Astronomy 141 - Life in the Universe Serial http://www.astronomy.ohio-state.edu/~pogge/Ast141/ en-us 2009-2026 Richard W. Pogge Richard Pogge An Introduction to Life in the Universe for non-science majors Astronomy 141, Life in the Universe, is a one-quarter introduction to Astrobiology for non-science majors taught at The Ohio State University. This podcast presents audio recordings of Professor Richard Pogge's lectures from his Autumn Quarter 2009 class. All of the lectures were recorded live in 1005 Smith Laboratory on the OSU Main Campus in Columbus, Ohio. no Richard Pogge pogge.1@osu.edu mkitem.pl v1.2.1 Fri, 04 Dec 2009 00:00:00 EST Fri, 04 Dec 2009 13:30:24 EST Richard Pogge Welcome to the Astronomy 141 Lecture Podcasts. This is a brief message from me explaining the podcasts, and welcoming new and old listeners. University. Lectures will begin on Wednesday, 2009 Sept 23, and run through Friday, 2009 Dec 4. New lectures will appear shortly before 6pm US Eastern Time each day there is a regular class. Recorded live on 2009 Sep 23 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1253731035 Wed, 23 Sep 2009 14:37:15 EDT astronomy Richard Pogge A brief overview of the topics we will cover in Astronomy 141, setting the stage for how we can make a serious scientific inquiry out of the question of whether or not there is life elsewhere in the Universe. It is a short lecture, the first half was an overview of course mechanics (tests, homework, office hours, etc.) that I did not record. Recorded live on 2009 Sep 23 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1253731100 Wed, 23 Sep 2009 14:38:20 EDT astronomy 00:19:24 Richard Pogge An introduction and review of the basic notation and physical units we will be using throughout this course. In particular, we will be using the Metric (SI) system for lengths, masses, times, and temperatures, and special astronomical units for distances (AU and Light Years) and masses (Earth Masses and Solar Masses) appropriate when discussing interplanetary and interstellar scales. Recorded live on 2009 Sep 24 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1253819828 Thu, 24 Sep 2009 15:17:08 EDT metric system, astronomical units 00:43:56 Richard Pogge What is the cultural history of our imaginings of other worlds and their possible inhabitants? I will draw examples from history, philosophy, literature, cinema, and popular culture. In the end, our imaginings about other worlds inform us more about ourselves, our hopes and our fears, than about extraterrestrial life. The scientific inquiry we are undertaking must therefore approach the problem from a different direction. Recorded live on 2009 Sep 25 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1253901283 Fri, 25 Sep 2009 13:54:43 EDT 00:40:09 astronomy, other worlds, alien life, pop-culture views of alien life Richard Pogge Modern science was borne of an effort over many centuries to understand the motions of celestial bodies. The Copernican Revolution of the 16th and 17th centuries was the crucial moment in history when we finally understood the nature of celestial motions, and opened the door to the modern world. This lecture reviews the problem of celestial motions, the two competing models for explaining them, and the final revolution in thought starting with Copernicus and ending with Newton. Mid-lecture my classroom AV system lost power, and the recovery slowed things down a bit. These are recorded live, after all. This lecture was conducted on 2009 Sep 28 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254159478 Mon, 28 Sep 2009 13:37:58 EDT 00:43:56 astronomy, Copernican Revolution, Heliocentric Model, Geocentric Model, Copernicus, Kepler, Galileo, Newton Richard Pogge What is the nature of matter, and how did we come to understand the chemical elements and atomic structure? This lecture is a brief and selective overview of the history of our understanding of the nature of matter and chemistry. We will also introduce spectroscopy and radioactivity, two very powerful tools that came out of the chemical revolution that are crucial for the inquiry in this class into the question of life on other worlds. Recorded live on 2009 Sep 29 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254245317 Tue, 29 Sep 2009 13:28:37 EDT 00:45:17 astronomy, chemistry, atoms, elements, the periodic table of the elements, spectroscopy, isotopes, radioactivity Richard Pogge The geological revolution revealed that the Earth is of great antiquity and yet has a history we can read in the land. We will discuss ideas of cyclic and linear time, historical versus physical age estimates, the discovery of geological time, and radiometric dating methods that give us our present estimate of 4.54+/-0.05 Gyr for the age of the Earth. Recorded live on 2009 Sep 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254332029 Wed, 30 Sep 2009 13:33:49 EDT 00:46:11 astronomy, geology, historical ages of the Earth, physical ages of the Earth, radiometric dating, radioactivity Richard Pogge What is the nature of life? In this lecture I will review the revolution in biological thinking that has dramatically changed how we view life. I will review such persistent ancient ideas as spontaneous generation and why it took so long to disprove this notion, the impact of the microscope on biology, and the discovery of the laws and agency of heredity. This is obviously a highly-selective view of a vast topic, and my goal is to highlight those episodes in the history of biology that inform us about the nature of science (its successes and failures), and which we will concern ourselves with in the rest of the course. Listeners will note that I do not introduce Evolution (more precisely, Natural Selection) since that is a huge other topic for another day. Recorded live on 2009 Oct 1 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254418330 Thu, 01 Oct 2009 13:32:09 EDT 00:44:16 astronomy, biology, spontaneous generation, heredity, microscopy, Mendel, fruit flies, DNA, genes Richard Pogge Cosmology is the study of the entire Universe as a physical system. The past century has witnessed a revolution in cosmological thought that has revealed the vastness of space and the depths of cosmic time, a revolution that is still playing out in the present day. The lecture will review the Earth's place in the Universe, the age of the Universe as reckoned by the time since the Big Bang, and the origin of the elements. We will return to many of these topics later in the course, but this presents the big picture. Recorded live on 2009 Oct 2 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254512458 Fri, 02 Oct 2009 15:40:58 EDT 00:46:29 astronomy, cosmology, solar system, planets, cosmic distance scale, big bang, nucleosynthesis Richard Pogge What is the interior structure of the Earth and how does it drive the Earth's magnetic and geologic activity? We will review our current knowledge of the interior of the Earth, how we measure it using Seismology, the origins of the Earth's magnetic field, and discuss the workings of plate tectonics. the Earth is a dynamic, geologically active world, which has interesting implications later for understanding the past and future history of life on Earth. Recorded live on 2009 Oct 5 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254765624 Mon, 05 Oct 2009 14:00:24 EDT 00:42:47 astronomy, geology, Earth, interior of earth, crust, mantle, core, geodynamo, plate tectonics, continental drift, earthquakes, volcanism Richard Pogge This lecture was to be about the Earth's atmosphere, its composition and structure, the greenhouse effect, and the primordial atmosphere, but about 2 seconds into the lecture, unbeknownst to me, the battery compartment on my digital voice recorder came open in my pocket. At the end of lecture, I took it out of my pocket to turn it off and the battery didn't come with it. Oops! Fail. My apologies, I'll put in some work to prevent a recurrence in future lectures. Recorded live on 2009 Oct 6 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254850760 Tue, 06 Oct 2009 13:39:20 EDT 00:01:17 astronomy Richard Pogge How have we pieced together the geological history of the Earth? This lecture reviews the different types of rocks and the cycle of transformation between them, with particular emphasis on stratigraphy. I will outline the 4 major Eons in Earth's history, and focus on the earliest Hadean Eon which proceeded from the formation of the Earth to the end of the epoch of Heavy Bombardment. The Hadean Eon saw the formation of the primordial atmosphere of the Earth and the formation of the Oceans. Recorded live on 2009 Oct 7 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1254936490 Wed, 07 Oct 2009 13:28:10 EDT 00:42:39 astronomy, geology, geological time scale, types of rock, rock cycle, stratigraphy, Eons, Hadean Eon, heavy bombardment, moon formation Richard Pogge What are the main mechanisms of climate regulation and climate change that have operated through Earth's history? The Earth's climate is regulated by a Carbon Dioxide thermostat that is the interaction between the Greenhouse Effect and the CO2 Cycle. I describe the CO2 cycle and its role in regulating global temperature. I will then discuss other influences on climate, and periods of glaciation (ice ages) in the recent and distant past, including the possible Snowball Earth events in the early and late Proterozoic Eon. Recorded live on 2009 Oct 8 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255022906 Thu, 08 Oct 2009 13:28:26 EDT 00:45:19 astronomy, climate, geology, carbon dioxide, greenhouse effect, carbon cycle, glaciation, Malankovitch Cycles, Snowball Earth Richard Pogge How do we define life? This lecture reviews the six basic criteria for living systems described by biologists: order, reproduction, growth and development, energy utilization, reaction to environment, and evolution that characterize life. The last third of the lecture is an admittedly whirlwind review of natural selection (I got off my stride and got a little rushed for time at the end). The goal is not a complete survey of current biological thought, but to highlight those characteristics of "life" that may best inform us as to how to look for signs of life elsewhere in the Universe. Recorded live on 2009 Oct 12 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255368884 Mon, 12 Oct 2009 13:34:44 EDT 00:46:16 astronomy Richard Pogge Cells are the basic structural and functional unit of all life on Earth. This lecture reviews the basic building blocks of cells, the main chemical components, the two basic types of cells (Prokaryotes and Eukaryotes), and introduces the Phylogenetic Tree of Life, the way biologists order life by their biochemical and genetic relationships. Understanding life at the cellular level gives us important insights into the nature and history of life on Earth, and clues as to what we might look for elsewhere. Recorded live on 2009 Oct 13 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255455686 Tue, 13 Oct 2009 13:41:26 EDT 00:45:32 astronomy, life, cells, prokaryotes, eukaryotes, carbohydrates, lipids, proteins, amino acids, nuclei acids, bacteria, Archaea, Eukarya, Phylogenetic Tree of Life Richard Pogge What is the basic chemistry of living organisms? We introduce the requirements for metabolism (raw materials and energy), the ATP/ADP energy cycle in cells, auto- and heterotrophs, photosynthesis and chemosynthesis, and the role played by liquid water. The goal of today's lecture is to seek insights into the basic requirements for life from a consideration of the needs of the cells' chemistry. Recorded live on 2009 Oct 14 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255555858 Wed, 14 Oct 2009 17:30:58 EDT 00:45:04 astronomy, astrobiology, cells, cell metabolism, ATP cycle, autotrophs, heterotrophs, photosynthesis, chemosynthesis, water Richard Pogge DNA and RNA are the key molecules of living cells. DNA plays a vital role in storing and transmitting the hereditary information that constitutes the "operating instructions" of living cells; how to construct the functional and structural proteins that perform vital cell functions, control developmental pathways, and basically "build" the organism. RNA is the crucial actor in protein synthesis and other cell functions. Mutations, changes in the DNA coding, are the molecular basis for evolution, providing the genetic variation required by natural selection. Understanding the molecular basis of heredity and evolution gives us important insights into the functional requirements for life. Recorded live on 2009 Oct 15 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255628586 Thu, 15 Oct 2009 13:43:06 EDT 00:46:53 astronomy, biology, DNA, RNA, replication, transcription, translation, mutation, heredity, evolution Richard Pogge Extremophiles are organisms that are adapted to survive in extreme environments. This lecture describes the challenges that extremes of heat, cold, acidity, salinity, and radiation pose to organisms, and show examples of how evolution has nonetheless allowed some organisms to adapt to not just survive but thrive in such extreme conditions. Finally, we will explore the possible limits of life on Earth, and find that while you can make things pretty extreme and still have organisms adapt, you reach the limit if there is no water. Rather than being oddballs, these organisms give us important insights into the origins of life on Earth, and widens the possibilities for life on other worlds. Recorded live on 2009 Oct 16 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255715653 Fri, 16 Oct 2009 13:54:13 EDT 00:46:54 astronomy, biology, extremophiles, thermophiles, psychrophiles, halophiles, acidophiles, radiation resistance, endoliths, Atacama desert, limits of life Richard Pogge What are the first recognizable forms of life that we find in the geological record? How far back can we go in geological time and still find life? This lecture reviews three lines of evidence that have emerged in recent years to suggest that life may have emerged very early on the young Earth, perhaps within a few hundred million years of the end of the epoch of heavy bombardment. I will describe fossil stromatolites, microfossils, and carbon isotope data that are used to explore these questions. Recorded live on 2009 Oct 19 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1255982869 Mon, 19 Oct 2009 16:07:49 EDT 00:46:08 astronomy, earth, earliest life, archaean eon, stromatolites, microfossils, isotopes, proterozoic eon Richard Pogge How did life arise from non-life? Frankly, we don't know, but current experimental work is aimed at trying to understand how it might work in biochemical terms. This lecture sets out the problem of "abiogenesis", and describes our current thinking about the likely origins of life on Earth. We will review the classic Miller-Urey experiment, and look at its insights and limitations, discuss meteoritic sources of amino acids, and the basic requirements needed for protolife. I will then describe in outline two scenarios that are active areas of origins research: the RNA World model and the Metabolism First model. Finally, I will very briefly mention Exogenesis and Panspermia, which don't really address the problem of abiogenesis so much as move it elsewhere. Recorded live on 2009 Oct 20 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256066865 Tue, 20 Oct 2009 15:27:45 EDT 00:46:08 astronomy, origins of life, Miller-Urey experiment, RNA World, Metabolism First, lipid vesicles, exogenesis, panspermia Richard Pogge In this lecture we step back and look at the history of life on Earth from the first signs of life at start of the Archaean Eon 3.5 billion years ago to just up to the present day. We will review the appearance of photosynthesis and the rise of oxygen in the atmosphere in the Proterozoic, the appearance of the first eukaryotes and sexual reproduction, and the Cambrian explosion of plant and animal species at the start of the Phanerozoic Eon, and briefly review the changes in life to the present day from the Cambrian Explosion to the colonization of land by plants and then animals. Most of the lecture will be where most of the time was spent, in the early, microbiological Earth. Recorded live on 2009 Oct 21 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256147632 Wed, 21 Oct 2009 13:53:52 EDT 00:47:19 astronomy, biology, Archaean, Proterozoic, Phanerozoic, Oxygen, Banded Iron Formations, anaerobic bacteria, Cambrian Explosion, colonization of land, dinosaurs, mammals Richard Pogge We end our exploration of life on the Earth with a look at death in the fossil record. This lecture looks at the role asteroidal impacts have played in the history of the Earth, and their possible role in mass extinction events in the fossil record. We will discuss near-earth asteroids, historical impacts, and the K-T event in which a massive asteroid impact caused a mass extinction of species that included all non-avian dinosaurs among its victims, opening up the biosphere to the dominance of mammals. We'll look at other mass extinctions during the past 500Myr, and talk about whether extinction-class impacts are in our future. Recorded live on 2009 Oct 22 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256232553 Thu, 22 Oct 2009 13:29:13 EDT 00:46:31 astronomy, asteroids, near-earth objects, impacts, Tunguska Event, Sudan Event, 2004 FH near miss, K-T boundary, K-T extinction, dead dinosaurs, Permian-Triassic extinction Richard Pogge This first lecture of Unit 4 - Life in the Solar System - is a quick tour of our Solar System reviewing the planets, dwarf planets, moons, and small bodies that make up our celestial home. This lecture will introduce many of the places we will be considering in detail over the next two weeks, and which we'll find around other stars. Recorded live on 2009 Oct 26 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256578128 Mon, 26 Oct 2009 13:28:48 EDT 00:46:22 astronomy, Solar System, Terrestrial Planets, Jovian Planets, Gas Giant, Ice Giants, Dwarf Planets, Asteroids, Comets, Trans-Neptunian Objects, Kuiper Belt, Sun Richard Pogge We follow our tour of our Solar System with an in-depth comparison of the Terrestrial Planets. In particular, we want to contrast and compare their geological and atmospheric histories. This will inform our inquiry into whether or not we expect to find life on these worlds. Recorded live on 2009 Oct 27 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256666047 Tue, 27 Oct 2009 13:54:07 EDT 00:46:41 astronomy, Solar System, Terrestrial Planets, Mercury, Venus, Earth, Mars, interiors, atmospheres, greenhouse effect Richard Pogge We turn our attention to the Giant Planets of the outer Solar System: the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune. We will review their structure and properties, and then examine their systems of moons, with special attention to the giant moons. While the Jovian planets themselves seem unlikely places to hunt for life in our Solar System, a few of their largest moons may be more promising than appears at first sight. We'll explore this further in subsequent lectures in this unit. Recorded live on 2009 Oct 28 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256753184 Wed, 28 Oct 2009 14:06:24 EDT 00:47:50 astronomy, Jovian Planets, Gas Giants, Jupiter, Saturn, Ice Giants, Uranus, Neptune, Galilean Moons, Europa, Titan, Enceladus, Triton Richard Pogge Having completed our tour of the Solar System, we now turn to a discussion of the requirements for life, and where those requirements might be satisfied elsewhere in the Solar System. Some - energy, complex chemistry, and liquid water - seem obvious, but they are not the only possibilities or considerations. At the end, we will have a short list of possible places to look, some expected, others surprising. Recorded live on 2009 Oct 29 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256853377 Thu, 29 Oct 2009 17:56:17 EDT 00:47:04 astronomy, life, sunlight, inverse square law of brightness, equilibrium temperature, albedo, water, liquids, atmosphere retention, Solar System, Mars, Titan, Europa, Enceladus Richard Pogge For many, the most likely place in the Solar System to search for life beyond the Earth is Mars. This lecture describes the properties of Mars, a desert world with a thin, dry, cold carbon dioxide atmosphere. I will review evidence that has begun to point unequivocally to the conclusion that Mars had flowing and standing liquid water on its surface in the past, perhaps during the first billion years or so. If Mars had a warm, wet past, did life also get a start there? Recorded live on 2009 Oct 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1256923744 Fri, 30 Oct 2009 13:29:04 EDT 00:47:26 astronomy, Mars, space exploration, water on Mars, Martian atmosphere Richard Pogge Is there life on Mars? We begin with a brief historical survey of the idea of inhabitable Mars, from Herschel to Lowell, and look at how the idea of Mars and Martians is deeply embedded in the popular culture. We then turn to spacecraft explorations of Mars, and how they have changed our view of the Red planet. We will discuss the on-going search of Martian life, past and present, particularly the Viking 1 and 2 experiments, the Allan Hills Meteorite controversy, Mars Methane, and recent important results from the Phoenix lander. We'll end by briefly noting future directions in Mars exploration. Recorded live on 2009 Nov 2 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257187867 Mon, 02 Nov 2009 13:51:07 EST 00:47:04 astronomy, mars, martians, life, canals, Herschel, Schiaparelli, Lowell, Viking, ALH84001, mars methane, Phoenix Richard Pogge The four large Galilean Moons of Jupiter seem unlikely places to look for life; at first glance they should be cold, dead, icy worlds. Instead we find tremendous geological diversity, and two big surprises: volcanically-active Io, and icy Europa. Io is the most volcanically active world in the Solar System, heated by tides from Jupiter. Europa is even more surprising: its icy surface is young, with few impact craters and extensive signs of recent repaving by liquid water. Even more surprising is the distinct possibility that underneath Europa's ice is a deep liquid water ocean, heated by tides from Jupiter. We will review the evidence for Europa's liquid sub-ice ocean and look at its potential as an abode of life. If there is life to be found anywhere in the Solar System beyond Earth, beneath the ice of Europa may be the best place to look. Recorded live on 2009 Nov 3 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257273949 Tue, 03 Nov 2009 13:45:49 EST 00:44:57 astronomy, Jupiter, Io, Europa, Ganymede, Callisto, tidal heating, Io volcanoes, water on Europa, life on Europa Richard Pogge Among the 61 known moons of Saturn, two stand out: Enceladus and Titan. Giant Titan is the only moon in our Solar System with a substantial atmosphere, composed of nitrogen and methane, dense enough to maintain a weather cycle with methane analogous to the water cycle on Earth, even including great lakes of liquid methane and ethane at the poles. Enceladus has fountains of water vapor and ice particles that coat its surface in fresh ices, and indicates the presence of liquid water beneath its icy surface. Is this just pockets of tidal-heated water, or hints of a deep global liquid water ocean. I will describe new results on these two children of Saturn, and the possibilities they have for finding life, or life-like conditions, elsewhere in our Solar System. Recorded live on 2009 Nov 4 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257359553 Wed, 04 Nov 2009 13:32:33 EST 00:46:10 astronomy, Saturn, Titan, Enceladus, life, methane, methane lakes Richard Pogge Why is the Earth habitable today but Venus and Mars not? This lecture explores the question of planetary habitability from the perspective of the stability of liquid water on the surface of planetary bodies. We will see how the amount of sunlight and the greenhouse effect in the atmosphere combine to create a classic Goldilocks problem: whether or not a planetary surface has stable liquid water is a question of not being too hot or too cold. This defines the Habitable Zone for the present-day Sun. However, the size of a planet also plays a role, and we will expand the concept of habitability to include the type of atmosphere a planetary body can or cannot retain. Finally, because the Sun changes brightness slowly over its lifetime, the location of the habitable zone is time-dependent. We will define the Continuous Habitable Zone, and discuss implications, and limitations, of the idea of habitable zones, looking forward expanding our search for life to worlds around other stars. Recorded live on 2009 Nov 5 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257446168 Thu, 05 Nov 2009 13:36:08 EST 00:46:19 astronomy, habitability, solar radiation, greenhouse effect, Goldilocks problem, habitable zone, continuously habitable zone Richard Pogge What are the observed properties of stars? This lecture is a quick review of the basic observational properties of stars, introducing luminosity, spectral classification, the luminosity-radius-temperature relation, and the Hertzsprung-Russell (H-R) diagram. This sets up the empirical basis of subsequent lectures on the lives and deaths of stars. Recorded live on 2009 Nov 9 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257792425 Mon, 09 Nov 2009 13:47:05 EST 00:46:37 astronomy, stars, luminosity, temperature, spectra, spectral classification, radius, mass, H-R Diagram Richard Pogge Why do stars shine? How long do they shine? This lecture describes the physics of stars on the main sequence, describes the mass-luminosity relation of main sequence stars, introduces nuclear fusion power and the nuclear fusion lifetimes of stars. From this we gain an important insight into one of the criteria we might apply to the search for life around other stars: we want planets around low-mass main sequence stars that can shine more or less steadily for more that 500 Myr to 1 billion years - maybe longer if our goal is to find intelligent life. Recorded live on 2009 Nov 10 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1257878314 Tue, 10 Nov 2009 13:38:34 EST 00:46:51 astronomy, stars, main sequence, luminosity, mass, nuclear fusion, hydrogen fusion, nuclear time scale, main sequence lifetime Richard Pogge What happens to a star when it runs out of hydrogen in its core? This lecture describes the post main-sequence evolution of stars. What happens depends on the star's mass. Low mass stars swell up into Red Giants, and eventually shed their envelopes and end their lives as white dwarf stars. High mass stars become Red Supergiants, and if large enough, end their lives in a spectacular supernova explosion that leaves behind a neutron star or black hole. The explosion itself creates massive quantities of heavy elements, which then seed interstellar space with metals to be incorporated into subsequent generations of stars. Recorded live on 2009 Nov 12 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258050511 Thu, 12 Nov 2009 13:28:31 EST 00:47:23 astronomy, stars, stellar evolution, white dwarfs, supernovae, heavy element synthesis Richard Pogge Which stars are the most hospitable for life? This lecture examines the factors affecting the habitability of stars, with a goal of understanding where we should search for life-bearing planets. We will do this by generalizing the idea of a Habitable Zone developed for the Sun back in Lecture 30. In this context, we find that the best places to search for life would be rocky planets in the habitable zones of low-mass main-sequence stars. There are a number of caveats we will discuss - tidal locking, stellar flares, and UV radiation - and limitations to the approach, but it seems to be a good place to start our search. Recorded live on 2009 Nov 13 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258137041 Fri, 13 Nov 2009 13:30:41 EST 00:47:29 astronomy, planets, stars, habitability, habitable zone, flare stars, UV radiation, tidal locking Richard Pogge What stars are near the Sun? Now that we have some idea of what we are looking for - rocky planets in the habitable zones of low-mass main-sequence stars - what are the prospects near the Sun? This lecture examines the hunting ground for planets, the nearby stars that make up the Solar Neighborhood. I will describe our nearest neighbor, the Proxima Centauri/Alpha Centauri triple system, and then look at the properties of our nearest stellar neighbors. What we will find is that G-type stars like the Sun are uncommon, only about 7% of all nearby main-sequence stars. Red dwarfs, on the other hand, are very common, about 75%. To find Sun-like main sequence stars, we will have to extend our search to larger distances into our Milky Way galaxy proper. Recorded live on 2009 Nov 16 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258396773 Mon, 16 Nov 2009 13:39:33 EST 00:46:03 astronomy, stars, solar neighborhood, Alpha Centauri, Proxima Centauri, red dwarfs, stellar census, Milky Way, Galactic Bulge. Richard Pogge Are there planets around other stars? This lecture reviews the methods used to hunt for exoplanets and the results thus far. I will describe direct imaging methods, indirect methods relying on the gravitational influence of the planet on its parent star, planetary transits in which a planet blocks part of its parent star's light, and gravitational microlensing. There has been an explosion in our knowledge of planets around other stars, from little or nothing in the early 1990s to more than 400 planets around some 340-odd stars as of today. Recorded live on 2009 Nov 17 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258486932 Tue, 17 Nov 2009 14:42:12 EST 00:47:10 astronomy, stars, exoplanets, direct imaging, Doppler wobble method, transit method, gravitational microlensing method Richard Pogge What are the properties of the 400+ exoplanets we have discovered so far? This lecture reviews the properties of exoplanets, and finds a couple of surprises: Jupiter-mass planets orbiting close to their parent stars, and Jupiter-mass planets in very elliptical orbits. Both seem to require some mechanism for migration: strong gravitational interactions with either the protoplanetary disk or other giant planets to cause the planets to move inward from their birth places beyond the "Ice Line". We will then briefly discuss why we are seeing systems very different from our own, mostly we think a selection effect due to our search methods to date. Microlensing, however, is more sensitive to systems like ours, and is starting to find them. Earths, however, remain elusive so far, but the hunt is on. Recorded live on 2009 Nov 18 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258569204 Wed, 18 Nov 2009 13:33:24 EST 00:46:50 astronomy, stars, exoplanets, hot jupiters, solar systems, earth-like planets Richard Pogge Are there other Earths out there? Do they have life on them? This lecture looks at the search for ExoEarths - Earth-sized planets in the habitable zones of their parent stars, and what we might learn from measuring them. The ultimate goal of all planet searches is to find other Earth's, what the late Carl Sagan so poetically called the "pale blue dot" as seen from the depths of space. This lecture discusses what we might learn about such planets from studies of our own Earth, spectroscopic biomarkers that might reveal life, and variability studies that might give us insight into surface features (continents and oceans) and weather (clouds and even climate). Recorded live on 2009 Nov 19 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1258655681 Thu, 19 Nov 2009 13:34:41 EST 00:44:09 astronomy, stars, other earths, pale blue dots, life in the universe, biomarkers, red edge, reflectance spectroscopy, thermal spectra Richard Pogge How many intelligent, communicating civilizations live in our Galaxy? We have no idea. One way to approach the question and come up with quasi-quantitative estimates is the Drake Equation, first introduced by radio astronomy Frank Drake in the 1960s. I will use the Drake equation as an illustration of the issues related to the question of extraterrestrial intelligence, and to set the stage for future lectures on the likelihood of finding other intelligences in our Universe. Recorded live on 2009 Nov 23 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259001589 Mon, 23 Nov 2009 13:39:49 EST 00:45:31 astronomy, Drake Equation, SETI, intelligent life Richard Pogge Is anybody out there? This lecture reviews the ideas behind SETI, the Search for Extra-Terrestrial Intelligence, an effort to find other intelligent communicating civilizations by tuning in on their radio or other electromagnetic communications. I will discuss the basic approaches being taken by various SETI efforts, and what we expect to find. In addition to listening, we have also been broadcasting, intentionally or otherwise, messages into space, and we have sent physical artifacts with descriptions of our home on robotic spacecraft headed out of our solar system into interstellar space. Recorded live on 2009 Nov 24 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259087264 Tue, 24 Nov 2009 13:27:44 EST 00:46:28 astronomy, life, SETI, Voyager, Pioneer, SERENDIP, Allen Telescope Array, Arecibo Richard Pogge If we ever detect life elsewhere, how will we go visit? This lecture considers the challenges of interstellar travel and colonization. The problem is one of basic physics (the enormous energy requirements of star flight) coupled with the vast, irreducible distances between the stars. I will describe various starship concepts that use reasonable extrapolations of current technologies (nuclear propulsion and solar sails), ignoring for our discussions science-fiction exotica like faster-than-light drives and wormholes. My interest is in the scientific aspects of the problem, not an exploration of speculative fiction. I then turn to interstellar colonization, and how even a relatively modest star-flight capability might allow a determined civilization to colonize the entire galaxy very rapidly. This has implications for how we might interpret the results of Drake Equation type arguments about the frequency of intelligent life in the Galaxy, and leads to the Fermi Paradox that will be the topic of the next lecture. Recorded live on 2009 Nov 25 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259173962 Wed, 25 Nov 2009 13:32:42 EST 00:45:36 astronomy, interstellar travel, starships, Project Orion, Project Daedalus, colonization Richard Pogge So, Where is Everybody? Interstellar colonization, in principle, is an exponential growth process that would fill the galaxy in a few million years even with a very modest star flight capability. This is a small fraction of the lifetime of the Milky Way Galaxy, so the Galaxy should be teaming with life. But, we so far have no compelling evidence of extraterrestrial visitations, alien artifacts, or any other evidences that the Galaxy is populated. Physicist and Nobel Laureate Enrico Fermi's apparent paradox and some of the proposed resolutions are the topic of this lecture. I will review the Fermi Paradox and describe the most common possible resolutions. The Fermi Paradox is useful in helping to frame the question of extraterrestrial life, even if we so far have no answers. At the end I only touch on the Rare Earth Hypothesis, but this is a very nuanced question which requires a whole other lecture to explore that I have not had time to fully prepare for during this busy quarter. Recorded live on 2009 Nov 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259605940 Mon, 30 Nov 2009 13:32:20 EST 00:44:58 astronomy, Fermi Paradox, colonization, exponential growth, doomsday hypothesis, zoo hypothesis, prime directive, Rare Earth hypothesis Richard Pogge What does extraterrestrial life look like? This lecture explores current thinking about what extraterrestrial life might be like not by guessing their appearances, but instead applying lessons learned from our growing understanding of how evolution and biochemistry work on Earth. I will discuss Universal versus Parochial characteristics, Convergent Evolution, Radical Diversity, and other ideas from evolutionary biology that might inform how life might emerge on other worlds. We will then look at alternatives to carbon biochemistry, specifically the possibility of silicon-based life, and alternatives to liquid water as a solvent medium for biochemistry, specifically the possible role of Ammonia. Finally I will give one example of a highly speculative idea about life without chemistry. In the end, the outcome of such studies may not be to tell us much about extraterrestrials as to help focus questions on how we ourselves arose. Recorded live on 2009 Dec 1 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259693467 Tue, 01 Dec 2009 13:51:06 EST 00:45:14 astronomy, life, extraterrestrials, evolution, convergent evolution, radical diversity, carbon chemistry, silicon life, ammonia-based biochemistry, neutron star life Richard Pogge What is the future of life on Earth and in our Solar System? The Sun is the source of energy for life on the Earth, but it will not shine forever. This lecture looks at the impact of the various stages of the evolution of the Sun on the habitability of the Solar System, with particular emphasis on the continued habitability of the Earth. I will refer to state-of-the-art computer models of the Sun to get is properties at various stages in its past and future life. NOTE: Due to a recorder malfunction this lecture was re-recorded later in the day on 2009 Dec 2, rather than being live from the class room in Smith Laboratory. As such, it is about 10 minutes longer than usual (my pacing is off when not in front of class). Ast141_Au09_1259787260 Wed, 02 Dec 2009 15:54:20 EST 00:55:49 astronomy, life, habitability of Earth, Sun, stellar evolution, ages of the Sun, death of the Sun Richard Pogge How will life, the Universe, and everything end? This lecture looks at the evolution of our expanding Universe to project the prospects for life into the distant cosmological future. Recent observations show that we live in an infinite, accelerating universe. I will trace the evolution of the universe from the current age of stars into the future. The final state of the Universe will be cold, dark, and disordered, and ultimately inhospitable to life as we understand it or perhaps can imagine it. Recorded live on 2009 Dec 3 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259865161 Thu, 03 Dec 2009 13:32:41 EST 00:44:04 astronomy, cosmology, expanding universe, accelerating universe, stelliferous age, degenerate age, black hole age, dark age Richard Pogge Course finale and summary. We look back over where we've been the last eleven weeks, and bring together all of the main themes of this course on Life in the Universe. Recorded live on 2009 Dec 4 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University. Ast141_Au09_1259951449 Fri, 04 Dec 2009 13:30:47 EST 00:41:00 astronomy, life, the universe, everything