I like nautical metaphors as applied to the stars, my favorite being the words attributed to Antoine de Saint-Exupéry, French writer/aviator and author of poetic works about flight like Wind, Sand and Stars (1939), and a work familiar to most American students of French, Vol de nuit, published in English as Night Flight (1931). I think the Saint-Exupéry quote captures what it takes to contemplate far voyaging: "If you want to build a ship, don't drum up the men to gather wood, divide the work and give orders. Instead, teach them to yearn for the vast and endless sea." Image: Antoine de Saint-Exupery, whose work inspired, among many other things, my own decision to take up flying. I had to track down the quote because the last time it appeared in these pages, a reader wrote to tell me he had never found it in Saint-Exupéry. I hadn't either, which bothered me because I am a huge fan of the man's work. It certainly sounded like him. So I did some digging and turned...

Proxima Centauri b is back in the news, although I'll confess that in my case, it's rarely out of my thoughts -- I've been obsessed with the Alpha Centauri system since my youth. The latest comes through work by Anthony Del Genio and colleagues (NASA GSFC), who describe in Astrobiology their new simulations with regard to potential habitability. You'll recall the issues here. A planet this close to its host star may well be tidally locked, with one side always facing the M-dwarf Proxima Centauri. Martin Turbet (Sorbonne Universités, Paris) and colleagues described possible climates on Proxima b in a 2016 paper, using a 3D climate model (GCM) to simulate the atmosphere and water cycle of the planet for its two possible rotation modes, a 1:1 and a 3:2 spin resonance (in other words, gravitational forces could keep Centauri b locked to Proxima or rotating 3 times for every 2 orbits of the star). The Solar System offers analogues: The Moon is in a 1:1 spin resonance with the...

Thinking about supplying a young planet with water, the mind naturally heads for the outer reaches of the Solar System. After all, beyond the 'snowline,' where temperatures are cold enough to allow water to condense into ice grains, volatiles are abundant (this also takes in methane, ammonia and carbon dioxide, all of which can condense into ice grains). The idea that comets or water-rich asteroids bumping around in a chaotic early Solar System could deliver the water Earth needed for its oceans makes sense, given our planet's formation well inside the snowline. We've just looked at Ceres, in celebration of the Dawn mission's achievements there, and we know that Ceres has an icy mantle and perhaps even an ocean beneath its surface. At 2.7 AU, the dwarf planet is right on the edge of traditional estimates for the snowline as it would have occurred in the early days of planet formation. Obviously, the snowline has a great deal to do with various models about the accretion of solid...

Not long ago, Ramses Ramirez (Earth-Life Science Institute, Tokyo) described his latest work on habitable zones to Centauri Dreams readers. Our own Alex Tolley (University of California) now focuses on Dr. Ramirez' quest for 'a more comprehensive habitable zone,' examining classical notions of worlds that could support life, how they have changed over time, and how we can broaden current models. We can see ways, for example, to extend the range of habitable zones at both their outer and inner edges. A look at our assumptions and the dangers implicit in the term 'Earth-like' should give us caution as we interpret the new exoplanet detections coming soon through space- and ground-based instruments. by Alex Tolley The Plains of Tartarus - Bruce Pennington In 1993, before we had detected any exoplanets, James Kasting, Daniel Whitmire, and Ray Reynolds published a modeled estimate of the habitable zone in our solar system [1]. They stated: "A one-dimensional climate model is used to...

Who among us hasn't speculated about the ultimate fate of the Solar System? The thought of our Sun growing into a vast red giant has preoccupied writers and readers since the days when H. G. Wells so memorably captured a far future scene through the eyes of his Time Traveler. And what a scene that was: "I cannot convey the sense of abominable desolation that hung over the world. The red eastern sky, the northward blackness, the salt dead sea, the stony beach crawling with these foul, slow-stirring monsters, the uniform poisonous-looking green of the lichenous plants, the thin air that hurts one's lungs: all contributed to an appalling effect. I moved on a hundred years, and there was the same red sun—a little larger, a little duller—the same dying sea, the same chill air, and the same crowd of earthy crustacea creeping in and out among the green weed and the red rocks. And in the westward sky, I saw a curved pale line like a vast new moon." Wells was working on a...

We've recently looked at gas giant planet formation, and specifically the stages in which Jupiter seems to have formed -- this is the work of Thomas Kruijer (University of Münster) and colleagues as summarized in A Three Part Model for Jupiter's Formation. Whether or not the details of Kruijer and team's model are correct, it seems evident that gas giants must form quickly, based on current theories. These involve the formation of a large solid core, with gas accretion building up a thick atmosphere at a time when the disk around the parent star is still rich in materials. In this thinking, planets like the Earth come along much later than the gas giants that are the first to form. Get a few million years into the evolution of a stellar system and there should be evidence of a gas giant, if one is going to form, but terrestrial worlds can take up to 100 million years to emerge. This has captured the interest of Nader Haghighipour (University of Hawaii), whose work was presented at...