Our Solar System
What
you need to learn
l
How gravity and orbits are related
l
The characteristics of planets and interplanetary
bodies
l
What theory is used to describe the formation of the
solar system
Overview
l
Earth is one of nine planets orbiting the Sun
l
All planets and most of their moons (satellites) orbit
the sun in the same direction
l
Their orbits (except for Pluto’s) orbit in the same
plane
Early
Ideas
l
Early astronomers assumed that the Sun, planets, and
stars orbited a stationary Earth (geocentric model)
l
They observed that most planets would travel toward
the eastern sky, but they couldn’t understand why sometimes they would go in
the opposite direction (retrograde motion)
Early
Ideas Continued
l
Nicolaus Copernicus suggested that the Sun was the
center of the solar system (heliocentric model)
l
This explained why there was retrograde motion
l
The inner planets move faster than the outer
Early
Ideas Continued
l
Kepler’s first law: each planet
orbits the Sun in a shape called an ellipse
l
Each planet has it’s own ellipse and
can be measured
l
1.496 x 108 km = 1
astronomical unit (AU)
l
The average distance between the Sun
and each planet are measured in astronomical units
l
Perihelion: when a planet is closest
to the sun
l
Aphelion: when it is farthest away
l
Eccentricity: describes the shape of
the ellipse
Early
Ideas Continued
l
Kepler’s second law: an imaginary line between the Sun
and a planet sweeps out equal amounts of area in equal amounts of time
l
Kepler’s third law:
l
The square of the orbital period (P) equals the cube
of the semimajor axis of the orbital ellipse (a)
l
P2 = a3
Other
important Scientists
l
Galileo Galilei
l
First person to use a telescope
l
Discovered that Jupiter has 4 moons
orbiting it
l
Helped prove that the Sun was the
center of the universe
l
Isaac Newton
l
Published mathematical and physical
explanations for motions of celestial bodies
l
Discovered the law of gravity which
helped explain how the Sun governs the motion of all planets
The
Terrestrial Planets
l
Include Mercury, Venus, Earth, and Mars
l
All are made up of solid, rocky surfaces
l
Have similar properties
Mercury
l
Closest planet to the Sun
l
No moons
l
1/3 the size of Earth
l
Has a very slow spin (it takes 2
Mercury years for 3 days to pass)
l
No atmosphere
l
Temperature ranges from 700K to 100K
l
Surface similar to our Moon
l
Interior probably mostly nickel-iron
core
Venus
l
No moons
l
Brightest planet in Earth’s nighttime
sky
l
Highest albedo of all planets
l
Very thick sulfuric acid clouds in the atmosphere with
high pressure on the surface
l
Surface very hot (737K or 464°C)
l
Slow clockwise spin (1 day = 243
Earth days)
l
Very smooth surface
l
Internal structure very similar to
Earth
Earth
l
Third planet from the Sun
l
Contains all 3 states of water
l
Moderately dense atmosphere
l
Tilted axis with slight wobble
(precession)
l
Caused by gravitational pull from the
Moon
Mars
l
4th planet from the Sun
l
Reddish surface due to high iron
content
l
2 irregularly shaped moons
l
Atmosphere similar to Venus, but much
less dense and thick
l
Surface has evidence of plains, lava
flows, craters, huge mountains and valleys, dried river and lake beds, polar
ice caps (dry ice)
l
Interior probably has an iron and
nickel core
Mars
The
Gas Giant Planets
l
Interiors consist of mostly gas or liquid and possibly
have small solid cores
l
Exterior surfaces are very cold
l
Very large in size
Jupiter
l
Largest planet (diameter is 11 times
larger that Earth’s, 10 times smaller than the Sun’s)
l
Makes up 70% of all planetary matter
in our solar system
l
4 major satellites; at least 12
smaller ones
l
Low density (made up of mostly
hydrogen) atmosphere
l
Contains highly pressurized liquid
metallic hydrogen
l
1 day = less than 10 hours
l
Causes the surface shape to distort
and the gases for from belts (low, warm, dark colored) and zones (high, cool,
light colored)
Jupiter
Saturn
l
6th planet from the Sun
l
2nd largest planet
l
Low density atmosphere (H, He)
l
Magnetic field is aligned with its
rotational axis (unusual for most planets)
l
Rotates rapidly
l
Has belts and zones
l
Has a ring system composed of rock
and ice in 7 layers
l
Contains 18 known satellites
Saturn
Uranus
l
7th planet from the Sun
l
Discovered accidentally in 1781
l
Has at least 18 moons and 10 rings
l
4 times larger than Earth, 15 times more massive
l
Atmosphere contains methane gas (blue colored)
l
The rotational axis is almost inline with its orbital
plane
Neptune
l
Its’ location was predicted before it
was discovered
l
4 times larger than Earth
l
Atmosphere is slightly smaller and
denser than Uranus, but similar in composition
l
8 moons
Pluto
l
9th planet in our solar system
l
Very different from the other planets
l
It has a solid surface, but it is still classified as
a gas planet
l
It is made up of half rock and half ice
l
The elliptical pattern is unusual
l
1 satellite almost identical to Pluto
Formation of Our Solar System
l
Stars and planets form from clouds of
gas and dust called interstellar clouds
l
The collapsing of these clouds may
have led to the beginning of our solar system
l
Grains of dust would accumulate
together and produce large objects called planetesimals
l
The planetesimals would sometimes
collide and merge forming larger bodies called planets
l
Jupiter was the first to form, then
others formed as more and more planetesimals formed and gathered up more
particles
Other
material
l
The leftover particles that were not
picked up are called asteriods
l
Meteoroid: interplanetary material
that falls toward Earth
l
Meteor: meteoroid that burns up in
our atmosphere
l
Meteorite: Meteoroid that falls to
Earth
l
Comets are small, icy bodies that
orbit the Sun in highly eccentric orbits
l
Made up ice and rock
l
Coma: head of comet
l
Nucleus: small solid core
l
Meteor shower: particles of comets
that burn up in our atmosphere