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?

1st 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 = 149.6 × 106 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 measurement1761 and 1769

1 AU = 149.6 × 106 km

Accurate positionsNew clocks!

aE

aM

We know the orbits of (say) Earth and Mars

aE

aM

We know the orbits of (say) Earth and Mars

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

aE

aM

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

d

265,206

d

D

d

Planetary Diameters

Mercury .38Venus .95Earth 1Mars .53

Jupiter 11.2Saturn 9.4Uranus 4.0Neptune 3.9

km756,12eD

eDD /

Jovian

Terrestrial

Masses of the Planets ?

Newton!

Earth’s Mass: measure acceleration of gravity at surface g = 9.80 m/s2

2e

e

r

GMg

-2211 kg m N 106742.6 G

m 1038.6 6rkg 1098.5 24eM

Other planets ? …….

(from experiments here on earth)

Masses of the Planets ?

32

2

)(

4a

MmGP

sec mkg

-2211 kg m N 106742.6 G(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:

MMm

000,000,000,000,000,000,000,980,5

000,000,000,000,000,000,000,000,000,990,1

000,000,000,000,000,000,000,980,005,990,1

Masses of the Planets ?

32

2 4a

GMP

whence

2

324

P

a

GM

Masses of the Planets ?

32

2 4a

GMP

whence

2

324

P

a

GM

mass of a planet need something smallto orbit it!

Mercury 0Venus 0Earth 1Mars 2

Jupiter 63Saturn 61Uranus 27Neptune 13

moons

Jovian

Terrestrial

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

moons

Satellites!

Planetary Masses

Mercury .055Venus .82Earth 1Mars .11

Jupiter 318Saturn 95Uranus 15Neptune 17

kg1098.5 24eM

eMM /

Jovian

Terrestrial

The Terrestrial Planets

Mercury Venus Earth Mars

Small and rocky

700 K100 K

740 K 290 K 220 K

5.4 g/cc 5.2 g/cc 5.5 g/cc 3.9 g/cc

The Jovian Planets

Jupiter Saturn Uranus Neptune

Big and gassy/icy

125 K 95 K 60 K 60 K

1.3 g/cc 0.7 g/cc 1.3 g/cc 1.6 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

Asteroid belt(main)

Trojan asteroids

~1600known

~300,000known

Not like this at all!

Total mass asteroids < moon’s mass

CeresVesta

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