ASTEROIDS AND COMETS

You are going to read an article about asteroids and comets. Six sentences have been removed from the article. Choose from the sentences A – G the one which fits each gap (1-6). There is one extra sentence which you do not need to use.

Asteroids and comets have a few things in common. 1 ………………..... They are both “leftovers” — made from materials from the formation of our Solar System 4.5 billion years ago. However, there are a few notable differences between these two objects, as well. 2 ………………..... While asteroids consist of metals and rocky material, comets are made up of ice, dust, rocky materials and organic compounds. When comets get closer to the Sun, they lose material with each orbit because some of their ice melts and vaporizes. 3 ……………….....

Right now, most of the asteroids are in the asteroid belt, a region between the orbits of Mars and Jupiter which may hold millions of space rocks of varying sizes. 4 ………………..... They are either in the Kuiper Belt — a region just outside the orbit of the dwarf planet Pluto that may have millions of icy comets (as well as many icy dwarf planets like Pluto and Eris); or the Oort Cloud, a region where trillions of comets may circle the Sun at huge distances of up to 20 trillion kilometres (13 trillion miles).

Another difference between asteroids and comets is in their orbital patterns. Asteroids tend to have shorter, more circular orbits. 5 ………………..... 1 AU equals the distance from the Earth to the Sun.

How likely is it that our planet could be destroyed by a large asteroid or comet? 6 ………………..... But NASA, ESA and other space agencies have search programmes that have discovered hundreds of thousands of main-belt asteroids, comets. None at this time are considered a threat to Earth.

This text is adapted from universetoday.com