Chapter 25
The Solar System
25.1 Exploring the Solar System
•Planets – Greek word for wanderers
•The planets earned that name because they appeared to “wander” among the stars.
•The stars appeared to rotate around a fixed point- the North Star – Polaris.
Geocentric Model
•Earth is stationary while objects move around it.
•Accepted theory for 1400 years
Heliocentric Model
•Greek Astronomer Aristarchus developed this model.
•Earth and other planets revolve around the sun.
Planetary Orbits
•Johannes Kepler discovered that orbits had an elliptical pattern instead of circular.
•Newton explained the reason that the planets stay in orbit is because of his first law and the reason that they don’t go out into space is because of sun’s gravity.
•Animation of the Geocentric Model
Components of a Solar System
•Sun, planets, their moons and smaller objects that revolve in the same plane around the sun.
•Distances are very large when measuring between components of the solar system so scientist use astronomical units (au) which is the average distance from Earth to the sun.
Exploring the Solar System
•Started in 1940’s-50’s
•Sputnik 1 was first satellite to space in 1957
•April 12,1961, Soviet cosmonaut Yuri Gagarin was first human to orbit Earth.
•May 5,1961, Alan Shepard first American in space
•July 20, 1969, Neil Armstrong was the first person to set foot on the moon.
•1972 was last mission to the moon on Apollo 17.
Recent Space Missions
Scientists today mostly rely on space probes and telescopes, like the Hubble Telescope, to gather new information about the solar system.
•The space shuttles are reusable space vehicles that launch like a rocket but land like a airplane.
The International Space Station is used by 16 different countries.
Chapter 25.1
25.2 The Earth-Moon System
Earth’s Moon
•The moon is Earth’s closest neighbor. If you traveled 55 mph it would take 6 months to get there.
•The gravity is too weak to hold an atmosphere so the temperatures vary greatly.
Surface Features
•Maria is Latin for “seas.” They are the flat parts of the moon. They are the darker parts of the moon and make up about 15% of the surface.
•Highlands are the lighter areas that are rough mountain ranges.
Craters
•Occur from impacts from meteoroids.
•Show that erosion and plate movements are not occurring.
Formation of the Moon
•Scientist theorized that the moon formed after a collision of a Mars-sized object caused debris to orbit the earth.
•This ejected material orbited Earth until it came together to form the moon.
Phases of the Moon
•Phases are caused by changes in the relative positions of the moon, sun, and Earth as the moon revolves around the Earth.
•A lunar month is 29.5 days
•Same side of the moon is always facing the Earth.
•Animation of phases
Eclipses
•Occurs when the shadow of one body in space falls on another.
•Moon’s orbit is offset by 5 degrees from Earth’s orbit so they do not occur that often.
Solar Eclipse
•During a new moon the moon is between the sun and Earth and Earth can pass through its shadow.
•The darkest part of the shadow is the umbra and only a small part of the Earth will have this total eclipse. The penumbra is less dark and more people would see this partial eclipse.
Lunar Eclipse
•A lunar eclipse occurs when the Earth between the moon and the sun when the moon is in the full moon stage. The shadow of Earth falls on the moon.
•Lunar eclipses, unlike solar eclipses, can be seen from all over the Earth.
Tides on Earth
•Cased by differences in the moon’s gravitational pull on Earth.
•During spring tides, the Earth, moon, and sun are in a straight line so there is great differences between the high and low tides.
•Neap tides occur when the moon is in the 1st and 3rd quarter and it is at right angles to the line of the sun and Earth. This causes the lowest changes in high and low tides.
View spring and neap tide video
25.3 The Inner Solar System
Mercury
Terrestrial Planets
•Mercury, Venus, Earth, and Mars are called terrestrial planets because they have similar structure as Earth.
•They have crust, mantle, and iron core.
•They have rocky crusts. Mercury and Mars have more craters because Earth’s and Venus surface has eroded them.
•They are warmer than the outer planets because they are closer to the sun.
Mercury
•Smallest of terrestrial planets
•Closest to the sun
•Geologically dead – no mantle convection, very little erosion
•Fastest moving – 88 days to orbit
•Sunrise to sunset is 88 days
•Very hot
•No atmosphere
•Visited by space probe- Mariner 10 in 1974-1975
Venus
•Called evening star and morning star because it can only be seen in the west after sunset or east after sun rise.
•Brightest object in Earth’s sky except for the moon.
•Takes 243 days to rotate around its axis
•Rotates in the opposite direction that it revolves
Venus
•This atmosphere composed of carbon dioxide
•Very hot – 460 degrees Celsius
•High sulfur content in atmosphere indicates volcanoes
Earth
•Unique because water can exist as a liquid
•Gravity can hold gas molecules
•The carbon dioxide in the air has been dissolved by Earth’s oceans.
Mars
•Most like Earth of all of the planets
•“red planet” because of high iron content on its surface
•Last volcanic activity about 100 million years ago
•Olympus Mon is largest volcano in solar system. If on Earth, its base would cover the space between Cleveland and WashingtonD.C.
Mars
•Very thin atmosphere -95% carbon dioxide – similar to Venus
•Once has an ocean. Water is now frozen in poles, underground, or escaped into space.
•Seasons marked by huge dust storms
•There have not been found any signs of life.
Asteroids
•Asteroids are small rocky objects that orbit the sun.
•The asteroid belt is beyond Mars.
•Scientists hypothesis that the asteroids are remnants of the early solar system that never came together to form a planet.
Relative size of inner planets
25.4 The Outer Solar System
Gas Giants
•They are larger than the terrestrial planets
•Composed of hydrogen and helium
•They are so large that the pressure is so great that the hydrogen and helium is in the liquid form.
Jupiter
•Largest Planet – can hold 1300 Earths
•One day is equal to 10 hours
•Brown bands are colder and move faster than the white bands
•Storms occur at the borders of these bands. The Great Red Spot is a storm that was first seen in 1664.
Jupiter
•Has at least 50 moons
•Two of them are the size of Mercury
•Two of them are about the size of Earth’s moon
Ganymede
•About the size of Mercury
•Metal core rocky mantle
•Covered with ice
Callisto
•Close to same size as Mercury
•Cover in ice
Europa
•About the size of the moon
•Has metal core and rocky mantle
•Covered with ice
•Icy crust appears to rest on top of a liquid salt-water ocean
•Hypothesized that it is most likely place in the solar system to supportlike
Io
•About the size of the moon
•Metal core and rocky mantle
•Has activevolcanoes
Saturn
•Second largest planet
•Has rings – made of particles of ice and ice-coated rock
•Least dense of all of the planets
•Helium and Hydrogen comprise the atmosphere
•Scientist hypothesis that helium condenses, falls, gains potentialenergy and generates heat
•It releases more energy than Jupiter
Saturn’s Moon – Titan
•Has at least 30 moons
•Titan is the largest
•Titan is bigger than Mercury
•Only moon with an atmosphere
•Covered by rivers and lakes of liquid hydrocarbons
Uranus
•Very cold – farthest from the sun
•Atmosphere hydrogen and helium with methane which gives it the blue-green appearance
Uranus
•Probably has a rocky core
•Mantle is liquid water an ammonia
•Liquid hydrogen and helium surrounds the mantle
•Axis of Uranus’s rotation is tilted more than 90°
Neptune
•One revolution takes 165 Earth years
•Same composition and size of Uranus
•Has clouds of methane gives it the bluish color
•Has 8 moons – Triton is the largest and has a thin atmosphere and icy surface
•Has rings similar to those like Uranus
Pluto
•Small so some scientists don’t consider it to be a planet
•Smaller and denser than the other outer planets
•About the size of the gas giant’s moons
•Rotates like Uranus 90° axis
Charon
•Pluto’s only moon
•Has a diameter about half the size of Pluto
Comets
•Are dusty pieces of ice and rock that partially vaporize when they pass near the sun
Meteoroids
•Pieces of rock that travel through the solar system
•Oldest remnants of the early solar system
•Scientists have radioactive dating to determine that the solar system is about 4.6 billion years.
Kuiper belt
•Wide belt that extends from Pluto’s Orbit to about 100 AU
Oort cloud
•Lies beyond the Kuiper belt
•Great reservoir of comets
•Occasionally objects from the Oort loud enter the inner solar system as a comet
25.5 The Origin of the Solar System
Nebular Theory
•Material expelled by previous stars
•Makes think cloud of dust and gas – solar nebula
•Rotating cloud of dust and gas formed the solar system.
Protoplanetary Disk
•As the nebula rotated faster it flattened out
•Density increases at the center until fusion reactions with hydrogen occur
Planetesimals
•Asteroid-like bodies that grew by adding mass as they collided - accretion
•All plants are revolving the same direction as the protoplanetary disk