Life Beyond Earth PDF

Life Beyond Earth Just because a place CAN host life, doesn’t mean that it DOES host life Class 1-Universe of Life What do we mean by “life”? ​ Simple, complex, or intelligent ​ Earth like or alien (someone is considered to be a human from earth and somebody who isn’t considered to be...

Life Beyond Earth Just because a place CAN host life, doesn’t mean that it DOES host life Class 1-Universe of Life What do we mean by “life”? ​ Simple, complex, or intelligent ​ Earth like or alien (someone is considered to be a human from earth and somebody who isn’t considered to be a human and is from outside of earth would be known as an alien) ​ Life is difficult to define -Reproduction? -Movement and Growth? ​ Use Earth as a starting point -wide range of life forms, but just one planet Is it reasonable to imagine life beyond Earth What do we think we know? ​ No macroscopic life in the solar system (there is no life in the solar system which is visible to the naked eye) -as far as we know there is no life like us existing ​ Microbial life in the solar system possible(life that is too small can be possible in the solar system) ​ Many potentially habitable worlds have been discovered beyond our solar system (myriads of potentially worlds which can habitable have been discovered beyond just our solar system) -earth isn’t geographically special, life can exist somewhere else ​ No detection of past or present habitability beyond Earth (there's been no evidence found to suggest that life exists in the present or the past anywhere other than Earth) ​ Capabilities are growing(are tools and technology are advancing which can lead to a discover of potential life outside of earth) -technology to travel to different world to test for existence of life -ex.sending a Titan Submarine to the largest moon of saturn “titan” -titan has lakes of liquid methane have a very strong possibility of life existing in those lakes Starshot ​ A program that aims to send nanocrafts to other star systems -plans on using solar winds to accelerate tiny satellite speeds that would take them to different worlds the hope is to travel centauri the sun nearest neighbour which also hosts a potentially habitable world travel there in 20 years The Search for life beyond Earth ​ Interdisciplinary Approach (using knowledges from different fields of science and studies to get a better understanding of life beyond earth) - Astronomy - Planetary Science (study of planets) -Including geology and atmospheric science ​ Biology(biology can help us discover life by teaching us what life needs tos youtube and how it might look like. For ex. We know that water and certain chemical are essential for life like how earth has these biological traits which makes this planet habitable or if mars had water that would be a potential life since has conditions to support life) Astronomy ​ Earth is not special (earth is just one of the countless planets, its special to us because its our home, but the universe enormous and earth is just a small part of it) -Universal Laws of Physics -laws of physics can be different in each of the universe but the universe will behave all out the universe -Nothing unique about our place in the Galaxy or the Universe (myriads planets we are just a small part of the universe) ​ 200 Billion, Trillion stars in the Universe - At least as many planets (if not more) - e.g. Kepler 11 has at least 6 known planets ( Kepler 11 is a star system) -Image is an artist’s conception Planetary Science ​ How do planets form? - A natural by-product of star formation ​ How and why do planets differ? -Rocky vs “Gas” planet - Atmosphere - Geological Activity -Composition ​ Vast numbers of stars should have habitable planets -understanding the conditions that make a planet habitable -modern understanding of how planets form -evidence that most stars have planets Biology ​ Universal Laws of Biology? - Only have one reference point -Earth ​ Early Earth chemistry can lead to organic molecules - Also seen in meteorites and clouds of gas in interstellar space - these molecules can form in extreme conditions is a point to life being common in different worlds  -laws of chemistry appear to be universal because observation of star and made with the same chemicals found in our solar system, interstellar gas cloud contain the same molecules which are on earth -atoms come in the same types and combined the same throughout the universe ​ Transition from Chemistry to Biology not terribly difficult? ​ Microscopic life exists over a wide range of conditions -e.g. extremophiles(-an organism that thrives in extreme environments.) ​ Biology may be common in the universe -Evidence that earth life can survive under a wide range of conditions -evidence that organic molecules form easily and naturally -evidence that appeared early in the history of the Earth ( there is evince of what happened in the early history of earth appearing in the universe which could be a sign of life in the future) Where should we search for life in the universe Anywhere with the “ingredients” for life ​ A liquid or solvent (i.e. water) seems important -getting molecules together ​ Heat (i.e. Sun) ​ Time -Need to develop complex molecules ​ Protection - Harmful radiation for space (i.e. atmosphere) Our own solar system ​ Planets, dwarf planets, moons, asteroids, comets - Evidence for past surface waterflow on Mars (there is evidence of possible life being or happening or mars) - Evidence for sub-surface water on Mars and several moons -Europa, Ganymede, Callisto, Enceladus -theory that life on earth suggests that life might have begun in the big oceans ​ Thick atmosphere and methane lakes on Titan -Protection and solvents - Alien life? Beyond our solar system ​ Statistically more likely ​ Difficult due to distances to other stars - Spacecraft travel time of 100,000 years to nearest stars ​ Telescopes can find planets and measure basic properties - Spectral analysis just now a reality(is a method that separates light into its various hues, or wavelengths, in a way similar to how a prism divides light into rainbows) Could aliens be searching for us? Direct communication ​ Search for Extraterrestrial Intelligence (SETI) Institute -Search for alien signals from intelligent lifeforms ​ Messaging to Extraterrestrial Intelligence (possibility of intelligent life beyond earth in the universe) -Send signals to aliens Should we be contacting extraterrestrials? ​ Pursuit of the answer to the fundamental question - “Are we alone in the Universe?” ​ Peace or War - Humanity does not have the best track record - A unified Earth? ​ Knowledge exchange -Medical, environmental, philosophical -Weapons How do we study the possibility of life beyond earth? Collaborative and interdisciplinary science ​ Studying the conditions conductive to the origin and ongoing existence of life ​ Looking for such conditions on other planets in our solar system and around other stars ​ Looking for the actual occurrence of life elsewhere Bring it all together it's one thing for life existing in one place and its another thing a place can habitable ​ To search for life, we must first define it! ​ Armed with a definition, the search for life is interdisciplinary and difficult ​ Astronomy, biology, planetary sciences ​ Many places within the solar system have many (or all) of the ingredients we “think” are necessary for life ​ Many places beyond the solar system “could” have the ingredients we think are necessary for life, but its hard to be sure ​ Communicating with extraterrestrials a more direct way of finding intelligent life, but is it worth it? Class 2: The Science of Life in the Universe Science of life in the universe ​ Conditions under which we expect to find life ​ Possible characteristics of life beyond earth ​ Methods for finding life beyond earth How did attempts to understand the sky start us on the road to science? The Sky ​ The Sun ​ Moon ​ Stars ​ Planets Measuring the sky The sun ​ Sun rises in the East, sets in the West  ​ Governs daylight and darkness ​ Path across the sky varies with seasons ​ Half a degree in diameter The moon ​ Moon goes through phases -Otherwise looks the same ​ Related to tides -Two high tides a day -Moon at maximum altitude -12 hours after maximum altitude ​ Highest tides during full and new moon ​ Weakest tides during quarter moons The stars ​ At night, stars move across the sky ​ Different groups of stars (i.e. constellations) visible at different times of the year ​ Some groups of stars (i.e. constellations) visible year round ​ Others only visible at certain times of the year The planets ​ Brighter than stars  -Don’t twinkle! ​ Planets appear to move through the stars ​ Planets sometimes appear to move backwards across the night sky The beginnings of Astronomy ​ Ancient Chinese star charts date back 5000 years ​ Babylonian (present day Middle East) eclipse predictions date back 2500 years - Also seen in Maya of Central America ​ Oral Aboriginal Australian observe variability in brightness dating back thousands of years Distance in astronomy ​ Universe is projected onto the two-dimensional plane of the sky -Inner surface of a sphere ​ We only see the apparent size of an object not its true size -I.e sun and moon are both half a degree in diameter ​ Measuring the distance to objects requires special methods and instruments What is the universe made of? Thales of miletus (600 BCE) A “model” of the universe The celestial sphere Planetary Motion ​ Patterns of the constellations seem not to change ​ Sun, Moon, planets move across the constellations ​ How can planets move differently than stars if both fixed to a celestial sphere? ​ Speed and brightness also change over time ​ Planets appear to temporarily move backwards across the sky - Retrograde motion - Can last for weeks or months, depending on the planet Geocentric Model v2.0 ​ Concentric spheres! ​ Sun, Moon, planets and stars fixed to the inside of their own celestial spheres ​ Spheres rotate at different rates Ptolemy model ​ Planets move around earth on small circles that turned around larger circles ​ Some additional layers of complexity needed to match observations -i.e. some circles are off-centre An alternative model ​ Planets orbit the sun and the moon orbits earth -Aristarchus (260 BCE) ​ Easily explains retrograde motion  -Planets closer to the sun travel faster -Other planets appear to move backwards across the sky ​ Roots of “Modern” Science -Ensure models match observations ​ Long-standing ”Model” of the Universe - 100 CE – 1500 CE Heliocentric model ​ If earth went around the sun, stars, stars should change position over the course of the year -Stars should get farther apart earth gets closer to them -This back and forth shifting of a star location relative to distant stars is called its parallax ​ No such shift observed -Model rejected -Physiological reasons also played a role Life beyond earth in the age of ptolemy Model Dependent ​ Greek’s were open to the possibility that other worlds exist -Our “world” consisted of the Earth and the surrounding spheres -Whatever the Universe was made of is infinite, all things rise from and return to it ​ Two emerging philosophies: -Atomists – our world consists of an infinite number of fire, water, earth and air atoms -Aristotelians - fire, water, earth and air only on Earth, everything else made of a fifth element Atomist ​ Earth and the “heavens” created by the random motions of atoms -Since atoms are infinite, other worlds are implied ​ “There are infinite worlds both like and unlike the world of ours…we must believe that in all worlds there are living creatures and planets and other things we see in this world” -Epicurus (341 -270 BCE) Aristotle ​ Each of the four elements has its own natural motion and place -Earth moves towards the centre of the Universe -Fire moves away from the centre  ​ “The world must be unique. There cannot be several worlds” - Aristotle (384-322 BCE) Lasting Impact ​ Work of Aristotle became associated with many religions -Islamic scholars, Christian theology ​ Atomist approach associated with atheism ​ Debate about extraterrestrial life intertwined with religion -Both in the past and today The copernican revolution Moving West ​ Islamic scholars sought knowledge of math and astronomy -Translated and saved Greek works from Library of Alexandria (Egypt) in Baghdad -Developed algebra and observational instruments - Collaborated with Hindu scholars from India, who also shared knowledge from China ​ Byzantine capital conquered in 1453 - Eastern scholars head west European Renaissance The Copernican Revolution ​ Revived Heliocentric Model with mathematics -Natural relationships between periods and distances of planets - Geometrically aesthetic -Predictions were comparable to Ptolemy’s models -Didn’t solve issue about stars not shifting positions ​ Debate of Copernican vs Ptolemy models formed foundation of ”modern” science Tycho Brahe ​ Improved observations with a naked eye observatory -Better data to compare models to! ​ Did not measure parallax for any stars - Earth is fixed or stars are incredibly far away! ​ Did not help distinguish between two models View in telescope positions of a nearby star should shift relative to stars that are farther away Non -“Circular” Reasoning ​ Kepler worked to develop model based on Brahe’s observations ​ Unsuccessful until he stopped forcing orbits to perfect circles -Trust in the data - Dramatic shift in thinking from personal beliefs Kepler’s First Law ​ The orbit of each planet about the Sun is an ellipse with the Sun at one focus Kepler’s Second Law ​ A planet moves faster in the part of its orbit nearer the Sun and slower when the farther from the Sun, sweeping out equal areas in equal times. Circular Orbit ​ Same orbital speed along entire orbit ​ Fraction of area covered equals fraction of orbital period spent travelling Kepler’s Third Law ​ More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship P 2=a 3 Heliocentric Model Lives Again! ​ Sun-centred Universe ​ Planets move around Sun on elliptical orbits -Although most are VERY close to circular ​ Moon moves around Earth ​ Very accurate predictions of planetary motions Heliocentric Model Fights for Acceptance ​ Kepler’s publication confusing and observational data had some errors ​ Why aren’t we left behind as Earth moves? ​ Still no explanation for lack of observed shift in stars Maria Cunitz ​ Self-Published Urania Propita in 1650 - Corrected errors in Kepler’s work - Simplified derivations and presentation of three laws -Written in Latin and German Galileo Galilei ​ Rolling ball experiments ​ Imperfections through improved observations  -Brahe observed SN and comets -Galileo observed sunspots on the Sun and mountains and valleys on the Moon ​ Stars were even more far away than people though, such that measuring parallax required better instruments - Milky Way resolved into stars ​ Moons of Jupiter and Phases of Venus - Earth not the centre of everything Physics behind the heliocentric model Newton – Explaining the Model ​ Why do planets move in elliptical orbits with varying speeds? -Tools to answer the question did not exist ​ Newton invented calculus -Developed Newton’s Laws of Motion and Newton’s Law of Gravitation in 1687 Newton’s First Law ​ A force is needed to alter an objects velocity - Velocity is the combined information of speed and direction Newton’s Second Law ​ Force = mass x acceleration -F= M A ​ I prefer acceleration = Force / mass -Stronger force = higher acceleration -High mass = lower acceleration Newton’s Third Law ​ For any force, there is always an equal and opposite reaction force ​ The Roller Skates / Roller Blades / Ice Skates Law Universal Law of Gravitation ​ Every mass attracts every other mass through the force called gravity ​ The strength of the force attracting any two objects is directly proportional to product of their masses ​ The strength of the force attracting any two objects is inversely proportional to distance between them How did the copernican revolution alter the ancient debate on extraterrestrial life? Indirect Consequences ​ Earth is not the centre of the Universe ​ Earth is not special ​ Other Worlds are Possible ​ Galileo thought Moon had an atmosphere and Kepler even suggested it was inhabited William and Caroline Herschel (1700s) discovered Uranus - Assumed all planets had life ​ Percival Lowell (1800s) believed he saw artificial canals on Mars Is there life beyond Earth? “The existence of life beyond Earth is an ancient human concern. Over the years, however, attempts to understand humanity's place in the cosmos through science often got hijacked by wishful thinking or fabricated tales.” – Jill Tartar (SETI) The nature of modern science “Good” Science ​ Step 1: Formulate a Model ​ Step 2: Test Against Observations - If model fails, modify or replace The scientific method Approaches to science ​ The Scientific Method -Idealization -“Real” science rarely follows this course ​ Observations of nature are often generalized, not a careful set of observations ​ Not everything can be observed -Models can make observable predictions Example: Extinction of Dinosaurs ​ Can’t observe history ​ Can study fossils to piece together a story ​ Massive impact theory can’t be observed, but leads to other observable predictions -Finding an impact crater of the right age and size Hallmarks of science Simplicity - Occam’s Razor ​ Science progresses through the creation and testing of models of nature that explain the observations as simply as possible Verifiable Observations ​ A scientific model must take testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions did not agree with observations ​ What counts as an observation? - Personal testimony cannot be verified -A test can be repeated and verified Objectivity ​ Cultural Bias -Spheres and circles are geometrically perfect -Religion vs Science ​ Individual Bias: -Artificial canals on Mars -Link between childhood vaccines and autism ​ Community Bias -Dark Matter -Einstein’s Theory of Relativity It is good to think inside the box, that is the best way to test your box for weaknesses. It is good to think outside the box, that is the best way to build new boxes. Proceed with caution if only one or the other is happening What is scientific theory? Fact vs Theory ​ FACT of gravity -Things fall when we drop them -Planets orbit the Sun ​ Suggested Theories of Gravity: -Gravity a property of heavy objects -Heavier objects fall faster than lighter objects - Things falling on Earth and Planets orbiting the Sun due to the SAME thing - Universal Law of Gravitation Acceptance of Newton’s Law of Gravitation ​ Explained Galileo’s observations of falling objects ​ Explained Kepler’s Laws of Planetary Motion ​ Predicted motion of comets - Halley’s comet ​ Predicted orbit of Uranus was being affected by an 8th planet -Predicted exact location of Neptune to within a degree Problems with Newton’s Law of Gravitation ​ The orbit of Mercury -Missing planet? -Bad observations? ​ Mysterious “Gravitational Force” - Even Newton didn’t like it Einstein’s Theory of Relativity ​ All objects exists in a fourdimensional spacetime ​ Massive objects curve spacetime -Like marbles following the contours of a bowl -Bowling balls on a sheet ​ Gravity IS the curvature of spacetime -Predicted the orbit of Mercury -Massive objects bend light Theory ​ A model that is powerful, simple, and makes predictions that survive repeated and varied testing - Darwin’s Theory of Evolution ​ Can never be proven beyond doubt due to possibility of future observations - i.e. Newton’s Theory of Gravity ​ Requires replacement - i.e. Einstein’s Theory of Relativity Newton’s theory is not necessarily wrong, but is better taken to be an approximation. Einstein’s theory gives slightly better predictions for very precise measurements or when gravity is very strong Einstein’s theory has passed every test it has been subjected to, but we still suspect a better theory exists. Einstein’s theory and Quantum Mechanics yield contradictory predictions in extreme gravity (near a black hole) A Theory of Life in the Universe? ​ Currently does not exist ​ We only have one data point -With a few million lifeforms! ​ Extreme range in allowable hypotheses: - Life ONLY exists on Earth - Life exists THROUGHOUT the Universe ​ Astrobiology will help verify hypotheses with future observations Bringing it all together and looking ahead…. ​ Copernican revolution changed the discussion about life in the universe ​ We are only just now collecting data that may lead to a Theory of Life in the Universe, with the help of the hallmarks of science and the scientific method ​ What does the structure and history of the Universe tell us about life? ​ What does Earth’s history tell us about life? ​ Can we predict where else life could be? In our solar system and beyond Class 3: The Universal Context of Life Earth ​ Our home ​ Only known place in the Universe that hosts life ​ 150,000,000 km for the Sun ○​ Lets call this 1 Astronomical Unit (AU) Is the Solar System Big? ​ Shrink entire solar system by a factor of 1.4 Billion! ○​ Sun’s diameter is 1 m ○​ Earth’s diameter is 1 cm ○​ Human’s the size of microbes ​ Place the “Sun” in the middle of Sobey’s Stadium ○​ Earth over 100 m away ​ Shrink entire solar system so the Sun’s diameter is 1 m ○​ Earth’s diameter is 1 cm ○​ Human’s the size of viruses ​ Place the “Sun” in the middle of Sobey’s Stadium ○​ Earth over 100 m away ○​ Saturn over 1 km away ​ Shrink entire solar system so the Sun’s diameter is 1 m ○​ Earth’s diameter is 1 cm ○​ Human’s the size of viruses ​ Place the “Sun” in the middle of Sobey’s Stadium ○​ Earth over 100 m away ○​ Saturn over 1 km away ○​ Pluto over 4 km away  The Sun’s Nearest Neighbour ​ Triple star system ​ Alpha Centauri A,B, and C ​ Alpha Centauri C has 2 known planets ​ 1 potentially habitable ​ 37.8 Trillion km away ​ This number is ridiculous! Light Years ​ Light has a finite speed ​ 300,000,000 m/s ​ How far can light travel in a year? ​ 1 light year = 9.46 trillion km When looking at objects that are extremely far away, we are technically seeing them as they were in the past! Lookback Time ​ It takes time for light to travel large distances ​ When we receive light from an object, we need to remember that light was emitted in the past ○​ Light takes one billionth of a second to travel from your toes to your eyes ○​ You are seeing your toes as they were one billionth of a second ago Our Local Neighborhood 131 stars, white dwarfs (dead stars) and brown dwarfs (failed stars) within 20 ly of the Sun Only 22 visible with your eye There are 200,000,000,000 stars in a Galaxy like ours. Around the number grains of sand in a dump truck. Most have at least one planet. Parsecs ​ On galaxy-scales, it is sometimes easier to work with parsecs ​ A star 1 parsec away will have a parallax of 1 second of arc (1/3600th of a degree) ​ 1 pc = 3.2 ly The Local Group ​ Milky Way  ​ 200+ Billion Stars ​ Andromeda ​ Comparable to Milky Way in mass ​ approx. 800 kpc away ​ Triangulum ​ 1/10th mass of Milky Way ​ approx. 800 kpc away ​ 80+ Dwarf Galaxies ​ Some are satellites of Milky Way, Andromeda, or Triangulum Virgo Supercluster ​ We are gravitationally bound to Virgo Cluster ​ As are 100 other galaxy groups and clusters ​ 33 Mpc across ​ A node of something larger? Laniakea ​ Galaxy Supercluster ​ 100,000 galaxies ​ 160 Mpc across ​ Net motion towards a ”Great Attractor” ​ Massive supercluster near centre? ​ Not gravitationally bound ​ Slowly dispersing Could life only exist around 1 in every 10 sextillion (1022) stars? Let’s look and see if the ingredients for life exist elsewhere! What is the Universe made of? Matter and Energy Matter ​ Subatomic Particles ​ Quarks, leptons, …. ​ Atoms ​ Protons (+) and neutrons in nucleus ​ Electrons (-) around nucleus ​ Atoms often neutrally charged ​ Ions are atoms that have lost or gained an electron Elements ​ Atomic number determines type of atom  ​ 118 known elements ​ Number of neutrons in the nucleus can vary ​ Isotopes of an element Isotopes ​ Atomic number determines type of atom ​ 118 known elements ​ Number of neutrons in the nucleus can vary ​ Isotopes of an element Molecules ​ Elements combine to create molecules ​ Atoms share electrons to form a chemical bond ​ Life as we know it built on carbon-based molecules ​ Organic matter Phases of Matter ​ Phases differ by strength of chemical bonds that hold atoms and molecules together ​ Pressure and temperature can cause phase changes Energy ​ Kinetic Energy ​ Objects in motion carry kinematic energy ​ Radiative Energy ​ Energy carried by light, allowing light to interact with matter ​ Potential Energy ​ Stored energy that be converted into kinetic or radiative energy Mass-Energy ​ Mass itself is a form of potential energy ​ Energy = mass x c2 Thermal Energy ​ Collective kinetic energy of many atoms or molecules moving within a substance ​ Heating up a substance increases the motion of if its atoms and molecules ​ Chemical and biochemical reactions occur faster at higher temperatures  Conservation of Energy ​ Energy cannot be created or destroyed ​ It can change forms ​ Energy generation in the Sun is a conversion of mass-energy to radiative energy How do we study the matter and energy of things that are light years away from us? What is light? ​ Radiative energy that travels through space at a fixed speed ​ 3,000,000 m/s in a vacuum ​ Characterized by rapidly changing electric and magnetic fields ​ Electromagnetic wave For any wave: wavelength = speed /frequency For light: wavelength = c /frequency energy = Plank’s Constant x frequency ​ Wave-Particle Duality ​ Light can sometimes behave as a particle ​ Photons ​ Exert pressure ​ Scatter ​ Transfer energy What can we learn from light? Learning from the Light ​ Imaging ​ All the light that you see ​ Spectroscopy ​ Disperse incoming light into a spectrum ​ Analyzing light at specific wavelengths Blackbody Radiation ​ Spectrum always has the same shape ​ Law 1: for hotter objects, whole spectrum moves up ​ Law 2: for hotter objects, the peak of the spectrum moves to the left (shorter wavelength, higher energy) Blackbody Radiation ​ Can measure an objects temperature based on spectrum peak ​ Sun peak emission at visible wavelengths ​ approx. 5600 C on surface ​ Can learn about an object’s composition from light in reflects and absorbs Image Credit: Princeton University Press The Spectrum of the Sun ​ shortest wavelength ​ increasing wavelength Different stars have different spectra Absorption LIne Spectrum electron -”orbital” Electron Nucleus (protons+neutrons) Orbitals have specific energies ​ outer=higher energy ​ inner=lower energy An electron can absorb a photon and JUMP energy levels The photon’s energy MUST correspond to the energy difference between levels Energy difference between first and second level = Red Light Energy difference between first and third level = Green Light Orange light =Nothing Happens! Spectral Lines of Hydrogen Spectral Lines are Unique to Each Element Chemical Composition of the Sun ​ includes iron, chromium, titanium, cobalt, magnesium, copper, zirconium, Emission Line Spectrum ​ Warm gas has electrons in excited states ​ Less stable ​ Electron will spontaneously emit photons and return to ground state ​ Thermal radiation  ​ Emission in random direction What if the source is moving? The Doppler Effect ​ Kicking duck being held in place would create ripples in every direction ​ Like continuously dropping pebbles ​ Movement leads to close ripples ahead of duck and farther apart ripples behind The Doppler Effect - Sound ​ Sound is a wave in air whose pitch is determined by its frequency. ​ When a source of sound is coming towards you, the frequency/pitch is higher ​ When a source of sound is moving away from you,​the frequency/pitch is lower The Doppler Effect - Light ​ The same thing happens when a source of light is moving ​ Sources moving towards you shifter to higher frequency (shorter wavelengths) ​ Sources moving away from you shift to lower frequency (longer wavelength) ​ The effect depends on how close the source speed is to the speed of the wave. ​ But the speed of a light wave is very fast – so generally it’s a small effect. The Doppler Effect - Spectra Object 1: At rest, absorption lines are at the wavelengths we expect Object 2: Lines shifted to longer wavelength (“redshift”) – moving away from us. Object 3: lines shifted farther ​ moving away from us faster Object 4: Lines shifter to shorter wavelength (“blueshift”) – moving toward us Object 5: Lines shifted farther ​ moving toward us faster. Shift Only Due to Line of Sight Motion An object moving directly away: ​ Shift due to all of its speed Moving across our line of sight: ​ No shift Moving diagonally:  ​ Partially shifted due to component of its motion moving away for us What does light from the universe tell us? Dark Matter (matter we can’t see) ​ In the solar system, planet’s farther from the Sun have slower orbital speeds ​ Expect the same for stars far from Galactic centre ​ In the Galaxy, we see stellar velocities increase as you move away from Galactic centre and then stay constant beyond the disk ​ Must be matter we can’t see or model for gravity is wrong The Universe is Expanding ​ Distant galaxies are all moving away from us ​ Would expect random distribution of relative velocities ​ The farther away a galaxy is, the faster its moving away from us ​ Space itself is expanding! ​ Driven by some unknown energy we call Dark Energy ​ (Probably) not related to Dark Matter Bringing it all together and looking ahead…. ​ The interplay between matter and energy allows us to study the Universe through images and spectroscopy ​ The Universe is vast and old ​ Lots of opportunities for life! ​ The Universe is expanding at an accelerating rate! ​ Can we come up with a model for the Universe? ​ From birth to formation of our Solar System? Class 4: A Model for the Universe Previously on Life Beyond Earth ​ A Universe of Life ○​ Life is difficult to define and search for life beyond Earth ​ The Science of Life in the Universe ○​ Early attempts to model the behaviour of ”the heavens” led to philosophical debates about the possibility of life beyond Earth ○​ Earth is not the centre of the Universe. Earth is not special. Other worlds are possible ​ The Universal Context for Life ○​ The interplay between light and matter allow us to study the Universe ○​ The Universe is vast and old, yielding many opportunities for life to begin! How did we get from the birth of the Universe to life on Earth? Need a Model for the Universe The Scientific Method Make Observations of the Universe ​ Observable Universe has a radius of 14 billion light years ○​ Universe is 14 billion years old ​ The Universe is expanding at an accelerating rate ○​ Dark Energy (68.5%) ​ Galaxies found in groups, clusters, and superclusters ○​ Cosmic Web ​ Stars orbit within galaxies ○​ Dark Matter (26.6%) ​ Planets orbit stars ○​ Life exists on Earth Starting with a Bang! ​ Expansion implies the Universe began as a singularity 14 Billion years ago ​ Universe born out of massive explosion ○​ Big Bang! ​ Early Universe hot and dense! ​ Universe expands Expansion of the Universe ​ Initial Conditions: ○​ Raisin cake with raisins spaced 1 cm apart ​ Bake the cake! ​ Cake expands! ​ Final Conditions ○​ Raisins now spaced 3 cm apart ​ From the outside expansion is obvious, but what if you lived on the surface of a raisin? ​ Can’t directly observe the Big Bang or the ensuing expansion ○​ Indirectly “observed” from behavior of distant galaxies ​ Can make observable predictions! An expanding Universe will cool ​ At the beginning, the Universe is a hot dense plasma EVERYWHERE ​ As per Laws of Physics, increasing the volume of the Universe will cool it! As the Universe Cools ​ 1/10,000th of a second after the big bang  ○​ Protons, neutrons, and electrons form ​ 10s – 20 minutes after the big bang ○​ Nuclear fusion reactions can occur to create nuclei After Big Bang Nucleosynthesis ​ Exact composition of Universe depends on expansion rate, proton-neutron ratio, baryon-photon ratio ​ Best models predict 75% H, 25% He, trace quantities of Li ○​ Pitrou et al. 2018 PhR Testing the Model ​ Can’t observe Big Bang Nucleosynthesis ○​ Early Universe so dense that photons are repeatedly absorbed or scattered ○​ Information lost! ​ Model consistent with abundances of oldest stars and and distant (i.e. youngest) galaxies ○​ Oldest star in the Milky Way approximately 13.2 Byr old 380,000 Years: Time of Recombination ​ Universe has cooled to the point nuclei and electrons combine to form atoms ​ Universe becomes “transparent” ○​ Radiation can flow freely through most of the Universe ​ Should be an afterglow of radiation from this time Why Microwave Light? ​ Entire Universe was approximately 3000 K at time of recombination ○​ Infrared Light ​ Expansion of Universe “stretches” light to longer wavelengths ○​ At present day, light from time of recombination predicted to be microwave light ○​ approx. 2.7 K Key Take-Aways from the Big Bang Theory ​ Predicts an expanding Universe ​ Predicts abundances of elements in the early Universe ○​ Know the relative abundances and how they match to observations ○​ Don’t need to know exact reactions or reaction rates ​ Predicts a uniform microwave afterglow from the time of recombination ○​ Know why the CMB exists and why it is so uniform ○​ Don’t need to know exact times and temperatures How do we get from Hydrogen, Helium, and Lithium to Life on Earth? We can see light after the time of recombination with a good enough telescope! 100-500 Myr : First Stars and Galaxies ​ Universe continues to cool until over densities of gas collapse due to gravity ​ 100 to 500 Myr after the Big Bang, stars and galaxies begin to form ​ Stars are powered by nuclear fusion in the cores ○​ Creates new elements! 100 -500 Myr : First Supernovae ​ First generation of stars, made of only H and He, were very massive with short lifetimes ​ Once nuclear fusion ends in a massive star’s core, it collapses in on itself and explodes ○​ Supernova explosion also creates new elements as nuclei collide Enrichment ​ As stars live and die, the Universe becomes polluted with “heavy” elements ○​ Necessary for planet formation ○​ Necessary for organic molecules ○​ Necessary for life ​ New stars form out of polluted material Universal Enrichment ​ Galactic recycling occurs throughout the Milky Way ○​ Similar in other galaxies as well ​ Chemical composition of other star systems will be similar ○​ Slight dependence on system’s age ​ Raw ingredients for life should be everywhere! The origin of the solar system elements ​ Big bang fusion ​ Merging neutron stars ​ Dying low mass stars ​ Cosmic ray fission ​ Exploding massive stars ​ Exploding white dwarfs We are “star stuff” Molecular Clouds ​ Dense regions of gas in interstellar space ○​ Comparable to artificial vacuums created in Earth laboratories ​ 99% Gas ○​ 90% Hydrogen Molecules ○​ 9% Helium Atoms ○​ 0.01 % Carbon Monoxida ○​ 0.001% other stuff  ​ 1 % Dust Dust in Molecular Clouds ​ Grains of carbon and silicon ○​ Sand or soot ​ Less than 0.001 mm in diameter ○​ Serve as formation sites for molecules Organic molecules ​ Enrichment of giant molecular clouds with “heavy” elements ​ Allows for formation of organic molecules via dust ○​ polycyclic aromatic hydrocarbons (PAHs) ​ simple amino acids. ​ Time limit for first lifeforms in the Universe? How did our solar system form? The scientific method Patterns of Motion ​ Planets orbit Sun in counter-clockwise direction ○​ As viewed looking down at North Pole ○​ Same direction as Sun’s rotation ​ Planets have nearly circular orbits ​ Most planets rotate in counter-clockwise direction too Two Types of Planets Dwarf Planets ​ Massive enough that their own gravity has made them spherical ​ Orbit the Sun ​ Have not cleared their orbit of other material Asteroids ​ Weakly bound rubble piles of rock and metal that orbit the Sun ○​ Not massive enough to be spherical ○​ Often share an orbit with lots of other asteroids ​ Large collection in asteroid belt between Mars and Jupiter ○​ Some move through inner solar system, threatening Earth Comets ​ Similar to asteroids, but with a significant amount of ice  ​ Typically found farther from the Sun ​ Sometimes pass close to the Sun ○​ Vaporization of ice ○​ Dust and ice ejected into “tails” ​ Kuiper Belt and Oort Cloud Oort Cloud ​ Tracing backwards the orbits of some comets reveal they have long orbital periods ○​ 1,000-10,000 AU away from the Sun ​ Hundreds to billion of comets predicted to make up the Oort cloud ○​ Objects to small to observe ​ Oort cloud currently a theoretical prediction Expectations ​ Tilt of earth and uranus ​ Rotation direction of venus(backwards) ​ Some moon’s with backwards and/or inclined orbits ​ Earth’s moon ○​ One of the most massive in the solar system Hypothesis 1: Close Encounter Model Stellar Encounters ​ Buffon (1745) suggested planets formed from debris due to a comet that collided with the Sun ​ Revised models suggested planets form from blobs of gas pulled from Sun due to a close encounter with passing star ○​ Popular during early 20th Century An Incomplete Model ​ Could not explain orderly motions of planets ​ Could not explain two types of planets ​ Required a rare event ○​ Stellar encounter! Incompatible with Life Beyond Earth ​ Predicts that planetary systems are very rare ​ Predicts that life likely only exists in our Solar System Hypothesis 2: The Nebular Theory 9,200 Myr - Our Birth Cloud Collapses ​ After 9.2 Billion years of pollution, 2% of H and He converted to heavy elements  ​ Solar system born out of the gravitational collapse of a giant molecular cloud / nebula ○​ Cold gas and dust ○​ Slowly rotating ○​ Collapse externally triggered Gravity takes over ​ Law of gravity ensures collapse continues ​ As size of cloud decreases, force of gravity gets stronger ○​ Inverse square law ​ Collapse initially spherically symmetric, until the effects of ○​ Heating ○​ Spinning ○​ Flattening Heating and Spinning ​ Conservation of Energy ○​ Cloud heats up as it collapses ​ Conservation of angular momentum ○​ Cloud spins faster as it contract Linear Momentum ​ Momentum ○​ Mass x Velocity ​ Strongly related to Newton’s Laws ○​ Force is required to change an object’s momentum ○​ Colliding with an object that has high momentum imparts a large force. ​ Conserved quantity Conservation of Angular Momentum ​ Angular Momentum of Rotating Object ○​ Mass x Size x Velocity ​ For a given amount of initial angular momentum imparted on object of mass M ○​ Large object spins slowly ○​ Small object spins quickly Flattening ​ As clumps of gas and dust collide and merge, the resulting clump has average velocity of the progenitor clumps ○​ Everything ends up with moving in same direction as cloud rotates ○​ Very little motion in other directions ​ Flatting a natural consequences of collisions between particles in a spinning cloud A Flat Protoplanetary Disk Protostar Formation ​ Central core of cloud continues to collapse ○​ Heats up! ​ Collisions between molecules creates photons, which helps radiate away energy ○​ Core can get denser without radiation pressure ​ Eventually becomes too dense for photons ○​ Collapse halted and temperature rises Ignition ​ Gravity keeps compressing the protostar’s core ​ Core temperatures exceed 10 million K ​ Nuclear fusing begins ○​ Core collapse halted by radiation pressure ​ Solar wind eventually clears remaining gas The Frost Line ​ Inner parts of disk are warmer than outer parts ​ Inside frost line ○​ Rock, metal, gas ​ Outside frost line ○​ Rock, metal, gas, and ice ○​ Hydrogen compounds like water, methane, and ammonia are solid beyond the frost line Gas Accretion ​ Gravity draws planetesimals and gas together to form planets ​ Ices in the outer regions of the disk allow for the formation of large cores ○​ Can accrete more gas! Does the Nebular Theory explain observations of our Solar System? Matching to Observations ​ Orderly Motion ○​ Conservation of Energy and Angular Momentum lead to all particles orbiting in a flat disk around host star ​ Two types of planets ○​ Ices beyond the frost line contribute to formation of Jovian planets Matching to Observations ​ Dwarf planets, asteroids, comets ​ ​ Leftover planetesimals ​ Asteroid Belt  ○​ A failed planet protected by Jupiter ​ Kuiper Belt ○​ Too low density to form anything ​ Oort Cloud ○​ Ejected by planetary interactions Exceptions - Moons ​ Jovian Moons ○​ Large number of leftover planetesimals beyond the frost line ○​ Accreted in random directions ​ Terrestrial Moons ○​ Small number of leftover planetesimals within the frost line ​ But why is Earth’s Moon so big How did of the Moon form? ​ Moon formed along with Earth ​ Moon formed separately and was later gravitationally captured ​ Young molten Earth was spinning so rapidly that it split in two Flaws in the Models ​ Joint Formation ○​ Gravitational interactions should disrupt the process ○​ Why is moon less dense if formed out of same material? Flaws in the Models ​ Capture ○​ Low Probability ○​ Gravitational capture requires loss of orbital energy, so harder to capture massive objects ​ Splitting ○​ Unlikely Earth ever spun fast enough Apollo Missions ​ Moons rocks have different composition than Earth rocks ○​ Rules out joint formation ​ Moon rocks contain no easily vaporizable material (volatiles) ○​ i.e. Water ○​ i.e. Lead and gold at low temperatures ○​ Moon should have volatiles if split off from Earth or formed in same way as Earth and then captured Revisit the Observations ​ Moon less dense than Earth ○​ Comparable to density of Earth’s mantle ○​ Suggests no iron core  ​ Composition of Moon rock’s similar to Earth’s mantle, except for missing volatiles Giant Impact Model ​ The Moon was made out of material that accreted in Earth’s orbit after being blasted out of Earth’s mantle ​ Early Solar System potentially filled with several planet-sized bodies ○​ Some scattered by close encounters ○​ Some collide While we can’t observe the formation of our Solar System, we can observe the formation of other systems! Modifications to Nebular Theory ​ Jets ​ Planets in-between terrestrial and Jovian categories ○​ Accretion timescale vs expulsion of gas ​ Exo-Jovian planets observed with eccentric orbits within frost line ○​ Migration Planetary Migration ​ Comets in Oort Cloud will have gained energy from planet interactions ○​ Planet loses energy and migrates inwards ​ Drag force from gas ○​ Depends on formation time and gas expulsion time ​ Planet-planet interactions ○​ Depends on relative orbits Implications for Life Beyond Earth ​ Other planetary systems should exist, with significant diversity ○​ Life friendly planetary system layouts still numerous, even if rare ​ Most of the Universe is older than the Sun/Earth ○​ Lots of time for Life to form on older planets ○​ More advanced civilizations than our own? Is the Universe fine-tuned for life? “We are here today, able to study the Universe and its basic properties. But if any of those properties were much different, we could never have come to exist in the first place” – Bennet et al. The Fine-Tuned Universe ​ Expansion ○​ If too fast, galaxies won’t form ○​ If too slow, Universe would collapse in on itself ​ Ratio of strengths of difference forces  ​ Why? ○​ Multiverse? ○​ Specialness? ​ Incomplete knowledge ○​ Higher being(s)? Bringing it all together and looking ahead…. ​ We have a working model for the Universe that explains a wide range of observables ​ Life should be plentiful in the Universe ○​ Ingredients for life are everywhere and the laws of physics, chemistry, and biology are Universal ○​ Life has a had a lot of time to form and develop on other worlds ​ But we still don’t have a model for life! ○​ How did life begin on Earth? Glossaries Extraterrestrial Intelligence-possibility of intelligent life beyond earth in the universe Extremophile-an organism that thrives in extreme environments. Interdisciplinary-relating to more than one branch of knowledge. Macroscopic- visible to the naked eye Microbial-relating or characteristic or caused by microbes Microbes-organisms that are too small to be seen without microscope Spectral analysis-is a method that separates light into its various hues, or wavelengths, in a way similar to how a prism divides light into rainbows