the solar system solar system = sun + 8 planets +...
TRANSCRIPT
10/5/2010
1
The Solar System solar system = Sun + 8 planets + satellites + asteroids + comets
Pluto is no longer considered a planet!
Why study?
• understand the Earth better and our impact on it
• understand how planets form so we can search for Earth-like planets around other stars
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
(Pluto)
Order of the Planets
A mnemonic to help you remember this!
MyVery
EroticMate
JoyfullySatisfiesUnusualNeeds
(Passionately)
Planetary Orbits
10/5/2010
2
Characteristics of Planetary Orbits
Low eccentricity ellipses (except Mer, Mar, Plu)
Revolve about Sun in same direction
Revolve about Sun in same plane (except Plu)
Rotate in same direction as revolution (except Ven, Ura, Plu)
The Building Blocks of Planets
Mean Density (ρ)
ρ = m / V
where:
ρ = mean density (kg/m3)
m = total mass (kg)
V = total volume (m3)
ρ is a measure of the overall or bulk composition of a planet
Common Building Block Mean Densities
Material Density (kg/m3)
Iron 8000
Rock 3000
Water Ice 1000
Hydrogen Gas 1
Determining the Bulk Properties of the Planets
Compare the mean density of a planet or moon with the densities of the main building blocks
Examples
10/5/2010
3
A planet has a mean density of 3100 kg/m3
What is it made of?
A planet has a mean density of 3100 kg/m3
What is it made of?
Mostly rock!
A moon has a mean density of 2000 kg/m3
What is it made of?
A moon has a mean density of 2000 kg/m3
What is it made of?
A mixture of rock and ice!
Main difference between stars and planets
Stars generate their own light while planets reflect light from the Sun!
Stars are Blackbodies
The color of a star is a measure of its temperature!
Example:
A blue star is hot while a red star is cool
10/5/2010
4
Planets are NOT Blackbodies
The color of a planet is determined by its chemical composition!
Example:
Mars is red because of iron oxides on its surface
Chemical compositions are determined from the spectroscopy of reflected sunlight from a body
By comparing the spectrum the object with the spectrum of materials in a lab
we can determine the chemical composition of surface or atmosphere of
a planet or moon!
The Spectrum of Europa
Europa has an icy surface!
There are two kinds of planet!
Terrestrial Planets
‘Earth-like’
Small, rocky, close to the Sun (< 1.5
AU)
High mean densities
Mercury, Venus, Earth and Mars
10/5/2010
5
Jovian Planets
‘Jupiter-like’
Large, gaseous, far from Sun (> 5 AU)
Low mean densities
Jupiter, Saturn, Uranus, Neptune
Sizes of Terrestrial and Jovian Planets
Planetary Satellites (Moons)There are 169 currently known (Sept 2007)
All have except Mercury and Venus
Terrestrial have few (2 or less)
Jovian have many (13 or more)
7 ‘giant’ satellites (size similar to Mercury)
The Seven ‘Giant’ Satellites of the Solar System
Terrestrial and Jovian Planets Compared Asteroids – rocky debris
10/5/2010
6
Comets – icy debris Location of Asteroids and Comets
Robotic Space Probes
• enable direct measurements
• radio data back to Earth
• all planets visited except Pluto (New Horizons mission launched Jan 2006)
Types of Space Mission
• Flybys – quick look
• Orbiters – extended study from orbit
• Landers – direct measurements
• Sample return – return samples to Earth
• Human visits – using astronauts
The Voyager Flyby Missions Made Flybys of Jovian Planets in 1980’s
10/5/2010
7
The Magellan Venus Orbiter
Mapped the surface of Venus with radar in the 1990’s
The Mars Exploration Rovers
Currently searching for evidence of water on the surface of Mars in the past
The Stardust Mission to Comet Wild 2
Jan 2004: collected dust from comet
Jan 15th 2006:
Samples safely returned to Earth
The only human visit – the Apollo missions to the Moon!
Lunar Reconnaissance Orbiter (2009)
Apollo 12 Landing Site
10/5/2010
8
Apollo 12 astronaut visiting Surveyor 3
The Formation of the Solar System
Condensation (Nebular) Theory
Stars form from huge clouds (nebulae) of gas and dust
Interstellar clouds are normally stable!
Because the inward force of gravity is balanced by the outward force of pressure!
10/5/2010
9
To form a star and planetary system we need the cloud to become unstable:
gravity > pressure
causing the cloud to collapse under gravity
size ↓ temp ↑ spin ↑
This can happen when clouds are compressed externally!
This can be caused by a nearby supernova explosion!
The Conservation of Angular Momentum
As a rotating object gets smaller it spins faster!
Similarly, as a cloud collapses, it spins faster forming a
rotating protoplanetary disk (proplyd) around a central protostar
Particles of gas and dust stick together within the disk in a process called accretion
10/5/2010
10
Leading to the formation…. of a family of planets….
Explains the characteristics of Planetary Orbits!
Low eccentricity ellipses
Revolve about Sun in same direction
Revolve about Sun in same plane
Rotate in same direction as revolution
Condensation Temperature
Maximum temperature that a given material will stick together (condense):
iron > rock > ices > gases
high low
The type of planet formed depends on the distance from the center of the disk…
The Frost Line
10/5/2010
11
In the inner disk within the frost line only rocks and metals could condense forming Terrestrial
planets
In the outer disk beyond the frost line ices could also condense which then attracted gas from the
solar nebula forming Jovian planets
This explains why our own solar system has inner rocky Terrestrial planets and outer gaseous Jovian
planets…
Other Evidence?
The Orion Nebula
A star formation region 1500 ly away
Protostars and Protoplanety disks are seen inside the Orion Nebula!
Infrared (IR) Image
10/5/2010
12
Disks of gas and dust are seen around other, mature solar-type stars!