= Destiny Or Chance Revisited = === Stuart Ross Taylor 2012, 523.2 === ------ "Uniqueness, it appears, is the common property of planets." ---- "... while the possibility of intelligent life resembling ''Homo sapiens'' elsewhere was assessed to be zero." "Has the situation changed? Yes, in the sense that it has gotten worse. ... our familiar solar system itself, with its tidy circular orbits, appears to be a rarity. The very architecture of the solar system, familiar to every schoolchild, appears to have arisen through chance collisions and migrations..." Combined with David Waltham's recent "Lucky Planet", Ward and Brownlee's "Rare Earth", and the realization that the Earth would be too hot for our existence had we needed 10% more time to evolve, it appears unlikely that other humans, or even "shirtsleeve-compatible" environments, exist elsewhere, close enough to be observed. Which suggests: .1 We must be ''extremely'' careful with the planet we have. If we destroy it, we not only wipe out life on Earth, we might wipe out intelligent life anywhere in the galaxy. .2 The rest of the galaxy is ours. If our descendants develop the discipline to protect habitable worlds implied by #1, they are unlikely to do damage if they encounter primitive life-forms elsewhere. ---- ==== A brief divergence from Taylor ==== Shirtsleeve environments and humanlike beings may be rare, but we have no evidence (pro or con) that other kinds of intelligent life may form in other environments. We have large brains because they were needed for survival, both in a rapidly changing environment, and in the eusocial tribes we evolved into. Other situations might have evolved other kinds of intelligence. Eusociality is probably the key - isolated individuals could have large brains, but without culture and language, those isolated brains might be crafty, but not really intelligent - they could not pass a Turing test. A collection of organized transistors might pass Turing's test, someday. Perhaps an ant colony could pass as well. Ant social organization is governed by pheromones and chemical signals; our brains work because neurons move action potentials electrically. Chemical signals are too simple, undirected, and slow to form a colony into anything like a mind. But in a world with different chemistry, conductive filaments might be excreted to move signals around a large colony; perhaps the hyphae of fungus would do, which can connect over tens of kilometers. Humans are composite beings, with perhaps a kilogram of gut bacteria tuned for mutual survival. Other creatures elsewhere, in different conditions, might find different ways of solving the "intelligence problem". And those creatures might develop different ways to be mobile, perhaps enhancing their filaments into wires, transistors, motors, and radio connections. We may be rare, but other forms may not be. We just don't know. ---- .CI = carbonaceous chondrite meteorites .pXX : "one of the most striking features of our planetary stystem is that the planets orbit close to a plane." ... and low eccentricity. .p1 : "... dust, asteroids, Trojans, Centaurs, comets, TNOs our eight planest from tiny Mercury to mighty Jupiter and their 160 satellites. All differ from one another in some salient manner." .p6 : "... the formation of our rocky or terrestrial planets ... was essentially stochastic." .p6 : Al Cameron, impactor the size of Mars to produce rapid spin and a low-density moon. .p7 : our water came in later from Jupiter zone. Plate tectonics (and ore deposits) are unique to Earth. Venus is a one-plate planet. .p8 : pre-Apollo speculation, every possible composition suggested for lunar surface, except for what was found. . history omitted .p34: Our galaxy makes 4 new stars a year, rate varies widely. Core collapse to ignition, 100kY. Planets contain 99% of solar system angular momentum. .p35: Star formation rates peaked 3Gy , declining since. .p36: Coldest observed brown dwarfs 300K, Jupiter is 150K accretion heat .p37: Red dwarfs range down to 0.1 Msun, vast majority. "Habitable zones" are tidally locked. Variable, flares, x-rays. . noted elsewhere, not energetic enough to break water bonds. .p40: Sun has more "metals" 1.4% than other nearby stars .p41: Andromeda collision 2MY, approaching 120 km/s .p44: graph - carbonaceous chondrites very closely match metals in sun .p45: graph - inner solar system depleted of volatiles like potassium .p56: snow line, water condensed as ice at 3 to 5 AU .p79: outer planets have very different moon systems, evidence of chaotic formation .p83: Earth has only tertiary crust, formed by dehydration or melting of secondary crust. 0.4% of mass, granitic upper crust is 0.1%. .p93: Funding happens because of "a search for habitable planets" .p99: Kepler multiple-planet systems have smaller-than-Neptune planets .p99: Hot jupiters migrating inwards from snow line .p100: detected exoplanets less than 9% ( no transit or radial) .p101: 0.8% of stars have transiting planets - microlensing suggests most do. .p104: Fig 12: Most exoplanet orbits are far more eccentric than Earth .p104-106: Migration of gas giants a puzzle to Taylor - I've seen explanations MoreLater .p109: Fig: 13 - ugly plot (should be log-log) shows high metallicity stars have more planets - 6x more for 3x more iron .p110: Multiple planet ordering varies wildly .p119: Planets less than 15 Earth masses are called Earth-like (making 14.5 Me Uranus, earthlike? phooey) .p122: Carbide planets unlikely. Carbon in methane, CO or CO,,2,, will be swept away. .[[http://www.nature.com/nature/journal/v523/n7560/full/nature14566.html |''but what about C,,60,,?'']] .p132: Nice (the city) model. . A. Morbidelli & H. F. Levison, Planetary science: Kuiper-belt interlopers, News and Views Nature 422, 30-31 (6 March 2003) | doi:10.1038/422030a . many other M&L papers on this subject .p138: Jupiter formed at 3.5 AU, moved in as far as 1.5 AU then Saturn pulled it back out .p140: Neptune and Uranus formed at 6 and 8 AU, moved by resonant encounters to 20 and 30 AU. .p148: Kuiper belt 39 to 48 AU, 70K bodies larger than 100km, several million larger than 10km .p173-p175: Taylor says Martian water was brief bursts from ice body impacts, 50 to 500m of rain, then evaporate into space or sink into ground. Not convincing, maybe nothing is? .p178: Venus 243 earthday retrograde rotation, 225 earthday orbit. (atmosphere rotates in 4 earthdays) 93x air density, mostly CO,,2,,, 460C, no magnetic field .p201: Granite is hard to make, unique to Earth .p207: Earth D/H ratio matches CI meteorites from far out in the asteroid belt, and at least two Kuiper belt comets, Halley from the Oort cloud D/H too high MoreLater