1. Today’s APODAPOD  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 The Sun Today A100 Survey of the Solar System

2. 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.

3. 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 4 th floor Auditorium, Room 438  Use general activity worksheet

4. 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

5. 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

6. 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

7. 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

8. 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

9.  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 Inner (“Terrestrial”) Planets Mercury Venus Earth Mars

10. 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” (H 2 O, CO 2, CH 4, NH 3 )

11. 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

12. 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

13. Lots of Moons!  More and more moons of the outer planets are still being discovered!  Jupiter > 62  Saturn > 31  Uranus > 27  Neptune > 13  Mars - 2  Earth - 1  Mercury, Venus have no (known) moons  Plutoids and asteroids have moons

14. 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)

15. Where are Asteroids Found?  Asteroids may be the failed building-blocks of a planet  Some asteroids lead or trail Jupiter around its orbit  known as “Trojan Asteroids” Most asteroids orbit the Sun in a band between Mars and Jupiter

16. 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

17. 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

18. 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

19. 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

20. Densities of Terrestrial Planets  Average densities ranging from 3.9 to 5.5 g/cm 3  Largely rock and iron  Iron cores  Relative element ratios similar to the Sun except for deficiencies in lightweight gasses (hydrogen and helium)

21. Densities of Jovian Planets  Average densities from 0.71 to 1.67 g/cm 3  Compositions similar to the Sun – with hydrogen and helium  Contain Earth-sized rocky cores

22. Atmospheres Interiors

23. ASSIGNMENTS this week  Chapter 7  Homework and quiz on Friday  Kirkwood Obs. open on Weds. Dates to Remember