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Earth / Environmental Science Ch. 23 – Touring Our Solar System THE SOLAR SYSTEM • • • Every planet travels in the same direction, and moves in an elliptical orbit Mercury is the closest planet to the Sun Pluto is the farthest planet from the Sun The Planets: An Overview • • • Terrestrial planets - relatively small and rocky (Mercury, Venus, Earth, Mars)- also known as the inner planets Jovian planets - huge gas giants (Jupiter, Saturn, Uranus, Neptune)also known as the outer planets (and Pluto) Terrestrial and Jovian planets differ by size, density, chemical makeup and rates of rotation. The Interiors of the Planets • • • Substances that make up the planets are divided into 3 groups: 1. The gases- hydrogen and helium- have melting points near absolute zero 2. The rocks- mainly silicate minerals and metallic iron- melting point above 700 degrees Celsius 3. The ices- include ammonia, methane, carbon dioxide and water Terrestrial planets are dense and mostly rocky and metallic substances Jovian planets contain large amounts of gases and ices The Atmospheres of the Planets • • • • • Jovian planets have thick atmospheres (hydrogen, helium, methane, ammonia) Terrestrial planets have little atmosphere A planet’s ability to retain an atmosphere depends on it’s mass and temperature More massive terrestrial planets (Earth, Mars, Venus) hold heavy gases Jovian planets have greater surface gravities Formation of the Solar System • • • Nebula- a cloud of dust and gas in space A nebula is made of 92% hydrogen, 7% helium, and less than 1% of remaining heavier elements The Nebular Theory states that the sun and planets formed from a rotating disk of dust and gases Planetesimals • • Planetesimals- small, irregularly shaped bodies The growth of planets began as solid bits of matter collided and clumped together through a process called accretion THE TERRESTRIAL PLANETS Mercury: The Innermost Planet • • • • • Mercury is the innermost and second smallest planet (hardly larger than Earth’s moon) Has cratered highlands, smooth terrains, and deep slopes One full rotation of Mercury takes 59 Earth-days, therefore, one night on Mercury lasts about 3 months Temperatures drop to about –173o Celsius at night and reach 427 o Celsius during noontime Mercury has the greatest temperature extremes of any other planet Venus: The Veiled Planet • • • • • • • • Named for the goddess of love and beauty Orbits around the sun every 255 Earth-days Similar to Earth in size, density, mass and location in the solar system Covered in thick clouds that cannot be penetrated by visible light Venus’ surface is shaped by basaltic volcanism and tectonic activity About 80% of the surface consists of plains covered by volcanic flows and 8% consists of highlands that might be similar to the ones on Earth Tectonic activity may be driven by upwelling and downwelling of materials in the planet’s interior The temperature reaches 475 o Celsius and the atmosphere is 97% carbon dioxide Mars: The Red Planet • • • • • • • • Known as The Red Planet because it looks like a reddish ball when seen through a telescope The atmosphere has 1% the density of Earth’s, and many dust storms occur even though it has a thin atmosphere Has hurricane-force winds up to 270 km per hour that can go on for weeks There are many canyons that are much bigger than the Grand Canyon There are many giant volcanoes, one is about the size of Ohio The first spacecraft that orbited Mars found many large volcanoes, about the size of Ohio There was evidence of liquid water found on the planet Temperatures range from –70 degrees Celsius to –100 degrees Celsius THE JOVIAN PLANETS The Outer Planets- Jupiter • • • • • • • • • • Jupiter’s mass is 2½ times greater than the mass of all of the other planets and moons combined Rotates more rapidly than any other planet Atmosphere is made of hydrogen and helium (contains small amounts of methane, ammonia, water and sulfur compounds) The interior heat of Jupiter produces huge convection currents in the atmosphere Is thought to be a gigantic ocean of liquid hydrogen Has 28 discovered moons Galileo discovered the 4 largest moons One of the moons, Io, is one of the three volcanically-active bodies in our solar system The planet’s rings are made of fine, dark particles The rings are thought to be fragments dispersed by by meteorite impacts from the surfaces of Metis and Adrastea, two small moons of Jupiter. Saturn • • • • • • • Almost twice as far from the sun as Jupiter The first rings found on Saturn were discovered by Galileo Saturn has very strong winds and big cyclone storms Saturn has seven rings that are all made of different individual particles The 2 main rings contain particles called “moonlets” that are very thin and collide as they orbit the planet Saturn’s satellite system contains 31 moons Titan is the largest moon (second biggest in the solar system) and is bigger than the planet Mercury Uranus • • • Uranus’ axis of rotation lies almost parallel of its orbit, instead of lying perpendicular Has 9 distinct ring belts Has long, deep canyons and linear scars Neptune • • • • Has very strong winds (over 1000 kilometers per hour) Has a large, rotating storm called the Great Dark Spot Contains cirrus-like clouds over the main cloud deck Triton is the largest of Neptune’s 13 moons Pluto • • • • About 40 times farther from the sun than Earth It takes around 248 Earth-years to orbit the sun Has a diameter of about 2300 kilometers, which makes it the smallest planet The average temperature is –210 degrees Celsius MINOR MEMBERS OF THE SOLAR SYSTEM Asteroids: Microplanets • • • • Asteroids are small rocky bodies that have been likened to “flying mountains” Most asteroids lie between the orbits of Mars and Jupiter Some asteroids travel near the sun and some travel near the Earth Many asteroids have irregular shapes Comets • • • Comets are pieces of rocky and metallic materials held together by frozen gases(such as ammonia, water, methane, carbon dioxide and carbon monoxide) Travel in elongated orbits Take hundreds of thousands of years to complete a single orbit around the sun Coma • • • • A coma is a fuzzy, gaseous component of a comet’s head A small glowing nucleus can be detected in a coma Radiation pressure and solar wind contribute to the formation of a coma As comets move away from the sun, the gases forming a coma recondense Kuiper Belt, Oort Cloud and Halley’s Comet • • • • • • • Short orbital periods are thought to orbit in a region called the Kuiper belt Most Kuiper belt comets move in almost circular orbits A spherical shell around the solar system is called an Oort cloud Tiny portions of oort clouds pass into the inner solar system The most famous short-period comet is Halley’s comet Its orbital period is about 76 years Halley’s comet developed a tail about 1.6 million kilometers long Meteoroids • • • • • • • • A meteoroid is a small solid particle that travels through space Most meteoroids from one of 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 The meteoroids that do not enter Earth’s atmosphere and burn up are called meteors Meteor sightings are also known as meteor showers A meteoroid that actually reaches Earth’s surface is called a meteorite