Ideas About the Solar System • Chapter 24-1 • Objectives: • Compare models of the solar system. • Explain that gravity holds planets in orbits around the sun.
Ptolemy • In the second century AD, the Greek scientist Ptolemy proposed a theory that placed Earth at the center of the universe. • He also proposed that all objects in the sky traveled in orbits around an unmoving Earth.
Orbits • He also proposed that all the orbits were circular. • His model included the Earth, the Moon, the Sun and five planets, mercury, Venus, Mars, Jupiter and Saturn.
Nicolaus Copernicus • Between 1500 and 1530 the Polish astronomer Copernicus developed a new theory about the solar system, that the Earth and the other planets revolved around the sun. • He stated that each planet took a different amount of time to complete their revolution in a perfect circle.
Copernican Theory • He also stated that the daily movement of the planets and stars was caused by the Earth’s rotation. • This is known as the sun centered theory.
Galileo • Galileo Galilei gave support to Copernicus’ theory. • He observed that Venus went through phases like the moon. This could only be explained if Venus were orbiting the Sun.
Modern View of the Solar System • As of 2006, the solar system is made up of eight planets and many smaller objects that orbit the Sun. • The distances between planets and the Sun are measured in astronomical units (AU).
Solar System • The Sun contains 99.86% of the mass in the Solar System. • The Sun’s gravity holds the planets and other objects in their orbits.
The Nebular Theory • The solar system began as a huge cloud of ice, dust and gas, which later condensed to form the sun and its planets.
Nebular Theory of Formation • A nearby super massive star exploded in a supernova. • The shock waves from the explosion caused the nebula to begin to spin in a counterclockwise direction. (b)
The Sun Forms First • It began to spin faster and the most of the matter moved to the middle. As it continued to spin, it became very hot and when fusion began our sun was born. (c)
Planetesimals • As particles collide with each other the clump together to form planetesimals in the swirling disk. (c)
The Planets Form • Because of their greater gravitational attraction, the larger planetismals begin to collect the dust and gas. (d) • Smaller planetismals collide with the larger ones and the planet begin to form. (e)
The Asteroid Belt Some of the matter was not able to pull together and formed the pieces of the asteroid belt. • The matter that was left formed moons that began to orbit the planets.
Inner Planets • The planets near the sun became so hot, most of their gases burned boiled away. • The inner, hotter planets were left as collections of metal and rock. • The inner planets are Mercury, Venus, Earth and Mars.
The Gas Giants • The planets farther from the sun were less affected by the sun’s heat. • They retained their gases and grew to enormous sizes. • The gas giants are Jupiter, Saturn, Uranus and Neptune.
Motions of the Planets • The Greeks noticed that although the stars appeared to move across the night sky, their position relative to each other was constant. • The Greeks also noticed that some of the stars appeared to wander among the other stars. • The Greeks called these objects, planets, or wanderers.
Johannes Kepler • The sixteenth-century German mathematician and astronomer Johannes Kepler discovered something new. He proposed that the planets orbit in an ellipse, or oval orbit (egg shaped).
Sir Isaac Newton • Newton proposed that the elliptical orbit is caused by two factors: gravity and inertia. • Inertia causes the planet to move in a straight line. • Gravity pulls the planet toward the sun. • When the two combine, the planet moves in an elliptical orbit.
Period of Revolution • A planet’s period of revolution, or time it takes to orbit the sun, is called a year on that planet. • The time it takes a planet to complete one rotation is called its period of rotation.
The Inner PlanetsChapter 24-2 • Objectives: • To describe the main characterisitics of the inner planets. • To compare and contrast the inner planets and the outer Planets.
Mercury • Mercury was named for the Roman god.
Mercury –Faster than a Speeding Bullet • Mercury moves quickly around the sun at the pace of 48 km per second and was named after the speedy messenger of the Roman gods. • Mercury rotates 3 times for every 2 revolutions. Sunrise occurs every 175 Earth-days making it one of the hottest and coldest planets in the solar system.
Exploration of Mercury • Mariner 10 flew by Venus and Mercury in 1973-1975 and sent back images. • It photographed 45% of the surface. • It has many craters and cliffs as high as 3 km. • It has a weak magnetic field.
Current Mission • Messenger began a flyby of the planet in 2008 and an orbit in 2011. • It is currently mapping Mercury.
Theory about Mercury • Some scientists hypothesize that Mercury’s crust solidified while the iron core was still molten and hot. A • As the core began to solidify, it contracted and cliffs resulted.
Atmosphere of Mercury • Because of Mercury’s low gravitational pull, most of the gases that could have formed an atmosphere have escaped into space.
Venus – Greenhouse in the Sky • Venus was named for the Roman goddess of beauty and love. • Venus rotates east to west, retrograde rotation. • Venus has a toxic atmosphere that is mostly carbon dioxide.
Exploration of Venus • Astronomers believed Venus to be the twin of Earth until explored by the Soviet spacecraft Venera. Venera landed but stopped working after an hour due to the extreme temperature and pressure.
Exploration of Venus • Pioneer Venus Mariner 2 (1962), and Mariner 5 (1967) which found land forms due to once active volcanoes. Clouds are made of sulfuric acid. The atmosphere is very thick.
Magellan • Between 1990 and 1994, the U.S. Magellan prove used radar to map the surface.
Venus • In early days, the sun was cooler and Venus may have had oceans. (Remains of coastline and beds can still be detected.) • As sun grew hotter, the water evaporated into the atmosphere.
Greenhouse Effect • Clouds on Venus are so dense only a small percentage of sunlight that strikes the top of the clouds reaches the surface. • Much of the heat is absorbed by carbon dioxide in the atmosphere. • Water vapor and later carbon dioxide in the atmosphere created a greenhouse and made the planet very hot (475ºC).
Earth • The distance from Earth to the Sun is 93 million miles or 150 million km or 1 astronomical unit. • Unlike the other planets, Earth has liquid water and supports life.
Mars • Mars was named after the Roman god of war because the planet looked bloody. • The two moons are Phobos and Deimos, fear and terror.
Mars – the Rusty Planet • Mars known as the rusty planet because it appears reddish. The reddish appearance is due to the iron oxide in the soil. • Other features visible from earth are the polar caps, made of frozen water covered by frozen carbon dioxide.
Mars • The temperature difference between day and night produces strong winds. • Since the atmosphere is so thin, Mars temperature always stays below 0 degrees C.
Olympus Mons • Mariner 9 (1971) discovered the largest volcano in the solar system, Olympus Mons. It is probably extinct.
Discoveries on Mars • Mariner 9 also found long channels that might have been formed by flowing water. • Large rift valleys were also found on the surface. • Valles Marineris is shown at right.
Viking Probes • Viking I and II landed on Mars in 1976. Each consisted of an orbiter and a lander. • They analyzed the soil found that soil is covered in iron oxide. • They found no evidence of life.
Pathfinder • The Mars Pathfinder carried a robot named Sojourner to test samples of the rocks and soil. • The data showed that the iron may have been leached out by groundwater.
Global Surveyor • Cameras on Global Surveyor showed features that looked like sediment gullies and deposits formed by running water.
Odyssey and Mars Exploration Rover • In 2002, Mars Odyssey began orbiting Mars. • It measured elements in the crust and searched for water. • It detected high levels of hematite a mineral that forms in water near the poles.
Odyssey and Mars Exploration Rover • Odyssey also relayed information to Earth from the Mars Exploration Rovers Spirit and Opportunity in 2004. • They confirmed that there were once bodies of water on the surface.
Mars Atmosphere • The Viking and Global Surveyor probes analyzed gases in the atmosphere and determined that the atmosphere is much thinner than earth. • It is mostly carbon dioxide with some nitrogen and argon. • Surface temperatures range from -125º to 35º, resulting in strong winds and dust storms.
Seasons on Mars • Mars axis tilt is 25º which is close to Earth’s. Mars goes through seasons like the Earth. • The polar ice caps change with the season. Frozen carbon dioxide changes to gas in summer.
Moons on Mars • Mars has two small irregularly shaped moons, Phobos (25km) and Deimos (13 km). • Phobos orbits every 7 hours. Deimos orbits every 31 hours.
Phobos and Deimos • Deimos is the outer moon. It is one of the smallest moons in the solar system. It is smoother than Phobos. • Phobos has many craters such as Stickney Crater.