Astronomy 141
Life in the Universe
Prof. Scott Gaudi

Lecture 1: The Solar System: Formation and Overview

Key Ideas

Solar System formed from a gas+dust disk

Rocky planets formed in the inner part of the disk

Gaseous planets formed in the outer part

Mercury - no atmosphere

Venus - thick atmosphere, hot, no tectonic plates

Mars - smaller than Earth, thin atmosphere, cold

Jovian planets - no rocky surface

Large moons - some are heated by tides, some have subsurface oceans, some have thick atmospheres

Origin of the Solar System

Stars are born in large clouds of gas and dust called molecular clouds.

Gas and dust collapse to form a disk around the protostar.

The central clump eventually ignites to form the Sun.

Origin of the Planets

Small grains stick together to form bigger grains

Big grains eventually form boulders and begin to attract each other gravitationally

Largest planetisimal runs away to for a Mars-mass body.

Interior to the ice line, you only have rocks, and form rocky bodies.

Exterior to the ice line, form bigger cores, eventually get big enough to grab gas.

At the very outer edge of the disk, there's not enough time to form planets.

Solar System Tour

Properties of particular interest:

--Size

--Rotation Rate

--Surface Properties

--Chemical Composition

--Atmosphere

--Surface Temperature

Terrestrial Planets

Mercury

--Close to Sun

--Small

--Rocky

--No atmosphere

--Temperature Extremes

--No liquid water.

--No plate tectonic activity.

Venus

--Slightly closer to Sun than Earth

--Almost as big as Earth

--Rocky surface

--Slow rotation (243 days!)

--Thick atmosphere (90 atmospheres)

--No plate tectonic activity

Mars

--Almost twice the orbital period

--10% mass of Earth

--Rocky surface

--Fast Rotation (25 hours)

--Thin atmosphere (1% of Earth)

--Temperatures: 187-244K

--No plate tectonic activity

--Ice, maybe liquid water

Jovian Planets

Jupiter & Saturn

--Distant, long periods, cold.

--Massive: 95 and 318 times the mass of Earth

--No solid surface!

--Rapidly rotating

--Lots of Hydrogen

Uranus & Neptune

--More distant, longer periods, colder

--Massive: 15 and 17 times the mass of Earth

--No solid surface!

--Rapidly rotating

--Lots of Hydrogen

--Ice mantles

--Uranus tipped on its side

Giant Moons

Moon

--Dry

--Small

--Temperature extremes

--No liquid water

Jupiter

--Many, many moons

--Four Galilean moons most interesting:

--Io, Europa, Ganymede, Callisto

--Thin atmospheres

--Evidence for subsurface water

--Geologically active

--Powered by tides

Saturn

--Many, many moons

--Titan and Enceladus moons most interesting:

--Titan has a thick atmosphere

--Enceladus has evidence for subsurface oceans

--Geologically active

--Powered by tides

Neptune

--Triton

--Orbits retrograde

--Cold, icy

--Thin atmosphere

--Geologically active

Kuiper Belt

Distant 'debris' of planet formation.

May be a source of water.

See A Note about Graphics to learn why the graphics shown in the lectures are generally not reproduced with these notes.

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