字幕表 動画を再生する 英語字幕をプリント There is a vast amount of rocks and debris floating around in space. Around 100 tons of it falls to earth every day. You might have been lucky enough to have seen a shooting star, but do you know what a shooting star is? Is it a comet?, meteorite? Maybe an asteroid? Comet A comet (also called a dirty snowball) is essentially ball of ice, rock and dust that orbits the sun ranging in size from around 1km to 20km. Astronomers believe they are leftovers from the early formation of the solar system that reside in one of two places on the very outskirts of the solar system; The Kuiper belt and the Oort Cloud. These two areas are made up of small icy bodies of frozen gases such as methane, ammonia, nitrogen and water mixed with rock and dust. Occasionally a comets orbit will be altered by a gravitational tug of another large object or through a collision with another body that might send it into the inner solar system or sometimes even straight towards the sun. As a comet starts to move closer the sun it heats up and ice starts to evaporate and form a cloud around the nucleus, called the coma. Two tails form as well, the ion tail and the dust tail. The dust tail is made from the dust forming around the nucleus it is being pushed by solar radiation from the sun following the orbit of the comet The ion tail is generally blue made of ionized gas and points directly away from the solar winds coming from the sun. Asteroid Nearly all Asteroids are odd shaped chunks of rock that orbit the sun n the asteroid belt between mars and Jupiter. The asteroid belt is thought to be either left over mass from a failed planet forming due to the close gravitational pull of Jupiter or the leftovers from a planet that broke up due to a collision. Sizes vary from 10 meters to 1000 kilometers wide Ceres is the largest we have ever found and is 960km wide which is about as wide as Texas and big enough to be classed as a dwarf planet. Some asteroids also have their own moons! Meteoroid Space debris smaller than 10 meter asteroids are called meteoroids. They can be as small as a grain of sand They are usually bits of asteroids that have collided or leftover debris from a comet. When a meteoroid enters earths atmosphere it will hurtle towards Earth as it starts to burn up completely and creates a dazzling trail of light due to the air resistance it encounters. This is called a meteor or as we sometimes call them, shooting stars. When a rock is large enough to survie entry It will end up hitting the Earths surface, usually the size of a pebble. It is then known as a meteorite. The largest ever found is a 3 meter wide 66 ton tablet shape meteorite Found in Namibia, that fell 80,000 years ago. Every year around mid July to mid August the Earth's orbit takes us through the dust and debris left behind by a comet. This is called the Perseid meteor shower and creates an incredible display of shooting stars with around 80 shooting stars an hour. You can find out more about this and how to view the spectacle in the link at the end of the video or in the description below.