Các tiểu hành tinh, thiên thạch, và sao chổi Ngoài ra các hành tinh lớn, hệ thống năng lượng mặt trời có chứa hàng tỷ của các đối tượng quay quanh nhỏ hơn. Nhiều trong số này là cục đá, sắt và nickel còn lại từ sự hình thành của các hành tinh. | ASTEROIDS METEORITES ASTEROIDS The Asteroid Belt between the orbits of Mars and Jupiter contains vast numbers of asteroids. AND COMETS Most are too small to have names but a few such as Gaspra and Ida are big enough to have been photographed by passing space probes. In addition to the big planets the solar system contains many billions of smaller orbiting objects. Many of these are lumps of rock iron and nickel left Some asteroids orbit outside the main belt including Eros which passes within 14 million miles 22 million km of Earth. over from the formation of the planets. These include the asteroids that -big speed urn Peĩ sPeed Pe orbital sPe miles 2o p COMETS There are billions of comets in the Oort Cloud a region of the solar system beyond the orbit of Neptune. A few of these icy bodies travel close to the Sun. As they approach they are blasted by solar radiation that makes them trail long tails of glowing dust and gas. After several weeks the comets vanish but some reappear many years later. This is Halley s Comet which orbits the Sun every 76 years. mainly orbit the Sun between Mars and Jupiter. There are also comets-chunks of ice and dust that loop around the Sun before vanishing into the far reaches of the solar system. Smaller pieces of rock and ice shoot through Earth s sky as fl meteors. Some of these pieces may even fall to Earth as meteorites. IMPACT CRATERS This crater in Arizona is one of about 170 that have been found on Earth. Formed by an asteroid strike about 50 000 years ago it is miles km across. The impact would have caused a colossal explosion killing everything in the region. Luckily these large impacts are very rare. The last occurred in 1908 when an asteroid exploded high above a remote region of Siberia called Tunguska. 12 METEOR SHOWER ì Shargottite Sayh al Uhaymir 008 meteorite ------ METEORITES Thousands of meteorites hit Earth every year although few are big enough to be dangerous. Most are stony but others are largely made of iron
