How well do humans know the solar system?
Humans have been exploring the solar system for centuries. Mostly we have used telescopes or simply our eyes. But the Sun, all of the planets, and many dwarf planets, asteroids and comets have been studied more closely. Spaceships have taken rovers, probes or other technologies to study these bodies. Sometimes a spacecraft just flies by to take a look. So while it's very difficult to get humans very far from Earth, our spacecraft have become our eyes. We know an incredible amount about the solar system compared with even a few decades ago. This is because of the tremendous spacecraft and the instruments they carry. In this concept, we will explore a small fraction of what scientists have learned about our solar system.
At the center of the solar system is our star, the Sun. The Sun gets its power from the fusion of hydrogen and helium. The Sun has no solid parts, but it has layers. Much of what the Sun is made of is plasma. The Sun's surface features, like sunspots, can affect Earth. Eight planets orbit the Sun. The four nearest the Sun are small, dense, and rocky. The four farthest from the Sun are large and gaseous. Mercury is the smallest planet. It is closest to the Sun so it is extremely hot. Venus has a thick, atmosphere with a lot of carbon dioxide. The carbon dioxide gives the planet a large greenhouse effect so it is very hot. Earth, the third rock from the Sun, is the only one of the inner planets with a large moon. The Moon is the only body in the Universe, besides Earth, where humans have walked. The red planet, Mars, is the most Earth-like. The planet has volcanoes, channels where water once flowed and an enormous canyon. The four gas planets are Jupiter, Saturn, Uranus, and Neptune. They are made of hydrogen, helium, and some methane and other gases. All have rings and moons. The solar system also includes at least five dwarf planets. After decades as a planet, Pluto was recently made a dwarf planet. There are also asteroids, and comets. An object that strikes Earth is a meteorite. Increasing numbers of planets are now being found in other solar systems.