TOURING OUR SOLAR SYSTEM

1. CHAPTER 23 TOURING OUR SOLAR SYSTEM

2. The Solar System The sun is the hub of a huge rotating system of 8 planets, their satellites, and numerous smaller bodies. 99.85% of the mass of our solar system is contained in the sun. 0.15% of the mass of our solar system are the planets. The planets are as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

4. The Solar System Guided by the sun�s gravitational force, each planet moves in an elliptical orbit, and all travel in the same direction. The nearest planet to the sun, Mercury, has the fastest orbital motion at 48 kilometers/second (107 000 mph). 1 revolution around the sun takes 88 Earth days. The outermost planet, Neptune, has the slowest orbital motion at 5.3 kilometers/second (12000 mph). 1 revolution around the sun takes 248 Earth years.

5. The Solar System The planets fit into two groups: Terrestial Planets: Earth-Like (Mercury, Venus, Earth, and Mars) � also called inner planets. Jovian Planets: Jupiter-Like (Jupiter, Saturn, Uranus, and Neptune) � also called outer planets. Size is the most obvious difference between the terrestial and Jovian planets. Density, chemical makeup, and rate of rotation are other ways in which the two groups of planets differ.

7. The Solar System The substances that make up the planets are divided into three groups: Gases: Hydrogen and Helium � those with melting points near absolute zero (-273�C) Rocks: Mainly silicate minerals and metallic iron, which have melting points above 700�C. Ices: Include ammonia (NH3), methane (CH4), carbon dioxide (CO2), and water (H2O). They have intermediate melting points. The terestial planets are dense, consisting mostly of rocky and metallic substances, and only minor amounts of gases and ices. The Jovian planets contain large amounts of gases and ices, which accounts for their low densities. They also contain substantial amounts of rocky and metallic materials, which are concentrated at their cores.

8. The Solar System The Jovian planets have very thick atmospheres of hydrogen, helium, methane, and ammonia. The terrestrial planets have meager atmospheres at best. A planet�s ability to retain an atmosphere depends on its mass and temperature, which accounts for the difference between Jovian and terrestrial planets. Simply stated, a gas molecule can escape from a planet if it reaches a speed known as the escape velocity. Earth = 11 kilometers/second (25000 mph).

10. The Solar System Between the existing stars is �the vacuum of space.� Not really a vacuum, as it is populated with clouds of dust and gases. A cloud of dust and gas is space is called a nebula. A nebula often consists of 92% hydrogen, 7 percent helium, and less than 1% of the remaining heavier elements. For some unknown reason, these clouds begin to rotate slowly and contract gravitationally.

11. The Solar System Scientific studies of nebulae have led to a theory concerning the origin of our solar system. According to the nebular theory, the sun and planets formed from a rotating disk of dust and gases. As the speed of rotation increased, the center of the disk began to flatten out. Matter became more concentrated in this center, where the sun eventually formed.

12. The Solar System The growth of planets began as solid bits of matter began to collide and clump together through a process known as accretion. The colliding matter formed small, irregular shaped bodies called planetesimals. As the collisions continued, the planetesimals grew larger and eventually acquired enough mass to exert a gravitational pull on surrounding objects. In this way, they added still more mass and grew into true planets.

14. The Terrestrial Planets Mercury Innermost and second smallest planet. Absorbs most of the sunlight that strikes it � reflects only 6% back into space. Surface Features: Cratered highlands, smooth terrains, iron core, and very long scarps (deep slopes). One revolution around the sun takes 88 Earth-days. One rotation about its axis takes 59 Earth-days. Night lasts three months, followed by three months of daylight. Nighttime temperatures drop as low as -173�C, and noontime temperatures exceed 427�C. Mercury has the greatest temperature extremes of any planet.

16. The Terrestrial Planets Venus Second only to the moon in brilliance in the night sky. Named for the goddess of love and beauty. Referred to as Earth�s twin. Similar size, density, and mass. One revolution around the sun takes 225 Earth-days. One rotation about its axis takes 244 Earth-days. Daylight is about 117 Earth-days long. Covered in thick clouds (25 km thick) of sulfuric acid that visible light cannot penetrate. Radar images have confirmed that basaltic volcanism and tectonic activity shape it�s surface. About 80% of its surface consists of plains covered by volcanic flows. Scientists have identified 1000�s of volcanic structures. Surface temperatures reach 475�C. 97% of atmosphere is carbon dioxide.

18. The Terrestrial Planets Mars Known as the Red Planet because it appears as a reddish ball when viewed through a telescope. Most prominent telescopic features are its brilliant white polar caps. One revolution around the sun take 687 Earth-days. One rotation about its axis takes 24 hours, 37 minutes, and 23 seconds. Atmosphere is primarily made of carbon dioxide with tiny drops amounts of water vapor. Polar caps are made of water ice, covered by a thin layer of frozen carbon dioxide. Temperatures vary on Mars from -125�C near the pole of nearly 20�C near the equator. Average temperature = -60�C. Extensive dust storms occur and may cause the color changes observed from Earth. Hurricane force winds up to 270-km/hr can last for weeks. Has numerous large volcanoes. Olympus Mons is the largest at 23 kilometers high (it is about the size of Arizona and 2.5 times higher than Mount Everest. Has several large canyons. Valles Marineris is the largest and is much larger than the Grand Canyon. The composition and markings of some Martian rocks indicate that liquid water was once present on Mars�s surface.

20. The Outer Planets Jupiter 2.5 times the greater than the mass of all the planets and moons combined. One rotation on its axis takes 9 hours and 50 minutes. One revolution around the sun takes 12 years. Its most striking feature is its Great Red Spot. Great Red Spot = Cyclonic Storm Atmosphere = Hydrogen, Helium, with small amounts of Methane, Ammonia, and Sulfur compounds. Its wind systems create its light and dark-colored bands. Jupiter gives off twice as much heat as it receives from the Sun. It is thought to be a giant ocean of liquid hydrogen with metallic hydrogen in its interior, and a rocky/metallic core. Has 63 satellites (4 major moons): Io, Europa, Ganymede, and Callisto. Has rings composed of fine, dark particles. Thought to be from fragments blasted by meteorite impacts from the surfaces of Metis and Adrastea (two small moons).

22. The Outer Planets Saturn 1 Revolution = 29.5 Years 1 Rotation = 10 hours 14 minutes Atmosphere, composition, and internal structure are thought to be similar to Jupiter. Most prominent feature is its system of rings. Other features: Atmosphere is very active, winds up to 1500 km/hr. Large cyclonic storms similar to Jupiter�s Great Red Spot, although smaller. 31 natural satellites (Titan is its largest moon) Rings are composed of individual particles � �moonlets� of ice and rock � that circle the planet while regularly impacting one another.

24. The Outer Planets Uranus 1 rotation = 17 hours, 14 minutes 1 revolution = 84 years Known as the sideways planet because it rotates on its side. May have been altered by a giant impact. Has a ring system with at least 9 distinct ring belts. 25 satellites.

26. The Outer Planets Neptune 1 Rotation = 16 hours, 3 minutes 1 Revolution = 84 years Atmosphere much like Jupiter and Saturn. Winds exceeding 1000 km/hr encircle Neptune. Has a blemish called the Great Dark Spot that is reminiscent of Jupiter�s Great Red Spot. Assumed to be a large rotating storm. Has clouds of frozen methane that look like white cirrus-clouds. 13 known satellites (largest moon = Triton). Triton has the lowest surface temperature measured on any body in the solar system (-200�C). Has a ring system. Blue in appearance.

28. The Outer Planets Pluto No longer considered a planet (after 2005), now considered a �dwarf planet.� 1 rotation = 6.4 days 1 revolution = 248 years During its orbit around the sun, it travels inside the orbit of Neptune. 1 satellite (Charon). Average temperature -210�C, which is cold enough to solidify most gases. Described as a dirty ice-ball of frozen gases with lesser amounts of rocky substances.

30. Minor Members of the Solar System Asteroids A small, rocky body, which can range in size from a few hundred kilometers to less than a kilometer. Largest = Ceres is about 1000 km in diameter. Most asteroids lie between the orbits of Mars and Jupiter. Orbital periods of 3 to 6 years. Many have irregular shapes. Many impact craters on the moon and Earth were probably caused by collisions with asteroids. Future collisions will also occur.

32. Minor Members of the Solar System Comets They are pieces of rocky metallic materials held together by frozen gases, such as water, ammonia, methane, carbon dioxide, and carbon monoxide. Many travel in elongated orbits that carry them far beyond Pluto. Some take hundreds of thousands of years to complete a single orbit around the Sun. A few have orbital periods of less than 200 years. As a comet approaches the Sun, solar energy begins to vaporize the frozen gases and produces a glowing head called a coma. As they approach the Sun, some comets develop a tail that extends for millions of kilometers. A comet�s tail always points away from the Sun. Two solar forces contribute to the formation of a tail: Radiation Pressure: Pushes dust particles away from the coma. Solar Wind: Responsible for moving the ionized gases. Sometimes a single tail composed of both dust and ionized gases can be observed, but often there are two tails. As the comet moves away from the Sun, the gases recondense and the tail disappears. Most comets are believed to only be able to encounter a few hundred close orbits to the Sun before all the gases are expelled. The remaining material (metallic and stony particles) continue to orbit without a coma or tail.

33. Minor Members of the Solar System Comets originate from two regions: Kuiper Belt: Those with short orbital periods. Oort Belt: Those with long orbital periods. The most famous short-period comet is Halley�s comet. Orbital Period of 76 years. Next predicted appearance = 2061

35. Minor Members of the Solar System Meteoroids Small solid particles that travel through space (shooting stars). Originate from three sources: Interplanetary debris that was not gravitationally swept up by the planets during the formation of the solar system. Material from the asteroid belt. The solid remains of comets that once traveled near Earth�s orbit. A few fragments are believed to be fragments of the moon or Mars that were ejected upon asteroid impact. Most are the size of a grain of sand and vaporize before they reach Earth�s surface (meteors). Sightings can reach 60 or more per hour (meteor showers). Results when Earth encounters a swarm of meteoroids traveling in the same direction and at nearly the same speed as Earth. Perseid meteor shower occurs each year around August 12. When a meteoroid reaches Earth�s surface, it is called a meteorite. Most famous = Meteor Crater in Arizona (1.2 km across, 170 m deep, and rim rises 50 m above the surrounding countryside.