A Nod to ‘Stapledon Thinking’

Taking a long walk in the early morning hours (and I do mean ‘early,’ as I usually walk around 4 AM – Orion is gorgeously high in the sky this time of year in the northern hemisphere), I found myself musing on terminologies. The case in point: The Fermi Paradox. Using that phrase, the issue becomes starkly framed. If there are other civilizations in the galaxy, why don’t we have evidence for them? Much ink, both physical and digital, has been spilled over the issue, but I will argue that we should soften the term ‘paradox.’ I prefer to call the ‘where are they’ formulation the Fermi Question. I prefer ‘question’ rather than ‘paradox’ because I don’t think we have enough data to declare what we do or do not see about other civilizations a paradox. A paradox is a seemingly self-contradictory statement that demands explanation. But is anything actually demanded here? There are too many imponderables in this case to even frame the contradiction. How can we have a paradox when we are...

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Biosignatures: The Case for Nitrous Oxide

Are we overlooking a potential biosignature? A new study makes the case that nitrous oxide could be a valuable indicator of life on other worlds, and one that can be detected with current and future instrumentation. In today’s essay, Don Wilkins takes a close look at the paper. A retired aerospace engineer with thirty-five years experience in designing, developing, testing, manufacturing and deploying avionics, Don tells me he has been an avid supporter of space flight and exploration all the way back to the days of Project Mercury. Based in St. Louis, where he is an adjunct instructor of electronics at Washington University, Don holds twelve patents and is involved with the university’s efforts at increasing participation in science, technology, engineering, and math. by Don Wilkins Biosignatures, specific signals produced by life, are the focus of intense study within the astronomical community. Gases such as nitrogen (N2), oxygen and methane are sought in planetary atmospheres as...

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Mapping Black Holes in (and out of) the Milky Way

Some years back, I reminisced in these pages about reading Poul Anderson’s World Without Stars, an intriguing tale first published in 1966 about a starship in intergalactic space that was studying a civilization for whom the word ‘isolation’ must have taken on utterly new meaning. Imagine a star system tens of thousands of light years away from the Milky Way, a place where an entire galaxy is but a rather dim feature in the night sky. Poul Anderson discussed this with Analog editor John Campbell: One point came up which may interest you. Though the galaxy would be a huge object in the sky, covering some 20? of arc, it would not be bright. In fact, I make its luminosity, as far as this planet is concerned, somewhere between 1% and 0.1% of the total sky-glow (stars, zodiacal light, and permanent aurora) on a clear moonless Earth night. Sure, there are a lot of stars there — but they’re an awfully long ways off! For more on galactic brightness, see The Milky Way from a Distance. The...

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Ion Propulsion for the Nearby Interstellar Medium

When scientists began seriously looking at beaming concepts for interstellar missions, sails were the primary focus. The obvious advantage was that a large sail need carry no propellant. Here I'm thinking about the early work on laser beaming by Robert Forward, and shortly thereafter George Marx. Forward's first published work on laser sails came during his tenure at Hughes Aircraft Company, having begun as an internal memo within the firm, and later appearing in Missiles and Rockets. Theodore Maiman was working on lasers at Hughes Research Laboratories back then, and the concept of wedding laser beaming with a sail fired Forward's imagination. The rest is history, and we've looked at many of Forward's sail concepts over the years on Centauri Dreams. But notice how beaming weaves its way through the scientific literature on interstellar flight, later being applied in situations that wed it with technologies other than sails. Thus Al Jackson and Daniel Whitmire, who in 1977 considered...

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Ion Propulsion: The Stuhlinger Factor

How helpful can electric propulsion become as we plan missions into the local interstellar medium? We can think about this in terms of the Voyager probes, which remain our only operational craft beyond the heliosphere. Voyager 1 moved beyond the heliopause in 2012, which means 35 years between launch and heliosphere exit. But as Nadim Maraqten (Universität Stuttgart) noted in a presentation at the recent International Astronautical Congress, reaching truly unperturbed interstellar space involves getting to 200 AU. We'd like to move faster than Voyager, but how? Working with Angelo Genovese (Initiative for Interstellar Studies), Maraqten offers up a useful analysis of electric propulsion, calling it one of the most promising existing propulsion technologies, along with various sail concepts. In fact, the two modes have been coupled in some recent studies, about which more as we proceed. The authors believe that the specific impulse of an EP spacecraft must exceed 5000 seconds to make...

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M-Dwarfs: The Asteroid Problem

I hadn’t intended to return to habitability around red dwarf stars quite this soon, but on Saturday I read a new paper from Anna Childs (Northwestern University) and Mario Livio (STScI), the gist of which is that a potential challenge to life on such worlds is the lack of stable asteroid belts. This would affect the ability to deliver asteroids to a planetary surface in the late stages of planet formation. I’m interested in this because it points to different planetary system architectures around M-dwarfs than we’re likely to find around other classes of star. What do observations show so far? You’ll recall that last week we looked at M-dwarf planet habitability in the context of water delivery, again involving the question of early impacts. In that paper, Tadahiro Kimura and Masahiro Ikoma found a separate mechanism to produce the needed water enrichment, while Childs and Livio, working with Rebecca Martin (UNLV) ponder a different question. Their concern is that red dwarf planets...

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M-Dwarf Habitable Planets: The Water Factor

Small M-dwarf stars, the most common type of star in the galaxy, are likely to be the primary target for our early investigations of habitable planets. The small size of these stars and the significant transit depth this allows when an Earth-mass planet crosses their surface as seen from Earth mean that atmospheric analysis by ground- and space-based telescopes should be feasible via transmission spectroscopy. Recent studies have shown that the James Webb Space Telescope has the precision to at least partially characterize the atmospheres of Earth-class planets around some M-dwarfs. Soon-to-be commissioned ground-based extremely large telescopes will likewise play a role as we examine nearby transiting systems. But M-dwarfs make challenging homes for life, if indeed it can exist there. In addition to flare activity, we also have to reckon with the presence of water. Too much of it could suppress weathering in the geochemical carbon cycle, but too little does not allow for the...

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Great Winds from the Sky

Do we need to justify pushing our limits? Doing so is at the very heart of the urge to explore, which is embedded in our species. Recently, while doing some research on Amelia Earhart, I ran across a post on Maria Popova's extraordinary site The Marginalian, one that examines the realm of action within the context of the human spirit. Back in 2016, Popova was looking at Walter Lippmann (1889-1974), the famed journalist and commentator, who not long after Earhart's fatal flight into the Pacific discussed the extent of her achievement and the reasons she had flown. Here's a passage from Lippmann's New York Herald Tribune column, written on July 8, 1937, just six days after the aviator and her navigator, Fred Noonan, disappeared somewhere near Howland Island between Hawaii and Australia. Lippmann asks whether such ventures must be justified by a utilitarian purpose and concludes that what is at stake here transcends simple utility and speaks to the deepest motivations of our...

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Charter

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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