37. Planetary Geology p

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1 37. Planetary Geology p The Solar System Revisited We will now apply all the information we have learned about the geology of the earth to other planetary bodies to see how similar, or different, they are to our planet. There are a total of planets that comprise our solar system. Once the most distant planet from the Sun, Pluto is now relegated to the status, and is 40 times further from the Sun than Earth, which we represent by the abbreviation 40 AU. An AU is an (1 AU is the distance from the Earth to the Sun). At a distance of AU is a wide ring of small icy bodies outside of the region of named planets. This part of the solar system is called the. Even further out from here is the : an enormous collection of icy bodies that is the source of many comets. Other comets come from the Kuiper Belt. What Kuiper Belt object discovered in 2002 is over 1000 km in diameter? Since then, several other distant solar system bodies have been discovered inside the Kuiper Belt, including one object discovered in 2005 and determined in April 2006 to be larger than Pluto. This object is now officially a dwarf planet named. In 2004, a body was discovered orbiting the Sun outside the Kuiper Belt but inside the Oort Cloud, at about 90 AU. This body is slightly smaller than Pluto and is the most distant known body that orbits the Sun (once every 10,500 years). Its name is. More Kuiper Belt objects may be discovered in future that rival Pluto in size and may even be considered for designation as dwarf planets. All of the planets revolve around the Sun in the same direction. If we were to look down on the solar system from above its north pole, all the planets would be moving in a direction in approximately circular orbits around the Sun. The planets are all aligned within a flat imaginary plane, called the. In contrast, has a highly elliptical orbit inclined at 17 to this plane, causing it to sometimes pass inside Neptune's orbit. When viewed from above, six of the planets rotate in a manner around their rotational axes. So, like Earth, on most planets, the Sun rises in the east and sets in the west. What two planets rotate in a clockwise manner? and One of the planets has somehow managed to roll over on its side with respect to the plane of the ecliptic. The northern hemisphere always faces the Sun and the southern hemisphere always faces away from it. What planet is this? 1

2 Between the orbits of Mars and Jupiter is a huge belt of rocks and debris called the. They owe their existence to Jupiter's large size and strong gravitational field which prevented early solar system planetesimals in this region from ever coalescing into a planet. The composition and evolutionary history of the planets are a consequence of their distance from the Sun. The innermost planets are called the. List the terrestrial planets (in order from the Sun): The terrestrial planets are all composed of rocks with metallic and nonmetallic elements. So they also have high densities. The rocks and metallic elements that constitute the terrestrial planets must have condensed at high temperatures, which would be expected closer to the center of the collapsing disk during the formation of the solar system. That's why the terrestrial planets are closest to the Sun. The planets further away from the Sun are called the. List the Jovian planets (in order away from the Sun): The Jovian planets all have low densities because they are mostly made of the gases and, with frozen compounds like ammonia and methane, surrounding small rocky cores. These predominantly gaseous bodies must have condensed at much lower temperatures, which would be expected around the outer portions of the collapsing disk of the primordial solar system. Because they are so large and gaseous, the Jovian planets are also referred to as the. During the early development of the solar system, collisions between planetesimals were common. That's why we see so many on the surfaces of the planets and moons. A large collision between a planetesimal and Venus may be the reason for its clockwise rotation. Similar collisions may be responsible for Uranus lying on its side and for Pluto revolving so far off the plane of the ecliptic and making fun of the rest of the solar system. Meteorites Space debris that enters the Earth's atmosphere are called. They usually vaporize in the upper atmosphere due to frictional heating, producing so-called shooting stars. If they collide with the Earth s surface they are called. Meteorites don't have to be very big to cause a lot of damage. Small meteorites hit Earth every day (10-50 of them), and have the potential to cause damage, injuries, or death. Larger meteorites, perhaps a few 100s of meters across, can create enormous craters, like Barringer Meteor Crater in Arizona, which resulted from an asteroid hitting the Earth years ago. Even larger meteorites can irrevocably alter the evolution of the planet, such as the 10 km big meteorite impact that ultimately caused the extinction of the dinosaurs. Where did this impact occur?. 2

3 When did it occur? years ago. What two geologic time periods have their boundary at this point in geologic time? and (the K-T Boundary) What element, known to be common in meteorites, is enriched in clay layers that formed at the K-T boundary? Despite being a potential threat, meteorites have helped us learn a lot about the earliest times of the solar system because many of these meteorites are actually bits of debris that formed when the solar system first began to form. The solar system cleared out most of this debris through collisions early in its history, so there is less meteorite activity today than there would have been early in Earth's history. Meteorites are classified into 3 categories based on their compositions: TYPE ABUNDANCE meteorites 93% meteorites 6% meteorites 1% Most meteorites are stony meteorites, which are composed of iron and magnesium silicate minerals that formed during the very beginning of the solar system's history. What are the three types of stony meteorites? 1. (like mantle or crustal material) 2. (rare primordial solar nebula material) 3. (like Earth basalts- but come from the Moon or Mars) Iron meteorites are composed of iron and nickel alloys so they are often considered to be an analog for the Earth s core. They likely represent the cores of asteroids that were broken apart by collisions with other asteroids. Stony-iron meteorites are composed of almost an equal ratio of Fe/Ni alloys and silicate minerals. Planets and Moons Terrestrial Planets The terrestrial planets had similar beginnings to Earth. The mass, density, and composition of each planet suggests that each developed an surrounded by a and. Atmospheres developed through the outgassing of light gases from the planetary interiors during periods of volcanism. 3

4 Mercury: is about 40% the size of Earth and has changed little since it first formed. About 80% of its mass is due to a large metallic core. A slight magnetic field indicates that the core must be. The surface is heavily cratered and many craters appear to be filled with undisturbed lava flows. Because of its small gravity, all the gases escaped into space so Mercury has no atmosphere. Does Mercury have any current tectonic activity? Venus: is about % the size of Earth but otherwise is very different. Its surface temperature is C (Earth is about 25 C!). The atmosphere contains 96% CO 2. Venus has a core, mantle, and crust. There is no evidence of active volcanism, although volcanic lava domes and old lava flows are visible. Does Venus have any current tectonic activity? Has Venus been tectonically active in the past? Mars: about % the size of Earth; has a core, mantle and crust. The atmosphere is thin, with 95% CO 2. The southern hemisphere is heavily cratered, including the largest impact crater in the solar system, called, which has a crater 2,000 km wide. The northern hemisphere is a flat, smooth plain, and is believed to represent an, with evidence of ancient erosional shorelines. The largest volcano in the solar system is on Mars: It is 27 km high, 3 times higher than Mt. Everest. It is so large because Mars has no plate tectonics, so the hotspot that formed it stayed in the same place below the Martian crust. Does Mars show evidence of tectonic activity? Evidence: Mars has numerous faults, as well as the largest rift valley in the solar system, called. It is 250 km wide, 7 km deep, and 4,000 km long. It would stretch from San Francisco to New York. Recent images have provided strong evidence that has flowed across the Martian surface in the past as giant rivers. Could liquid water exist on the surface of Mars today? Despite the extreme cold, there is evidence of recent water or ice flows out of rock faces- perhaps surface seeps that come from vast groundwater aquifers. Jovian Planets The Jovian planets were imaged by the Voyager spacecraft missions. Jupiter is 11 times bigger than Earth, Saturn is 9.5 times bigger, and Uranus and Neptune are both about 4 times bigger. All are predominantly gaseous, with rocky cores, and all have ring systems around them. 4

5 Jupiter has at least 28 moons, including the most volcanically active body in the solar system, called. There are only 3 other volcanically active bodies: Earth, Neptune s moon, and Saturn s moon (which erupts water ice). Another of Saturn s moons, is larger than planet Mercury and is the only moon in the solar system with an atmosphere (mostly nitrogen, like Earth). It is also the only moon (other than our own) on which we have landed a human-made spacecraft (the Huygens probe, during the Cassini mission). Titan has a surface covered in pools of liquid hydrocarbons and shows evidence of frozen methane sand dunes. Jupiter also has a moon which has the greatest potential of all the other bodies in the solar system of harboring life due to a vast water ocean below an ice crust. Its name is. The Earth-Moon System The Moon is about % the size of Earth, and, like Earth, has a metallic core, and a silicate mantle and crust. We know the innermost part of the mantle is partially molten because it doesn't transmit S-waves generated by small moonquakes deep in the mantle. The surface is mostly composed of the igneous rock, which is mostly feldspar. The other rock type present is which forms the low-lying dark plains, called (singular: mare) which cover about 17% of the surface. They probably formed from partial melting of a silicate mantle, possibly during meteorite impacts. How did Earth s moon form? This happened about 4.6 to 4.4 billion years ago. A large portion of Earth's hot early mantle material was ripped away and coalesced and differentiated to form the Moon, which remained in orbit around the Earth. FINAL QUESTIONS: What s your favorite celestial body?! Your favorite class this semester was (pick from the following list): (a) Geol 101 5