Questions from Asteroids: Deadly Impact (and some sample answers).
Who was Gene Shoemaker?
Gene Shoemaker was a geologist. He is generally credited with having proven that meteor crater in Arizona was due to the impact of an object from space, not to a volcanic event as had been believed. He was the world's leading expert on impact phenomena throughout his career in the late 1900's, and helped train Apollo lunar astronauts in lunar geology.
What is coesite?
Coesite is a mineral that is formed under conditions of sudden high heat and pressure, such as sites of impacts or nuclear explosions.
What event was responsible for a mass extinction about 65 million years ago? Where did it probably happen?
The impact of an asteroid (or comet nucleus) about 65 million years ago raised large amounts of dust and debris into the upper atmosphere, which blocked sunlight from reaching Earth's surface for weeks or perhaps months. This led to the extinction of approximately 2/3 of all living species, plant and animal, on the Earth (including all the dinosaurs).
The impact took place on the northern part of what is now the Yucatan Peninsula of Mexico, as revealed by a large impact feature there of approximately the right age.
About how often does Earth get hit by big impacts (capable of causing large-scale destruction)?
The program did not give a specific frequency because we don't know with precision. However, we do know that Earth has suffered many of them in the past -- and will suffer them again in the future.
Dr. David Morrison, one of the world's leading planetary astronomers, estimates that we can expect one or two of them every million years. That's rare on the scale of a human lifetime, but the Earth has existed for more than four thousand million years (more than four billion years), so, in geological terms, that's a lot.
What happened in the Tungas River region of Siberia in 1908?
A relatively small piece of a comet nucleus impacted Earth's atmosphere and exploded with the force of a large nuclear weapon. It flattened the forest for miles around, but left no crater in the ground. Comet nuclei are made of low-density ices (not rock and metal like asteroids), so the "Tunguska" impact event did not actually reach the ground before it detonated.
It should be noted (even though it wasn't in the program) that impacts of objects from space happen at thousands of miles per hour, 25,000 mph at minimum. When something travelling this fast comes to a sudden stop, either in the atmosphere or at the surface, its energy of motion is converted to heat energy nearly instantly -- producing an explosion.
How did Comet Shoemaker-Levy 9 end? When?
Comet Shoemaker-Levy 9 broke into many pieces and collided with Jupiter in 1994. It provided very dramatic confirmation of Gene Shoemaker's contention that large, violent impact events still take place in the solar system, and can happen to the Earth in the future.
If you are not a student in an astronomy course at DeAnza College and have found this page by way of a search engine, please be aware that it is designed with very specific, limited pedagogical ends in mind. Also, this page is accessible only for a short time whenever it is of use in an active course. It is taken down at other times.
Questions or comments should be addressed to Sherwood Harrington, the astronomy program co-ordinator.