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What is the solar system? The solar system can be defined as matter that is gravitationally bound to our Sun 1. Sun 2. Planets & their Moons 3. Asteroids, Kuiper belt objects, & Oort cloud 4. Comets & Meteors 5. Dust How would we go about describing the solar system? 1. What does it look like? 2. What are the bulk characteristics of solar system materials? 3. What are the masses of the solar system and its individual constituents? 4. What is the elemental composition of the solar system? 5. What are the angular momenta of the solar system and its individual constituents? 6. What are the energy sources in the solar system? How would we go about describing the solar system? 1. How can we describe the motions of the bodies of the solar system? • What accounts for the motions? 2. What is the mass distribution of the solar system? • Why is most of the mass in the center of the solar system? 3. What is the chemical composition of the solar system and its constituents? • Do each of the constituents of the solar system have the same mix of elements? • What controls what compounds are formed? 4. What processes are likely responsible for the formation and subsequent evolution of the solar system? Planetary motion - orbital direction Planetary motions - orbital inclinations Orbits of the asteroid belt Orbits of the Kuiper belt objects Orbits of the Oort cloud objects Evolution of dust in the solar system A simple conceptual model – or at least questions • Based on these observations what could we say about the formation of the solar system? • How old is the solar system? • From what did it form? • Was the starting material uniform in composition? • What are the energy sources in the solar system? • Why did the sun form? • How did planets form? What are the bulk characteristics of solar system materials? Similarities in bulk characteristics may imply similar physical processes. The Sun • The bulk of the mass is concentrated in the Sun, it controls the dynamical evolution of the solar system • The Sun is the only body in the solar system that generates energy by fusion • The Sun generates magnetic fields • The Sun can accelerate particles Bulk characteristics of solar system materials – inner planets The terrestrial planets are denser and are located in the inner solar system ( Mercury, Venus, Earth,and Mars) Bulk characteristics of solar system materials – outer planets The gas-rich giant planets, Jupiter, Saturn, Uranus, and Neptune, are located further away from the Sun Bulk characteristics of solar system materials - satellites Some moons are comprised of silicates Other moons have icy compositions Bulk characteristics of solar system materials – asteroids? • Located between the orbits of Mars & Jupiter (2.2 to 3.8 AU) are thousands of asteroids Bulk characteristics of solar system materials – outermost planet? Pluto seems somewhat out of place Bulk characteristics of solar system materials – Kuiper belt? • Kuiper belt asteroids are located outside the orbit of Neptune – Pluto is considered to be the largest member of this group What are the bulk characteristics of solar system materials – small objects? • Far outside (up to 105 AU) of even the Kuiper belt is a 3-dimensional cloud of objects, hunks of “dirty ice” What are the bulk characteristics of solar system materials – small objects? • Cosmic Dust A simple conceptual model based on bulk characteristics • With only the information we have in hand can we form a model of how the solar system formed that explains the motions and mass distributions of planets, small bodies, and dust? • What are some questions we could ask? – Was the starting material uniform in composition and why is it not now evenly distributed? – What are the energy sources in the solar system? – What controls the motions of the planets? How do we describe the solar system elemental abundance? • The solar system is 90% H,, ~9% He • The terrestrial planets are depleted in these elements • What does this say about the homogeneity of the starting composition? • What could account for the depletion of volatiles in the terrestrial planets? Our model could be that the starting gas was homogeneous in composition, to first order, and something occurred to the terrestrial planets that caused them to lose their volatiles How do we describe the solar system – angular momentum? • All the planets have the same orbital direction • Most solar system material is on a plane • Jupiter contains most of the angular momentum of the solar system • Angular momentum is conserved so the angular momentum now present in the solar system was probably there even before it exited in its current state A simple model for the formation of the solar system • The solar system formed out of a rotating cloudlike structure, dominated by H and He • Something triggered the fragmentation of this cloud and it became gravitationally unstable, allowing its collapse • In the center temperatures were hot enough to trigger fusion • Moving radially outward from the sun temperatures decreased in the nebula A simple model for the formation of the solar system • At any given distance from the Sun there was a ~ unique temperature • The temperature controlled the nature of materials condensing • As material condensed out of a gas they were swept up to form larger and larger bodies, eventually forming planets • In the region of the terrestrial planets all volatiles were lost What is the mass of the solar system and its constituents? • The sun accounts for 99.87% of the total mass of the solar system • The mass of the sun is 1.99 x 1030kg • Jupiter’s mass is 1.899 x 1027kg • An accounting by mass essentially ignores all the rest Solar system processes? Solar processes – Nuclear fusion – Hydrostatic equilibrium – Radiation transport – Generation of magnetic fields and particle acceleration Solar system processes? Planetary Processes – Volcanic activities – Radio-active decay – Plate tectonics – Atmospheric processes – Impact processes – Dynamical evolution of orbital parameters – Core formation and planetary scale differentiation processes Solar system processes? Cometary and asteroidal Processes – Evolution of orbital parameters – Creation of dust in the inner solar system – Surface heating Processes affecting multiple solar system bodies – Solar insolation – Gravitation