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Evidence for design: earth and solar system 1. Introduction – two conflicting viewpoints 2. Factors that make the earth habitable 3. Quantifying – is the earth one in a million, one in a trillion? How exceptional is the Earth? The Copernican principle vs the anthropic coincidences The Copernican principle "However we are not able to make cosmological models without some admixture of ideology. In the earliest cosmologies, man placed himself in a commanding position at the centre of the universe. Since the time of Copernicus we have been steadily demoted to a medium sized planet going round a medium sized star on the outer edge of a fairly average galaxy, which is itself simply one of a local group of galaxies. Indeed we are now so democratic that we would not claim that our position in space is specially distinguished in any way. We shall, following Bondi (1960), call this assumption the Copernican principle.” Hawking, S.W. and Ellis, G.F.R., The Large Scale Structure of SpaceTime, Cambridge University Press, Cambridge, p. 134, 1973. How exceptional is the Earth? “Most of the Universe is too cold, too hot, too dense, too vacuous, too dark, too bright, or not composed of the right elements to support life. … of all the known celestial bodies, Earth is unique in both its physical properties and its proven ability to sustain life….” “From the biased viewpoint of Earthlings, however, it does appear that Earth is quite a charmed planet.” P. Ward and D. Brownlee, Rare Earth, 2000, p 37. How exceptional is the Earth? “The Earth is a precious jewel in space possessing a rare combination of qualities that happen to make it almost perfect for life. … Personally, I no longer have doubts. The evidence points towards the Earth being a very peculiar place; perhaps the only highly-habitable planet we will ever find. David Waltham, Lucky Planet, 2013, p 1,2. Probability of another habitable planet ~ 1011 planets in our galaxy 1 1012 1 1 1 1 1 1 x x x x x 100 100 100 100 100 100 ( )( )( )( )( )( ) = If 6 finely-tuned factors exist, then we have no right to expect another earth-like planet in the entire galaxy!! ~ 1022 planets in the observable universe 1 1 1 1 1 1 1 1 1 1 1 (100 )x (100 )x(100 )x (100 )x(100 )x (100 )x(100 )x (100 )x (100 )x (100 )x(100 ) = 1 1022 If 11 finely-tuned factors exist, then we have no right to expect another earth-like planet in the entire observable universe!! The probability of a planet suitable for supporting complex life (Hugh Ross) The probability of a planet suitable for supporting complex life The probability of a planet suitable for supporting complex life Earth’s orbit around the sun Freezing and boiling of water set conservative limits Earth’s orbit around the sun “One of Earth’s most basic life-supporting attributes is indeed its location, its seemingly ideal distance from the sun.” Rare Earth, p 16. “Astrobiologists James Kasting and his colleagues … estimated in 1993 that the width of the CHZ is from 0.95 to 1.15 AU.” (1 AU = distance from the Earth to the Sun) Rare Earth, p 19. Orbital characteristics of extra solar planets The Privileged Planet pg 95 Earth’s tilt about spin axis “Although our viewpoint is certainly biased, our planet’s tilt axis seems to be “just right”. Rare Earth, p 224. +/- 1 deg for several thousand yrs larger tilt - temperature extremes smaller tilt - rain not distributed Privileged Planet, p 5. Earth’s tilt about spin axis “Constancy of the tilt angle is a factor that provides long-term stability of the Earth’s temperature. If the polar tilt axis had undergone wide deviations from its present value, Earth’s climate would have been much less hospitable….. Rare Earth, p 224. These results show that the situation of the Earth is very peculiar. The common status for all the terrestrial planets is to have experienced very large scale chaotic behavior for their obliquity, which in the case of the Earth and in the absence of the Moon, may have prevented the appearance of evoluted forms of life. We owe our exceptional climate stability to an exceptional event - the presence of the moon. Jacques Laskar, quoted in Rare Earth p 224. The Moon Just right size and distance from the Earth to -stabilize tilt -slow Earth’s rate of rotation “our moon is somewhat of a freak because of its large size in comparison to its parent planet.” Rare Earth p 222. “Without the moon it is … likely that no birds, redwoods, whales, trilobites, or other advanced life would ever have graced Earth. … Although there are dozens of moons in the solar system, the familiar ghostly white moon that illuminates our night sky is highly unusual, and its presence played a surprisingly important role …” Rare Earth p 222. The Moon “We owe our present climate stability to an exceptional event: the presence of the Moon.” Jacques Laskar, quoted in Rare Earth p 224. Produced by a “just right” collision? “to produce such a massive moon, the impacting body had to be the right size, it had to impact the right point on the Earth, and the impact had to have occurred at just the right time in the Earth’s growth process.” Rare Earth p 231. The Moon itability requires a stabilizing large satellite, like our Moon? small it would happen twice. Could instead catastrophic destruction of both bodies as shown below. “a very freakish event” Simulation of lunar formation event Typical: catastrophic destruction orlds collide:ofFinal stages of planet formation both bodies vie of this simulated collision of two planetesimals can be nd in the Links portion of the textbook web site Do po of ha to its ef fo pr fr th re fo pla Probability from data In a recent survey of debris disks nearby newly forming stars, 1 star in 400 showed a hot dense debris disk that likely was the result of a large collision. Gorlova et al, The Astrophysical Journal 2007, 670, 516 Just right collision to form a moon that is large and close like ours, must be << 1/400 Earth’s size “Earth’s size is just about right - not too small that its gravity was too weak to hold the atmosphere and not so large that its atmosphere would hold too much atmosphere including harmful gases … F. Press and R. Siever, Earth, 1986, p 4. Quoted in Nature’s Destiny p 92 Earth’s size is also important for a sufficiently strong magnetic field Earth’s atmosphere “… differs greatly from those of other terrestrial planets, which range from essentially no atmosphere (Mercury) to a CO2 atmosphere a hundred times denser (Venus) and a CO2 atmosphere a hundred times less dense (Mars).” Ward and Brownlee, Rare Earth, p 52. “It is difficult to see how the actual concentrations of these gases could be very different from what they are in any atmosphere supporting a carbon-based biosphere.” M. Denton, Nature’s Destiny, p 55. Earth’s atmosphere Oxygen is essential for the energy generating reactions of life, its reactivity is fine-tuned. “Oxygen is basically a very dangerous reactive substance and is highly toxic to life at levels above those normally encountered in nature. … Oxygen is fit because its chemical reactivity is attenuated at ambient temperatures (below 50 oC), allowing living systems to utilize this awesome energy source in a controlled and efficient manner.” M. Denton, Nature’s Destiny 123, 125 min. pressure is required to retain liquid water M. Denton, Nature’s Destiny Earth’s atmosphere Oxygen is essential for the energy generating reactions of life, its reactivity is fine-tuned. “This key reaction (oxidation of hydrocarbons) provides many times more energy than any of the multitude of alternative energy-generating reactions. … Could our atmosphere contain more oxygen and still support life? No! … the current percentage of oxygen in the atmosphere, 21 %, is close to the upper limit of safety for life at ambient temperatures.” M. Denton, Nature’s Destiny, p 120. “the present oxygen level is at a point where risk and benefit nicely balance.” J. E. Lovelock, Gaia, 1987, p 71. Earth’s atmosphere “Oxygen is … the only element in the most appropriate physical state, with a satisfactory solubility in water and with desirable combinations of kinetic and thermodynamic properties.” A. Naqui, B. Chance, E. Cadenas Ann. Rev. of Biochemistry 1986, 55, 137. “It turns out that the solubility of oxygen is just sufficient to allow organisms to utilize oxidation as a means of energy production. … Between 0 and 50 oC in an atmosphere containing about 21% oxygen, sufficient oxygen dissolves in water to support oxidative metabolism” M. Denton, Nature’s Destiny p 123, 126. Earth’s atmosphere “ It is surely a coincidence of enormous significance that several essential conditions are satisfied in this one tiny region of space of all possible atmospheres. Fire is possible, but runaway combustion is avoided, oxygen toxicity is relatively low, the solubility of oxygen is sufficient to support oxidative metabolism, and the density is sufficiently low that the work of breathing during strenuous exercise is not prohibitive.” min. pressure is required to retain liquid water M. Denton, Nature’s Destiny p 128. M. Denton, Nature’s Destiny Earth’s elemental composition Earth’s elemental composition number mass 46.6% O 35% Fe 27.7% Si 30% O 8.1% Al 15% Si 5.0% Fe 13% Mg 3.6% Ca 2.4% Ni 2.8% Na 1.1% Ca 2.1% Mg 1.1% Al Relative abundance of elements in the sun Earth’s elemental composition If too much water - all land is covered 0.1% water “with even twice as much water, Earth would have ended up as an abyssal planet entirely covered with deep blue water a true “water world” …” Ward and Brownlee Rare Earth, p 47 “thus the planet’s remarkable mixture of land and oceans is a balancing act. … This fortuitous combination may be the most important factor that ultimately made life possible. Ward and Brownlee Rare Earth, p 53. If too little water - global temperatures would fluctuate too much Ward and Brownlee Rare Earth, p 264 Earth’s elemental composition “Discovering how Earth acquired its supply of water is one of the most critical concerns of the new field of astrobiology. As we pointed out in an earlier chapter, water was not abundant in the inner regions of the solar system when planets formed. There was far more water in the outer regions of the solar system than among the inner planets. Where did our water come from?” Still subject of debate, comets - heavy bombardment? Ward and Brownlee Rare Earth, p 261. Earth’s elemental composition “An enigma of Earth’s formation is its composition and particular location in the solar system…. A grand paradox of terrestrial planets is that if they form close enough to the star to be in its habitable zone, they typically end up with very little water and a dearth of primary life-forming elements such as nitrogen and oxygen, compared with bodies that formed in the outer solar system. In other words, the planets that are in the right place, and thus have warm surfaces, contain only minor amounts of the ingredients necessary for life”. “the origin of biogenic elements is a subject of considerable speculation.” from “asteroidal and cometary debris” ? Rare Earth, p 45, 48. Earth’s elemental composition If too much water - all land is covered If too much carbon, CO2 will cause runaway greenhouse effect 0.05 % carbon Earth’s elemental composition If too much water - all land is covered If too much carbon, CO2 will cause runaway greenhouse effect Enough Fe in core for a magnetic field 35 % iron Earth’s elemental composition If too much water - all land is covered If too much carbon, CO2 will cause runaway greenhouse effect Enough Fe in core for a sufficient magnetic field Enough radioactive metals for long-lived furnace (uranium, thorium, potassium) Just right composition for thin crust - enables plate tectonics Earth’s elemental composition Enough metal for iron- and nickel-rich liquid core Enough radioactive elements for long period of radioactive heating (uranium, thorium, potassium) Composition allowed very thin outer crust of low density - plate tectonics “The thickness, and stability of the Earth’s core, mantle, and crust could have come about only through the fortuitous assemblage of the correct elemental building blocks”. Ward and Brownlee, Rare Earth, p 51. Earth’s elemental composition “… the Earth’s interior is a delicately balanced heat engine fueled by radioactivity … were it running too slowly … the continents might not have evolved to their present form… Iron may never have melted and sunk to the liquid core, and the magnetic field would never have developed…. If there had been more radioactive fuel, and therefore a faster running engine, volcanic dust would have blotted out the Sun, the atmosphere would have been oppressively dense, and the surface would have been racked by daily earthquakes and volcanic explosions.” F. Press and R. Siever, Earth, 1986, p 4. radioactive elements: uranium 238 – 0.0004% (by mass) thorium 232 – 0.0012% potassium 40 – 0.0028% Earth’s cycles Hydrological cycle Plate tectonics (earth, but nowhere else in solar system) Ensure the physical and chemical constancy of our environment -regulates greenhouse gases -builds continents -global thermostat (5 C - 40 C) -magnetic field (T difference across core, convection cells) “Like two gigantic cogwheels engineered to fit perfectly together, these two great cycles have turned together in perfect unison … ensuring the continual turnover and essential recycling of the vital elements of life.” M. Denton, Nature’s Destiny, p 84. Design aspects orbital distance orbital eccentricity tilt angle moon (size and proximity) planet size amount of atmosphere amount of O2 in atmosphere amount of CO2 in atmosphere amount of water amount of radioactive elements amount of Fe and nickel crustal composition plate tectonics The sun The sun (G-type, main sequence) Just-right size: bigger - hotter, burns faster, more erratic smaller - cooler, habitable zone closer in, its gravity would slow a planet’s rotation too much 5% of stars in our galaxy are similar to our sun 80% are red dwarf stars (highly unlikely to support habitable planets) Hertzsprung-Russel StarData.png main sequence stars: fusing hydrogen to helium The sun Temp range of stars: The sun: 30,000 oC - 1000 oC 5500 oC M stars: Habitable Zone = tidally locked M-type stars - thousand or million times more active ( flares) than sun Jupiter and outer planets Jupiter: just-right size and location: Jupiter and outer planets Jupiter: just-right size and location: “without a large planet positioned precisely where Jupiter is, the earth would have been struck a thousand times more frequently in the past by comets and meteors and other interplanetary debris.” “…we wouldn’t be around to study the solar system.” G. W. Wetherill, Nature 1995, 373: 470; Discover 1993, p 15. However, if Jupiter were too large, or too close, it would perturb Earth’s orbit. Jupiter and outer planets Gas giants: Jupiter, Saturn, Uranus, Neptune Orbits: -on the same horizontal plane -almost circular (avg eccentricity = 0.06 Priv. Planet p 96) Slight deviations would be catastrophic for Earth Our position in the Milky Way Some ways in which certain locations in our Galaxy might have low probabilities of planet formation or might be hazardous for life. Our position in the Milky Way Our position in the Milky Way Moreover, the Sun's circular orbit about the galactic center is just right; through a combination of factors it manages to keep out of the way of the Galaxy's dangerous spiral arms. Our solar system is also far enough away from the galactic center to not have to worry about disruptive gravitational forces or too much radiation. … More than 95 percent of stars in the Galaxy, says Gonzalez, wouldn't be able to support habitable planets simply because their rotation is not synchronized with the rotation of the galaxy's spiral arms. Add all the other factors involved in keeping a solar system habitable, and it seems that the odds of finding another solar system in a Galactic Habitable Zone are close to impossible. Galactic Habitable Zones, Astrobiology Magazine, May 18, 2001 Recent headlines or articles: Two Billion Earthlike Planets in the Milky Way: How Many Will Prove to Support Advanced Life? Found: An Earthlike Planet, at Last Earth-like planets pile up Time Nature.com Sept 2010 Newsblog Aug 19, 2011 What does it take to make a habitable planet? Nature 470, 5, 2011 What does it take to make a habitable planet? Nature 470, 5, 2011 What does it take to make a habitable planet? Nature 470, 5, 2011 What does it take to make a habitable planet? ~ 1011 planets in our galaxy 1 1012 1 1 1 1 1 1 x x x x x 100 100 100 100 100 100 ( )( )( )( )( )( ) = If 6 finely-tuned factors exist, then we have no right to expect another earth-like planet in the entire galaxy!! 1 8 1 1 1 1 1 1 1 1 1 1 (200 ) x (100 ) x (100 ) x ( 2 ) x ( 10 ) x (104 ) x (100 ) x (100 ) x (100 ) x (100 ) x (100 ) x (100 ) x earthG-type, galactic rocky sized main habitable in sequence zone Habitable star (Icarus 152 185-200, Zone (Nature 470, 27-29, 2011) 2001; the physics arXiv blog) circular orbit moon (large, close) …. magnetic Jupiter plate right right field(liqui (right tectonics right amount amount d iron location, atmosphere of of water core) (Venus and radioactive circular Mars) elements orbit) What does it take to make a habitable planet? Isaiah 45:18 For this is what the LORD says - he who created the heavens, he is God; he who fashioned and made the earth, he founded it; he did not create it to be empty, but formed it to be inhabited - he says: I am the LORD and there is no other. Recent discoveries of exoplanets Method 1 (HARPS): Doppler spectroscopy – shift in a star’s spectral lines as it wobbles around a mutual center of gravity with a planet sampling bias – only able to detect large planets (but getting better) Method 2 (Kepler): change in brightness as a planet passes in front of its star -orbital size from period of transit and mass of star -radius of planet from drop in brightness and size of star -atmosphere if close enough Kepler is sensitive enough to detect earth-sized planets in earth-like orbits “How is it that hardly any major religion has looked at science and concluded, “This is better than we thought! The Universe is much bigger than our prophets said, grander, more subtle, more elegant?” Instead they say, “No, no, no! My god is a little god, and I want him to stay that way.” A religion, old or new, that stressed the magnificence of the Universe as revealed by modern science might be able to draw forth reserves of reverence and awe hardly tapped by the conventional faiths.” Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space methods Recent discoveries of exoplanets Kepler’s region of study Recent discoveries of exoplanets Kepler’s region of study Recent discoveries of exo-planets Kepler: -sensitive enough to detect earth-sized planets in earth-like orbits -designed for 3-4 yr mission – could confirm an earth-like orbit -fixed field of view – 150,000 stars in Cygnus and Lyra constellations -unable to determine planet mass and composition “The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we’ll have to use a validation process, rather than a confirmation process. We’re going to have to make statistical arguments.” Bill Cochran, Kepler Co-Investigator Recent discoveries of exoplanets Kepler discoveries: -1100 planets candidates (Feb 2011) -40 candidates smaller than twice earth’s size -5 estimated to be within star’s habitable zone Kepler 4-10, 11 Kepler10b: -mass from ground based measurements -4.6 x earth’s mass -1.4 x earth’s radius -0.84 day orbit -Kepler’s first rocky planet Kepler11: “five planets packed into a region that’s smaller than mercury’s orbit around the sun” Kepler16 Kepler16: binary star system, planet 16b confirmed to orbit both stars http://www.nasa.gov/multimedia/videogallery/index.html?col lection_id=14471&media_id=111565131 Kepler18 10% larger than the sun, 97% of sun’s mass HD 85512b and Gliese 581d Both likely to be tidally locked! DiscoveryNews HD 85512b and Gliese 581d Both likely to be tidally locked! DiscoveryNews