Planets

Our solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was considered a planet too, until 2006, when the International Astronomical Union proclaimed Pluto a dwarf planet. For a celestial object to be considered a planet it must orbit the sun, have enough mass for it's own gravity to shape into a sphere, and massive enough to clear other large objects from its orbit. Pluto is not massive enough to knock other objects out of its orbit, so it is considered a dwarf planet. Out of the eight planets in our solar system, the Greeks noticed five that really stand out. They named them after the Greek gods: Hermes, Aphrodite, Ares, Zeus, and Chronos. When the Romans conquered Greece, they renamed the planets: Mercury, Venus, Mars, Jupiter, and Saturn. They also named the new planets after their Roman gods. =Mercury:= Mercury is the closest planet to the sun. Mercury is very small and is not sen very well through a telescope. Barely anything was known about Mercury until 1973, when //Mariner 10// flew past it and sent back images that they took. //Mariner 10// discovered that Mercury has thousands of craters, many cliffs, and large dark plains on it's surface. It makes one trip around the sun every 88 Earth days. Mercury is the slowest moving planet, apart from Earth. It also has a slow gravitational pull. Mercury is so close to the sun that temperatures can reach 800˚F. At night, temperatures can reach -280˚F, because Mercury's atmosphere is very small so it cannot keep very much heat. Mercury rotates from west to east, and does not have a satellite. =Venus:= Venus is the second closest planet to the sun. It is also the closest planet to Earth, although we cannot see very much because Ve nus is surrounded by thick clouds. Venus is sometimes the brightest object in the sky, besides the sun and moon, because its clouds reflect the sun's light. Venus is the slowest moving planet. It rotates around the sun every 224.7 Earth days. Venus's atmosphere is mostly made up of carbon dioxide. The carbon dioxide keeps the heat from the sun in, so temperatures can be more than 800 ˚F! By using radar waves, scientists have learned that most of Venus is covered by plains and two main mountain ridges the size of small continents. Although, unlike Earth, Venus is made of one continental plate. Venus rotates from east to west, and does not have a satellite. =Earth:= The planet we live on is called Earth. Earth is the third closest planet to the sun. It completes one orbit in 365.25 days. Our atmosphere is very thin, and made up of nitrogen and oxygen. 29% of Earth is land, and 71% of Earth is water. Earth is always changing. Earth is very different now from when it was first formed. Earth is the only planet we know of that has life. Earth rotates from west to east, and has one satellite: the moon. =Mars:= Mars is the fourth closest to the sun. It is a small, rocky, and dry planet and looks reddish in the night sky. Also known as the Red Planet, it takes 687 Earth days to rotate around the sun. Mars has two satellites: Phobos(terror) and Deimos(fear). In Greek mythology, Phobos, and Deimos were the horses that pulled the chariot of Ares, the god of war. The gravitational pull of Mars is weaker than Earth's. Mars rotates from east to west. =Jupiter:= Jupiter is the fifth closest to the sun. Jupiter is the largest planet, and it takes 11.9 days to make a complete orbit around the sun. Cold-tipped clouds surround Jupiter, and the temperature at the tip of their atmosphere can reach -186 ˚F! Jupiter's gravitational pull is 1 and a half times more than Earth's! As far as we know, Jupiter has 63 satellites. The main ones are Ganymede, Callisto, and Europa. All of Jupiter's satellites are covered in ice and craters. =Saturn:= Saturn is the third farthest planet from the sun. It takes Saturn 29.5 Earth years to orbit around the sun. Saturn has 61 known satellites. The largest is Titan. Saturn has rings around it, which makes it one of the most beautiful planets in the sky. Saturn has a deep atmosphere that can range in temperature. The pressure around Saturn is one and a half times greater than Earth's. With it's soft appearance and majestic rings, it is many people's favorite planet. =Uranus:= The second farthest planet from the sun is Uranus. It takes 84 Earth years for this planet to make a complete orbit around the sun. Methane in Uranus's atmosphere makes the planet look blue and green. The tips of Uranus are warmer than the area around it's equator. This is because Uranus is tilted on it's side. This also causes Uranus to have winter and summer and day and night last up to 42 Earth years each!(Imagine living in winter or summer half of your life!) Uranus has 27 known satellites. The largest one is Titania. =Neptune:= Taking 165 Earth days to make a complete orbit around the sun, the farthest planet away from the sun is Neptune. Neptune is basically a large ball of gas surrounded by a thick atmosphere. Neptune has 13 known satellites and the largest is Triton. Neptune's atmosphere is made up of an ocean of water, methane, and ammonia. While temperatures at the oceans surface can reach 4500 ˚F, the temperatures in the upper atmosphere can reach -355˚F! =Astronomy Home= = =