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AstroBiology Chapter 5 - 11 Notes

by: Renae Notetaker

AstroBiology Chapter 5 - 11 Notes ASTROBIO115

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Renae Notetaker
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Intro to Astrobiology
Rory Barnes

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Intro to Astrobiology
Rory Barnes
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Date Created: 11/29/15
Astrobiology Chapter 5 The Nature of Life on Earth 102 52015 General Properties of Life on Earth 6 parts Order Reproduction Growth and Development Energy Utilization 0 First Law of Thermodynamics Energy can be neither created nor destroyed but only transformed from one form to another Also known as the Conservation of Energy Second Law of Thermodynamics When left alone the energy in a system undergoes conversions that lead to increasing disorder Example If a living organism is placed into a sealed box it will eventually use up the available energy and therefore no longer be able to build new molecules or fuel processes needed for life Loss of oxygen for example leads to death Response to the Environment 0 Necessary but not sufficient condition for life Evolutionary Adaptation Most Fundamental 0 Species Groups of organisms that are genetically distinct from other groups though the precise border between one species and another is not always clear especially with microorganisms Scienti c name consists of 2 parts n 1 Genus Describes generic category to which the organism belongs a 2 Species Distinguishes multiple species within the same genus Evolution Charles Darwin 1 Overproduction and Competition for Survival Species can potentially produce far more offspring than the environment can support in terms of food shelter and that leads to competition for survival among individuals Individual Variation Individuals in population vary in heritable traits No two individuals are exactly the same some possess traits that make them more able to compete for resources than others 3 Unequal Reproductive Success Conclusion Those individuals whose traits best enable them to survive and reproduce will on average leave the largest number of offspring that in turn will survive to reproduce Therefore heritable traits that enhance survival and reproduction will become more common in generations 0 Natural Selection Advantageous genetic traits will naturally win out over less advantageous traits because they are more likely to be passed down through many generations Life is something that can reproduce and evolve through natural selection THE BASIC UNITS OF LIFE 0 Cells Microscopic units in which the living matter is separated from the outside world by a barrier called the membrane a While life elsewhere might be composed of cells we shouldn t expect those cells to have the same biochemistry as the cells on Earth Four elements make up 96 of the mass of typical living cells 0 Oxygen Carbon Hydrogen and Nitrogen The rest calcium phosphorus potassium and sulfur 1 CarbonBased Life All Life on Earth is CarbonBased 0 Chemical Bonds Sharing electrons between the individual atoms of a molecule 0 Organic Molecules Carbon molecules The simplest organic molecules that consist of carbon skeletons bonded only to hydrogen atoms Hydrocarbons 0 Carbon can bond to as many as four atoms at a time 2 NonCarbon Based Life Silicon Silicon is the only other element that can have four bonds at once However it cannot support the basis for life because 1 Bonds formed by silicon are weaker than bonds formed by carbon Fragile cannot support life 2 Unlike carbon silicon doesn t form double bonds but rather forms only single bonds Limits the variety of molecular structures it can form 3 Carbon can be mobile in the environment in the form of gas carbon dioxide but silicon dioxide is a solid No mobility Molecular Components of a Cell Carbohydrates Stores and provides energy to cells create important cellular structures 0 Lipids Fats Store energy for cells important in cell membranes 0 Proteins Molecules that serve as structural elements in cells 0 Enzymes Crucial to all important biochemical reactions that happen in cells including copying DNA 0 Catalyst Any substance that facilitates or accelerates a chemical reaction that would otherwise occur much more slowly Enzymes are catalysts because they greatly accelerate the reactions in which they are involved 0 Amino Acids Proteins are made up of large molecules that are built from long chains of smaller molecules called amino acids Righthanded Lefthanded amino acids are mirror images of each other Living cells use only the lefthanded versions of amino acids to build proteins 0 Nucleic Acids DNA and RNA Three Domains of Life Bacteria Include microbes Achaea Include microbes Eukarya Cells that have a cell nuclei but this is no longer considered to be fundamental in their biochemistry Includes microbes and some plants animals and fungi o Eukaryotes Cells with nuclei 0 Prokaryotes Cells without nuclei Tree of Life 3 features 1 Large multicellular organisms plants animals fungi represent just three small branches of one domain eukarya 2 Diversity of life on Earth is found almost entirely within the microscopic realm 3 Branch lengths represent amount of genetic difference between speCIes Metabolism 0 The chemical reactions that occur in living organisms and that are involved in providing energy or nutrients to cells 0 Biochemical Manufacturing Process 1 Source of raw materials to build new products Molecules that provide cell with carbon and basic elements for life 2 Source of energy To fuel metabolic processes that break down old molecules and makes new ones 0 ATP Every cell uses the same molecule Used to store and release energy for nearly all its chemical manufacturing 0 ATP recyclable Every time a cell draws energy from a molecule of ATP it leaves a closely related ADP which can be turned back into ATP Carbon Sources Autotrophs and Heterotrophs 1 Heterotroph Organism that get carbon by consuming pre existing organic compounds by eating 2 Autotroph An organism that gets its carbon directly from the environment Selffeeding taking carbon dioxide from environment Plants Energy Sources Light or Chemicals Cells usage to make ATP three sources 1 Photosynthesis 2 Food Eating 3 Inorganic chemicals Chemicals that don t contain carbon Metabolic Classi cations Four 1 Photoautotrophs Energy from sunlight carbon from carbon dioxide in environment Plants 2 Chemoautotrophs Energy from chemical reactions carbon from environmental carbon dioxide 3 Photoheterotrophs Energy from sunlight carbon by consuming other organisms or remains of organisms 4 Chemoheterotrophs Energy from food carbon from food Humans The Role of Water in Metabolism 1 Metabolism requires that organic chemicals be readily available for reactions i Liquid water makes possible by allowing organic chemicals to essentially oat within the cell 2 Metabolism requires a means of transporting chemicals to and within cells and of transporting waste products away i Water is used as this transportation 3 Water plays a role in many metabolic reactions within cells i Water molecules necessary for reactions that storerelease energy in ATP DNA and Heredity 0 DNA is a double helix 0 DNA bases The quotzipper teethquot that represent molecular components that link the two strands together 4 o Adenine A o Guanine G o Thymine T o Cytosine C T can ONLY pair with A C can ONLY pair with G 0 DNA Replication Process where DNA is copied Helix unzips and single strands go on to replicate the DNA Genes and Genomes 0 Gene Basic functional unit of an organism s heredity that consists of a sequence of DNA bases that provides the instructions for a single cell function NonCoding DNA DNA that does not seem to carry the instructions for any particular cell function Essentially does nothing o Biologists think that noncoding DNA represent evolutionary artifacts pieces of DNA that may once have played an important part in ancestral cells but are no longer important ex appendix Genome Complete sequence of DNA bases in an organism that encompasses all the organism s genes and noncoding DNA Genetic Code Set of rules for reading DNA that consist of 3 DNA bases in a row RNA 0 Molecule that plays an important role in carrying out genetic instructions Replaces T Thymine with U Uracil Different types of RNA attach amino acids into chains to make proteins Translation translating the genetic instructions into the protein Transfer collecting amino acids from the cell and bringing it to the ribosome Mutations Any change in the base sequence of an organism s DNA Mutations that change proteins and the cell survives the mutation will be copied every time its DNA is replicated Permanent change in cell s hereditary information If the cell is one that gets passed down to the organism s offspring the offspring will have a gene that differs from the parents Lateral Gene Transfer When organisms transfer entire genes to other organisms Genetic Engineering Taking one gene from one organism and inserting it into another In What Conditions Can Life Survive Extremophiles Organisms that can survive in extreme environments of any kind 0 Thermophiles Lovers of the heat o Hyperthermophiles Lovers of the highest temperatures 0 Psychrophiles Lovers of the cold 0 Endospores Special cells produced by some bacteria They allow the organisms that create them to become dormant neither dying nor growing in extremely inhospitable conditions Extremophiles apparently evolved earlier than other forms of life we should begin the search for life elsewhere by searching for extreme organisms 0 Due to the fact that extremophiles can survive such a broad range of conditions suggests that life may be possible in more places than we think Any world that contains an environment in which some type of extremophile might survive Evolution 0 Evolution is a fact but we use the theory of evolution to explain how and why changes occur Fossil Evidence for Early Life on Earth 3 1Stromatoites Rocks characterized by a distinctive layered structure 0 Living stromatolites colonies of microbes contain layers of sediment intermixed with different types of microbes Microbes near the top generate energy through photosynthesis and those beneath use organic compounds left as waste that have been left by the photosynthetic microbes 0 Scientists state that if photosynthetic life already existed some 35 billion years ago then we can infer that more primitive life must have existed even earlier 2 Microfossils Individual microscopic fossilized cells found in rocks 3 Isotopic Evidence Isotopic analysis of ancient rocks on Earth 0 New Evidence Falls Into 2 Categories 0 If the Greenland rocks hold evidence of life we would expect to nd similar evidence in other rocks dating to the same general time 0 Life can also alter the isotopic ratios of other elements such as iron nitrogen and sulfur Where Did Life on Earth Begin o Unlikely that life on land occurred rst because early Earth didn t have a protective layer of ozone so intense radiation would have been subjected to organisms Life could have arisen in shallow ponds Darwin s Theory But shallow water would not have offered much protection against UV rays BEST THEORY Deepsea or underground environments which would have been able to provide protection from radiation 0 Impacts from asteroids during the late bombardment would have ONLY allowed for the survival of life in deepsa or underground environments How Did Life on Earth Begin Earth s early atmosphere should have been oxygenfree and sunlightfueled chemical reactions could have led to the spontaneous creation of organic molecules MillerUrey Experiment An experiment used to gure out what occurred in the early Earth years which showed that the building blocks of life can form naturally and abundantly Other Sources of Organic Molecules on Early Earth Chemical reactions near deepsea vents As undersea volcanoes heat surrounding water chemical reactions occur between the water and the minerals Should have resulted in the production of organic molecules needed for life Material from Space Meteorites usually contain organic molecules so stuff in space that crashed down on Earth might ve been loaded with organic molecules and amino acids needed for life Heavy bombardment era could have brought organic molecules to Earth RECAP Three Sources of Organic Molecules Chemical Reactions near ocean surface Chemical Reactions near deep sea vents Material from Space RNA RNA molecules can catalyze reactions in the same way at enzymes meaning the early Earth might ve been constituted by RNA molecules DNA must ve also arisen from RNA How might an RNA world gotten started 0 Spontaneous production of selfreplicating strands of RNA needed 0 Concentration of organic molecules on early Earth would have been too low to allow building blocks to assemble into RNA molecules but lNorganic molecules can facilitate the assembly of organic molecules Silicate minerals are inorganic molecules that scientists believe helped form RNA When organic molecules stick to the clay it can be forced into close proximity of other organic molecules and react with one another to form longer chains Eventually produces strands of RNA RNA in PreCells Could Have Facilitated Origin of Life By 0 Keeping molecules concentrated and close together should have increased the rate of reactions among them making it far more likely that a selfreplicating RNA would have risen Once selfreplicating RNA molecules came to exist precells would habe kept them isoled from the outside in a way that should have facilitated a molecular analog to natural selection ie RNA molecules that replicated faster and more accurately would come to dominate the population RECAP RNA Creating Life on Earth 1 Through some combination of atmospheric chemistry chemistry near deepsea vents and molecules brought to Earth from space the early Earth had at least localized areas with signi cant amounts of organic molecules that could serve as building blocks for more complex organic molecules 2 More complex molecules including short strands of RNA grew from the organic building blocks probably with the aid of reac tions catalyzed by Clay minerals The minerals also helped catalyze the production of microscopic precells in which RNA and other organic chemicals became enclosed 3 The concentration of RNA molecules within precells facilitated reactions that eventually led to selfreplicating RNA at which point molecular natural selection favored the spread of those RNA molecules that replicated most accurately and efficiently 4 Natural selection among the RNA molecules in precells gradually led to an increase in complexity until eventually some of these structures became true living organisms 5 DNA evolved from RNA and its advantages made it the preferred hereditary molecule Natural selection continued enabling organisms to adapt to a great many environmental niches on planet Earth Life Might39ve Migrated to Earth from Space 0 For microbes to survive the journey to Earth it would have to survive 3 things the impact that blasts it off the surface of the home world the time it spends in the harsh environment in space and the plunge through our atmosphere Reasons to Consider Migration 0 Life does not form as easily as we have imagined at least under the conditions present on the early Earth So the only explanation for life on Earth would be that it migrated here from somewhere else 0 Life forms so easily that we should expect to nd life originating on any planet with suitable conditions This means that life might ve arose on Venus or Mars for example and then migrated to Earth Life Might39ve Migrated from Earth to Another Planet 0 Due to plenty of impacts that have blasted pieces of Earth into space it s possible that microbes or organisms have be transported to other planets 0 IMPORTANT ISSUES If we nd life on Mars we will have to gure out if it s native to Mars or if it arrived there from Earth The possibility of life migrating among the planets raises the question of whether we could ever distinguish between an indigenous origin of life on Earth and an origin based on migration from elsewhere What Major Events Have Marked Evolutionary History 0 Early Microbial Evolution 0 All early life on Earth must ve been anaerobic meaning it did not require molecular oxygen aerobic means needing molecular oxygen Ex Humans 0 First microorganisms were chemoautotrophs 0 Natural selection probably caused rapid diversi cation among the early life forms on Earth due to mutations which lead to evolution needing to be rapid to create new metabolic processes and make the organisms better 0 Evolution of Eukarya Humans are part of eukarya 0 Some early species of eukarya may have developed specialized infoldings of their membrances that compartmentalized certain cell functions ultimately leading to the creation of a cell nucleus 0 Some large ancestral host cells absorbed small bacteria within them creating a symbiotic relationship in which both the invading organism and the host organism bene ted from living together Mitochondria Cellular organs in which oxygen helps produce energy by making molecules of ATP Chloroplasts Structures in plant cells that produce energy by photosynthesis Host cell would have bene ted from the energy produced by the incorporated bacteria mitochondria whiel the bacteria would have bene ted from the protection offered by the host cell cholorplasts 0 The Cambrian Explosion o Earliest fossil evidence for complex multicellular organisms all eukarya date to only about 12 billion years ago 0 Most of the animals found in the phyla kingdom classi cation appeared 0 Marks the only major diversi cation of body plans 0 Why did the Cambrian Explosion occur so suddenly and why hasn39t any similar diversi cation happened since 0 First oxygen levels in our atmosphere may have remained well below its present level until about the time of the explosion 0 Second is the evolution of genetic complexity where as eukaryotes evolved they developed more genetic variation 0 Third is climate change End of the Snowball Earth 0 Fourth is the absence of ef cient predators Colonization of Land Microbial life established themselves wherever they could nd liquid water and protection from UV rays 0 Colonization of land by plants 475 million years ago Why Was the Rise of Oxygen 50 Important To Evolution 0 PAGE 231 Oxygen carbon hydrogen and nitrogen make up 96 of the mass of living organisms The energy available in sunlight decreases with the square of the distance from the Sun 1distancequot2 Water plays 3 roles for life on Earth Dissolves organic molecules making them available for chemical reactions within cells 0 Involved directly in many of the metabolic reactions that occur in cells 0 Allows for the transport of chemicals in and out of the cell Advantages of Water that make it a liquid medium for life 0 Water remains liquid over a wider and higher range of temperatures 0 Higher temperatures means chemical reactions occur more rapidly which makes the ability for life to arise Ice is less dense than liquid water Most substances are denser as solids than as liquids but water is the exception o In winter when surface temperatures are low enough for water to freeze oating ice forms layers on top of lakes which insulates the water beneath allowing it to remain liquid and for life to survive Within water molecules electrons tend to be distributed in a way that makes one side have a new positive charge and the other side has a net negative charge 0 This affects the way in which water dissolves other substances 0 Living cells have membranes that do not dissolve in water due to the electron composition in water molecules 0 The charge separation allows for the formation of a hydrogen bond which is important to the biochemistry of life RECAP 1 a wider and higher range of temperatures over which it remains liquid 2 the fact that solid water oats 3 the fact that the charge separation of water molecules Environmental requirements for habitability 1 It must have a source of molecules from which to build living cells 2 It must have a source of energy to fuel metabolism 3 It must have a liquid medium most likely liquid water for transporting the molecules for life 0 A world can be habitable only if it has a liquid medium of some sort Habitability requires only the presence of a liquid somewhere not necessarily on the surface Jovian planets are primarily composed of hydrogen helium and hydrogen compounds such as water methane and ammonia Viking Lander mission Viking 1 landed on Chryse Planitia Viking 2 landed on the other side of Mars 2 Viking orbiters studying planet from above 0 Provided television quality pictures and data of Mars to learn about the past and present habitability of life No liquid water exists anywhere on the surface of Mars 0 Mars is so cold that liquid water would freeze Even when temperatures rise above freezing the air pressure is so low that liquid water would quickly evaporate 0 Liquid water is unstable on Mars Mars Seasons Axis tilt at 25 degrees Martian year is nearly twice as long as Earth s year so each season lasts about twice as long on Mars 0 Mars seasons are also affected by the ellipticity of its orbit 0 Mars signi cantly closer to Sun during southern hemisphere summer and farther during southern hemisphere winter 0 Mars southern hemisphere has more extreme seasons than the northern hemisphere 0 Carbon dioxide moves seasonally between north and south polar caps The cycling causes huge dust storms especially during the more extreme summer I Also causes dust devils Northern Mars has LESS craters than Southern Mars meaning Northern Mars craters were probably erased due to volcanism Volcanos are larger on Mars because 0 1 Mars weaker gravity makes it easier for tall structures to be built up 0 2 Lack of plate tectonics on Mars means that mantle plumes remain stationary relative to the surface building up huge single mountains Valles Marineris may be one of the best places to look for fossil evidence for past martian life due to the fact that the valley network appear to have been shaped by owing water and show presence of minerals formed in water Mars Geological History Noachian Era Heavily cratered era due to heavy bombardment 38 billion years ago Hesperian Era In between heavily cratered and young 0 Amazonian Era Youngest regions lightly cratered Mars is not geologically dead Radiometric dating of meteorites show some of them to be made of volcanic rock that solidi ed from molten lave as little as 180 million years ago recently 0 Means Mars still retains some internal heat What evidence tells us that water once owed on Mars 0 Mariner 9 and Viking orbiters Provided photos which showed pictures that look like dry riverbeds on Earth The channels definitely carved by running water 0 Indicate that liquid water must have been stable at orjust below the surface at the time of the carving Because low temperature and atmospheric pressure makes liquid water unstable Mars must have had a warmer and thicker atmosphere in the past 0 Images that tell us about the mineral composition of surface 0 Three tyes of hydrated minerals that contain water Clay minerals Hydrated sulfates and Hydrated silica Opal n Opal signi cant because 1 thought to form in hot springs or hydrothermal environments which were important environments to the origin of life on Earth 2 Some of the regions where they re found appear to have formed billion years later than the clay deposits This means Mars remained wet for long periods of time which would mean life might ve arose o Opportunity Rover Found hematite which is formed in water or volcanic processes Evidence points to water formation Found similar ones on Earth Climate History of Mars 0 Greenhouse Gas Effect Mars has weak greenhouse effect despite 95 of its atmosphere composed of carbon dioxide Calculations show that volcanoes on Mars should have outgassed enough carbon dioxide to make the atmosphere 400 times dense as it is today which would allow water to ll oceans o If Mars had that much carbon dioxide today its surface pressure would be about three times that of Earth s and a freezing temperature which would allow liquid water ows Because Sun was dimmer in past even more greenhouse warming would have been needed to allow for liquid water when Mars was young Loss of Carbon Dioxide and Water 0 Mars had molten convecting metals in its core Combo of convection with Mars rotation should have produced a magnetic eld and magnetosphere Magnetic eld would have weakened as the small planet cooled and core convection ceased leaving atmosphere vulnerable to solar wind particles which could have stripped gas out of atmosphere 0 Due to lack of UV stratosphere UV rays easily broke apart water molecules and hydrogen atoms broke away into space RECAP The hypothesis we have described suggests that Mars changed primarily because of its relatively small size It was big enough for volcanism and outgassing to release plenty of water and atmospheric gas early in its history but too small to maintain the internal heat needed to prevent this loss of water and gas As its interior cooled its volcanoes quieted and released far less gas into the atmosphere while its relatively weak gravity and the loss of its magnetic eld allowed existing gas to be stripped away to space If Mars had been as large as Earth so that it could still have outgassing and a global magnetic eld it might still have a pleasant climate today Mars s distance from the Sun also helped seal its fate Even with its small size Mars might still have some owing water if it were signi cantly closer to the Sun where the extra warmth could melt the water that remains frozen underground and at the polar caps Axis Tilt Jupiter s gravity affects Mars as it orbits the Sun which causes Mars to experience wild wings in its axis tilts over millions of years ago 0 When Mars axis tilt is small Mars is frozen and with carbon dioxide frozen at poles atmosphere becomes thinner lowering the pressure and weakening the greenhouse effect 0 When axis is highly titled summer pole becomes warm enough to allow substantial amounts of water ice to sublimate along with carbon dioxide into atmosphere Pressure increases and Mars becomes warmer due to stronger greenhouse effect The surface of Mars was habitable during some periods of its early history and it might still sometimes be habitable when the axis tilt is greater while the subsurface probably contains habitable zones even today Life on Mars Viking Landers and Martian Meteorites 0 Viking Landers Studied soil to look for living microbes o 1 Carbon Assimilation Experiment Mixed sample of martian soil with carbon dioxide and carbon monoxide from Earth Wanted to see if any of the carbon would become incorporated into soil as would be the case if living organisms were using either gas as a source for metabolism Conclusion Carbon incorporation due to chemical reaction not biological process 0 2 Gas exchange Experiment Mixed martian soil with broth containing organic nutrients from Earth Looked for gases that might be released by respiration of microbes including hydrogen nitrogen oxygen etc Conclusion Chemical reaction not biological o 3 Labeled Release Experiment Mixed martian soil with organic nutrients tagged with radioactive carbon14 and su un35 Looked to see if nutrients would be consumed by microbes and metabolism would release gases and level of radioactivity would rise Conclusion Life may be on Mars 0 4 Gas ChromotographMass Spectrometer Experiment Measured abundance of organic molecules in soil Found no measurable level of organic molecules which meant experiment 3 was a chemical process not biological Methane on Mars Methane found on Mars comes from o 1 Comet Impacts Unlikely Because would have had happened recently 0 2 Volcanic Activity 0 3 Life CHAPTER 8 SECTION 5 ALH84001 meteorite expected to be from Mars due to abundance of oxygen16 oxygen17 and oxygen18 0 Signs of life from the meteorite o 1 Carbonate grains have layered structure with magnesium iron and calcium rich carbonates formed due to biological activity 0 2 Carbonate grains contain LOTS of complex organic molecules known as PAHs Abundance caused by decay of dead organisms or reactions between decay and environment 0 3 Crystals of minerals within iron layers Similar to those of magnetite grains found on Earth made by bacteria 0 4 Carbonate grains reveal rodshaped structures that look like fossilized bacteria 0 Explanation that it s NOT life 1 Possible to get layered carbonate via nonbiological ways 0 2 PAHs can be produced by chemical processes not biological processes alone High abundance might be due to terrestrial contamination during time the rock was in Antarctica water 0 3 Resemblance between magnetite crystals and ones made by bacteria on Earth is coincidental Occurred nonbiologically o 4 Rodshaped structures couldn t be bacteria due to extremely small size Tidal Heating Arises from effects of tidal forces lo s Tidal Heating occurs due to 0 Its proximity to Jupiter means it experiences a strong tidal force from the massive planet 0 lo has a slightly elliptical orbit which causes the strength and direction of the tidal force to change slightly as lo moves through each orbit o Tidal heating generates tremendous heat on lo more than 200 times as much heat 0 Due to this tidal heating lo is the most volcanically active world 0 Why is lo39s orbit slightly elliptical when most large satellites have nearly circular orbits Orbital resonance Which occurs among lo Europa and Ganymede The three moons periodically line up because during the time Ganymede takes to complete one orbit ofJupiter about 7 days Europa completes two orbits and lo completes four orbits In this case these gravitational tugs cause the orbits to be more elliptical than they would be otherwise JUP Europa Does it have liquid water oceans Calculations show that tidal heating can supply enough heat to keep most of Europa s ice melted beneath a solid ice crust o The relatively small number of craters implies that the moon s surface is young perhaps only a few tens of millions of years old indicating that it has been recently repaved Various features on the surface chaotic and ooded terrain suggest that liquid water sometimes wells up from below Europa has a magnetic eld that is likely caused by currents produced in something that conducts electricity like a salty ocean as Jupiter s magnetic eld changes Possible Life on Europa There is strong indirect evidence that a liquid water ocean exists 0 We expect the elements needed for life to be present in that ocean and on its oor 0 There are possible energy sources to support life but the total available energy is small compared to the energy available for life on Earth o Is there enough energy in a useful form to support biology If so is there enough energy to support a reasonable total biomass of ongoing life 0 Would need energy source in addition to chemical reactions near the deep sea vents High energy particles accelerated and trapped in Jupiter s magnetic eld regularly slam into the surface ice These particles and photons hit the surface with enough energy to break up molecules of ice leading to production of small quantities of other molecules such as hydrogen peroxide molecular oxygen and hydrogen molecules for life Potassium contained in the rocks of Europa could dissolve in the ocean and the natural decay of potassium s radioactive isotopes would produce hydrogen and oxygen molecules JUP Ganymede Possibly has an ocean under the surface Ganymede has its own magnetic eld which indicates that it might have a molten convecting core 0 Data showed a small part of Ganymede s magnetic eld varies with Jupiter s 10hour rotation just like Europa s magnetic eld SALTY OCEAN UNDER THE SURFACE What source of heat could keep the water melted under the surface Ganymede has less tidal heating than Europa however due to the larger size of Ganymede it should retain heat better than Europa Possible that tidal heating of Ganymede was greater in its youth and still cooling off JUP Callisto Never very warm inside and neither radioactive decay nor tidal heating ever heated the moon enough to melt it through 0 Magnetic eld found presence of a salty subsurface ocean possible What source of heat is keeping the ocean liquid if true Radioactive decay because the orbit is too far out to cause tidal hea ng But it s not enough to be suf cient for life due to the thick icy skin SAT Titan 0 Substantial atmosphere that s thicker than Earth s 90 nitrogen Habitability Zone Star s habitable zone is range of distances around it at which a planet could potentially have surface temperatures that would allow for abundant liquid water 1 Habitable zone based on range of distances at which worlds similar to Earth could exist Zone which is possible for world to have liquid water 2 Being in a star s habitable zone is not sufficient for habitability 3 Habitable zones evolve with time Because stars like the Sun brighten with age Could Life Exist Outside the Habitable Zone 0 Tidal heating and radioactive decay can supply heat in the absence of sunlight and melt subsurface ice 0 Earth like planets internal heat could keep the liquid water warm if there was a thick hydrogen atmosphere 0 Planets ejected into interstellar space during formation can have the thick hydrogen atmosphere for billions of years Venus Potential Habitability Venus high temperature is due to an extreme greenhouse effect produced by atmospheric carbon dioxide 200000x as much carbon dioxide in atmosphere as Earth 0 Why did Venus keep its atmospheric carbon dioxide and Earth did not 0 Venus carbon dioxide is in its atmosphere Earth s is nearly all locked up in carbonate rocks or dissolved in oceans through the carbon dioxide cycle So due to the fact that Venus doesn t have liquid water to have carbon dioxide undergo the carbon dioxide cycle Venus carbon dioxide is all in its atmosphere 0 Where did all the outgassed water go on each planet 0 Earth s outgassed water from volcanoes are in oceans However because Venus surface is too hot for water so only a tiny bit is in its atmosphere Venus might ve never had much water in the rst place or somehow lost it all 0 Ongoing volcanic activity Evidence Venus clouds contain sulfuric acid which is made from sulfur dioxide and water Recent observations show evidence of geologically recent lava ows 0 UV rays broke apart water molecules in Venus atmosphere Hydrogen atoms escaped to space ensuring water molecules could never reform 0 Due to the fact that Venus doesn t have a magnetic eld because of its slow rotation the solar wind stripped away atmospheric gases Deuterium lsotope of hydrogen Water molecules that contain an atom of deuterium chemically behave like water and can be broken apart by UV rays easily but a deuterium atom is twice as heavy as an ordinary hydrogen atom and thus cannot escape to space as easily as a normal water molecule Runaway Greenhouse Effect Form of positive feedback In regards to the Earth being the same distance from the Sun as Venus where the average temperature on Earth would increase by 30 degrees Celsius and cause water evaporation into the atmosphere However due to the fact that water vapor is a greenhouse gas it would cause the temperature on Earth to increase higher which would in turn increase the water evaporation which results in a continuous loop Optimistic Assumption Positive Feedback What Factors In uence Surface Habitability o Planet39s Distance From Its Star Earth s proximity vs Venus proximity o Star s luminosity Brighter stars have widermore distant habitable zone than the Sun Dimmer stars have narrowercloser in habitable zone 0 Planet39s Size 0 A planet has to be big enough for plate tectonics to exist in order for them to directly affect the carbon dioxide cycle which in turn affects the climate regulation 0 Role of an Atmosphere wo atmospheric pressure water cannot be abundant and stable 0 Necessary to protect surface against solar radiation 0 Planet w outgassing and sufficient size to hold gas gravitationally might lose atmosphere by RECAP 1 Large impacts that can blast signi cant amounts of atmospheric gas into space 2 Solar wind can strip atmospheric gas from any planet that lacks a global magnetic eld Magnetic elds not found on slowly rotating planets o The planet must be neither too close to nor too far from its star that is it must be within its star s habitable zone 0 The planet must be large enough to retain internal heat and have plate tectonics for climate regulation We don t know the precise minimum size required but it is certainly larger than Mars 0 The planet must have enough of an atmosphere for liquid water to be present on its surface This probably means that it must have had gases trapped in its interior so that an atmosphere could form through outgassing and that it has not since lost too much of this atmospheric gas to impacts or solar wind stripping Protection against the latter may require a global magnetic eld which in turn may require at least moderately rapid rotation Sun39s Inner Boundary Inner boundary lies between Venus and Earth 0 Moist Greenhouse Effect When moderate warming causes water vapor to circulate to much higher altitudes in Earth s atmosphere where water molecules would be above the ozone layer and then be broken apart by UV rays Hydrogen would escape to space causing Earth to lose this water and thus allowing more water to rise into the upper atmosphere and be lost in turn Upper atmosphere would become moist w water Conservative Assumption Negative Feedback 0 The inner boundary of the presentday habitable zone in our solar system may be at 084 AU if we allow for only a simple runaway greenhouse effect but as far out as 095 AU if we allow for water loss by a moist greenhouse effect Sun39s Outer Boundary Distance from Sun at which even a greenhouse effect could not warm a planet enough to keep liquid water from freezing If we allow for a thick atmosphere with a strong greenhouse effect the outer boundary of the presentday habitable zone lies at about 17 AU o If atmosphere of planet is too cold atmospheric carbon dioxide that produces greenhouse warming will condense into snow akes and fall to surface The carbon dioxide snow might limit how much carbon dioxide could reside in atmosphere preventing atmosphere from staying thick enough for strong greenhouse effect gtgt Optimistic Estimate Presentday habitable zone extends from about 084 to 17 AU Conservative Estimates From about 095 to 14 AU ltlt Sun39s Luminosity Sun shines by fusion of hydrogen into helium where each fusion reaction changes four hydrogen nuclei into one helium nucleus reducing the number of independent particles in the core The reduction leads to core shrinkage which in turn causes the core temperature to increase and nally it causes the fusion rate to increase causing the Sun to increase its brightness Continuous Habitable Zone Distances from the Sun where conditions have remained habitable from 4 billion years ago to present day meaning it has been habitable since the heavy bombardment Sun Large ball of gas that generates energy by nuclear fusion in its hot central core 90 of Star life spent fusing hydrogen into helium White Dwarf Low mass stars like our Sun eject their outer layers into space as planetary nebulae and end up as white dwarf Supernovae Higher mass stars die in titanic explosions in which their cores collapse to form stellar remnants that may be either neutron stars or black holes How Do We Categorize Stars Luminosity Total amount of light that a star emits into space Spectral Sequence OBAFGKM 0 Our Sun is a spectral type 62 star HertzsprungRussell Diagram Graph that shows the relationship between luminosity and surface temperature 0 Star39s surface temperature and luminosity are determined primarily by the star s mass Which Stars Would Make Good Suns Types A and F because they d offer a longer time for the formation of planets and life Hotter than the Sun so habitable zones would be wider and further out 0 Limitations Because A and F stars have higher temperatures they emit more UV light than the Sun does and that could affect the survival of life Ways Around 1 UV light does not penetrate far into the ground oceans or ice So life could survive with an A or F star as long as life was underground near deep sea vents in the oceans or ice 2 An ozone layer in the atmosphere will prevent much of the UV rays n In order to have an ozone layer planets would need to have a suf ciently thick atmosphere or an atmosphere that contained suf cient oxygen Type A and F stars 3 all stars Type G stars 7 all stars 0 Type K and M stars 90 all stars 0 Type K and M These stars are dimmer than the Sun so temperatures would be dimmer meaning the habitable zones will be smaller Limitations Habitable zones are smaller meaning the probability that planets would be found are lower a BUT There are tons of M stars Every M star ever born is still burning which means that there must be a large number of inhabited worlds 0 Brown Dwarfs An object with a mass less than 8 that of the Sun Gravity isn t strong enough to compress the core to high enough temperatures to sustain hydrogen fusion 0 Hotter surfaces than planets which means they emit moderate amounts of infrared radiation 0 No habitable zones because of the dimness but some brown dwarfs have planets Multiple Star Systems 13 of galaxy s stars Two or more stars that orbit each other closely o Potentially Stable Planet orbits both stars together Planet s orbit larger than the separation between the stars I Habitable Zone Region surrounding the two stars 0 Potentially Stable Planet orbits one star and the radius of the orbit is smaller than the separation between the stars Habitable Zone De ned solely by star the planet orbits 0 Not Stable Orbit of planet is neither much larger nor smaller than separation between stars How Do We Detect Planets Around Other Stars 0 Directly Pictures or spectra of planets o Indirectly Precise measurements of a star s properties 0 Astrometric Technique Making precise measurements of stellar positions in the sky If star wobbles gradually around average position center of mass there must be unseen planets Limitations n Requires extreme precision n Takes a long time 0 Doppler Technique Star s orbital movement around center of mass studied by looking at a star s spectrum to look for signs that the star is moving Shifts in wavelengths of spectral lines Object moving towards us Spectrum shifted to shorter wavelengths Blueshifted Object moving away from us Spectrum shifted to longer wavelengths Redshifted I Can only observe Doppler shifts in the star s spectrum only if we view its planet orbiting at some angle other than faceon 0 Transit Used to see if a star s brightness diminishes due to a planet crossing in front of it Sensitive to planets close to their star Can be used to determine planetary size orbital perioddistance not mass or type of orbit n Limitations Probability of transit is low NEEDS EDGEON VIEW 0 Microlensing When an object passes between distant star and ourselves the star is not darkened as might be expected When light is coming from distant star as it passes to a star close to us the light gets bent because space gets warped due to the heavy mass of the object a Einstein39s Theory of General Relativity Hot jupiters Planets that are extremely hot because the orbits are so close to their stars orbits highly elliptical If jovian planets should only form in the cold outer regions of a solar system then how are Hot Jupiters a thing 0 1 Maybe something is fundamentally wrong with our model of the solar system formation But due to no evidence of fault scientists suspect hot jupiters were born with circular orbits far from their stars and might ve underwent some sort of planetary migration or suffered gravitational interactions with other massive objects 0 How might planetary migration occur 0 Waves passing through a gaseous disk A planet s gravity and motion tend to disturb the otherwise evenly distributed disk material generating waves that travel through the disk These waves cause material to bunch up and the clumps in turn exert their own gravitational pull on the planet robbing it of energy and causing it to move inward Can cause young planets to spiral slowly toward their star o Elliptical orbits may be result of close encounters between young jovian planets So the encounters between two planets might send one planet out of the star system while the other is ung inward into a highly elliptical orbit Nebular theory correct but needs new features planetary migration and gravitational encounters How Could We Detect Life on Extrasolar Planets Crude images Learn about ratio of ocean to land Light changes from day to day seasons Spectrum Measure properties See if the planet was able to sustain life via elements Spectra from IR telescopes Search absorptionemission features of gases in atmosphere ex look for oxygen carbon dioxide Are EarthLike Planets Rare or Common RareEarth Hypothesis Circumstances that have made it possible for evolution to progress beyond microbes to complex creatures might be so rare that our might be the only inhabited planet in the galaxy LUCK Galactic Constraints Earthlike planets can only form in a small region of the Milky Way making the number of potential homes for life far smaller than we expect Galactic Habitable Zone Jupiter Having Jupiter was essential to life on Earth because without Jupiter comets might ve remained in the solar system and not out in the Oort Cloud and could ve posed a danger to Earth The heavy bombardment might never had ended either Climate Stability o 1 Existence of plate tectonics The Sun gets gradually brighter but because of the plate tectonics and the carbon dioxide cycle Earth remains habitable o 2 Existence of the Moon Thanks to the Moon Earth has an axis tilt which allows for climate stability If the Moon didn t exist gravitational tugs from other planets especially Jupiter would cause large swings in Earth s axis tilt HertzsprungRussell Diagram Star s brightness depends on 1 its distance 2 its luminosity and 3 the dimming effect of any intersteller dust that might lie between us and the star Drake Equation Used to calculate the number of civilizations existing elsewhere in our galaxy from which we could potentially get a signal Gives us a way to calculate the number of civilizations capable of interstellar communication that are sharing the Milky Way with us 0 Number of civilizations Nhp x fIife x fciv x Know 0 Nhp Number of habitable planets in the galaxy Only term we can make educated guess on o fIife Fraction of habitable planets that actually have life 0 fciv Fraction of lifebearing planets on which a civilization capable of interstellar communication has at some time adsen 0 Know Fraction of the civilizationbearing planets that happen to have a civilization now as opposed to the past


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