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A100 Survey of the Solar System Read Chapter 7 – Survey of the SS Homework 6 – Impact Craters, due on Friday Kirkwood Obs. open Wednesday This week’s Quiz via Oncourse T&S Today’s APOD The Sun Today EARLY VOTING WHERE? Curry Building (7th & Morton, one block west of College Ave) EVERY day until November 3rd Monday – Saturday: 8:30am – 6:00pm Sunday: 1:00pm – 5:30pm November 3rd: 8:30am – 12:00 TRANSPORTATION: Students may take a free early vote shuttle any weekday between the hours of 11:00am – 5:30pm. The shuttle leaves every 15 minutes from the IMU circle drive and the 10th street side of the Wells library. Voters MUST present their Indiana drivers license, student id, or passport when they go to vote. Another possible activity: Close Encounters at Ivy Tech Bloomington An academic panel discussion will explore how different academic disciplines might aid in welcoming extraterrestrial visitors Thursday, Oct. 30, 6 PM, Ivy Tech 4th floor Auditorium, Room 438 Use general activity worksheet The Solar System A diversity of objects – The Sun, planets, dwarf planets, asteroids, comets, dust, gas An underlying order in the dynamics of their movements Two main families of planets: solid rocky inner planets gaseous/liquid outer planets The Sun The Sun is a star A ball of hot, incandescent gas Energy comes from nuclear reactions in its core Composed mainly of hydrogen (71%) helium (27%) Plus traces of nearly all the other chemical elements The Sun The Sun is the most massive object in the Solar System 700 times the mass of the rest of the Solar System combined The Sun’s mass provides the gravitational force to hold all the Solar System bodies in their orbits around the Sun The Planets Orbits are almost circular and lie in nearly the same plane Plutoids do not lie in the plane of the planets’ orbits Pluto’s orbit has an inclination of 17° Rotational axes are not lined up Revolution and Rotation All of the planets travel counterclockwise around the Sun (as seen from high above the Earth’s north pole) Six planets rotate counterclockwise; Venus rotates clockwise (retrograde rotation), and Uranus and Pluto appear to rotate on their sides Mercury Venus Earth Mars Inner (“Terrestrial”) Planets Small “rocky” bodies Differentiated crust, mantle, core Mainly silicon and oxygen crust and mantle Iron/nickel cores Relatively thin or no atmospheres Large differences in surface structures and processes Outer “Gas Giant” “Jovian” Planets Jovian planets are much larger than terrestrial planets Jupiter’s radius is 11 times larger than Earth’s No well-defined surface Gaseous, liquid, or “icy” (H2O, CO2, CH4, NH3) What is a surface? Terrestrial planets – the surface is the hard boundary between the crust and the atmosphere Jovian planets (and the Sun!) – the “surface” is the top layer we can see Jovian planets don’t have a real surface – we see the tops of the clouds Dwarf Planets & Plutoids Pluto and similar objects don’t fit either planet family Astronomers have discovered more than 200 objects like Pluto orbiting the Sun In 2006, a new family was introduced – the dwarf planets Massive enough to pull themselves spherical Orbits have not been swept clear of debris Lots of Moons! Jupiter > 62 Saturn > 31 Uranus > 27 Neptune > 13 Mars - 2 Earth - 1 Mercury, Venus have no (known) moons Plutoids and asteroids have moons More and more moons of the outer planets are still being discovered! Comets and Asteroids Comets are icy bodies about 10 km or less across Comets can grow very long tails of gas and dust as they near the Sun and are vaporized by its heat Asteroids are rocky or metallic bodies ranging in size from a few meters to 1000 km across (about 1/10 the Earth’s diameter) Where are Asteroids Found? Most asteroids orbit the Sun in a band between Mars and Jupiter Asteroids may be the failed building-blocks of a planet Some asteroids lead or trail Jupiter around its orbit known as “Trojan Asteroids” Where Are Comets Found? Most comets orbit the Sun far beyond Pluto in the Oort cloud, a spherical shell extending from 40,000 to 100,000 AU from the Sun Some comets may also come from a disk-like swarm of icy objects that lies beyond Neptune and extends to perhaps 1000 AU, a region called the Kuiper Belt How Do We Determine the Composition of the Planets? Since the inner and outer planets differ dramatically in composition, it is important to understand how composition is determined A planet’s reflection spectrum can reveal a planet’s atmospheric contents and the nature of surface rocks Seismic activity has only been measured on Earth for the purposes of determining interior composition Density tells us about composition A planet’s average density is determined by dividing a planet’s mass by its volume Mass determined from the planet’s moons using Kepler’s modified third law Volume derived from a planet’s measured radius Composition from Density Once average density known, the following factors are taken into account to determine a planet’s interior composition and structure: Densities of abundant, candidate materials Variation of these densities as a result of compression due to gravity Surface composition determined from reflection spectra Material separation by density differentiation Mathematical analysis of equatorial bulges Densities of Terrestrial Planets Average densities ranging from 3.9 to 5.5 g/cm3 Largely rock and iron Iron cores Relative element ratios similar to the Sun except for deficiencies in lightweight gasses (hydrogen and helium) Densities of Jovian Planets Average densities from 0.71 to 1.67 g/cm3 Compositions similar to the Sun – with hydrogen and helium Contain Earth-sized rocky cores Atmospheres Interiors Dates to ASSIGNMENTS Remember this week Chapter 7 Homework and quiz on Friday Kirkwood Obs. open on Weds.