From Tony Caporn
Surely if an asteroid is a porous pile of rubble (and hence not easily deflected by a nuclear explosion) it is likely to burn up and disintegrate as it enters the Earth’s upper atmosphere. In such an event the Earth’s environment will surely be affected, but not in the way of a direct impact. Earth might suffer a “nuclear winter” but not the firestorm scenario.
Eugenie Samuel writes:
• According to Erik Asphaug, associate professor of earth sciences at the University of California, Santa Cruz, a more porous asteroid will burn up more quickly in Earth’s atmosphere. However, a killer asteroid several hundred metres across will enter the atmosphere at 20 kilometres per second. At this speed, it will spend about 1 second in the atmosphere before reaching the ground and making a crater. This is not nearly enough time for the asteroid to burn up, even if it is very porous.
Sunbury-on-Thames, Middlesex, UK
