Asteroids and Earth Impacts

Films such as Deep Impact and Space Cowboys presents stories about major meteorite impacts on Earth. These films discussed what could happen if a meteor or asteroid was discovered on a collision course with Earth. Both films with space ships to the asteroid and try to blow it up or steer it with nuclear weapons. In the end, humanity was saved just in time.

If an asteroid or meteorite impact? Could this really be the case, or is it just "Hollywood" fantasy? If so, when will it happen?

We know in the geological past that meteorites have an impact on the earth. A good example is the meteorite crater left in the Arizona desert (Meteorite Crater). I have several photos of Meteor Crater in Arizona during a visit in the middle of the 1990s. Some of these images are on my website.

Roy A. Gallant, in his book Meteorite Hunter, ISBN 007137224-5 writes;

"According to NASA, a 10-meter-diameter rocket cosmic passes closer to us than the moon the distance every day. An object 100 meters in diameter of the Earth crosses the orbit at about the distance of the Moon at an average of once a month. In January 1991 10 - meter-diameter object from Earth missed only half the distance of the moon just 12 hours after astronomers discovered. On December 9, 1994, 1994XM asteroid missed us by 100 kilometers. It was 13 meters in diameter. Size of a house, the small asteroid would have been completely wiped out the Greater New York, he had a hit in Manhattan. We can expect to be most affected by such a house-size objects to once every 100 years. Every 1000 to 3000 years we can expect That most of Near Earth Objects (NEOS) ranges in size from 100 to several hundred meters. Fortunately, we do not have to worry about the Stoney objects smaller than about 50 meters in diameter, because most burn in the atmosphere. But if an object of iron, then some concern is justified. For example, a metal asteroid 30 meters in diameter carved a crater 1.2 kilometers in Arizona in the desert 50000 years.

Asteroids about 100 meters and greater deserve our greatest respect, and we know of some 100000 of them live, that the solar system this side of Mars. A direct hit from one of these would wipe out a continent. They visit Earth once every 50000 to 500000 years. More annoying are the 1000 to 2000 Neos about 1 km or larger in diameter, collide with the earth once every 300000 years or so. There are real world crunchers cause mass extinctions. Chicxulub was one, but that was before 65 million years. If our numbers game is a reliable, then where are all the younger impact sites? In any case, as one writer put it, "we live in a cosmic shooting gallery."

One thing that alerted astronomers just how often the Earth is targeted by bombs from outer space was a U.S. military report made public in early 1994. According to the report, from 1975 to 1992 military satellites discovered 136 high altitude explosions with a force of 500 to 15000 tonnes of high explosives-in effect, small nuclear bombs. The report went on to show that the astonishment of the scientific community, that the objects in the atmosphere at 16 to 48 kilometers per second, that it exploded 27 to 32 kilometres above the ground, and that there were probably 10 times more than the events have been identified. If this were so, then there are about eighty such explosive events per year.

Currently, the University of Arizona's Space Watch program recognizes some twenty new Neos per month. After Space Watch director Robert S. McMillan as many as nine hundred 1-km-diameter asteroid capable of wreaking global havoc can be a risk of collision with the earth.

How much energy has a moderately large asteroid - say, a 1-km-wide object pack? Tom Gehrels says that we can use the mathematical expression 1/2mv2 to calculate the kinetic energy. Let m represent the object of a mass and speed for its entry into the atmosphere. If the object has a density of 3grams per cubic centimetre, we meteorites and the candidate speed is 20 km per second, then an asteroid 1 km in diameter packs a striking force of millions of times the explosive power of the atomic bomb dropped on Hiroshima. Gehrels is reassuring when he tells us that the Space Watch-team knows only about ten Chicxulub-size objects with Earth-crossing orbits. "

A list of potentially hazardous asteroids (PHAs) is updated by the Space Watch project. This list can be found on the website of Harvard University and can be found by clicking on the concept of potentially hazardous asteroids.

According to the PHA website:

"... The average distance of the Moon is 0.0026 AU = 384400 km = 238900 miles. (1 AU is about the average distance between the Earth from the sun = 149597870 km = 92955810 miles."

AU stands for Astronomical Unit distance: One AU is about 1.5x10 ^ 8 km (about the average distance between the Earth and the sun).

NASA and JPL have a common future rapprochement table. This table predicts close approaches between 2001 and May 2040, for planned approaches within 0.2 au. This table is available on the JPL / NASA website.

From these studies were made, and research has not yet been completed, it is impossible to think that a large meteorite impact will not happen. How big earthquakes in fault zones, meteorite impacts are part of our physical world. The only real variable is time.