Homework 2: Crater formation and real-life collisions

(due at the start of class on the 6^th March 2003)

1. Write a paragraph each for comets and asteroids, describing their distribution in the Solar system, composition (what are they made of), range of sizes, and anything that you think is relevant.

2. We believe that Tunguska-like events occur somewhere on the Earth’s surface approximately once per century. Using this fact, estimate how many times humankind have witnessed such an event in the past 4000 years. Be sure to explain your calculation carefully, listing any assumptions that you make. You will need to know that approximately 70% of the Earth’s surface is covered by water. You will also need to make an estimate for the fraction of the land that has been inhabited by humans. How would such events have been interpreted by ancient societies? If such an event had occurred over the USA or the Soviet Union in the 1960s, how would it have been interpreted?

3. Vasiliy Dzhenkoul was a trapper and herder in Siberia and was only about 40km from the Tunguska explosion. He had just got out of bed when the explosion occurred – he tells of how he was suddenly surrounded by a blinding flash, and then how everything around him (the trees, his animals, his tent, and his clothes) spontaneously erupted into flame. At that point he passed out. He woke to utter devastation – the trees had been flattened and were burning, and his animals (about 200 of them) were dead. Two weeks later, he died with symptoms often described as being similar to radiation sickness (of course, we only realized this years later; radiation sickness had never been catalogued in the year 1908!). Which part of this true story is not fully explained by the asteroid/comet impact theory?