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Ch. 7-9 (no 6) NATS 1880 midterm notes

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Natural Science
NATS 1880
Paul Delaney

Chapter 7 • Temperature, atmosphere, water = life on earth • Search for life does not always mean human life • Constraints: materials o Life on earth use 25/92 elements o C, O, H, N make up 96% of mass of living organisms o Amino acids must also be present o Fluids (water) essential • Constraints: energy o Not always supplied by sun o Life further from sun handicapped by lack of solar energy  Inverse square law e.g.: at 3AU the sun is only 1/(3x3)=1/9 as bright as at 1 AU • Constraints: liquids o Liquid substitutes must be abundant and remain liquid over reasonable temperature range • Advantages of water o Chemical reactions proceed faster at higher temps o Wider liquid range = higher likelihood of remaining liquid o Ice is less dense than water; provides insulation for liquid and life beneath it o Polar molecule = assists in molecule dissolution and chemical bonding • Cell membranes do not dissolve in water • Heath capacity: a measure of how much heat energy a material can store per kilogram as it changes temperature • Surface tension: property a surface has to resist an external force • Habitable world: liquid medium (preferably water) above or below surface • Moon o Small; no plate tectonics or volcanoes; basalt & old rock; craters vary in size and amount per area (mare: less/terrae: more); weak gravity (1/6 of Earth’s); little to no atmosphere; surface temp ranges from -150C on dark sides, +110C on light sides; probes suggest water may be frozen at poles; probably not habitable. • Mercury o Close to sun = high temp during day, low during night (425C to -150C); no atmosphere; no liquid water, maybe some frozen in poles, not habitable. • Venus o 475C surface temp; 90x earth’s atmospheric pressure; 95% CO2; sulphuric acid clouds; no plate tectonics; life may have existed in the past; life only possible now in high clouds; not habitable. • Mars o Cold and cry; evidence of past liquid on surface, probably now underground; too little atmosphere for liquid on surface; harsh radiation; past candidate for past habitability; not habitable now. • The 4 Jovian worlds o Less sunlight, atmospheres primarily hydrogen and helium + other hydrocarbons, low densities, cores about 10 times the mass of Earth o Very cold cloud top temps; Hot within ∴ liquid can exist at certain depths in atmosphere • Jupiter & Saturn o Vertical winds that carry chemical building blocks go from very cold to very hot in a short time; no way for elements to remain at the right altitude for life to develop; not habitable • Uranus & Neptune o Greater distance from sun means probably larger cloud top surfaces; higher pressures and vertical winds unfavourable to life; liquid interiors near core may offer possibility of life but unlikely; not habitable. • Large & medium moons o Comparable in size to mercury; formed in environments richer in volatiles; may possess ice geology; enough self-gravity to be spherical; substantial amounts of ice; formed in orbit around Jovian planets; maybe habitable? But probably not I mean really • Small objects o None large enough to have significant internal heat, no atmosphere; no liquid water ever; not habitable. • Visiting the Solar System o Space crafts have visited all 8 planets and smaller objects; collected material for analysis o Flyby: one pass to obtain data; inexpensive; voyager 1 and 2 o Orbiter: long term surveillance; more expensive because more fuel; long term study; often includes radar o Lander or entry probe: in situ measurements of object; long term monitoring; chemical/biological search for life can be conducted o Sample return: collect piece of object to be examined in greater detail on earth Chapter 8 • Mars is about half the size of earth; low density; temperatures well below freezing; little atmosphere, almost all CO2; no oxygen; harsh UV radiation; dry, arid, and desert-like • Livable? : less harsh than moon; thin atmosphere regulates extreme temps; pressurized habitats an option for humans and crops; soil similar to earth’s; gravity about 40%; similar diurnal cycle • Liquid water on the surface? o temp and atmospheric pressure too low to allow liquid water; o liquid water unstable, freezes/evaporates almost immediately • Seasons o tilt of axis rotation of 25°; seasons twice as long because of longer orbital period o closer to sun during southern hemisphere summer, farther from the sun during southern hemisphere winter o S. hemisphere: summer is short and warm, winter is cold and long; n. hemisphere has more even seasons • Ice caps o Large because carbon dioxide freezes out of atmosphere; Ice sublimes into the atmosphere in summer; shrinks ice cap; Causes significant vari
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