The Solar System

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).

Orbits

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.

Chapter 23-3The Outer Planets

• Objectives:

• To describe the characteristics of the outer planets.

• To describe some of the largest moons of the Outer planets.

Solar System

Jupiter

• In 1979 Voyager 1 and Voyager 2 flew past Jupiter and found that it had faint dust rings and one moon had an active volcano.

• Galileo arrived in 1995.

• Cassini in 2000.

• New Horizons in 2007.

Jupiter

• Our sun contains 99.7% of all the matter in our solar system.

• Jupiter contains 70% of all the remaining matter in the solar system.

• Romans named this planet after the king of the Gods.

Jupiter-Almost a Star?

• The core reaches 30,000º C (5 times the surface of the sun).

• Some scientist hypothesize that if Jupiter had grown larger during formation, it would have become a star.

• Jupiter gives off more heat than it receives from the sun.

Atmosphere of Jupiter

• Jupiter is main primarily of hydrogen and helium gases with ammonia, methane and water.

• This atmosphere changes to a liquid hydrogen and helium ocean near the middle of the planet.

• Below this is what might be a rocky core.

Great Red Spot

• Continuous storms of swirling, high pressure gas have been detected on Jupiter.

• The greatest of these is called the Great Red Spot.

Moons of Jupiter

• At least 63 moons orbit Jupiter.

• The four largest moons are Gannymede, Europa, Io and Callisto.

Io

• Both Jupiter and Europa pull on Io causing it be the most

• Volcanically active moon in the solar system.

Europa

• Europa is composed mostly of rock with a thick smooth crust of ice. Under the ice might be an ocean as thick as 50 km. If it is water this is the only other place in the solar system, besides Earth, where liquid water exists. It has a thin oxygen atmosphere.

Ganymede

• Ganymede has a heavily cratered crust of ice covered with grooves. It has a rocky interior surrounding a molten iron core. It has a thin atmosphere.

Callisto

• Callisto is composed mostly of rock and ice.

• It has a heavily cratered surface , a rock core and a thin atmosphere of carbon dioxide.

Galileo

• Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003. Galileo was the first to measure Jupiter's atmosphere.

Galileo Probe

• Galileo (found evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of volcanic activity on Io.

• New Horizons arrived at Jupiter in 2007.

Saturn

• The Voyager probes studied Saturn inn 1980 and 1981. Cassini reached Saturn in 2004.

• It is the second largest planet in the solar system.

Saturn’s Atmosphere

• Saturn is a large gaseous planet. It has a thick outer atmosphere composed mostly of hydrogen and helium. The atmosphere also contains ammonia, methane and water vapor.

Saturn’s Atmosphere

• The atmosphere gradually changes to liquid as you go deeper into the atmosphere.

• Below the atmosphere and liquid layer, it may have a small rocky core.

Saturn – A World of Many Rings

• The Voyager and Cassini gathered information about the ring system. There are several broad rings. Saturn has seven major rings (A-G).

• Each ring is made of tiny ringlets made or ice and rock particles.

Moons of Saturn

• Saturn has 47 known moons. The largest moon , Titan, is larger than Mercury.

• Cassini delivered the Hyugens probe to study the atmosphere of Titan and found it composed of nitrogen, argon and methane.

Saturn

• It is the least dense planet.• Saturn spins so fast, it flattens at the poles

and bulges at the equator.

Uranus

Uranus – A Planet on its Side

• Uranus named for the father of Saturn, was discovered by Sir William Herschel in 1781.

• The axis of Uranus is tilted at a 98 degree angle. Uranus has 11 thin, dark rings and 27 known moons.

• Uranus’ largest moon, Titania has many deep valleys. The valleys indicate that the moon was reshaped by some force after formation.

Atmosphere of Uranus

• The atmosphere of Uranus is composed of hydrogen, helium and some methane.

• The methane gives the planet a bluish-green color because methane absorbs the red and yellow light while the clouds reflect the green and blue light.

• Scientists think that under the atmosphere of Uranus it is mainly rock and ice. There is no separate core.

Voyager 2

• Voyager 2 studied Uranus and found the methane in the atmosphere gives it a bluish appearance.

Neptune - the Mathematician’s Planet

• Mathematicians predicted the location of Neptune as early as 1845.

• It was discovered in 1846.

• Neptune was named for the Roman god of the sea.

Characteristics of Neptune

• Neptune, like Uranus, is covered by clouds of hydrogen, helium and methane and has a bluish appearance.

• The disappearance and reappearance of the Great Dark Spot on Neptune in images from the Hubble show that the atmosphere changes rapidly.

• Voyager found Neptune to have 13 moons and 5 rings. Triton, Neptune’s largest moon, orbits in a retrograde pattern.

• Under its atmosphere, Neptune has a mixture of rock and ice made of methane and ammonia. It probably has a rocky core.

Triton – a moon of Neptune

Dwarf Planets

• There are five dwarf or minor planets, Pluto, Ceres, Eris, Makemake and Hamauea.

Pluto – a Dwarf Planet

• When discovered, Neptune did not orbit as predicted. Although astronomer Percival Lowell predicted the existence of Pluto in the early 1900’s, it was not located until 1930.

• Pluto was named for the Roman god of the underworld.

Moons of Pluto

• Pluto has three moons, Charon, Hydra and Nix.

Reclassification of Pluto

• A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape, and (c) has cleared the neighbourhood around its orbit.

• Pluto is considered a dwarf planet because it does not clear the neighborhood.

Other Dwarf Planets

• Ceres is a dwarf planet with a diameter of 940 km in the asteroid belt.

• Eris, another dwarf planet, is slightly larger than Pluto. It has a very elliptical orbit that varies between 38 and 98 AU from the Sun. It has one moon.

• Makemake is the third largest dwarf planet. It orbits outside of Neptune.

• Hamuea is in the Kuiper Belt.

Other Objects in the Solar System

Chapter 24-4• Objectives:

• To describe the other objects that orbit the sun, comets, asteroids and meteoroids.

• To describe how comets change as they approach the Sun.

• To explain how objects from space sometimes impact the Earth.

Composition of a Comet

• The core of a comet is called the nucleus.

• The cloud of dust surrounding the nucleus is called the coma. Together they form the head.

• The solar wind of the sun blows the coma outward into a long tail. The tail of an incoming streams behind, an outgoing streams in front.

Comets

• When a comet melts, some of the rocks fall into space and become meteoroids.

• Most of 100,000 comets in the solar system orbit over and over.

• Halley’s comet returns every 75-79 years. Some take thousands of years.

Oort Cloud

• The Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun.[a][1]

• Sometimes the comets in the Oort Cloud are pulled toward the sun. As they near the sun, they begin to melt which forms a cloud around its core.

Comet Hale-Bopp

• Hale-Bopp was discovered in 1995 as it approached the sun. It was larger than most comets and very bright.

Kuiper Belt

• The Kuiper belt rhyming with "viper"),[1] is a region of the Solar System beyond the planets extending from the orbit of Neptune (at 30 AU) to approximately 55 AU from the Sun.[2] It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive.[3][4] Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. While the asteroid belt is composed primarily of rock and metal, the Kuiper objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water.

Meteoroids, Meteors and Meteorites

• When the meteoroids fall into our atmosphere and rub against the gases, friction causes it to burn, producing a streak of light known as a meteor or shooting star.

• Those that strike earth are called meteorites. They can cause craters such as Barringer Crater in Arizona.

The Asteroid Belt

• Asteroids are made of rock, metal or a combination of the two. NEAR (2000) spacecraft went to the asteroid Eros to collect samples.

• It is believed this matter did not form a planet due to the strong gravitational pull of Jupiter.

Death of Dinosaurs?

• One theory states that the collision of a huge asteroid 65 million years resulted in the extinction of dinosaurs and almost 90% of all other life on Earth.

• It is believed the force of the collision was 10,000 times greater than the force of all nuclear weapons on Earth.

The Asteroid Belt

Exploring Asteroids

• The Near Earth Asteroid Rendezvous (NEAR) occurred in 2000 when a spacecraft went in to orbit around the asteroid 433 Eros and gathered data. The data showed that Eros has many craters and is similar to meteorites on Earth.

• The Japanese probe, Haryabusa arrived in 2005 to collect samples.