Making Solar Systems and Planets present-day solar system -- kinds of planets newly-forming stars -- conditions during planet formation planets around other stars -- mass, radius, density for other planets EVIDENCE:

Characteristics of the Solar System 1) ORBITS Planets orbit in almost same plane (Pluto and Eris don’t) and in same direction as Sun spins Planet orbits are nearly circular (except Pluto, Eris, and Mercury) flipping a coin to determine if planet is going to go one way or another…

Thought Question: If you flipped a coin to decide which direction each of the 8 planets went around the Sun, what is the probability that all of them would end up going around in the same direction? More than 99% About 75% (only a 1 in 4 chance they wouldn’t) About 50% About 25% (only a 1 in 4 chance they would) Less than 1% Answer: 5. (%)

Characteristics of the Solar System VIEWS FROM ABOVE NORTH POLE: SUN 2) ROTATION Planets rotate in same counterclockwise direction as orbit (except Venus and Uranus) Moons orbit planet in same direction (with 2 exceptions) and near planet equator

THERE IS A SPECIAL DIRECTION IN THE SOLAR SYSTEM Mention spin axes of Venus and Uranus?

Characteristics of the Solar System 3) MASSES 99.9% of solar system mass is in Sun Most of rest is in Jupiter Sun and planets to scale:

FEW MASSIVE OBJECTS, MANY LOW-MASS OBJECTS MORE RAW MATERIALS FOR SOME?

Characteristics of the Solar System DISTANCE FROM SUN: 4) TYPES OF PLANETS Terrestrial planets: close to Sun (a < 1.5 AU) small, dense, mostly metals and rock

Characteristics of the Solar System EARTH (for comparison) Scale questions Jovian planets: Far from Sun (a > 5 AU) 4-11x Earth size, 14-318x Earth mass low density, mostly hydrogen and helium

Average Density HOLLOW PLANET ROCKY PLANET METALLIC PLANET LESS DENSE MORE DENSE Coke versus Diet Coke; thought question? density reveals something about mixture of materials in planet

Average Density Common Materials (units of g/cm3): Air: 0.001 Water: 1.0 -- Jovian Planets: 1-2 Rock: 3 - 5 -- Terrestrial Planets: 4-5 Iron: 8 Lead: 11 Gold: 19 Coke versus Diet Coke; thought question? Jovian planets are mixtures of light materials (hydrogen, helium, and “ices”)

Ceres (dwarf planet) in color About 1/3rd of asteroid belt’s entire mass! Ceres: M = 9.4x10^20 kg Moon: 7.35x10^22 kg (78x Ceres) Diameter = 950 km R = 1738 km (3.6x Ceres, 50x volume) Density: 2.1 g/cm^3 3.3 g/cm^3

Characteristics of the Solar System 5) LEFTOVERS Asteroids mostly orbit between Mars and Jupiter Comets usually come from far outside Neptune’s orbit something about all of the detected objects so far?

Characteristics of the Solar System asteroid Eros (computer reconstruction) nucleus of comet Halley 5) LEFTOVERS: small bodies less than 1000 km across Asteroids: rocky bodies Comets: icy/rocky bodies -- “ice” includes water (H2O), ammonia (NH3), methane (CH4)

Characteristics of the Solar System Scale questions Ice dwarf planets: VERY far from Sun small, low density (1-2 g cm-3), ice/rock

Ice Dwarfs orbits more elliptical than Pluto’s (which is more elliptical than planet orbits) thrown out by gravity of giant planets? SEDNA ERIS PLUTO

“SIDE VIEW” OF SOLAR SYSTEM Ice Dwarfs ERIS SEDNA “SIDE VIEW” OF SOLAR SYSTEM inclination: angle between planet orbit and Earth orbit ice dwarf orbits are more inclined than Pluto’s (which is more inclined than planet orbits)