Our solar system Solar system My topic today is our solar system, especally the planets. 1. Solar system What is the solar system? It is our sun and everything that travels around it. Our solar system is elliptical in shape. That means it is shaped like an egg. The Sun is in the center of the solar system. Our solar system is always in motion. Nine known planets and their moons, along with comets, asteroids, and other space objects orbit the Sun. The Sun is the biggest object in our solar system. It contains more than 99% of the solar system's mass. Astronomers think the solar system is more than 4 billion years old. 2. The Sun 44424llz94iep5b The sun is the star at the center of the solar system. It formed about 5 billion years ago from a huge cloud of gas and dust. About 109 Earths would fit across the face of the sun! One large sunspot could hold several Earths. The sun's diameter is 864 thousand miles. Most of the mass in the solar system is in the sun (99%). The sun spins on its axis from left to right. It takes about 26 days for the sun to spin one time. The sun's outer atmosphere is called the corona. Its inner atmosphere is called the chromosphere. Below the photosphere are the convective zone, the radiative zone, and the core. The sun's core converts 700 million tons of hydrogen gas into 695 million tons of helium gas every second. The remaining 5 million tons of matter is converted to pure energy. That 5 million tons is about 600 times the amount of water flowing over Niagara Falls in one second. The temperature at the sun's core is 15 million degrees (K). Although sunspots are very hot, they are slightly cooler than the rest of the photosphere so they look darker. Sunspots have a dark center called the Umbra and a lighter ring around the outside called the Penumbra. It takes 50 million years for the energy formed deep inside the sun to reach Earth. Earth only gets one-billionth of the total energy produced by the sun. Light, traveling at 186 thousand miles per second, takes just over 8 minutes to reach Earth from the sun. Apollo was both the Greek and Roman god of the sun. He brought life-giving heat and light to Earth and was the patron god of musicians and poets. 3. Planets 3.1 Mercury Mercury is the closest planet to the sun. Its average distance from the sun is 36 million miles. Mercury is about 3,030 miles (4,878 km) across. That makes it the second-smallest planet in the solar system; only Pluto is smaller. In fact, Mercury is just a little bigger than Earth's moon. It's also covered with craters just like the moon. Mercury's year (the time it takes to orbit the sun one time) is 88 Earth days long, but one day (the time it takes to rotate from sunrise to sunrise) is 176 Earth days long. Because Mercury is so close to the sun, it has the smallest orbit of all the planets. That means it goes around the sun very quickly (88 Earth days or about 3 Earth months). Although Mercury goes around the sun quickly, it spins very slowly on its axis. For every year on Mercury, the planet spins 1 1/2 times (about 59 Earth Days or 2 Earth months). But while Mercury is slowly spinning, it is still speeding its way around the sun. Mercury has to spin another 1 1/2 times for the sun to rise over the same spot. That means one day (sunrise to sunrise) on Mercury is about 6 Earth months long, and that's twice as long as Mercury's year! So every day on Mercury means 2 years! Mercury has a very, very thin atmosphere of helium and hydrogen. On Mercury you would either freeze or roast. The highest surface temperature is 870°F, while the lowest temperature is –300°F. Scientists who study the planets have found ice at Mercury's poles. Like Earth's moon, Mercury is covered with craters. At one time, Mercury may have had volcanoes. Scientists believe that Mercury has a very thin crust, followed by a rocky layer, with a metallic core, probably made of iron, at its center. To escape Mercury's gravity you have to travel at 9,600 miles per hour. Because Mercury moves so fast around the sun, early Roman sky watchers named it after their speedy-messenger god. To the ancient Greeks, Mercury is identified with the god Hermes. .2 Venus Venus is the second planet from the sun. Its average distance from the sun is 67 million miles. Sometimes called Earth's sister planet, Venus is slightly smaller than Earth. It's also our closest neighbor at about 25 million miles away from Earth. Venus is hot enough to melt lead. Its surface temperature can get close to 900°F. This makes Venus the hottest place in the solar system after the sun. After the sun and moon, Venus is the brightest object in the sky. Because its thick clouds reflect most of the light Venus gets from the sun, the planet looks like a very bright star in the morning (just before sunrise) or evening (just after sunset) sky. The surface of Venus is covered with craters, mountains, volcanoes, and lava plains. Maxwell Montes is the highest point on Venus. It is more than 7 miles high. Standing on Venus would be like standing in a shallow bowl. The atmosphere is so thick and heavy that it bends light, making the ground appear to curve upward in all directions. The planet's atmosphere is 90 times heavier than Earth's. Venus has sulfuric acid clouds. Its atmosphere is mostly carbon dioxide (96%), nitrogen (3.5%), and carbon monoxide, argon, sulfur dioxide, and water vapor (all less than 1%). It takes 225 Earth days for Venus to go around the sun one time. Venus spins on its axis once every 243 Earth days, but it spins in the opposite direction of Earth. On Venus, the sun rises in the west and sets in the east. To escape Venus's gravity you have to travel at 23,300 miles per hour. Venus was identified with the Roman goddess Aphrodite, the goddess of love and beauty. To the ancient Mayans, Venus was the patron planet of warfare called Kukulcan. 3.3 Earth Earth is the third planet from the sun, which is about 93 million miles away. From space, Earth looks like the blue water world it is. About 70% of Earth's surface is covered with water, and 97% of all that water is in the salty oceans. Only 3% of Earth's water is freshwater, the water we drink. Earth's atmosphere is a mixture of gasses that become thinner as we move away from the planet toward space. Most of the atmosphere is nitrogen (78%), oxygen (21%), argon and other gases (1%). Some of the oxygen in Earth's atmosphere has changed over time to form ozone. Earth's high ozone layer filters out the sun's harmful ultraviolet rays, protecting the creatures living on the surface. But too much ozone helps trap the sun's infrared rays. Infrared radiation is heat radiation. It is the warmth you feel when the sun shines on you. If too much heat is trapped in Earth's atmosphere, surface temperatures will rise. This is called the “greenhouse” effect and it's what makes Venus so hot. Earth goes around the sun in 365 and 1/4 days. Every 4 years that 1/4 day adds up to one whole day and we add a day to the end of February, creating a leap year. It takes only 24 hours (1 day) for Earth to spin on its axis one time. Earth is covered with mountains, volcanoes, lakes, rivers, and oceans. Most of the surface material is made of rocks high in silica, iron, and magnesium. The highest point on Earth's surface is Mount Everest on the border of Nepal and China at 29,035 feet (8,850 meters). Earth's average surface temperature is 45°F. To escape Earth's gravity you have to travel at 25,000 miles per hour. Earth has a diameter of 7,926 miles. 3.4 Mars Mars is the fourth planet from the sun. Its orbit is roughly 142 million miles from the sun. The planet's reddish color is caused by rust (iron oxide) in the soil. Mars is the planet most like Earth. It takes 687 Earth days (about 2 Earth years) for Mars to go around the sun one time, and Mars spins on its axis at about the same speed as Earth does. It takes 24 hours and 37 minutes (about 1 Earth day) for Mars to rotate one time. Mars has the largest canyon (Valles Marineris), and the highest volcano (Olympus Mons) in the solar system. If Valles Marineris were on Earth, it would span the United States, from New York on the East Coast to California on the West Coast. It is about 1,300 miles long, 310 miles wide, and about 5 miles deep. Olympus Mons is nearly 3 times higher than Mount Everest. It rises above the Martian surface more than 82 thousand feet. This giant volcano's base is the size of Missouri. There are also lots of channels on Mars, and they look like Earth's river channels. Most scientists believe water once flowed on the martian surface, but new studies suggest there may still be water in some places on the surface. The lowest surface temperature on Mars is –190°F, while the hottest temperature is 90°F. To escape the gravity of Mars, you have to travel 11,200 miles per hour. Mars is about 4,212 miles in diameter. The martian atmosphere is very thin and made of carbon dioxide (95%), nitrogen (3%), argon and other gases (1%). The polar ice caps on Mars are made of frozen carbon dioxide or dry ice. Mars has two potato-shaped moons, Phobos is about 17 miles long and Deimos is about 9 miles long. Because the Red Planet's color reminded ancient astronomers of blood, they named the planet after their gods of war. Mars was the Roman god of war. The planet's two moons also have names that relate to war. Phobos means fear, and Deimos means panic. 3.5 Jupiter Jupiter is the fifth planet from the sun. Its orbit is about 483 million miles away from the sun. That's 5 times farther than Earth! Jupiter would fit 11 Earths across its face. It is the biggest planet in the solar system, and has a diameter of 88,846 miles. It takes Jupiter 12 Earth years to go around the sun one time. So on your twelfth birthday, Jupiter is in roughly the same place of the solar system as it was on the day you were born. Although Jupiter takes a long time to go around the sun, it takes only 10 hours to spin on its axis one time. That's less than half the time it takes Earth to spin once. Jupiter has a thin, faint ring. The average temperature at the top of Jupiter's clouds is –244°F. Jupiter's atmosphere is made mostly of hydrogen (86%) and helium (14%). The colorful cloud bands we see are actually cloud layers. Darker clouds tend to be deeper in Jupiter's atmosphere, while the white clouds are higher. The atmosphere also has giant lightning storms in its upper clouds. The Great Red Spot on Jupiter can be seen in a small telescope. This gigantic storm would hold 2 Earths. The Red Spot has been around for more than 300 years. To escape Jupiter's gravity you have to travel at 133,100 miles per hour. Jupiter has 17 known moons. The four largest moons, Ganymede, Io, Europa, and Callisto, are called the Galilean moons because Galileo first saw them in 1610. Jupiter has a giant pizza moon. The moon Io is covered with volcanoes and is made mostly of sulfur. Sulfur at different temperatures gives different colors. These sulfur colors make Io look like a giant pizza Jupiter gives off more energy than it gets from the sun. Jupiter was the king of the Roman gods and lord of the sky, a fitting name for our largest planet. 3.6 Saturn Saturn is the sixth planet from the sun. It orbits the sun at a distance of 888 million miles (about 10 times as far from the sun as Earth). Saturn would fit 9 1/2 Earths across its face. It is the second-largest planet in the solar system and has a diameter of 74,898 miles. Saturn is also called the Ringed Planet. Although Jupiter, Uranus, and Neptune also have ring systems, Saturn's is the largest. Saturn's rings are 169,800 miles across, but only 10 yards thick. Saturn's rings are made of ice and rock particles, some as big as a mini-van. The average temperature on Saturn is –300°F. It takes Saturn 29 Earth years to go around the sun one time, but only 11 hours to spin on its axis one time. Saturn looks like a ball that is being squished. Because Saturn spins so fast, its middle bulges while its poles flatten out. This makes Saturn look like somebody is squeezing it. The atmosphere of this Ringed Planet is like Jupiter's atmosphere. Saturn holds mostly hydrogen (97%), helium (3%). Saturn also has beautiful bands like Jupiter, but these colorful features are hidden by haze and smog that make up the planet's high atmosphere. To escape Saturn's gravity you need to travel 79,400 miles per hour. Saturn was the Roman god of the harvest, and the father of Jupiter. He is identified as the Greek god Cronus. 3.7 Uranus The seventh planet from the sun, Uranus orbits at a distance of about 1,784 million miles (more than 19 times farther than Earth). Uranus is the planet tipped on its side. Uranus spins more like a barrel on its side than a top. This strange tilt may be the result of being hit by a fast comet that tipped Uranus on its side. Uranus spins on its axis one time every 17 hours and goes around the sun one time every 84 Earth years. About 4 Earths would fit across the face of Uranus. Its diameter is 31,763 miles, making it the third-largest planet in the solar system. Uranus is very cold. Its average temperature is –350°F. The atmosphere of Uranus holds hydrogen (83%), helium (15%), and methane (2%). Methane is what gives Uranus its blue-green color. There are 11 narrow rings that encircle Uranus. William Herschel discovered Uranus in 1781. To escape the gravity of Uranus, you need to travel 47,600 miles per hour. The planet's 5 largest moons are: Ariel, Umbriel, Titania, Oberon, and Miranda. There are at least 10 smaller moons orbiting closer than Miranda, and there may be another 6 moons farther away from the planet. Uranus was the father of Saturn and grandfather of Jupiter. 3.8 Neptune Neptune is the eighth planet from the sun. It orbits at an average distance of 2,794 million miles (30 times farther than Earth). About 4 Earths would fit across the face of Neptune. Neptune is slightly smaller than Uranus and has a diameter of 30,775 miles. It takes 165 Earth years for Neptune to go around the sun one time, but only 16 Earth hours for it to spin on its axis once. The average temperature on Neptune is –370°F. The atmosphere of Neptune holds hydrogen (79%), helium (18%), and methane (3%). Methane gives Neptune its blue color. Neptune's atmosphere has a striped pattern like Jupiter and Saturn. Neptune once had a Great Dark Spot similar to Jupiter's Great Red Spot. To escape Neptune's gravity you need to travel 52,600 miles per hour. Johann Galle and Heinrich D'Arrest discovered Neptune in 1846. Neptune has at least 8 moons. The two largest moons are Triton and Nereid. Triton is made of rock and ice. Its surface is rich in water ice, dry ice, and frozen carbon monoxide, methane, and nitrogen. Triton has cold geysers that spit nitrogen instead of the hot water that Earth geysers release. Neptune was the Roman god of the oceans. 3.9 Pluto Pluto is the ninth planet from the sun. It orbits at a distance of 3,647 million miles (nearly 40 times as far from the sun as Earth is). With a diameter of only 1,485 miles, Pluto is the smallest planet in the solar system. The temperature on Pluto is –390°F. It takes Pluto 248 Earth years to go around the sun one time, and 6 Earth days to spin on its axis one time. Scientists don't know if Pluto has an atmosphere or not. If it does, it may be made of methane and nitrogen. Pluto's surface has dark markings and is probably made of methane and nitrogen ice. Clyde Tombaugh discovered Pluto in 1930 at Lowell Observatory. Because Pluto is smaller than many of the moons that orbit other planets, some scientists think Pluto should be reclassified as an asteroid. But unlike most asteroids, Pluto is round like the planets. To escape Pluto's gravity you need to travel 2,500 miles per hour. Pluto has one known moon, Charon, which was discovered in 1978. This moon is about half as big as Pluto. Pluto was the god who ruled the dark underworld, a fitting name for the solar system's darkly lit outer world.
