1.1 Article_ Scale in the Solar System.pdf

Scale in the Solar System...

Scale in the Solar System In 1969, millions of people watched as humans visited the Moon for the first time. Since then, many astronauts have visited the area of space that’s just outside Earth’s atmosphere. We’ve even built the International Space Station, © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image credit: Getty Images which circles Earth and allows astronauts to live and do research in space! We have also explored more distant areas of the solar system using probes—spacecraft without people on board. However, humans have never set foot anywhere else in the solar system. Technology that helps humans travel and survive in In the night sky we can see objects in our solar space has improved since that first trip to the system, like planets, and objects outside our solar Moon—so why haven’t we traveled to any other system, like stars. planets? The answer lies in size and distance. Compared to the rest of our solar system, Earth There are eight planets in our solar system, and is just a tiny dot surrounded by a whole lot of they vary widely in size. Planets close to the sun empty space. are smaller, while planets far from the sun tend to be larger. In comparison with the rest of the Objects in the Solar System planets, Earth is near the middle: it’s the third Come in Different Sizes planet in distance from the sun and the fifth- largest planet in size. The smallest planet in our Earth is just one object in the group of objects solar system is Mercury—if Earth were hollow, we call our solar system. Our solar system about 18 Mercurys would fit inside. The largest includes the sun, the planets that move around planet in our solar system is Jupiter. It’s so big the sun, and the moons that move around that more than 1,000 Earths could fit inside! the planets. Some of the objects in our solar system, like the sun and the planet Jupiter, Many of the planets in our solar system have are so big that they’re hard to imagine. Others moons—objects that travel around planets. aren’t very big at all: some moons are only 3 or Earth has one Moon, which you sometimes 4 kilometers all the way around! see in the night sky and during the day as well. If Earth were hollow, about 49 Moons would The sun is by far the biggest object in our solar fit inside. Mars has two moons, and Jupiter system: it’s so big that about 1.3 million Earths and Saturn have many more than that: Jupiter could fit inside it! If the sun were the size of a has at least 63 moons and Saturn has 62, basketball, Earth would be the size of a grain of but scientists are still identifying more. Most rice and Mercury would be the size of a pinhead. moons aren’t very big, but even moons vary a Even planets that are much bigger than Earth, lot in size. Ganymede, a moon of Jupiter, is the Scale in the Solar System like Jupiter and Saturn, would only be about the largest moon in our solar system. It’s larger size of table-tennis balls. than the planet Mercury! Scale in the Solar System 1  Jupiter Saturn Uranus Neptune Mercury Venus Earth Mars Pluto sun © 2018 The Regents of the University of California. All rights reserved. Permission granted to purchaser to photocopy for classroom use. Image credit: NASA The planets in our solar system come in a variety of sizes, but they are all much smaller than the sun. To show the sizes of the planets accurately, this illustration shows them much closer together than they really are. Different Planets Are Different to explore other planets, they must think about where each planet will be at a certain time and Distances from the Sun when it will be easiest to reach. Even when our The objects in our solar system don’t just vary closest neighbor planets are as close to Earth as in size; each is also a different distance from the they can get, they’re still very far away: Earth’s sun. The closest planet to the sun is Mercury; neighbor planet Mars is so far away that it would it’s about 57 million kilometers from the sun. take 6 months to get there by rocket. Other That may seem pretty far, but it’s nothing planets are much farther from Earth than Mars considering how big the solar system is and is—a spacecraft launched from Earth would how far away some of the other planets are. The take about 12 years to reach Neptune! farthest planet from the sun is Neptune—it’s 4.5 billion kilometers from the sun. The distance of With all this empty space around us, it’s no each planet from the sun makes a big difference wonder humans haven’t traveled very far in its climate and whether it can support life. from Earth. Sending people into space and Planets that are close to the sun, like Mercury bringing them back safely is complicated: and Venus, get a lot of energy from the sun and scientists must take into account the amount are too hot to be habitable. Planets that are very of fuel needed to stay in space for months or far from the sun, like Uranus and Neptune, get years at a time, the weight of all the food and much less energy from the sun and are much equipment astronauts need for a long trip, the too cold to be habitable. On these planets, water way the human body might react to conditions exists only as ice. Earth is about 149 million on other planets, and lots of other important kilometers from the sun, which is good news information. Still, many people are working on for living things. Earth can support life partly solving these problems in hopes of sending because it has liquid water—and it has liquid humans to other planets someday. The National water because it’s just the right distance from Aeronautics and Space Administration (NASA) the sun. currently estimates that humans may make it to Scale in the Solar System Mars around the year 2030. Since all the planets in the solar system (including Earth) are always moving around the sun, the distances between them are always changing. When scientists send spacecraft out 2 Scale in the Solar System