Chapter Introduction Lesson 1 The Structure of the Solar System Lesson 2 The Inner Planets Lesson 3 The Outer Planets NASA/JPL/USGS Lesson 4 Dwarf Planets and Other Objects Chapter Wrap-Up Dwarf Planets and Other Objects • What is a dwarf planet? • What are the characteristics of comets and asteroids? • How does an impact crater form? Dwarf Planets According to the International Astronomical Union (IAU), a dwarf planet is an object that orbits a star and has enough mass and gravity to pull itself into a spherical shape. Dwarf Planets (cont.) • Unlike a planet, a dwarf planet has objects similar in mass orbiting nearby or crossing its orbital path. • Ceres is the smallest dwarf planet with a diameter of about 950 km. • Pluto is so far from the Sun that it takes about 248 years to complete one orbit. • Eris is the largest dwarf planet. All of the dwarf planets are smaller than Earth’s moon. Pluto: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA Ceres: NASA, ESA, and J. Parker (Southwest Research Institute) Eris: NASA, ESA, and M. Brown (California Institute of Technology) Most asteroids orbit the Sun in the asteroid belt between the orbits of Mars and Jupiter. Asteroid: NASA/JPL/JHUAPL Ida: NASA/JPL/USGS Vesta: Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University), NASA/ESA Eros: NASA/Goddard Space Flight Center Scientific Visualization Studio Asteroids • Asteroids are chunks of rock and ice that never clumped together to form a planet. • Some astronomers think the strength of Jupiter’s gravitational field might have caused the chunks to collide so violently that they broke apart instead of sticking together. Comets are mixtures of rock, ice, and dust. Comet: Roger Ressmeyer/Getty Images Wild 2: NASA/JPL-Caltech Comets • The particles in a comet are loosely held together by the gravitational attractions among the particles. • Comets orbit the Sun in stretched out elliptical orbits. • The solid, inner part of a comet is its nucleus. • As a comet moves closer to the Sun, it heats up and can develop a bright tail. Meteoroids • A meteoroid is a small rocky particle that moves through space. • A meteor is a streak of light in Earth’s atmosphere made by a glowing meteoroid. Meteoroids (cont.) • A meteorite is a meteoroid that strikes a planet or a moon. • An impact crater is a round depression formed on the surface of a planet, moon, or other space object by the impact of a meteorite. • An asteroid, such as Ida, is a chunk of rock and ice that orbits the Sun. NASA/JPL/USGS • Comets, which are mixture of rock, ice, and dust, orbit the Sun. A comet’s tail is caused by its interaction with the Sun. Roger Ressmeyer/Getty Images • When a large meteorite strikes a planet or moon, it often makes an impact crater. Which term refers to chunks of rock and ice that never clumped together to form a planet? A. meteoroid B. meteor C. comet D. asteroid Which is a round depression formed on the surface of a planet, moon, or other space object by the impact of a meteorite? A. coma B. impact crater C. meteor D. meteoroid Which objects orbit the Sun in stretched out elliptical orbits? A. asteroids B. comets C. meteoroids D. meteors Do you agree or disagree? 7. Asteroids and comets are mainly rock and ice. 8. A meteoroid is a meteor that strikes Earth.