpeter, the James Gilbert White Distinguished Professor of Physical Sciences Emeritus. Salpeter...

Just how many forms of life are there? We often speculate here about life on other worlds, but Paul Davies (Arizona State) is currently exploring the question from a different perspective entirely. Davies would like to know whether a 'second genesis' might have occurred, producing a fundamentally different form of life that would have evolved right here on Earth and might still occupy our planet. Life may, in other words, have started many times, perhaps with significantly different results we just haven't uncovered yet. Call it a 'shadow biosphere,' a concept the physicist calls for exploring: "...[It] is still just a theory. If someone discovers shadow life or weird life it will be the biggest sensation in biology since Darwin. We are simply saying, 'Why not let's take a look for it?' It doesn't cost much (compared to looking for weird life on Mars, say), and, it might be right under our noses." Finding these alternate life forms, if they exist, may be tricky, as they could be...

I promised a quick return to recent work on the Drake Equation, which helps us estimate the number of communicating civilizations in the galaxy, but a BBC story on Duncan Forgan has me back at it even sooner than I had intended. It's no surprise that the matters encapsulated in Drake's thinking should be in the news. After all, the era of Fermi and Drake was without firm knowledge of extrasolar worlds, of which we now know over three hundred. For that matter, the concepts of habitable zones around both stars and the galaxy itself had not come to fruition, nor had anyone ever heard of the 'rare Earth' hypothesis. We also work today with knowledge of Charles Lineweaver's studies of the median age of terrestrial planets in the Milky Way, which point to civilizations around other stars having had as much as two billion years-plus to emerge before our own Earth had even coalesced. Until we know more, I suspect we'll be adjusting Drake parameters for some time, as Duncan Forgan (University...

Centauri Dreams' recent post on the Drake Equation triggered a broad range of response, both in comments and back-channel e-mails, the latter of which produced a note from Kelvin Long quoting a rather controversial position on Drake by one leading scientist. Here it is. See if it raises your hackles: "I reject as worthless all attempts to calculate from theoretical principles the frequency of occurrence of intelligent life forms in the universe. Our ignorance of the chemical processes by which life arose on earth makes such calculations meaningless." The words are Freeman Dyson's, from his essay "Extraterrestrials" in Disturbing the Universe (Harper & Row, 1979), a book I re-read every few years as much to admire the author's rhetorical skills as to draw again on his insights. Kelvin has differing views on Drake and so do I, but I'm going to quote Marc Millis' reaction to the Dyson statement, reflecting as it does an approach toward scientific method that I share. Marc writes: "On...

The Drake Equation in its various forms has been tormenting us for decades, raising the question of how to adjust variables that range from astronomical (the abundance of terrestrial planets) to biological (the probability of life's emergence) and even sociological (the average lifetime of a technological civilization). Wildly optimistic estimates of the number of technological civilizations in our galaxy are now giving way to more sober reflection. Now Reginald Smith (Bouchet-Franklin Institute, Rochester NY) offers up a new analysis looking at how likely radio contact is given a civilization's lifetime, and how widely that civilization's signals can be clearly received. The key question: What if there is a reasonable horizon for the detection of a signal from an extraterrestrial sender? Signals and Their Lifetime This is useful stuff, because contact depends not just upon the density of communicating civilizations (CC) but their average lifetime and the maximum detectable distance...

If you're not a member of the Science Fiction and Fantasy Writers of America (still commonly known as the SFWA from the days before the 'fantasy' bit was added), you may not see the group's regular bulletin. That would be understandable, given that although it can be found on newsstands, the SFWA Bulletin now costs a solid $6.95 per copy. Nonetheless, keeping up with Robert Metzger's 'State of the Art' science column would keep me buying this journal even if it didn't come as part of my membership. Metzger, the author of the 2002 novel Picoverse and 2005's CUSP as well as a variety of short fiction in addition to his science writing (some of which is available online), speculates in his most recent column on a subject we've recently treated here. Would a species capable of star travel actually need to make the journey, given the advances in technology that would surely make it possible to learn more and more about exoplanets from its own star system? Metzger reviews current exoplanet...

By Larry Klaes Tau Zero journalist Larry Klaes gives us a look at the immense contribution of physicist Giuseppe Cocconi to SETI. It's sobering to realize how new a study SETI really is. Frank Drake's Project Ozma began less than fifty years ago, while estimates of the number of extraterrestrial civilizations are just now scaling back dramatically from the numbers Drake himself and Carl Sagan once used (Claudio Maccone's recent work on the Drake Equation arrives at an estimate of 250 such civilizations in the Milky Way -- more on this soon). If it weren't for the efforts of Cocconi and Philip Morrison, the theorizing behind the Drake Equation and the development of SETI itself might have been slowed for years, as Larry points out so ably below. On November 9, the world said farewell to physicist Giuseppe Cocconi, who passed away at the age of 94. Although his life's work was in particle physics and cosmic ray science, Cocconi will always be best known for co-authoring the paper with...

Here I was all set to write about the discovery of carbon dioxide on HD 189733b when Alpha Centauri made its way back into the news. Twentieth Century Fox will be transmitting the re-make of the science fiction classic The Day The Earth Stood Still to Alpha Centauri on Friday the 12th, timing the event to coincide with the film's opening here on Earth. The transmission is being handled by Florida-based Deep Space Communications Network, a private organization that offers transmission services to the public (not to be confused with the Deep Space Network that manages communications with our planetary probes). Why does Deep Space Communications Network offer transmission services to the stars? From its FAQ: For a number of reasons, one is because we have the equipment, and the know how so we can, and also because we thought it would be an interesting public service that is not currently available. We're doing it because we can... This dubious news comes on the heels of the in many ways...

A Dyson Sphere makes an extraordinary setting for science fiction. In fact, my first knowledge of the concept came from reading Larry Niven's 1970 novel Ringworld, a book that left such an impression that I still recall reading half of it at a sitting in the drafty little parlor of a house I was renting in Grinnell, Iowa. Ringworld had just come out as a Ballantine paperback with the lovely cover you see below. I was hooked after about three pages and read deep into a night filled with wind and snow. It could be argued, of course, that a ring made out of planetary material, a habitat so vast that it completely encircles its star, is actually one of the smaller Dyson concepts. It was in 1960 that Freeman Dyson suggested how a civilization advanced to the point of such astro-engineering might use everything it found in its solar system to create a cloud of objects, a swarm that would make the most efficient use of its primary's light. And as you keep adding objects, you point to the...

Now here's a comprehensive task for you. Take about a dozen primordial minerals found in interstellar dust grains and figure out what processes -- physical, chemical, biological -- led to the appearance of the thousands of minerals we find on our planet today. The job was undertaken by Robert Hazen and Dominic Papineau (Carnegie Institution Geophysical Laboratory) and colleagues, and it produced startling results: Of the roughly 4300 known types of minerals on Earth (fifty new types identified each year), up to two-thirds can be linked to biological activity. Mineral evolution? In a sense, although Hazen is quick to qualify the statement: "It's a different way of looking at minerals from more traditional approaches. Mineral evolution is obviously different from Darwinian evolution — minerals don't mutate, reproduce or compete like living organisms. But we found both the variety and relative abundances of minerals have changed dramatically over more than 4.5 billion years of...

Using eleven of the Allen Telescope Array's 6.1-meter dishes, the SETI Institute and the Radio Astronomy Laboratory at the University of California (Berkeley) have detected the New Horizons spacecraft on its way to Pluto/Charon. New Horizons transmits an 8.4 GHz carrier signal that showed up readily on the SETI Prelude detection system. What I hadn't realized was that snagging distant spacecraft transmitters is a standard part of SETI operations, as Jill Tarter notes in this brief article on the event posted at the New Horizons site: "We look forward to checking in with New Horizons as a routine, end-to-end test of our system health. As this spacecraft travels farther, and its signals grow weaker, we will be building out the Allen Telescope Array from 42 to 350 antennas, and thus can look forward to a long-term relationship." Image: New Horizons as tracked by the Allen Telescope Array. This plot shows 678 hertz (Hz) of spectrum collected over 98 seconds. The New Horizons signal can...

The Moon is, for obvious reasons, rarely considered an interesting venue for astrobiology. But I've been looking through Joop Houtkooper's presentation at the European Planetary Science Congress, noting his contention that some lunar craters might hold samples of life from the early Earth, and perhaps even from Mars. If the name Houtkooper rings a bell, it may stem from the splash he made last year by suggesting that the Viking probes to Mars may have discovered Martian microbes consisting of fifty percent water and fifty percent hydrogen peroxide. Although some extremophiles here on Earth put hydrogen peroxide to use, the theory is quite a long shot. But then, Houtkooper (University of Giessen, Germany) seems to thrive on remote possibilities. His lunar theory works like this: Certain craters on the Moon are effectively shielded from sunlight, at least deep within their recesses. Shackleton crater at the south pole is a case in point, a place that may contain sub-craters free of...

I've spent so much recent time on two SETI/METI papers by James, Gregory and Dominic Benford because they contain powerful arguments for re-thinking our current SETI strategy. By analyzing how we might construct cost-optimized interstellar beacons, the authors ask what those beacons might look like if other civilizations were turning them toward us. The results are striking: A distant beacon operating for maximum effect consistent with rational expense would offer up a pulsed signal that will be short and intermittent, recurring over periods of a month or year. It will, in other words, be unlike the kind of persistent signal that conventional SETI is optimized to search for. Searches designed to sweep past stars quickly, hoping to find long-lasting beacons whose signature would be apparent, would rarely notice oddball signals that seem to come out of nowhere and then vanish. Tracking such signals, looking for signs of regularity and repetition, calls for a different strategy. Image:...

If we want to consider how to pick up transmissions from a distant civilization, it pays to consider the most effective strategies for building interstellar beacons here on Earth. This is the method James, Gregory and Dominic Benford have used in twin papers on SETI/METI issues, papers that should be read in conjunction since the METI questions play directly into our SETI reception strategies. It pays to have a microwave specialist like James Benford on the case. Our METI transmissions to date have used radio telescopes and microwaves to send messages to nearby stars. Longer distances will cost more and take much more power. How much would a true interstellar beacon cost, one not limited to the relatively short ranges of recent METI transmissions? Count on something on the order of $10 billion. As to power, Jim is able to quantify the amount. To reach beyond roughly a thousand light years with a microwave beacon, an Effective Isotropic Radiated Power (EIRP) greater than 1017 W must...

Several interesting papers on SETI have appeared in recent days, among them Gregory, James and Dominic Benford's attempt to place SETI in the context of economics. Equally useful is Duncan Forgan's new look at the Drake Equation, presenting a way to estimate the distribution of the crucial parameters. I'll bypass the Forgan paper temporarily because I've asked Marc Millis to tackle it as soon as he gets back from the Jet Propulsion Laboratory, where he's gone to attend a workshop. Forgan's study has direct bearing on a Tau Zero initiative we hope to have in place by the end of the year and thus is a natural for Marc to write up. But back to the Benfords, who have offered up twin papers (as seems reasonable for the brothers), one on SETI (with Gregory as principal author) and the other on its METI offshoot (transmitting messages rather than listening for them). James Benford is lead author on the latter. This work is so rich that I won't try to encapsulate it in a single post, but...

A new look at Stanley Miller's experiments at the University of Chicago in the early 1950s offers up an intriguing speculation: Volcanic eruptions on the early Earth may have been crucial for the development of life. Miller used hydrogen, methane and ammonia to re-create what was then believed to be the the primordial atmosphere on our planet, operating with closed flasks containing water in addition to the gases. An electric spark was then used to simulate lightning, and as anyone who has ever cracked a textbook knows, the water became laden with amino acids after a few weeks. Image A: The apparatus used for Miller's original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Credit: Ned Shaw, Indiana University. It never occurred to me that samples from the original experiments might have survived after all...

Why would you want to take pictures of Earth from a spacecraft in orbit around Venus? Aside from the wish to see a familiar place from a distant location, our planet can also become an interesting testbed for exoplanetary studies. We've run into this idea before in the EPOXI mission, which is the combined extended mission of the Deep Impact spacecraft. Here the cometary component of Deep Impact was recently augmented with observations of Earth that can suggest how to study the glint of light off distant oceans, or the signature of land masses. The extrasolar component of EPOXI is called EPOCh, for Extrasolar Planet Observation and Characterization, and it primarily involves an examination of stars with known transiting planets, looking for other planets in the system (EPOXI can detect transits of objects down to about half the diameter of the Earth) or possibly moons around the known ones. Meanwhile, the spacecraft continues its journey to comet Hartley 2 for observations there, its...

The idea of a galactic habitable zone (GHZ) has a certain inevitability. After all, we talk about habitable zones around stars, so why not galaxies? A stellar habitable zone is usually considered to refer to those areas around the star where liquid water can exist on a planetary surface. Those who believe that confining habitable zones to regions like these carries an implicit bias -- limiting them to life much like our own -- miss the point. The habitable zone concept simply tells us where it makes the most sense to search for the kind of life we can most readily recognize, and as such, it hardly rules out other, more exotic forms of life. But while liquid water takes precedence in a stellar habitable zone, a galactic HZ is still being defined. Charles Lineweaver and team have examined it, among other things, in terms of stellar metallicity (the elements heavier than hydrogen and helium found in the body of a star), concluding that there is a ring several kiloparsecs wide...

The idea that life on Earth might have originated elsewhere, on Mars, for example, has gained currency in recent times as we've learned more about the transfer of materials between planets. Mars cooled before the Earth and may well have become habitable at a time when our planet was not. There seems nothing particularly outrageous in the idea that dormant bacteria inside chunks of the Martian surface, blasted into space by comet or asteroid impacts, might have crossed the interplanetary gulf and given rise to life here. But what of an interstellar origin for life on Earth? The odds on meteoroids from a system around the average galactic field star not only striking the early Earth but delivering viable microbes are long indeed. But if we consider the Sun's probable origin in a cluster of young stars, all emerging from the same collapsing cloud, the picture changes significantly. Now we're dealing with much smaller distances between stars and slow relative motion as well, conditions...

Making contact with an extraterrestrial civilization, whether by microwave, laser or neutrino, highlights the problem of time. Suppose you are looking for a newly emerging technological culture around another star. When do you transmit? After all, even the most powerful signal sent to Earth a million years ago would have no listeners, which is why some have suggested putting actual artifacts in promising solar systems. Rather than transmitting over time-scales measured in eons, you leave an object that can be decoded and activated for communications. All kinds of interesting science and science fictional scenarios flow from that idea. But what if you want to contact not just a few highly targeted systems, but instead send a signal intended for everyone in the galaxy with the means to receive it? As John Learned (University of Hawaii) and team speculate in a new paper, one way to do that would be to select highly visible and important stars to carry your message. Cepheid variables are...