Scientists believe that space is infinitely large because it is constantly expanding. There are eight planets in our solar system, but astronomers believe there are hundreds of thousands more in other solar systems. Space officially starts 100 kilometres above the Earth’s surface. This boundary is known as the “Kármán line”. Scientists have sent a spacecraft known as Voyager 1 out into space with a record on board containing many of the sounds you can hear on Earth. This spacecraft was launched in 1977. Scientists hope that if alien life forms find the record, they will know more about Earth and perhaps try to contact human beings. Other planets in our solar system can have many moons, for example, Jupiter has more than 67 moons. However, Venus and Mercury have no moons. One light-year is the distance that light travels in a year, which is nearly 10 trillion kilometres. Since many stars are more than several light-years away from Earth, the light they emit will only reach us long after the stars themselves have died out. Light from the Sun takes about 8 minutes and 20 seconds to reach Earth.
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