5 The Solar System A planet by any other name ….

5 Six Planets What is the Solar System? Answer: The system of objects in the solar neighborhood (near the Sun) What are these objects? One Star Nine Planets Dozens of moons Thousands of asteroidsTrillions of comets

5 Discovered Planets All planets through Saturn known since the ancients – all you have to do is look up to see them Uranus in 1781 by William Herschel – “Georgium Sidus” after George III of England Neptune in 1846 by Johann Galle using predictions by Urbain Jean Joseph Leverrier and John Couch Adams Pluto in 1930 by Clyde Tombaugh at Lowell Observatory

5 Planets The first step to studying planets? Compare and contrast What are important quantities? You have: –A stick –A tree –A car –A house

5 Planetary Properties

5 Concept Test Which of the following is a true statement about density? a.A stone and a boulder have the same density. b.A bowling ball and a soccer ball have the same density. c.A boulder has a higher density than a pebble. d.A soccer ball has a higher density than a billiard ball. e.None of the above.

5 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

5 Terrestrial Planets Close to the sun Small –Mass –Radius High density –Primarily rocky –Solid surface Weak magnetic field Few moons No rings

5 Terrestrial Planets

5 Interiors

5 Jovian Planets Far from the sun Large –Mass –Radius Low density –Primarily gaseous –No solid surface Strong magnetic fields Many moons Many rings

5 Jovian Planets

5 Interiors

5 Orbits

5 Planetary Rings All the “Jovian planets” have rings These are not solid, but composed of millions of tiny particles of ice and dust Rings have structure: gaps and spokes CompositionSize JupiterDustSmall grains SaturnWater ice< house size UranusCarbonaceousLarge particles Neptunedark, unknownunknown, small

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5 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 in 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

5 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

5 Concept Test Which of the following is NOT a reason why many astronomers think Pluto should not be classified as a planet. a.It is smaller than some moons. b.It has an orbit similar to many Kuiper Belt Objects (KBO). c.Pluto is more similar in shape to irregular asteroids and comets. d.Pluto is more similar in composition to many moons and KBOs. e.Its orbit is far more elliptical and inclined to the Sun relative to the other planets.

5 KBOs Belt of icy objects outside Neptune’s orbit.

5 Quaoar a = 43 AU Orbit nearly circular (e = 0.04) P = 285 years.

5 Sedna a = 479 AU Orbit (e = 0.84) Aphelion = 76 AU Perihelion = 884 AU –Currently = 90 AU P = 10,500 years

5 Sedna

5 “Xena” 2003 UB313 A = 68 AU E = 0.44 P = 560 years Coming soon: mass and density

5 Homework #6 For Wednesday 20-Sept: Read article and answer questions in handout.