6.1 Collisions in space
Collisions in space are a frequent occurrence. In the following audio, we describe how such collisions may be understood in terms of the concepts introduced in this course.
Transcript: Audio 1 Collisions in space
On an astronomical scale, entire galaxies can collide and merge. Our own galaxy, the Milky Way, in which the Sun is just one of about stars, has absorbed a number of small companion galaxies. One such ‘victim’, a dwarf galaxy in Sagittarius, was discovered in the late 1990s.
A large body of scientific evidence now exists that supports the idea that a major asteroid or comet impact occurred in the Caribbean region at the boundary of the Cretaceous and Tertiary periods in Earth’s geological history (about 65 million years ago). Such an impact is suspected of being responsible for the mass extinction of many species of plants and animals, including the large dinosaurs. The correctness of this hypothesis is still not certain, but the possibility of such a collision is very real; it is becoming increasingly clear that the Earth orbits the Sun in a sort of cosmic shooting gallery. The collision of the fragments of comet Shoemaker–Levy 9 with the planet Jupiter in 1994 was just one of the many side-shows in this gallery. The most dangerous asteroids and comets, those capable of causing major regional or global disasters, are extremely rare, impacting on the Earth perhaps once every 250 000 years or so. Nevertheless, a great deal of media and scientific attention has been focused on strategies of defence. These include the use of nuclear devices and high-speed collisions to deflect or fragment such an object heading for Earth. Calculations using the principles we have discussed in this course have shown that high-speed inelastic collisions, at or so, of wide projectiles with a kilometre-wide asteroid would only change the speed of the main body of the asteroid by about . Such collisions would have to take place years before impact in order for enough deflection to take place to avert catastrophe.