Potentially Habitable Exoplanets Course Announcements Quiz 3 Today Note about Attendance bonus Assignments Reading Assignments Chapter 7 Sections 7 1 7 3 Read by Monday 17 Oct Parallel Lectures No new episodes Mastering Astronomy Chapter 7 Homework Will be assigned Monday Removing planetesimals causes LHB As the small bodies get flung around the early Solar System Property 9 explained Planetary Migration of the forming gas giant planets moves through the leftover protoplanets and planetesimals slinging them all about and out of the early solar system This creates an era where these small bodies frequently impact the early planets i e The Late Heavy Bombardment Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids via their impact craters Modern Models of SS Evolution 1 Initial Disk determined by Condensation Hyp Nebular Hyp Rocky inner Icy Outer 2 Biggest planetesimals past iceline get big enough to experience gas drag and other forces and move inward 3 Inward migration drags icy materials inward and scatters some rocky material outward 4 Current Idea Gas giant planets then migrate outward scattering more materials Causes Late Heavy Bombardment Red Rocky Blue Water Ices Organics 1 2 3 4 DeMeo and Carry 2014 Evolution of Planetary Orbits The nitty gritty cutting edge ideas The foremost and growing in acceptance framework for how the gas giant planet motions interacted with the remaining protoplanets and planetesimals changed all their orbits to give the current structure of the solar system is called The Grand Tack plus Nice Model They are numerical simulations that give the current structure of the Solar System and make interesting predictions Now just to test them with observations At best can demonstrate that the structure of our Solar System can happen They cannot say that is exactly how it happened Nice Model Video The Nice Neese Model It s a city in France reference The Nice Model is a computer simulation to understand how the movement of the planets affected the small leftovers Also be careful googleing this one add the word planet or planetary Grand Tack Nice Model Nice Model Observational Constraints Much of my research provides observational evidence to test the validity of these predictions The Grand Tack Nice Model are very controversial amongst researchers trying to understand the origins and evolution of the Solar System However they do provide testable predictions 1 Amount of asteroids and KBOs 2 Amount of mixing of evolved rocky and primitive icy bodies 3 Entire removal of initial population of Jupiter Trojans and replacement with KBO objects My Jupiter Trojans Project aims to provide observational constraints on whether the Trojans formed with Jupiter were captured from the Kuiper Belt or a mixture of both A direct observational test to the predictions of these numerical models My Comet Project and Condensation Theory givea a basis for what compositional indicators to expect if the Trojans are from the Kuiper Belt or formed with Jupiter Comparative planetology and general planets DR LINDSAY S CUSTOM MATERIAL Terrestrial Planets The generalities of Earth like worlds Basic Concepts behind comparative planetology Being formed from the same materials the expectation is that overall the terrestrial planets are more alike than different Terrestrial planets should be largely the same all across the galaxy and universe How do we go from a big uniform ball of rock and metal to our current planets What processes are involved Physics Chemistry Geology Biology the same but each is quite unique How is this so and how does that relate to what a terrestrial planet is What does this tell us about solar system formation and what we should expect in other planetary systems That last stages of planet making From our accreted protoplanet to what we recognize as a terrestrial planet The accretion process builds us a terrestrial planet made of rock and metal but it is not yet structured like a planet All the materials rock and metal are mixed up relatively evenly homogeneously throughout the protoplanet BUT Earth the other terrestrial planets and many asteroids in the solar system are layered into a core mantle and crust To get to a layered planet the denser materials need to sink to the center and the lighter material needs to float to the top This process of separation according to density is called planetary differentiation Differentiation All the terrestrial planets are differentiated which implies it is a natural consequence of the formation process To separate according to density the planet needs to entirely or mostly molten To melt a planet however we are going to need a lot of energy heat where did that come from The Heat Needed to Differentiate Melting a planet Sources of Energy Heat 1 Gravitational energy from formation Not enough to melt planet 2 Kinetic energy energy of moving things from impacts Likely only sufficient to melt surface down to depths of a few to ten kilometers 3 Radioactive decay of unstable elements this is the strongest contributor Enough heat to melt the planet from inside out 4 The gravitational energy and friction of the differentiation process itself Once started this accelerates the process Radioactivity The release of radiation from an unstable nucleus The term radioactivity was coined and the field of nuclear radioactivity was pioneered by Marie Curie who won the Noble Prize for Marie Curie c 1920 her work Elements defined by the number of protons in their nucleus exist in several isotopic forms where all isotopes of an elements contain the same number of protons but have a varying number of neutrons Isotopes Same element different number of nuetrons When an element defined by number of protons has a different number of neutrons than the norm it is called an isotope Protium normal hydrogen so usually called just hydrogen is an isotope of hydrogen where the nucleus contains 1 proton and 0 neutrons Deuterium is an isotope of hydrogen where the nucleus contains 1 proton and 1 neutron Tritium is an isotope of hydrogen where the nucleus contains 1 proton and 2 neutrons All below are isotopes of hydrogen 1 H Protium Normal Hydrogen 2 H Deuterium 3 H Tritium Radioactivity The release of radiation from an unstable nucleus The normal number of neutrons for an element is simply the most common form e g Protium from the previous slide is normal hydrogen The normal isotopes of an element are generally stable and will remain as is
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