Solar System Inner and Outer Planets
What is the solar system? Almost all of the specks of light you can see in the night sky are stars. A few of the tiny lights are part of our solar system. Stars are much farther away than objects in our solar system.
Objects in the Solar System The largest object in the solar system is the Sun, a star. Planets orbit the Sun and have nearly spherical shapes. The mass of a planet must be much larger than the total mass of all other objects whose orbits are close by.
Objects in the Solar System Mercury, Venus, Earth, and Mars are the inner planets. The inner planets are mostly solid, rocky material.
Objects in the Solar System Jupiter, Saturn, Uranus, and Neptune are the outer planets. The outer planets are mostly ice and gases, such as hydrogen and helium.
Concept Check Describe how the inner planets differ from the outer planets.
Objects in the Solar System A dwarf planet is a spherical object that orbits the Sun and is not a moon or another planet. Dwarf planets are in regions of the solar system where there are many objects orbiting nearby.
Objects in the Solar System Ceres, a dwarf planet, orbits the Sun as planets do.
Objects in the Solar System Millions of small, rocky objects called asteroids orbit the Sun in the asteroid belt between the orbits of Mars and Jupiter. Asteroids vary in size and are usually not spherical. A cometis made of gas, dust, and ice and moves around the Sun in an oval-shaped orbit.
Objects in the Solar System Distances between objects in the solar system are extremely large. Astronomers do not use meters or kilometers to describe these distances. A more convenient unit is used—the astronomical unit. One AU is Earth’s average distance from the Sun—about 150,000,000 km.
Objects in the Solar System It is easier to express very large distances using astronomical units rather than kilometers.
Concept Check Define what an astronomical unit is and explain why it is used.
The Motion of the Planets The time it takes an object to travel once around the Sun is its period of revolution. The time it takes an object to complete one rotation is its period of rotation.
The Motion of the Planets A planet’s orbit is an ellipse—a stretched-out circle. Focus points, or foci, determine the shape of the ellipse.
Concept Check Describe the shape of a planet’s orbit.
Summary The solar system contains the Sun, the inner planets, the outer planets, the dwarf planets, asteroids, and comets.
Summary An astronomical unit (AU) is a unit of distance equal to about 150 million km.
Summary The speeds of the planets change as they move around the Sun in elliptical orbits.
Inner Planets http://www.youtube.com/watch?v=3K8NLwr6gnM
Planets Made of Rock • Earth and the other inner planets—Mercury, Venus, and Mars—are also called the terrestrial planets. • Like Earth, the other terrestrial planets are made of rock and metallic materials and have a solid outer layer.
The inner planets are roughly similar in size, with Earth being about two and half times larger than Mercury.
Mercury • Mercury’s gravity is not strong enough to hold an atmosphere. • Mercury’s temperatures are as high as 450°C on the side toward the Sun and as low as –170° on the side away from the Sun. • Like all inner planets, Mercury has a core made of iron and nickel.
Venus is the second planet from the Sun and is about the same size as Earth.
Venus • The atmosphere of Venus is about 97% carbon dioxide. • The pressure of Venus’s dense atmosphere is 90 times greater than that of Earth’s atmosphere. • A thick layer of acid clouds covers Venus.
Venus • The greenhouse effect occurs when a planet’s atmosphere traps solar energy and causes the surface temperature to increase. • Because of its greenhouse effect, Venus is the hottest planet in the solar system, with an average temperature of about 460°C.
Concept Check Why is Venus hotter than Mercury?
Earth • A mixture of gases, including water vapor, make up Earth’s atmosphere and produce a greenhouse effect that raises its surface temperature. • A protective atmosphere, moderate surface temperatures, and the presence of liquid water support a variety of life on Earth.
Mars is the fourth planet from the Sun and is about half the size of Earth.
Mars • Images of Mars show features that might have been made by water, though no evidence of liquid water or life has been found. • The atmosphere of Mars is thin and made of about 95 percent carbon dioxide. • Temperatures on Mars range from about –125°C at the poles to about 20°C at the equator during the summer.
Summary • The terrestrial planets include Mercury, Venus, Earth, and Mars.
Summary • The inner planets all are made of rocks and minerals, but the characteristics of the planets are different. Earth is the only planet with water.
Summary • The greenhouse effect greatly increases the surface temperature of Venus.
Outer Planets http://www.youtube.com/watch?v=43SHCRv4wdw http://www.youtube.com/watch?v=pMfaCY3moHQ
The Gas Giants • The outer planets, also known as the gas giants, are primarily made of hydrogen and helium. • The outer planets are extremely massive. They apply strong gravitational forces. • The interiors of the outer planets are mainly liquid. • These gas giants generally have gas and liquid layers around a small solid core.
The outer planets are large compared to the inner planets. The size of Earth is shown for reference.
Concept Check How are the outer planets similar?
Jupiter is the largest planet in the solar system. • Jupiter has a diameter 11 times larger than the diameter of Earth.
Jupiter • Jupiter’s atmosphere is about 90 percent hydrogen and 10 percent helium. • The planet itself is about 80 percent hydrogen and 20 percent helium. • Jupiter is a ball of gas swirling around a thick liquid layer that conceals a solid core. Scientists are not certain what makes up the core.
Jupiter Describe what makes up each of Jupiter’s three distinct layers.
Jupiter • Jupiter has at least 63 moons, more than any other planet. • The four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto— are known as the Galilean moons. • The Galilean moons are made of rock and ice.
Saturn is the sixth planet from the Sun. It rotates rapidly and has horizontal bands of clouds.
Saturn • Saturn is mostly hydrogen and helium. • Saturn has an outer gas layer, a thick layer of liquid hydrogen, and a solid core. • Saturn has seven bands of rings, each containing thousands of narrower ringlets.
Saturn The ice particles in the rings are possibly from a moon that was shattered in a collision with another icy object. Describe what makes up Saturn and its ring system.
Saturn has at least 60 moons. Titan is the only moon in the solar system with a dense atmosphere. Cassini, Rhea, Iapetus, Dione, Tethys: NASA/JPL/Space Science Institute
Saturn titan from Greek titan, means “member of a mythological race of giants”
Uranus is the seventh planet from the Sun, with a system of narrow, dark rings and a diameter about four times that of Earth. NASA/ESA and Erich Karkoschka, University of Arizona
Uranus • Uranus has a deep atmosphere composed mostly of hydrogen and helium and a small amount of methane. • Beneath Uranus’s atmosphere is a thick, slushy layer of water, ammonia, and other materials. • Uranus has a tilted axis or rotation that might have been caused by a collision with an Earth-sized object.
Uranus Uranus has at least 27 moons. Identify the substances that make up the atmosphere and the thick slushy layer on Uranus.