Astrobiology. Joseph Spitale

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1 Astrobiology Joseph Spitale 1

2 What is Astrobiology? Science that studies the origin, evolution, distribution, and future of life in the universe - Combines many sciences: Biology, Chemistry, Planetary Science, Climate, Astronomy, Geology Fundamental Scientific Questions: What is life? How does life begin and evolve? Does life exist elsewhere in the Universe? 2

3 Do you think life exists elsewhere in the Universe? 3

4 Why or why not? 4

The Drake Equation There are at least 70 thousand trillions (70 1015) observable stars in the universe What is the probability that we are not alone?

5 The Drake Equation There are at least 70 thousand trillions ( ) observable stars in the universe What is the probability that we are not alone? The Drake equation attempts to estimate the number of civilizations in our galaxy capable of interstellar communication: N = Rs fp np fl fi fc Lc Rs = rate of sun-like star formation (best known factor: 1-10/yr) fp = fraction of stars with planets (0.2-1) np = number of habitable planets per star with planets (0.1-5) fl = fraction of habitable planets with life ( ) fi = fraction of habitable planets with life where intelligent life evolves ( ) fc = fraction of intelligent civilizations capable of interstellar communication (0.01-1) 5 Lc= average lifetime of those civilizations (100-1,000,000,000 yrs?)

6 Why Astrobiology now? Although multicellular life is unlikely elsewhere in our Solar System, we are learning that microbial life is very robust Although we always knew the universe was full of stars, we have only very recently discovered it is full of planets We are finally gaining the technological capability to scientifically study the extremes of life, the Solar System, and extrasolar planets After thousands of years of speculation, YOURS is the generation with the capability to detect extraterrestrial life! 6

example of biosphere (so far) Earth But we have not

7 Present Challenges in Astrobiology Humans cannot make life out of the abiotic materials (so far) Only one example of biosphere (so far) Earth But we have not ruled out Mars yet! Humans are not good at space travel 7

8 What Is Life? How would we distinguish between living and not living? 8

9 Can You Think of some Properties That Are Important for Life? 9

10 Some Properties of Life Order, organization Energy utilization and production (metabolism) Maintenance of internal constancy (homeostasis) Reproduction, growth, and development Response to the environment Evolutionary adaptation (slow change) 10

The origin of species by means of natural selection (1859) Any population of a species tends to produce far more offspring than the environment can support The overproduction leads to a struggle for

11 The origin of species by means of natural selection (1859) Any population of a species tends to produce far more offspring than the environment can support The overproduction leads to a struggle for survival among individuals Individuals of any population are slightly different from one another in many heritable traits Some individuals possess traits that allow them to better compete for resources Conclusion: Charles Darwin ( ) In any local environment, heritable traits that enhance survival and successful reproduction will become progressively more common in the following generations 11

12 Natural Selection (Darwinian Evolution) All finches on the Galapagos Islands had a common ancestor from South America but all 13 species adapted to particular food sources in various micro-environments 12

13 Non-living objects are not subject to Darwinian Evolution 13

14 Definitions of Life A system capable of evolution by natural selection (Carl Sagan, 1970) A self-sustaining chemical system capable of undergoing Darwinian evolution (NASA s definition) 14

15 Problem: Looking for Life NASA s definition of life is not very useful in search for extraterrestrial life In searching for life we need to know the ecological necessities for life 15

16 Basic Necessities of Life Caveat: our limited knowledge of life is based on the only reference system available: planet Earth Life (as we know it!) requires: 1. Building blocks: organic molecules based on C plus a few other elements, like H and O, and nutrients N, P, S, Fe 2. A source of energy (food) 3. The presence of a solvent: liquid water (H2O) 4. Suitable environmental conditions Set of necessary and sufficient conditions to support life. Are these conditions necessary and/or sufficient to initiate life? 16

17 Building Blocks Constituents of life are abundant in the universe 17

Carbon that comes out of volcanoes is in the form of CO 2 CO2 gas mixture does not produce

18 Building Blocks of Life: Atmosphere Almost all organic carbon that we observe today is produced biologically (via photosynthesis): CO2 + H2O CH2O + O2 (CH2O any organic matter) Carbon that comes out of volcanoes is in the form of CO 2 CO2 gas mixture does not produce organic molecules on its own Where did organics come from before there was life? organic inorganic 18

19 Ancient atmosphere Urey-Miller Experiment CH4 NH3 H2O C HCN (cyanide) H H2CO (fomaldehyde) N O Spark discharge breaks the chemical bonds in CH4, NH3, H2O Amino acids Other simple organics C, H, N, O atoms can recombine into various organic molecules that eventually end up in the ocean 19

Organic synthesis in Hydrothermal Vents Hydrothermal vents were likely to be present in the pre-biotic environment Organic synthesis requires only CO2, H2O and silicate

20 Organic synthesis in Hydrothermal Vents Hydrothermal vents were likely to be present in the pre-biotic environment Organic synthesis requires only CO2, H2O and silicate rocks (and heat!) Processes Involved: Serpentinization: Olivine + Seawater & dissolved CO2 Spinel polymerization: Serpentine + Magnetite (spinel group) Ethane Hematite 20

21 Both atmosphere and hydrothermal vents have problems producing complex organics Can you think of any other source of organic matter? 21

22 Both atmosphere and hydrothermal vents have problems producing complex organics Can you think of any other source of organic matter? Space! Extraterrestrial origin organic material was synthesized in space and was brought to Earth somehow 22

23 Do we have examples of extraterrestrial material on Earth? 23

24 Do we have examples of extraterrestrial material on Earth? Meteorites! Murchison (1969, Australia) 24

25 Some of the amino acids synthesized in the Miller-Urey experiment and also found in the Murchison meteorite 25

26 The Tree of Life By looking at the differences in 16S rrna we can identify three domains of life Bacteria, Archaea, and Eucaryotes Prokaryotes Single- and multi-cell organisms Single cell organisms 26

27 Origin of Life on EARTH: Summary? Bada & Lazcano (Science, 2002) 27

28 What drives all of this? 28

29 Energy Widely used word: - A person may be referred to as energetic - Energy drinks, energy boosters - Clean Energy - Renewable Energy - Energy-efficient homes - Energy crisis What is Energy? Energy causes things to happen Ability to accomplish changes 29

30 Photosynthesis Life takes energy from the environment and stores it as chemical bonds A) Oxygenic (plants, algae): CO2 + H2O + Sunlight CH2O + O2 Water B) Anoxygenic (purple bacteria, green sulfur bacteria, green gliding bacteria): CO2 + 2H2S + Sunlight CH2O + 2S + H2O Hydrogen Sulfide More precisely: 6CO2 + 6H2O + Sunlight C6H12O6 + 6O2 Glucose 30

31 How does life extract the energy? In the presence of oxygen: Respiration (multicellular organisms) C6H12O6 + 6O2 6CO2 + 6H2O + Energy Without oxygen: Fermentation (some bacteria, yeast) (much less efficient! HOW CAN YOU TELL?) C6H12O6 2CO2 + 2C2H6O + Energy Ethanol 31

32 How does life utilize energy? ATP/ADP Every living cell uses ATP (Adenosine TriPhosphate) to transfer energy Energy in Energy out 32

33 Energy in terms of ATP Respiration C6H12O6 + 6O2 6CO2 + 6H2O + 38ATP Fermentation (much less efficient) C6H12O6 2CO2 + 2C2H6O + 2ATP 33

+ 2H2O + Energy Methanopyrus kandleri Sulfate

34 There are ways to get energy from the environment without photosynthesis Methanogenesis CO2 + 4 H2 CH4 + 2H2O + Energy Methanopyrus kandleri Sulfate reduction 4H2 + SO42- S2- + 4H2O + Energy Green sulfur bacteria 34

35 Earth, Mars, Venus: have adequate sources of energy for photosynthesis probably had similar delivery of organic molecules by comets and asteroids Why do we see life only on Earth? 35

36 Need for a Liquid Living systems need a medium in which molecules can dissolve and chemical reactions can take place In any living system, H2O: Dissolves organic molecules (hydrogen bond) Transports chemicals in and out of the cell Directly participates in metabolic reactions CO2 + H2O + energy CH2O + O2 Why water? 36

37 Elements in the Universe (by weight) Element H2O and NH3 are polar Parts per million Hydrogen 750,000 Helium 230,000 Oxygen 10,000 Carbon 5,000 Neon 1,300 Iron 1,100 Nitrogen 1,000 Silicon 700 Magnesium 600 Sulfur 500 All Others 500 Water, H2O Ammonia, NH3 O H H N H H H Methane, CH4 H C H Ethane, C2H6 H H H H H C H C H 37

Broader temperature range water stays liquid through climate changes b) Higher temperature range

38 Why water? Water is liquid over a broader range of temperatures and within Earth s surface temperature range a) Broader temperature range water stays liquid through climate changes b) Higher temperature range water allows faster rates of chemical reactions, but not hot enough to break important carbon bonds Other substances are liquid at temperatures that are problematic for biochemical reactions 38

39 Another H2O advantage: Ice floats! Most substances are denser as solids than as liquids Ice is less dense than liquid water, which is why ice floats The ice crust acts as a blanket, decreasing heat escape from the liquid water body below Lakes and oceans do not freeze out completely! Life can survive glaciations 39

water vapor (gas) Pressure and Temperature control which

40 Three states of water On Earth water can be present in all three states (phases): ice (solid), liquid water (liquid), water vapor (gas) Pressure and Temperature control which phase is the dominant in a particular planetary environment 40

Habitable Zone A circumstellar habitable zone (HZ) is defined as a region around any star where a planetary body can maintain liquid water on its surface Under the present Earth s

41 Habitable Zone A circumstellar habitable zone (HZ) is defined as a region around any star where a planetary body can maintain liquid water on its surface Under the present Earth s atmospheric pressure (1 atm ~ 105 Pa) water is stable if the temperature is 273K < T < 373K On a planetary surface temperature (T) is key assuming the planet has some atmosphere! 41

42 Habitable Zone The boundaries of the habitable zone depend on three main factors: Solar luminosity (energy emission from star) Planetary albedo, i.e., reflectance (on Earth it is also affected by clouds) Greenhouse Effect (CO2, H2O, CH4, O3 etc.) this requires the presence of an atmosphere! Complication: The amount of atmospheric greenhouse warming ( TGH) and the planetary albedo (A) can change as a function of surface temperature (Ts) through various feedbacks in the climate system 42

43 Solar System Habitable Zone Estimates for the Habitable Zone around our Sun range around 0.5 AU to 1.6 AU Dout Din Note: Venus ~0.7 AU Mars ~ 1.5 AU 43

44 Over 3.5 Gyr ago Earth had simple life What about Mars and Venus? 44

45 So is there life elsewhere in the universe? Building blocks are abundant in the universe Water is abundant in the universe Life appears to have existed on Earth 4 Gya However, there is only one tree of life on Earth! 45

46 If so, where might it be? Solar System Venus, Mars, icy satellites Other stars How to find planets? How to discover life? 46

47 Do you think life exists elsewhere in the Universe? 47

PTYS 214 Spring Announcements. Next midterm 3/1!

PTYS 214 Spring Announcements. Next midterm 3/1! PTYS 214 Spring 2018 Announcements Next midterm 3/1! 1 Previously Solar flux decreases as radiation spreads out away from the Sun Planets are exposed to some small amount of the total solar radiation A