Download Chapter 6 Lecture 1

Our Solar System
and Its Origin
6.1 A Brief Tour of the Solar
System
Our Goals for Learning
• What does the solar system look like?
The planets are tiny compared to the distances between them (a
million times smaller than shown here), but they exhibit clear
patterns of composition and motion.
The patterns are far more important and interesting than numbers,
names, and other trivia
Recall scale of solar system
Sun
• Over 99.9% of solar system’s mass
• Made mostly of H/He gas (plasma)
• Converts 4 million tons of mass into energy each second
Mercury
• made of metal and rock; large iron core
• desolate, cratered; long, tall, steep cliffs
• very hot and very cold: 425°C (day), –170°C (night)
Venus
• nearly identical in size to Earth; surface hidden by thick clouds
• hellish conditions due to an extreme greenhouse effect:
• even hotter than Mercury: 470°C, both day and night
• atmospheric pressure equiv. to pressure 1 km deep in oceans
• no oxygen, no water
Earth and
Moon to scale
Earth
• An oasis of life
• The only surface liquid water in the solar system; about 3/4 of
surface covered by water
• One surprisingly large moon
Mars
• Looks almost Earth-like, but don’t go without a spacesuit!
• Giant volcanoes, a huge canyon, polar caps
• Water flowed in the distant past; could there have been life?
Jupiter
• Much farther from
Sun than inner 4
planets (more than
twice Mars distance)
• Also very different in
composition: mostly
H/He; no solid surface.
• Gigantic for a planet:
300  Earth mass;
>1,000  Earth
volume.
• Many moons, rings
Moons can be as
interesting as the
planets themselves,
especially Jupiter’s
4 large “Galilean
moons” (first seen
by Galileo)
• Io (shown here): active volcanoes
• Europa: possible subsurface ocean
• Ganymede: largest moon in solar system — larger than Mercury
• Callisto: a large, cratered “ice ball” with unexplained surface features
Saturn
• Giant and gaseous
like Jupiter
• most spectacular
rings of the 4 Jovian
planets
• many moons,
including cloudcovered Titan
• currently under
study by the
Cassini-Huygens
spacecraft
Saturn
Rings are NOT
solid; they are
made of
countless small
chunks of ice
and rock, each
orbiting like a
tiny moon.
Artist’s conception
Saturn
Cassini probe
arrived July
2004
(Launched in
1997)
Link Enceladus
Uranus
• much smaller than
Jupiter/Saturn, but still
much larger than Earth
• made of H/He gas,
hydrogen compounds
(H2O, NH3, CH4)
• extreme axis tilt —
nearly tipped on its
“side” — makes
extreme seasons during
its 84-year orbit.
• moons also tipped in
their orbits
Neptune
• Very similar to
Uranus (but much
smaller axis tilt)
• Many moons,
including unusual
Triton: orbits
“backward”; larger than
Pluto.
Pluto
• A “misfit” among the planets: far from Sun like large jovian
planets, but much smaller than any terrestrial planet.
• Comet-like composition (ices, rock) and orbit (eccentric, inclined
to ecliptic plane, long -- 248 years).
• Its moon Charon is half Pluto’s size in diameter
• Best current photo above; New Horizons mission launch 2006,
arrival 2015
What have we learned?
• What does the solar
system look like?
• Our solar system
consists of the Sun,
nine planets and
their moons, and
vast numbers of
asteroids and
comets. Each world
has its own unique
character, but there
are many clear
patterns among the
worlds.