Presentation on theme: "Unit 9: Search for Extraterrestrial Intelligence What is Life? Conditions for Life How Big is the Universe? How many opportunities for life are out there?"— Presentation transcript:
Unit 9: Search for Extraterrestrial Intelligence What is Life? Conditions for Life How Big is the Universe? How many opportunities for life are out there? What types of life do we expect? What is SETI? Is SETI worthwhile science?
Unit 9: What is Life All life (as we know it) has the following characteristics: Capable of reproduction Has genetic material (excludes prions) Adaptation Made of one or more cells (excludes viruses) Respond to environmental stimuli Maintain homeostasis
Unit 9: Conditions for Life Raw materials (include hydrogen, oxygen, carbon, nitrogen, sulfur, and phosphorus). Energy source, either chemical or solar. Liquid water (H 2 O). Moderate temperatures, pH, salinity, radiation These conditions apply to life (mostly microbial) on Earth. May not apply in other, extraterrestrial locations. From NASA Ask an Astrobiologist (May 2003): http://astrobiology.nasa.gov/ask-an- astrobiologist/question/?id=589
Unit 9: Conditions for Life (Raw Materials) Why hydrogen, oxygen, nitrogen, sulfur, and phosphorus? Small, moderately reactive. Why carbon? Forms four stable bonds
Unit 9: Conditions for Life (Water 1) Water is the molecule H 2 O Made of two O-H bonds Each O-H bond is a sharing of electrons Electrons (negatively charged) are more attracted to the oxygen nucleus (8 protons) than to the hydrogen nucleus (1 proton). The oxygen side of the bond tends to have a surplus of electrons (partial negative charge) and the hydrogen side tends to have a deficit of electrons (partial positive charge). O HH
Unit 9: Conditions for Life (Water 2) Opposite charges attract water molecules stick together and water molecules stick to anything else with charge. O HH O HH O HH Hydrogen bond (weak)
Unit 9: Conditions for Life (Water 3) Some consequences of cohesiveness of water High surface tension (things float) Ice is less dense than liquid water (ice floats) Water has high boiling point (takes a lot of energy to make water boil) Water has a low freezing point Some consequences of adhesiveness of water Water is a good solvent (many things dissolve in water) Water makes sticks to things (makes things wet) Other important properties of water Pure water has neutral pH (neither acidic nor basic)
Unit 9: Conditions for Life (“Moderate” Temperatures) Low Temperature: Psychromonas ingrahamii was isolated from the arctic sea floor. It grows at -12ºC (water freezes at 0ºC). Image copyright Standards in Genomics Science, Creative Commons-BY High Temperature: Methanopyrus kandleri was isolated fro a “black smoker” 2000-meters below sea level in the Gulf of California. Has been grown at temperatures up to 122ºC (water boils at 100ºC). Image copyright PM Poon, Creative Commons-BY, SA For comparison,the surface of Mercury is -170ºC at night and 450ºC during the day.
Unit 9: Conditions for Life (pH, Salinity, Radiation) Extreme Acidity (pH: Ferroplasma acidarmanus was isolated from mine drainage in California. It grows at about pH 0. pH 0 is more acidic than battery acid. High Salinity: Salinibacter lives in environments that have 20-30% salinity (seawater is 3.1 t0 3.8% salt). High Radiation: Deinococcus radiodurans can withstand exposure to radiation at dosages 3000x higher than naturally occur on the Earth’s surface.
Unit 9: Conditions for Life (JPL-SAF) At the Jet Propulsion Laboratory in Pasadena, California, there is a building called the Spacecraft Assembly Facility (SAF). This is a super-clean facility where spacecraft, like the Mars Rovers, are built. No microorganisms should exist in this facility because we don’t want to send microbes into space and we don’t want to accidentally “discover” space microbes! Here are some of the 22 organisms adapted to life in the SAF (some found nowhere else on Earth!): Bacillus safensis (named after the SAF) Bacillus nealsonii (has two protective outer coats rather than one) Bacillus odysseyi (also has two protective outer coats rather than one)
Unit 9: Conditions for Life (Bacteria on the Moon) The unmanned spacecraft, Surveyor 3, landed on the moon on April 20, 1967. On November 12, 1969, Apollo 12 landed on the moon and astronaut, Pete Conrad, collected the camera casings from Surveyor 3. In 1970, NASA scientists isolated 50 to 100 cells of the bacterium, Streptococcus mitis, from the Surveyor 3 camer casings. These bacterial cells had survived unprotected space flight, radiation exposure, two years on the surface of the moon, and roughly three years without food or water. http://science.nasa.gov/science-news/science-at-nasa/1998/ast01sep98_1/
Unit 9: How Big is the Universe? Detecting Intelligent Life The Drake Equation (1961) is a back-of-the-envelope equation that attempts to give a ballpark number to the question, how many detectable, intelligent civilizations do we expect in the universe? Here is the equation: N = R* x f p x n e x f l x f i x f c x L where N = number of civilizations that might possibly communicate with us R* = the average rate of star formation per year in our galaxy f p = fraction of those stars that have planets n e = average number of those planets that are potentially habitable f l = fraction of habitable planets that go on to develop life f i = fraction of “living” planets that develop intelligent life f c = fraction of intelligent civilizations that develop detectable communication L= length of time civilizations release detectable signals Estimates of N range from around 2 to around 20,000. In other words, we don’t know.
Unit 9: How Big is the Universe? Detecting Intelligent Life Assuming that all intelligent civilations are made of things that we would consider living, we can re-work the Drake Equation to estimate the number of opportunities for life (intelligent or not): N life = R* x f p x n e x f l x L where N = number of civilizations that might possibly communicate with us R* = the average rate of star formation per year in our galaxy f p = fraction of those stars that have planets n e = average number of those planets that are potentially habitable f l = fraction of habitable planets that go on to develop life L= length of time civilizations release detectable signals Both of the omitted terms, f i and f c are fractions. Thus, N life must be higher than N intelligence. Drake estimated both f i and f c to be around 0.01 (based on pure guess). Thus Drakes estimate of the number of planets with life will be about 100,000. Again, this number is a pure guess.
Unit 9: Nearby Bodies Appropriate for Life Within our solar system (http://astrobiology.nasa.gov/tags/life-in-our-solar-system/) Mars: Evidence of flowing water on the surface of Mars within the past few years. Europa (moon of Jupiter): Has a salty ocean under a thick ice shell. Hyperion (moon of Saturn): Has craters containing hydrocarbons. Outside of our solar system Goldilocks Planet (Gliese 581g): 20 light years away from Earth (87th closest star). Vogt et al (2010) announced that it could support life (Vogt was quoted in the press as saying he thought thinks there is a 100% probability of life). Swiss researchers find no evidence of existence of this planet (ScienceNow 2010). ScienceNow. (2010). Recently discovered habitable world may not exist. Retrieved online from http://news.sciencemag.org/sciencenow/2010/10/recently-discovered-habitable-world.html http://news.sciencemag.org/sciencenow/2010/10/recently-discovered-habitable-world.html Vogt, S.S., Butler, R.P., Rivera, E.J., Haghighpour, N., Henry, G.W., and Williamson, M.H. (2010). The Lick-Carnegie exoplanet survey: A 3.1M planet in the habitable zone of the nearby M3V star Gliese 581. Astrophys. J. 723: 954-965.
Unit 9: What is SETI? SETI stands for Search for Extraterrestrial Intelligence. It is a program (briefly run by NASA, with federal funding and now privately funded) that attempts to detect nonrandom radio signals as evidence of technologically-advanced civilizations.
Unit 9: Is SETI Worthwhile Science? 1.What do you think scientists expect to find through SETI and SETI@home? 2.Why do you think NASA chose to eliminate funding for SETI in the 1990s? (Refer here for more information: http://history.nasa.gov/garber.pdf 3.Do you believe SETI and SETI@home are worthwhile projects? Why? 4.What outcome(s) do you think will result from SETI and SETI@home?
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