The Inner Planets: A Review Sheet: Sun Mercury Venus Earth Mars The Sun and our Solar System: - Our solar system is a part of a galaxy called the Milky Way. - Our sun is a medium sized star, made mostly of hydrogen. It is 93 million miles away from us. - It makes up about 98% of the mass of our solar system. - It takes about 8 ½ minutes for light to reach us, once it leaves the sun’s surface. - Light travels at 186,282 miles per second. - The sun has dark spots on it, called “sunspots.” These are electromagnetic storms. Mercury: - Mercury is the closest planet to our sun. - It is named for the Roman god Mercury who was the god of commerce (money and trade), travel, and thievery. - It is the planet that travels fastest across our sky. - Mercury goes around the sun once every 88 “earth days” - It rotates so slowly, that it takes two “Mercury Years” for one day to pass. Venus: - Venus is known as Earth’s twin because they are the most similar in size. - It is about 7,520 Miles across or 12,100 km. This is known as its diameter. - This is only about 600 km smaller than Earth. - Venus is named for the Roman goddess of love and beauty. - It is the 2nd planet from the sun, and travels in a nearly circular orbit. - It takes 225 earth days to go around the sun. - Venus is almost always surrounded by thick clouds of sulphuric acid. Earth: - Our home planet and the 3rd planet from the sun. - It is home to more than 6.9 Billion people. - It is over 12,765 km across - Earth is the only planet whose English name doesn’t come from Greek/Roman mythology. It actually comes from a mix of old English and German. - It has many other names like Terra or Tellus. - Temperatures at the center Earth's of the core may be as high as 7500 K, hotter than the surface of the Sun. - 71 Percent of the Earth's surface is covered with water. Earth is the only planet in our Solar System with liquid water. Mars: - Mars is the furthest of the inner planets. It is the 4th planet from the sun. - Its day is only 37 minutes longer than ours. Its year is 687 “Earth days.” - Mars is named after the Roman god of war and is known as the “Red Planet.” - It has about as much land as all of our continents combined. - Olympus Mons, a Martian mountain is the biggest mountain in the solar system. - It is almost 3 times as big as Mount Everest. - Tharsis is a huge bulge on the Martian surface. - It is about 4000 km across and 10 km high. It is almost as wide as North America. - Valles Marineris is a canyon system like the Grand Canyon in the United States except that it is 4000 km long and ranges from 2 to 7 km deep. - Mars has 2 moons: Phobos (fear) and Deimos (panic) - They are named after the two horses that pulled Mars’ chariot. - They are only 10 and 17 miles across and are thought to be “captured asteroids.” The Asteroid Belt: - A rocky space object, which can be from a few hundred feet to several hundred km wide. Most asteroids in our solar system orbit the Sun in a belt between Mars and Jupiter. - They act like a perfect border between the inner (rock-based) planets and the outer (gas-based) planets. - Astronomers think Jupiter's gravitational force on the asteroids keeps them from smashing into the inner planets. The presence of Jupiter actually protects Mercury, Venus, Earth, and Mars from many asteroid collisions! - Even though the Sun also pulls on the asteroids, they are closer to Jupiter, so astronomers believe that Jupiter keeps asteroids from drifting towards the Sun as well. - The asteroid belt orbits the Sun in an oval shape and takes about 6 Earth years to go around once. - When an asteroid hits a planet, it can often leave a huge crater. Scientists believe that one example of this is a massive crater in the Yucatan Peninsula in Mexico..