Physical Geology
Earth and the Planets
The nine planets in the solar system
inner rocky planets - Mercury, Venus, Earth, Mars
asteroids
gas giants / rocky moons - Jupiter, Saturn
ice giants / icy moons - Uranus, Neptune
‘iceteroids’ - Pluto, Kuiper Objects, comets
Geology: The study of the origin, history, materials and processes of the Earth. (Geo - Greek for earth)
The Earth is a rocky planet that orbits a medium sized yellow star called the Sun. It is one of nine planets, tens of moons, and millions of smaller rocky and icy objects in the Solar System.
The Solar Family
Sun : a large ball of hydrogen and helium gas, dense enough and hot enough to support nuclear fusion which transforms hydrogen into helium, releasing tremendous amounts of energy which radiates into space.
Located at the center of the solar system, 93 million miles away, the sun is almost a million times more massive than the Earth.
Inner rocky planets
The inner region of the solar system contains four relatively small planets with iron cores surrounded by rock. Beyond the orbit of Mars lies a belt of small rock and iron bodies called asteroids. These are either the remains of a rocky planet that broke apart, or of a planet that never fully formed.
Mercury
Venus
Earth / Moon
Mars (rocky moons)
Rocky Asteroids
Outer gas giant planets
The outer region of the solar system begins with two planets that are very similar in composition and size to the Sun. These Gas Giant planets do not shine because their mass is insufficient to cause nuclear fusion. Both have large families of both planet-sized moons and smaller, asteroid-like moons.
Jupiter (rocky and icy moons)
Saturn (icy moons)
Outer ice giant planets
The far outer region of the solar system contains two very large planets that are composed large cores of ice surrounded by thick atmospheres of gas. Both have families of large, icy moons.
Uranus (icy moons)
Neptune (icy moons)
Outer ‘iceteroids’
Beyond the ice giants are found several types of small, icy bodies. These are composed of ice and dust left over from the original formation of the solar system.
Pluto
Kuiper objects
Comets
Early History of the Solar System: After the planets first formed, there was a tremendous amount of leftover material drifting around in chunks of all sizes (from planet-sized to dust). As the newly formed planets moved in their orbits they collided with and swept up this material during a billion year period of intense bombardment. Early in this period the Earth collided with a Mars-sized object and the Moon was formed. Most of the large craters seen on the Moon and other planets formed during this bombardment.
The number of craters a planet has is a clue as to how early in the history of the solar system that planet became cold inside and inactive. Planets that have interior heat tend to lose their early craters because as the heat escapes to the surface it drives processes such as volcanism that cause the surface to be remade over time.
The Grande Tour (slides)
Now, let us take a short tour of this solar system.
We depart from the earth and set a course for the center of the Solar System
Earth Moon Voyager 1 Photo of the Earth / Moon system taken by the Voyager 1 space probe as it left on its mission to the outer planets.
Sun The sun, a medium sized star located in what Douglas Adams describes as "an unfashionable suburb of the galaxy". The sun is a giant ball of hydrogen gas that is being fused into helium releasing enormous quantities of electromagnetic radiation (including light).
Moving out from the sun we first encounter the ‘terrestrial’ or ‘rocky’ planets, which are composed of the denser elements not swept away by the solar wind.
Mercury..The innermost planet. Very dense with a large iron core, very hot on its day side. Mercury has a very tenuous atmosphere of helium. Surface is heavily cratered showing that Mercury is a ‘dead’ planet.
Venus Surface is hidden from sight under thick clouds of sulfuric acid in an atmosphere of carbon dioxide. Hottest planet in the solar system due to the greenhouse effect. Temperature at the surface reaches 890° F.
Venusian surface Venus is a dense, rocky planet. We have seen the surface thanks to Soviet Venera space probes.
Venus surface terrain Radar mapping by the Magellen space probe reveals two large continents, mountain ranges, and volcanoes like Gula Mons (2 miles high). The surface of Venus is less cratered than Mercury, showing that it has been geologically active and changing since the early bombardment.
Earthrise Next out at 93 million miles from the sun is the Earth / Moon system.
Earth Galileo The Earth is our home, and the planet we know best, so it will be the focus of this class. The Earth looks different from the other planets due to its abundance of water on the surface and in the atmosphere.
Meteor Crater AZ The Earth is unique in many ways. It has few craters relative to the other terrestrial planets because it is geologically active and its surface is constantly being reformed. Meteor Crater Arizona is 3600’ across and 600’ deep. A crater of this size could be created by a 100’ diameter asteroid impacting at 45 miles/sec (average meteor fall speed) with a resulting force of about 4 megatons of TNT.
Mars Hubble Telescope Mars is the outermost of the four ‘terrestrial’ or earth-like rocky planets. Once thought to harbor canalbuilding, intelligent life, it is now known to be an apparently lifeless world based on the results of the Viking Lander mission. However, recent studies of a piece of Mars recovered as a meteorite suggest that Mars may have harbored microbial life in its earlier history.
Viking 2 site with frost In many ways, Mars is the most earth-like of the planets, with polar caps, frost, windstorms, thin clouds, and evidence that liquid water once ran along the surface.
Now we have come to the end of the terrestrial planets. The outer worlds of the solar system are vastly different. First there are the ‘gas giant’ or Jovian planets, composed of lighter elements and gases. Even the moons of these giant planets, which look like terrestrial planets, are composed not primarily of rock but of a variety of ices.
Jupiter The first of the ‘gas giant’ or Jovian planets. 318 times more massive than the earth, could pack 1,300 earths within its volume. Jupiter has 16 moons and a thin, discontinuous system of rings.
Great red spot Jupiter has a small, rocky core, but is composed mostly of hydrogen (some in liquid metallic form!), helium, and other gases. It radiates 2.5 times more energy than it absorbs from the sun, causing its atmosphere to consist of turbulent belts and cyclonic storms. The Great Red Spot is a giant cyclonic storm 3X the diameter of the Earth. It was first observed in 1664, thus it has persisted for over 300 years.
Saturn Very similar to Jupiter, but with larger rings and moons composed predominantly of ices of water and ammonia. Saturn is 94X more massive than the Earth and has 17 moons. The largest moon is Titan, which has a thick nitrogen atmosphere and possibly a surface ocean of liquid methane.
Uranus Another gas giant, but apparently internally cold, with little heat to create atmospheric storms. Uranus is 14.6X more massive than the Earth and has 15 moons.
Neptune Even though it is farther out from the sun than Uranus, Neptune has enough internal heat to create atmospheric storms such as the ‘Great Dark Spot’ with winds up to 1200 MPH. Neptune is 17X more massive than the Earth and has 8 moons.
Pluto and Charon Not yet visited by spacecraft. Not very dense, probably composed of ices similar to Triton. Both of these are probably large Kuiper objects.
Halleys comet
Halleys nucleus
The solar system is also populated by chunks of rock and ice (dirty snowballs) called comets that drift out near and beyond the orbit of Pluto. Occaisionally, one will wander into the inner solar system forming a long, bright tail as part of it is melted away by the solar wind.