ATTENTION: EXAM this FRIDAY !! * Exam covers the reading Chapters 1-6 * Sample questions on the web. * 50 m.p. questions HW – due Wednesday midnight

OUR SOLAR SYSTEM How did it get this way? 1 st a very brief survey ….

How do we know stuff about the planets?

Distances between planets? all orbital data, e.g. eccentricity and inclinations …. (Brahe, Kepler) 1 AU = × 10 6 km But, all in terms of the a = 1 of earth

How big is an AU? Halley’s idea to accurately find the scale factor: The transit of Venus First accurate measurement 1761 and AU = × 10 6 km Accurate positions New clocks!

aEaE aMaM We know the orbits of (say) Earth and Mars

aEaE aMaM We also know where on their orbits they'll be be at any given time

aEaE aMaM We know the orbits of (say) Earth and Mars We also know where on their orbits they'll be be at any given time d So we can use analytic geometry to figure how far away a planet is from us at any given time

Sizes of the planets (and sun) ? Distance vs. apparent diameter

Planetary Diameters Mercury.38 Venus.95 Earth 1 Mars.53 Jupiter11.2 Saturn 9.4 Uranus 4.0 Neptune 3.9 Jovian Terrestrial

Masses of the Planets ? Newton!

Earth’s Mass: measure acceleration of gravity at surface g = 9.80 m/s 2 Other planets ? ……. (from experiments here on earth)

Masses of the Planets ? secm kg (from experiments here on earth)

Masses of the Planets ? When something very small ( m ) orbits something very big ( M ) you can say to very good accuracy:

Masses of the Planets ? whence

Masses of the Planets ? whence mass of a planetneed something small to orbit it!

Mercury 0 Venus 0 Earth 1 Mars 2 Jupiter 63 Saturn 61 Uranus 27 Neptune 13 moons Jovian Terrestrial

Mercury 0 Venus 0 Earth 1 Mars 2 Jupiter 63 Saturn 61 Uranus 27 Neptune 13 moons Satellites!

Planetary Masses Mercury.055 Venus.82 Earth 1 Mars.11 Jupiter318 Saturn 95 Uranus 15 Neptune 17 Jovian Terrestrial

The Terrestrial Planets MercuryVenusEarthMars Small and rocky 700 K 100 K 740 K 290 K220 K 5.4 g/cc5.2 g/cc5.5 g/cc3.9 g/cc

The Jovian Planets JupiterSaturn UranusNeptune Big and gassy/icy 125 K95 K 60 K 1.3 g/cc0.7 g/cc1.3 g/cc1.6 g/cc Gas giants Ice giants

Some things to note: Planets and other stuff orbit sun in a plane. All planets orbit ccw in near circular orbits. Most planets (Venus and Uranus) rotate ccw. Most big moons do the same thing. Two very different types of planets.

Other things out there Asteroids Dwarf-planets Kuiper-belt and Oort-cloud objects

Asteroids Rocky: iron, silicon composition

1.5 AU 5.2 AU

~ 1.5 AU 5.2 AU ~2 AU ~3.5 AU Asteroid belt

(main) Trojan asteroids ~1600 known ~300,000 known

Not like this at all! Total mass asteroids < moon’s mass

Ceres Vesta Largest object in Asteroid belt “Dwarf Planet” Largest “Asteroid”

243 Ida (53.6 × 24.0 × 15.2 km) Dactyls

Dwarf-Planets of the Kuiper Belt: TNOs/KBOs Ices (water, ammonia, methane) and rock:

The most famous TNO: Pluto!

Rocky and in the Asteroid belt

The Kuiper Belt

Comets Ices (water, ammonia, methane): Kuiper-belt and Oort-cloud

Oort Cloud objects

Single frame NAVCAM image of Comet 67P/C-G taken on 11 September 2015, 319 km from the nucleus. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Comet ISON