If we ever thought it would be easy to tell whether a planet was 'habitable' or not, Stephen Dole quickly put the idea to rest when he considered all the factors involved in his study Habitable Planets for Man (1964). In this second part of his essay on habitability, Dave Moore returns to Dole's work and weighs these factors in light of our present knowledge. What I particularly appreciate about this essay in addition to Dave's numerous insights is the fact that he has brought Dole's work back into focus. The original Habitable Planets for Man was a key factor in firing my interest in writing about interstellar issues. And Centauri Dreams reader Mark Olson has just let me know that Dole appears as a major character in a novel by Harry Turtledove called Three Miles Down. It's now in my reading stack. by Dave Moore In Part I of this essay, I listed the requirements for human habitability in Stephen Dole’s report, Habitable Planets for Man. Now I’ll go over what we’ve subsequently...

Dave Moore is a Centauri Dreams regular who has long pursued an interest in the observation and exploration of deep space. He was born and raised in New Zealand, spent time in Australia, and now runs a small business in Klamath Falls, Oregon. He counts Arthur C. Clarke as a childhood hero, and science fiction as an impetus for his acquiring a degree in biology and chemistry. Dave has kept up an active interest in SETI (see If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare) as well as the exoplanet hunt. In the essay below, he examines questions of habitability and how we measure it, issues that resonate in a time when we are preparing to evaluate exoplanets as life-bearing worlds and look for their biosignatures. by Dave Moore In this essay I’ll be examining the meaning of the word ‘habitable’ when applied to planetary bodies. What do we mean when we talk about a habitable planet or a planet’s habitability? What assumptions do we make? The first part of this essay...

SETI’s task challenges the imagination in every conceivable way, as Don Wilkins points out in the essay below. A retired aerospace engineer with thirty-five years experience in designing, developing, testing, manufacturing and deploying avionics, Don is based in St. Louis, where he is an adjunct instructor of electronics at Washington University. He holds twelve patents and is involved with the university’s efforts at increasing participation in science, technology, engineering, and math. The SETI methodology he explores today offers one way to narrow the observational arena to targets more likely to produce a result. Can spectacular astronomical phenomena serve as a potential marker that could lead us to a technosignature? by Don Wilkins Finite SETI search facilities searching a vast search volume must set priorities for exploration. Dr. Jill Tarter, Chair Emeritus for SETI Research, describes the search space as a “nine-dimensional haystack” composed of three spatial, one temporal...

Finding the right conditions for life off the Earth justifiably drives many a researcher's work, but nailing down just what might make the environment beneath an icy moon's surface benign isn't easy. The recent wave of speculation about Enceladus revolves around the discovery of phosphorus, a key ingredient for the kind of life we are familiar with. But Alex Tolley speculates in the essay below that we really don't have a handle on what this discovery means. There's a long way between 'habitable' and 'inhabited,' and many data points remain to be analyzed, most of which we have yet to collect. Can we gain the knowledge we need from a future Enceladus plume mission? by Alex Tolley  There has been abundant speculation about the possibility of life in the subsurface oceans of icy moons. Europa’s oceans with possible hydrothermal vents mimicking Earth’s abyssal oceans and the probable site of the origin of life, caught our attention now that Mars has no extant surface life. Arthur C...

Did Carl Sagan play a role in the famous Arecibo message transmitted toward the Hercules Cluster in 1974? I’ve always assumed so, given Sagan’s connection with Frank Drake, who was then at Cornell University, where Sagan spent most of his career. But opinion seems to vary. Artist/scientist Joe Davis, who now has affiliations with both MIT’s Laboratory of Molecular Structure and Harvard Medical School, noted in an email this morning that Sagan’s widow, Ann Druyan, supports the connection, but according to Davis, Drake himself denied Sagan’s role in the composition or transmission of the message. I mention all this because of Tuesday’s post on the simulated SETI signal being sent via ESO’s Mars ExoMars Trace Gas Orbiter, as a kind of work of art in its own right as well as a test case in building public involvement in the decoding of an unusual message. The idea of doing that irresistibly recalled Joe Davis because in 1988 Davis performed his own act of scientific art involving SETI,...

Now and again scientists think of interesting ways to use our space missions in contexts for which they were not designed. I’m thinking, for example, of the ‘pale blue dot’ image snapped by Voyager 1 in 1990, an iconic view that forcibly speaks to the immensity of the universe and the smallness of the place we inhabit. Voyager’s cameras, we might recall, were added only after a debate among mission designers, some of whom argued that the mission could proceed without any cameras aboard. Fortunately, the camera advocates won, with results we’re all familiar with. Now we have a project out of The SETI Institute that would use a European Space Agency mission in a novel way, one that also challenges our thinking about our place in the cosmos. Daniela de Paulis, who serves as artist in residence at the institute, is working across numerous disciplines with researchers involved in SETI and astronautics to create A Sign in Space, the creation of an ‘extraterrestrial’ message. This is not a...