Transcript Document
The Solar System An Inventory 3A What is the Solar System? • Answer: The system of objects in the solar neighborhood (near the Sun) • What are these objects? One Star Six Planets Nine Planets Dozens of moons Thousands of asteroids Trillions of comets 3A The Discovered Planets • All planets through Saturn known since the ancients – all you have to do is look up to see them • Uranus discovered in 1781 by William Herschel – He wanted to name the planet “Georgium Sidus” after his king and patron, George III of England • • Neptune was first seen in 1846 by Johann Galle using predictions by Urbain Jean Joseph Leverrier and John Couch Adams Pluto was discovered in 1930 by Clyde Tombaugh at Lowell observatory 3A Size and Scale 3A Planets • The first step to studying planets? • Compare and contrast • What are important quantities? • You have: – – – – A stick A tree A car A house • What are the important quantities? 3A Planetary Properties 3A Density and Mass • What is mass? – Mass is similar to weight, it measures how much stuff an object is made of – Example: A bowling ball and a soccer ball are about the same size, but have different masses • What is density? – Density is mass per volume. It helps to tell you what kind of stuff an object is made of – Example: A log and a tree have different masses (and sizes), but the same density because they are made of the same stuff 3A Terrestrial Planets • Close to the sun • Small – Mass – Radius • High density – Primarily rocky – Solid surface • Weak magnetic field • Few moons • No rings 3A Jovian Planets • Far from the sun • Large – Mass – Radius • Low density – Primarily gaseous – No solid surface • Strong magnetic fields • Many moons • Many rings 3A What About Pluto? • Pluto does not easily fit into either category – – – – – Far from the sun (jovian) Small (terrestrial) Neither rocky nor gaseous (icy) One moon No rings • It is similar is composition to some moons in the outer solar system and its orbit is similar to a group of objects called “Kuiper Belt Objects” or KBOs 3A Pluto • Only planet in our Solar System that has not been visited by a NASA (or any other) spacecraft 3A Charon • Largest of any moon in relation to the planet it orbits (1/2 the size of Pluto) • Pluto and Charon are tidally locked to each other (always show the same face) • Charon discovered in 1978 by astronomers at the US Naval Observatory 3A Formation • Where did the Solar System come from? • First, what observations can we make that will constrain the origin of the Solar System? 3A Model Requirements Planet’s are isolated Planetary orbits are nearly circular All planetary orbits lie in the same plane All planets orbit in the same direction as the Sun’s rotation 5. All planets rotate in the same direction as the Sun 6. Most moons rotate in the same direction as the planet they orbit 7. The planetary system is highly differentiated 1. 2. 3. 4. 3A Differentiation • In general, planets get less dense as they get further from the Sun • They go from being composed of metals, to rocks, to ices, to gases • In other words, they go from being made of things with high melting temperatures to things with low melting temperatures 3A Highlights of the current theory • Nebular contraction – Mutual gravity causes contraction – Conservation of momentum increases speed • Planetary formation (accretion) 3A Differentiation revisited • As the solar nebula contracted, the center became hotter than the rest of the cloud • As elements condensed out of the nebulae, temperature determined which could form 3A Clearing of the nebula • After the planets formed, some small debris still remained. All of these small objects were affected by the gravity of the much larger planets. The debris either: 1. Hit a planet 2. Hit the Sun 3. Was thrown out of the area near the planets – becoming KBOs 3A Explaining observation • Matching model requirements: – Point (1) is due to planetesimal growth – Points (2), (3), (4), (5), and (6) are due to conservation of angular momentum and gravitational collapse – Point (7) is due to the heating in the nebula • Anomalies: – – – – Retrograde rotation of Venus Uranus’ axial tilt The Earth’s moon All can be explained by impacts of protoplanets into the planet soon after its formation 3A