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Homework #6 Due 6:00 pm, Monday, Oct. 31

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Homework #6 Due 6:00 pm, Monday, Oct. 31

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  1. 1,235 Kepler mission planet candidates, as shown in transit with their parent stars ordered by size from top left to bottom right. Simulated stellar disks and the silhouettes of transiting planets are all shown at the same relative scale, with saturated star colors. Some stars show more than one planet in transit.

  2. Homework #6 Due 6:00 pm, Monday, Oct. 31 Exam #2 Wednesday, November 2

  3. Life in the Solar System?

  4. Essentials for life • Chemicals / Nutrients • Energy • Liquid solvent

  5. Chemical components of cells: • Oxygen • Carbon • Nitrogen • Hydrogen These elements make up 96% of the mass of living organisms on Earth.

  6. Where can we expect to find the necessary ingredients/chemicals for life? • These elements are abundant in the Universe, except in older star systems • As long as condensation and accretion occur during a star system’s formation, we can expect these elements to be present

  7. What are energy sources are available? • Sunlight(photosynthesis) • Consuming organic molecules (ex. eating plants) • Chemical reactions with inorganic compounds ofiron, sulfur, or hydrogen

  8. Light is most intense near the sun (or another star) Light intensity falls off with distance from the Sun/star, going as 1/(distance)2 Inefficient far from a star Sunlight?

  9. Chemical Energy requires a means for chemicals to mix & interact Atmospheres and/or bodies of liquids can provide this means Where can we expect to find energy for life?

  10. What to use as a solvent?

  11. Liquids exist only in specific temperature and pressure ranges. On the surface of a planet or moon, temperature alone is insufficient for the presence of liquids.

  12. On Earth, all life requires water: • Water dissolves organic molecules so they can be used for chemical reactions in cells • Water transports chemicals into and out of cells • Water is directly involved in many metabolic reactions within cells

  13. On Earth, the only other common liquid is molten rock (too hot)!

  14. Alternative Liquids for Life(under 1 atmosphere pressure) Water remains liquid over broader and higher range of temperatures The higher temperature range for liquid water allows faster rates of chemical reactions

  15. ethane/methane lakes on Titan • On colder worlds (e.g., Titan), other liquids may be more common, such as • Ammonia NH3 • Methane CH4 • Ethane C2H6 Chemical reactions are highly temperature sensitive, so on colder worlds with other liquids, reaction rates may be too slow for life.

  16. Advantages of water: • Water remains liquid over the widest range of temperatures • Water is liquid at a higher temperature than the others. High temp makes chemical reactions easier. • Water is less dense when it freezes (ice floats), allowing life to survive in the water under the ice

  17. Ice insulates the water underneath it, making it less likely to totally freeze, promoting greater climate stability • Water is POLAR. Many substances can dissolve in water, but many do not. Cell membranes do not dissolve in water. Earth-like cells can only survive in water.

  18. Water is the most likely candidate liquid as a solvent in life. • Searching for liquid water may be the best approach to searching for life. • We do not know if other liquids can support life.

  19. Time to begin the search!

  20. Is life possible on Mercury or the Moon ? • Small (weak gravity) • Airless • Heavily cratered • No significant tectonic activity • No volcanic gases to form an atmosphere • No liquids likely anywhere

  21. Is Life Possible on Venus? • Runaway greenhouse effect: too hot! • High Pressure • Life might be possible in upper clouds (though very acidic) • Conditions were better in early times when the Sun was not as bright

  22. Is Life Possible On Mars? Is life possible on Mars? Once had a thicker and warmer atmosphere and liquid water Liquid water may still exist underground

  23. Mars: A home to life? For a good and wide-ranging discussion of Mars, check out www.spacetoday.org/SolSys/Mars/Mars.html

  24. The “Canals” of Mars In 1877, the Italian astronomer Giovanni Schiaparelli announced that he saw canali on Mars. Canali means "channels" (a natural waterway) in Italian, but was promptly mistranslated into English as "canals" (a constructed waterway)

  25. The most famous proponent of the Martian canals was the American Percival Lowell (1855-1916), who took up astronomy after reading Schiaparelli, and founded an observatory in Flagstaff, AZ to study the canals.

  26. Lowell reported seeing a great many canals, intersecting at junctions he referred to as ‘oases’. • He published 3 famous & well read books describing the canals and arguing for life on Mars. • Mars (1895) • Mars and its Canals (1906) • Mars as the Abode of Life (1908)

  27. The works of Schiaparelli & Lowell formed the basis of the popular view of life on Mars. This was carried over into the popular literature, e.g., War of the Worlds by H.G. Wells and many subsequent works.

  28. Unfortunately, Lowell was wrong. Very few other astronomers reported seeing these canals. Those that did were inevitably using small telescopes and/or observing under adverse atmospheric conditions. Mars was is cold and has too little atmophere for canals to work. Long after most astronomers ceased to believe in canals, popular media continued to speculate about the canals.

  29. Much of current knowledge stems from robotic missions to Mars (partial list): Viking (1976-78): 2 landers and 2 orbiters Mars Pathfinder (1997): lander & rover Mars Global Surveyor (1997 - ): orbiter Mars Express (2003 - ): orbiter & lander Mars Explorer rovers (Jan. 2004 - ): Spirit Opportunity Mars Reconnaissance Orbiter (Jan. 2007 - ): orbiter Phoenix (2008): lander Human mission (2025)?

  30. An overview of what we know today…

  31. Two major terrains Southern Hemisphere: Ancient, heavily cratered highlands, ~ 4km higher than northern hemisphere Northern hemisphere: younger, lightly cratered volcanic plains

  32. Wide variety of surface features: • Craters, impact basins, uplifted regions, volcanoes, mountains, canyons, polar ice caps, river beds, flood plains

  33. The Tharsis Bulge is a massive uplifted region the size of North America, right between the northern plains and southern uplands. The Tharsis area bulges 10 km above its surroundings and is one of the least cratered (youngest) terrains on Mars. Surface less than 1 Byr old. Three of Mars’ four great volcanoes are located here and the fourth, Olympus Mons,is offset on its NW slope.

  34. Volcanoes Including the tallest volcano in the solar system Olympus Mons: 24 km tall, 500 km wide, a 6 km cliff at its base

  35. Cracks & Canyons Valles Marineris: 3000 mi long, 60 mi wide, 4 mi deep Origin - not running water but vertical tectonics • The only ‘canal’of Lowell’s to exist.

  36. Surface:soil, rocks Rocks - typically volcanic in origin Red color - iron oxides

  37. What are they? Dark streaks, everywhere! Many satellite images of the middle latitudes of the northern & southern hemispheres of Mars show wild patterns of criss-crossing dark streaks.

  38. Dust devils! Those seen by Spirit & Opportunity are about the same size as those that whip up desert dust and sand in the southwestern United States (few hundred feet). Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. Orbital images of Mars have detected dust devils that are up to several kilometers (a few miles) tall.

  39. Ice Caps Tiny compared to Earth. They are a mix of water ice + frozen carbon dioxide (“dry ice”).

  40. Ice caps show seasonal changes Spring at one pole: CO2 sublimates at that pole, thereby increasing the local atmospheric pressure. Fall at opposite pole: CO2 condenses out of the atmosphere, thereby decreasing the local atmospheric pressure. Winds flow from high pressure areas to low pressure areas, picking up dust along the way North Pole Frozen carbon dioxide (“dry ice” covering frozen water frozen water

  41. Windy, dusty place During summer, a lot of frozen CO2 in the summer hemisphere’s ice cap sublimates, increasing the local atmospheric pressure CO2 freezes out of the atmosphere in the opposite pole, decreasing atmospheric pressure there The change in pressure leads to strong winds blowing from one hemisphere to the other, picking up dust as it blows

  42. Really COLD place!

  43. Current Mars Atmosphere Predominantly CO2 (~95%) minor contributions from N2, Ar, H2O, O2, CO Global mean temperature = 220 K (brrr!!) Atmospheric pressure = 0.6% Earth (6 millibars) this means that water isn’t stable; even in places where the temp gets greater than the freezing point

  44. Now for the good stuff: could Mars once have been warm and soggy? And could Mars have/had life?

  45. Early Mars was similar to Earth

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