Exploring The Planets: Mercury By NASA.gov, adapted by Newsela staff on 02.28.17 Word Count 861 Level MAX The planet Mercury, the nearest planet to the sun, as seen from the spacecraft Mariner 10. Photo from: MPI/Getty Images. Mercury is the smallest of the eight planets in our solar system and the closest planet to the sun. It is covered in craters and it has no moons. Mercury is named after an ancient Roman god. The Romans believed that gods and goddesses were in charge of everything on Earth, and Mercury was said to be the messenger for the gods. Legend says Mercury's winged sandals gave him incredible speed. The planet Mercury is also incredibly fast. It travels around the sun at a speed of 31 miles per second, faster than any other planet in our solar system. No wonder it got its name from the quickest of the ancient gods. Rocky, Small And Cratered Along with Venus, Earth and Mars, Mercury is one of the terrestrial, or rocky planets. It has a solid outer shell similar to Earth's outer shell. At its center is a large metallic core, which is part liquid. Mercury, the smallest planet in our solar system, is just a little bit bigger than Earth's moon. It is made of heavier materials than the moon, such as iron. This article is available at 5 reading levels at https://newsela.com. 1
Mercury and the moon have something else in common: both are covered with impact craters. On Mercury, these deep holes were made nearly 4 billion years ago by asteroids and meteoroids that crashed into Mercury at high speeds. Mercury does have some large areas of smooth terrain, and it also has dramatic cliffs formed billions of years ago. Some of these cliffs are hundreds of miles long and soar up to a mile high. Closest To The Sun Mercury is the closest planet to the sun. It orbits the sun along a path shaped like a stretchedout oval. If you could stand on the surface of Mercury when it is at its closest point to the sun, the sun would look more than three times as big as it does when viewed from Earth. This article is available at 5 reading levels at https://newsela.com. 2
Standing on Mercury wouldn't be a very good idea, though. The planet is much too hot in the daytime and much too cold at night. During the day, temperatures on the surface can reach 800 degrees Fahrenheit, while at night they drop down to -290 degrees Fahrenheit. Why does the temperature swing from very hot to very cold? It's because Mercury does not have an atmosphere. An atmosphere helps planets like Earth hold onto their heat, kind of like a blanket of air that keeps the planet nice and warm. Since Mercury has no atmosphere to hold in all of the sun's intense heat, the heat simply escapes into space at night. A Short Year, But A Long Day A year is the amount of time it takes a planet to make one full revolution around the sun. Earth takes just over 365 days to make a full trip, so that is the length of a year on Earth. A Mercury year is just 88 days long. That is because Mercury is closer to the sun, and travels so quickly around it. If you lived on Mercury, you'd have a birthday every three months. Mercury speeds along its orbit, but it rotates very slowly. A single day is equal to the time is takes a planet to make a full rotation, or one full spin on its axis. Earth takes 24 hours to make one full rotation. Mercury's full rotation takes 59 Earth days. Flybys And Discoveries Because Mercury is so close to the sun, it is hard to directly observe it from Earth. However, 13 times each century, observers on Earth can watch Mercury pass across the face of the sun. This event is called a transit. These rare transits fall within several days of May 8 and November 10. The first two transits of Mercury in the 21st century occurred May 7, 2003, and November 8, 2006. Another transit took place on May 9, 2016, and and the next will happen on November 11, 2019. This article is available at 5 reading levels at https://newsela.com. 3
People have never gone to Mercury, but spacecraft have been sent there to collect data and images of the planet. The first spacecraft to visit Mercury was Mariner 10. It was launched by NASA, the U.S. space agency, in 1973. Mariner 10 flew by Mercury in 1974 and 1975, and took images of 45 percent of the planet's surface. After that, no spacecraft were sent to Mercury until 2004, when NASA launched the MESSENGER spacecraft. This spacecraft flew by Mercury in 2008 and 2009, and in 2011 it began to orbit the planet. MESSENGER provided scientists with a wealth of new data about Mercury. It showed that Mercury has a lot of sulfur and potassium, two very explosive elements. It also captured images of almost the entire surface of the planet. These images revealed a surface shaped by many meteorite and asteroid crashes. They also suggested that there was extensive volcanic activity at some point in Mercury's past. This article is available at 5 reading levels at https://newsela.com. 4
This article is available at 5 reading levels at https://newsela.com. 5