Earth as a Lovely and Placid Place

Earth as a Lovely and Placid Place

The Earth is a lovely and more or less placid place. Things change, but slowly. We can lead a full life and never personally encounter a natural disaster more violent than a storm. And so we become complacent, relaxed, unconcerned. But in the history of Nature the record is clear. Worlds have been devastated. Even we humans have achieved the dubious technical distinction of being able to make our own disasters, both intentional and inadvertent. On the landscapes of other planets where the records of the past have been preserved, there is abundant evidence of major catastrophes. It is all a matter of time scale. An event that would be unthinkable in a hundred years may be inevitable in a hundred million. Even on the Earth, even in our own century, bizarre natural event have occurred.

In the vast spaces between the planets there are many objects, some rocky, some metallic, some icy, some composed partly of organic molecules. They range from grains of dust to irregular blocks the size of Nicaragua or Bhutan. And sometimes, by accident, there is a planet in the way. The Tunguska Event was probably caused by an icy cometary fragment about a hundred meters across – the size of a football field – weighing a million tons, moving at about 30 kilometers per second, 70,000 miles per hour.

Could an asteroid trigger a nuclear war? Earth is a Placid Place. Photo: Elena

If an impact such as Tunguska Event occurred today it might be mistaken, especially in the panic of the moment, for a nuclear explosion. The cometary impact and fireball would simulate all effects of a one-megaton nuclear blast, including the mushroom cloud, with two exceptions: there would be no gamma radiation or radioactive fallout. Could a rare but natural event, the impact of a sizable cometary fragment trigger a nuclear war? A strange scenario: a small comet hits the Earth, as millions of them have, and the response of our civilization is promptly to self-destruct. It might be a good idea for us to understand comets and collisions and catastrophe a little better than we do. For example, an American Vela satellite detected an intense double flash of light from the vicinity of the South Atlantic and Western Indian Ocean on September 22, 1979.

Early speculation held that it was a clandestine test of a low yield (two kilotons, about a sixth the energy of the Hiroshima bomb) nuclear weapon by South Africa or Israel. The political consequences were considered serious around the world. But what if the flashes were instead caused by an impact of a small asteroid or a piece of a comet? Since airborne overflights in the vicinity of the flashes showed not a trace of unusual radioactivity in the air, this is a real possibility and underscores the danger in an age of nuclear weapons of not monitoring impacts from space better than we do.