100th Anniversary of Tunguska Blast event

I wrote this on June 30, 2008 at the request of an editor of Sky & Telescope

On a hot summer’s day in a mid-Atlantic state of the United States, it is hard to anticipate a natural disaster of any kind, much less one from outer space. Yet historical records of eye witness accounts of a powerful blast and subsequent scientific analysis of material around the forest that was flattened by the event near the Podkamennaya Tunguska river, Siberia, 100 years ago today, tell us that objects colliding with Earth of potentially devastating magnitude will probably happen again in the future. With modern upper atmospheric surveillance, air bursts from incoming fragments of near-Earth objects are detected on order of once a year. Unfortunately, we can’t predict when and with what magnitude these collisions occur. The Tunguska event is estimated to have been equivalent to 30 megatons of TNT, or measuring 5.0 on the Richter scale for earthquakes. What can we do, knowing that such an event can happen again? The best offense is a good defense, so the first thing to do is monitor the number and nature of Near-Earth objects and that is what NASA is doing in its Near Earth Object program
Scientists also project the orbital evolution of NEOs hundreds of years into the future to watch for potentially hazardous objects that might collide with Earth. From time to time, the U.S. Congress holds hearings on the existing NEO programs and calls for written reports on the topic of impact hazards to Earth.

On a hot summer’s day, it is possible to think about and plan for possible hazardous impacts in the future. Let’s keep our heads and continue to assess our plans and policy. Hopefully, our deliberate and thoughtfully designed programs will allow us to detect any hazardous incoming body and take preventative action.

This was posted as a follow-on commentary to an article by Kelly Beatty on the 100th Anniversary of the 1908 Tunkuska event over Siberia with individual’s comments including mine.