Astro 202Prof. Jim Bell ([email protected])Spring 2008Lecture 21: Introduction to Astrobiology:What is Life?But first...Paper 5 (Poster proposal) handed back Thurs.Paper 6 is due at start of class next TuesdayReading Assignment (G) for this Thursday is posted online: Jakosky (1998) Sci. Am. articleKeep up with the Reading in Pale Blue Dot You should be reading the last few chapters this weekYou will need to have read this book for Paper 7! (which will be posted online on Thursday)A few more words about your final Posters...Building a “Poster Talk”A Background Poster Board(typically 40” x 32”)We will provide you with one.Choose your color by Thursday(indicate on attendance form)Building a “Poster Talk”Your NameAstro 202; Spring ‘08SummaryWrite a high-level summary or “abstract” of the results of your studyIntroductionDescribe the “problem” or “issue” and why it interests you; Describe the topic’s background and historyTables or FiguresYou can use tables or graphs or photos to show data, or describe measurements or experiments, or to list interesting facts & figures...maybe other tables or lists or graphs...A summary of the main results or highlights is often useful; Could use a bulleted list ResultsDiscussionWhat do you think?How do you interpret the data/issue?maybe more tables or lists or graphs in support of your ideas...Succinct summary of your bottom line(s) ConclusionsReferences, Further reading, acknowledgmentsA Catchy Title in a Nice Big FontBuilding a “Poster Talk”Your NameAstro 202; Spring ‘08SummaryWrite a high-level summary or “abstract” of the results of your studyIntroductionDescribe the “problem” or “issue” and why it interests you; Describe the topic’s background and historyTables or FiguresYou can use tables or graphs or photos to show data, or describe measurements or experiments, or to list interesting facts & figures...maybe other tables or lists or graphs...A summary of the main results or highlights is often useful; Could use a bulleted list ResultsDiscussionWhat do you think?How do you interpret the data/issue?maybe more tables or lists or graphs in support of your ideas...Succinct summary of your bottom line(s) ConclusionsReferences, Further reading, acknowledgmentsA Catchy Title in a Nice Big FontExample Design OnlyFeel free to explore different ways to include these content elements6Lecture #21: Astrobiology!Introduction to Astrobiology– What is Life?– Case Study: Origin of Life on Earth• Data• Models• Experiments!Reading: NSS 27, PBD 21Astrobiology!Astrobiology (sometimes called Exobiology) is the study of life in the Universe– Origin of Life– Distribution of Life– Ultimate Fate of Life!Astrobiology today is an extrapolation from the one known example (Earth life), using the basic principles of chemistry & physics and observing the Universe around usWhat is Life?!The question is philosophical, poetic, spiritual, intangible...but also scientific!To find life we must define what we seek!"Intuitive" definition: – “I know it when I see it”• Not very rigorous• Applies only to Earth life?A Quote fromCarl SaganWhat is Life?!A more rigorous definition:– Something is alive if it has the ability to ingest nutrients, give off waste products, & reproduce– But what are nutrients? – What are waste products?– Is growth important? (mountains "grow"...)!Definition must acknowledge that life is hard to define and that there are likely to be exceptions to any rules proposedAttributes of Living Systems!Rather than defining life, can we describe it in terms of specific attributes?!Life has at least two unique attributes:(1) A living system must be able to reproduce, to mutate, and to reproduce its mutations(2) A living system must be able to convert external energy sources into useable internal energy sourcesBut even this gets dicey...!There are systems with one attribute but not both– Chemical Reactions•CO2 "reproduces"• But it's not alive!– Crystals• "reproduce" in regular patterns, get distorted (mutated)– Fire• Uses "nutrients", converts energy, "grows", "reproduces", ...– Many other "fuzzy" cases...• Mules? A virus? Computer programs? Robots?CO2 + sunlight --> CO + OH2O + sunlight --> H + OHCO2 + OH --> CO2 + HThe Essential Requirements!Liquid Water– "Medium" for the chemistry of life (mobility, nutrients)– Stable over wide range of temperatures– Unique freezing properties help maintain stability– Complex organic compounds don't dissolve in water!!Source of Excess Energy– Sunlight (photosynthesis)– Chemical (oxidation)– Thermal or geothermal...!Source of Organic Molecules– C, H, N, O, P, S combined in both simple and complex ways– "Simple" organic molecules appear to be abundant out there… Group DiscussionBreak up into groups of 3-5 with one person acting as the note taker, and try to reach consensus on an answer to the following question:Do you think that there is life beyond Earth?Explain why or why not...5 minutesThen I will poll the note-takers...Origin of Life on Earth!Key Questions:(1) Did life originate on Earth or in space?(2) If life originated on Earth:(a) What were the conditions like on early Earth that made possible the origin of life?(b) Did life originate on or near the surface, below the surface, or in the oceans?"Panspermia"!Swedish chemist Svante Arrhenius proposed in 1908 that life is ubiquitous in the Cosmos and that "spores" or the seeds of life were delivered to Earth essentially by accident– No attempt to explain how life originated, only how it got to Earth– How did the "spores" get off other planets? (impacts?)– How did the "spores" survive harsh interstellar radiation?!More recent variation: "intentional" panspermia– Life was planted on Earth by space travelers– Popular among science fiction fans and conspiracy groupies– Still doesn't explain how life originated though...Organic molecules in meteorites!Some complex organic molecules (molecules containing carbon) have been found in some of the most primitive carbonaceous chondrite meteorites– Alkanes, benzene, paraffins, amino acids, …e.g., Glycine: C2NH5O2e.g., Benzene: C6H6Organic molecules in exotic places!Complex organic molecules have also been found or inferred to exist in:–Interstellar molecular clouds–Comets–Interplanetary dust particles–Some dark asteroids, rings, & planetary satellites–Some other “anomalous” meteorites (e.g.,