Thought Question What does the solar system look like as a whole? Why does the solar system look the way it does? Can we explain how the solar system first formed?

In studying the solar system… n We look for patterns amongst the planets. n We look for characteristics that the planets share. n We look characteristics that they do NOT share. n Can we explain these similarities and differences?

Planet Comparisons Property Terrestrial Planets Jovian Planets Distance from Sun Mass Size Composition Moons Rings Density

Terrestrial Planet Comparisons Property Similarities Differences atmospheres Earth & Venus have thick atm. Mars & Mercury & Moon have thin composition of atmosphere Nitrogen, CO2 Earth has Oxygen composition of surface structures cratering temperatures

Jovian Planet Comparisons Property Similarities Differences atmospheres composition of atmosphere atmospheric storms and winds rings moons Appearance of planet

How are the planets classified? n Terrestrial: Mercury, Venus, Earth, Mars n Jovian: Jupiter, Saturn, Uranus, Neptune

Any patterns? n a simple rule that gives the distances of the planets from the Sun where N=0, 3, 6, 12, 24…for Mercury, Venus, Earth, Mars, etc.

____24(24+4)/10 = 2.8 AU_______ Planet N Bode’s Law Radii True Orbital Radii Mercury0(0+4)/10 = 0.4 AU0.39 AU Venus3(3+4)/10 = 0.7 AU0.72 AU Earth6(6+4)/10 = 1.0 AU1.00 AU Mars12(12+4)/10 = 1.6 AU1.52 AU Jupiter48(48+4)/10 = 5.2 AU5.2 AU Saturn96(96+4)/10 = 10.0 AU9.5 AU Uranus192(192+4)/10 = 19.6 AU19.2 AU Neptune??30.1 AU Pluto384(384+4)/10 = 38.8 AU39.5 AU Asteroid belt AU

What does Bode’s Law tell us? n Bode's Law predicted that there should be a planet between the orbits of Mars and Jupiter. n The "missing planet" turned out to be the asteroid belt.

The Origin of the Solar System should explain… 1. Motion of the planets Planets orbit in the same direction......in nearly the same plane......in nearly circular orbits. Most planets rotate in the same direction. Most moons orbit in the same direction. 2. Categorizing Planets Planets are either rocky or gaseous.

The Origin of the Solar System should explain… 3. Asteroids and Comets Most asteroids are found between Mars and Jupiter. Most comets have highly elliptical orbits. 4. Age of solar system Common age of rock samples, asteroids, meteorites (4.5 billion years). Common cratering age of ~3.8 billion years 5. Exceptions to the Rules What about Pluto’s elliptical orbit and composition? What about the odd rotation of Venus and Uranus?

Formation of the Solar System n We look for a simple, logical, physical explanation for the similarities and differences we see in the planets. We look for a framework that fits with observations—A THEORY! n The solar system formed from a cloud of gas and dust in a process known as accretion.

n We see evidence of accretion disk around other stars. n For example, this accretion disk around the star  Pictoris. Q: What is another reason we believe the solar system formed this way? A: ….because we see it happening elsewhere!

n n Accretion—the gradual accumulation of matter due to gravitational attraction n During the first few million years, matter in the accretion disk came together to form a Sun and little rocks came together to form… n...larger objects called planetesimals, with diameters of about 100 km. diameters of about 100 km. Then, planetesimals collide and sweep out debris until there’s just ONE planet in an orbit.