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Friday, 25 May 2007

Introduction

 

            What do you know about space? And, whats more important, what do you know about impact cratering? What is it? How did it influence the Earth? Why is it important?

 

            Impact cratering has been recognized as an important process for only the last few decades. In fact, at the beginning of the 20th century no one even believed in impact cratering on the Earth. But though not much spoken about, its an important process both for the Earth formation, evolution of all living beings (both now and in the past) and development of human culture

 

            Its widely speculated for the last decades that Solar System has been created via high velocity impacts and planetary landscapes are primarily defined by ancient giant impacts.  It is a well known theory (though still debated) that dinosaurs became extinct due to an impact of a large body onto the Earth. Enigmatic Tunguska explosion in 1908 inspired thousands of people to look for extraterrestrial guests in Russian Siberia. And all those theories and speculations only prove, that Earth-asteroid interaction made a deep impact on the evolution and human culture. However, the process itself didnt gain much publicity. It is still considered a kind of scientific mystery. Lets look behind the shadows!

 

General information

 

Crater formation is a result of a high velocity impact. A high velocity impact is a collision of a large body with a planet on a huge speed (several km/sec). Another commonly used synonym is asteroid impact. The body can be both a part of an asteroid or a comet.  Its important to mention, though, that crater formation is only one of the possible results of a high velocity impact. That only can happen if the extraterrestrial body is large enough (larger than a few hundred meters) to reach the Earth almost without substantial deceleration in the atmosphere. Otherwise the body wont the destroyed after the collision and can be found as a meteorite. I would also like to stress that such a well-known phenomenon as shooting stars is in fact the result of small bodies deceleration and burning in the atmosphere.

 

Meteorites and meteoroids mainly originate as a part of an asteroid from outer space, and to be specific, from the Main Asteroid Belt between Mars and Jupiter. Every day thousands of small bodies cross over their path with the Earths, but only few of them are large enough to be seen. The collision of a large body with the Earth is, thankfully, a rare event. But it can have an enormous effect on our life.

 

Historic review

 

            Impact cratering has only been recognized as a field for study for the last few decades. The process itself and its result have been observed for much longer. In fact, history of the research dates back to the 17th century, when Galileo published his Sidereus Nuncius in 1610. It is probably the first well-documented paper on astrophysics at all and especially on impact field. The book was devoted to crated formation on the Moon. Three centuries have passed before the process was properly understood, but this first step is still quite important.

 

            The second step was made in 1880s with the scientific acceptance of meteorites. Lunar craters were finally concluded to be meteoritic, not volcanic. But as you see, the possibility of impact cratering on the Earth was not even discussed. In fact, the very first hypothesis of crater formation on Earth was only suggested in 1906 when an engineer Barringer demonstrated that the widely known Coon Mountain crater must have had a meteoritic origin. This hypothesis was considered absolute rubbish, but it gave food for thoughts. In fact, 1906 can be considered the year of birth of impact cratering as a science field.

 

            Nowadays impact cratering is a perfect example of a synthetic science which was born and developed at the cross-road of astronomy, physics, geology and mathematics. Only by working side to side scientists from all over the world made it possible to discover some amazing facts o the history of our planet.

 

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