Origin of the Solar System
Solar nebular Theory
Theory to explain the formation of the solar system.
Occurred 5 billion years ago (5 bybp)
Not the same as the Big Bang
Theory to explain the formation of the universe
Occurred 15 bybp
Theory:
5 bybp, cloud of gas and dust forms and is pulled together by gravity
This cloud is known as a Nebula
Thought to have been several light years across
Due to gravity cloud begins to contract
Contraction causes increased in density and rotation
Contraction and rotation creates a disk shape 200 AU across
Heat is generate due to compression and collapse (kinetic energyà heat energy).
Heat concentrates in center and when temp reached 10 million Kelvin (~18 mil Fo)
nuclear reactions begin
Contractions stops as gas pressure equalizes gravity
99.8% of the solar systems mass is located in the sun
Cloud of debris around sun begins to warm and condense and form planetesimals.
Debris aggregates together to form the protoplanets.
Iron/silica form in high temperatures near sun
Lighter elements vaporize and accumulate in outer regions
What is the History of Discovery for our Solar System?
History of Observation:
Early Greeks:
Geocentric model …what does this mean?
Ptolemy: 87-150 AD
Noticed rotation of planets was not constant--> periodic retrograde action
Retrogradeà Planets move one direction, stop, reverse direction and then begin
moving in original direction again.
Ptolemy’s Earth centered universe. Various planets
have different orbits
Retrograde and epicycle motion for the universe known as the Ptolemaic system
Earth centered
Sun and 5 Planets known at this time
Explained observed motion by retrograde epicycles
More observation showed other inconsistencies with geocentric model
In 1543 Nicolas Copernicus suggested the Earth revolved around the sun.
Ptolemaic system lasted ~1400 years
Copernicus’s model:
Each planet moved around the sun in perfect circles at different distances
Planets closest to the sun orbit fastest
Other planets appear to have retrograde motion due to combined movement of
earth and other planets.
Known as a Heliocentric (sun-centered) solar system
Didn’t predict motion of planets accurately…Why?
Tycho Brahe and Johannes Kepler
Tycho Brahe (1546-1601):
20 years of detailed observations of planetary motion
Brahe died in 1601…unpublished
Johannes Kepler (1571-1630):
Assistant to Brahe
25 years analyzing Brahes data
Published the data showing reason Ptolemaic system was wrong
Kepler’s laws of planetary motion.
1) Each planet orbits elliptically about the sun
2) Planets speed up closer to the sun and slow down further away from
the sun www.kepler.arc.nasa.gov/johannes.html
3) The farther the planet is from the Sun, the longer the orbital period (or
year) (p2 = d3)
A closer look at p2 = d3
p = period of rotation around the sun
d = distance of planet from sun
Ex// If Mars is 1.52 AU from the sun, how many years is its orbit?
p2 =1.52 3 p2 = 3.51AU p = sqr rt of 3.51
p = 1.87 years
(1 year = 365 days)
Ex// If Saturn has a period of 29.46 years what is the distance from the sun?
(29.46 years) 2 = d3
867.89 years = d3
cubed root of 867.89 years = d
d= 9.54 AU
Your Turn!
If Jupiter has a period of 11.86 years what is its distance from the sun?
If 1 AU = 150 x 106 km, how far in km is Jupiter from the sun?
If Venus has a distance of 0.72 AU what is it period of rotation?
If a planet has a period of 1, what is its distance from the sun?
Can you name the planet?
Galileo Galilei (1564-1642)
Started career as mathematician and developed several ideas about motion of objects
Taught math at many universities.
1610 developed telescope
Mtn. on moon
Milky way
4 of Jupiter’s moons
Conflicted about what science showed him and what the church taught
Eventually imprisoned by inquisition (10yrs)
Isaac Newton (1642-1715)
Studied gravity and motion --> related physics with astronomy
Newton’s laws of motion (more in GS105)
Newton’s law of universal gravitation
Combined the life work of Copernicus, Kepler, Galileo and others to help develop his
ideas
Newton’s Law of Universal Gravitation:
Between any two objects in the universe there is an attractive force that is
proportional to the masses of the objects and inversely proportional to the square of
the distance between them.
What does this mean?
In equation form:
F = G (m1m2) / r2
F = Force
G = Gravitational constant (6.67 x10-11N m2/kg2)
m = mass
r = distance between m1 and m2
Any two objects exert a force on each other
How much force depends on mass and distance
ex// your weight is the gravitational force between your mass and the
distance to the center of the earth
Would your weight be different at sea level than on top of a 14,000’
mountain Why or Why not?
Ex// A man takes
his dog for a walk.
Calculate the gravitational force
between the man and his dog if the man
has a mass of 1.5 kg, the dog has a mass of
11.2 kg, and the leash is 10 m long.
Current Ideas:
Universe is expanding from big bang...how do we know this?
Use the Doppler effect.
Light, like sound, moves as waves
Light/sound moving towards an object compresses
Light/sound moving away, is stretched (Red Shift)
Many different exploration methods
Hubble
Apollo missions & Shuttles
International space station
Probes
Spirit and Opportunity
Voyager, Pathfinder, Galileo, Gemini, Genesis, Skylab and hundreds more!!!
Earth based scopes and observations
Direct sampling of material
Moon rocks, mars rocks, comets, meteorites…
The Solar System
Starting from the sun and moving out:
Mercury, Venus, Earth, & Marsà Terrestrial planets
Jupiter, Saturn, Uranus & Neptuneà Jovian planet
Pluto and Kuiper belt
Jovian Planets:
The gas giants (very large compared to the terrestrial planets)
Earth = 12,756 km diameter
Jupiter = 143,884 km diameter
Thick atmosphere
Planet composition mostly hydrogen, helium and ammonia in the form of ice and gas.
Terrestrial Planets:
Composed of rock and heavier elements such as iron and silicon
Thin atmosphere
Generally warmer temperatures than the Jovian planets (closer to the sun).
Why is there such a
difference in composition and atmosphere between the Jovian and Terrestrial
planets?
Minor Members of Our System
Asteroids:
Where did the asteroid belt come from?
Comets:
Meteor: Streak across sky (i.e. shooting star)
Meteorite: small fragments of meteorids that reach Earth’s surface intact.
Three types: Iron, stony and stony-iron
Why Are Meteorites Important?
Where did the Moon come from?
Original thoughts:
1) Originally part of the earth
2) Formed at the same time as the Earth
3) Formed elsewhere and was later captured by the earth’s gravity
The Big Whack http://www.pbs.org/wgbh/nova/tothemoon/origins.html
Earth’s Moon
No atmosphere...sky is always black on the moon
Topography consists of terrae and maria
Compositionally similar to some rocks on earth
A Tour of Our Planets:
Mercury:
Temperatures vary from 427oC to -183oC (most variable temp range in solar system)
Light magnetic field possibly due to iron core or solar winds
The surface of Mercury has been shaped impacts, volcanic activity and tectonic motion
during cooling
No moons
No atmos.
Venus:
Called Earth’s “twin” due to the size of the two planets
Heavy atmosphere (sulfuric acid and CO2)
No Liquid water due to heat (~465oC)
Volcanic structures, impact craters and unusual topography
Atmospheric pressure is ~ 90x greater than Earth
Earth
Mars
Mars has mountains that are higher than Mount Everest
Mars atmosphere is about 100 times less dense than the atmosphere of Earth. But
supports a weather system that includes clouds and winds
The average temperature on Mars is about -60o C.
channels, valleys, and gullies are evidence that water has flowed on its surface.
Spirit and Opportunity
landed Jan 2004
Mars Orbiter
http://hirise.lpl.arizona.edu/releases/sept_09.php
Jupiter
It would take more than 1,000 Earths to equal Jupiter’s volume.
Comprised of gas and liquid with little solid surface
Jupiter has 2.4 x Earth’s gravity. (a 100lb object on Earth would equal 240lbs on Jupiter.
The Great Red Spot is a hurricane of gas that has a diameter of 3x Earth.
Jupiter has 16 satellites that measure at least 6 miles (10 kilometers) in diameter (plus
many other small ones)
Saturn
First planet discovered with rings
7 rings made of ice particles
Saturn has 25 satellites at least 6 miles (10 kM) in diameter, (& many smaller ones)
Complex composition of layering of various material (iron, water, methane, hydrogen
Uranus:
axis is inclined 90o
Neptune:
High winds
Cirrus-like clouds
Pluto:
appox. 1/5 the size of Earth
Charon