Public Lectures for the Session 2000-2001 held in Room E7 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

15th February 2001

'The Bombarded Earth'

Dr. David W Hughes
University of Sheffield.

Dr. Hughes said that during the course of his lecture the earth would travel some 66000 miles. Its path was crossed by many asteroid orbits and collisions were inevitable, the frequency and severity of which would depend on the size of the impacting body.

The threat from earth strike was not recognised until about 50 years ago when the Arizona Meteor Crater was recognised as being formed in this way. Now some 200 fossil meteor craters ranging in size from a few metres up to tens of kilometres in diameter have been identified on Earth, mainly from satellite surveys. When combined with evidence from the moon and other cratered worlds in the solar system, it is obvious that collisions with small solar system objects have been and still are commonplace. The 1994 impact of Comet Shoemaker- Levi 9 with Jupiter showed the effect of such a strike and the potential threat to life on earth.

An asteroid or comet hitting Earth at 20km/second would be to excavate a crater some 20 times its own diameter. Even a 1km object would make a crater 20km across and would cause major, continent-wide destruction to life on Earth. The Earth is hit many times by small objects every year but as the size of the impactor increased, the chances of a collision reduces exponentially. A 1km crater might be expected every 30000 yrs and would produce major localised damage. The frequency of a collision with an object a kilometre in diameter would be about every million years whilst a 10km asteroid might hit every 100 million years.

The threat from earthstrike is being taken seriously by the astronomical community and now even by politicians. In the past ten years the number of known minor bodies in the solar system had doubled to well over 20,000. Whilst it may be some time before counter measures can be put in place to destroy or deflect potential hazards, active searches such as SpaceWatch are now being undertaken to identify earth-crossing asteroids.

Synopsis by Kevin J. Kilburn (Secretary)

Maintained by Michael Oates
Page modified 28 October, 2006