A Journey to Our Planetary Neighbors Our Solar System A Journey to Our Planetary Neighbors

Ideas about the night sky have changed over time… Earth-centered model – early Greeks thought planets, Sun, Moon and stars rotated around the Earth Modern view – The sun is the center of our solar system All other objects in the solar system revolve around the sun in elliptical orbits at different speeds.

How did our solar system form? A nebula of gas, ice, and dust slowly formed in space, and rotated in space. The cloud began to contract and the matter was squeezed into less space. The cloud became dense, heated up and triggered a nuclear fusion reaction that created the sun.

What happened next? All leftover matter became the planets and asteroids The four inner planets – (Mercury, Venus, Earth, and Mars) are small and rocky with iron cores The four outer planets – (Jupiter, Saturn, Uranus, and Neptune) are large, lightweight, and composed of gases.

Inner Planets Mercury - closest to the Sun, smallest planet Many craters and high cliffs No true atmosphere so temperatures can range from -292 to 806° F. It orbits the sun once every 88 days and is an average of 36 million miles from the sun.

Inner Planets Venus – second from the sun and similar to the Earth in size and mass Mostly smooth volcanic plains Extremely dense atmosphere of clouds Carbon dioxide gas traps solar energy resulting in temperatures between 842 to 887° F. It is an average distance of 67 million miles from the sun and orbits every 225 days

Inner Planets Earth – third planet from the Sun More than 70 percent of surface is covered with water Atmosphere consists of several layers, is mostly composed of nitrogen and oxygen, and protects the surface from meteors and Sun’s radiation It is an average of 93 million miles away from the sun, and completes its orbit in 365.5 days

Inner Planets Mars – fourth planet from the Sun Called red planet because of iron oxide in rocks Polar ice caps made of frozen carbon dioxide and water Surface contains gullies, mountains and canyons, plains and the largest volcano in the solar system The thin atmosphere mostly contains carbon dioxide It is an average of 141 million miles from the Sun, and completes its orbit in 1.9 years

Asteroids and Other Objects in Our Solar System Asteroids – rocks similar to that which formed the planets Asteroid Belt – group of asteroids that orbit the Sun between the planets Mars and Jupiter

Comets Comet - dust and rock particles combined with frozen water, methane, and ammonia Halley’s comet (occurs every 76 years), Hale-Bopp (1995) Look similar to a dirty snowball The ice and dust vaporize as it approaches the sun This forms a comets tail

Meteoroid, Meteor, and Meteorite Meteoroid – small pieces of debris in space Meteor – small meteoroid that burns up in Earth’s atmosphere (falling or shooting star) Meteorite – meteoroid that strikes Earth

Outer Planets Jupiter – Fifth planet from the sun and the largest in our solar system Atmosphere mainly consists of hydrogen and helium Surface is suspected to be composed of liquid hydrogen and helium, and may have solid core at the center It is an average of 484 million miles from the sun and 11.8 years to complete one orbit Has 16 moons

Outer Planets Saturn – sixth planet from the Sun Thick outer atmosphere of hydrogen, helium, ammonia, methane, and water vapor Might have rocky core Rings that circle around planet are composed of ice and rock particles It is an average of 887 million miles from the Sun, and completes one orbit in 29.5 years

Outer Planets Uranus – seventh planet from the sun Atmosphere of hydrogen, helium, and methane Rotates on its side Contains thin, dark rings It is an average of 1.8 billion miles from the sun, and completes one orbit in 84 years

Outer Planets Neptune – eighth planet from the Sun Atmosphere is similar to that of Uranus Storms on Neptune reveal an active and rapidly changing atmosphere It is an average of 2.8 billion miles from the sun, and completes its orbit every 165 years