Space debris colliding with Earth are primarily rocky (stones), metallic (irons), or ices. Metallic or stony bodies are called meteorites if less than 100-m diameter and asteroids if greater than 100-m diameter; icy masses are comets. Irons are the most common from found by collectors because they pass through the atmosphere more readily, are more resistant to weathering, and are more easily recognized. Impact scars are hard to find on Earth because they are destroyed by plate-tectonic actions and the agents of erosion. Conversely, the geologically dead Moon is a museum of impact scars.
Asteroids abound in a Sin-orbiting belt between Jupiter and Mars. The strong gravitational pull of the massive planet Jupiter sends collided fragments outbound on collision courses with nearby planets, including Earth.
Comets surround the Solar System in a vast envelope known as the Oort cloud. Some comets are pulled inward close to the Sun and may collide with the Sun or a Planet, as in July 1994, when the Shoemaker-levy 9 comet collided with Jupiter.
About 100,000 million meteoroids enter Earth’s atmosphere every 24 hours. Most are small and burn up due to atmospheric friction before reaching 35 miles above ground. Up to 1,000 tons of materials are added to Earth’s surface each day.
Meteoroids hit Earth’s atmosphere at speeds from 25,000to 70,000 mph; some are destroyed on impact, some are deflected into space, and others are slowed by friction as they pass through the atmosphere. Meteoroids weighing more than 350 tons are slowed little by the atmosphere and may hit the ground at high speeds, explode and excavate craters.
The impact of a large asteroid generates such tremendous heat and pressure that much of the asteroid and crater rock is vaporized. Rocks in the crater, and debris throw out of the crater, are broken, melted, and vaporized; minerals have new high-pressure atomic structures and include forms such as diamonds. As the initial or transient crater is emptied, the crater bottom rebounds upward, and the fractured walls slide inward toward the crater center, forming a final, enlarged crater. The crater may be 100 times wider than deep.
Life on Earth is subjected to great strees by an impact. A large asteroid impact can generate an earthquake over magnitude 11; cause widespread wildfires; create nitrous oxides in the atmosphere that fall as acid rain; and place dust in the atmosphere that blocks incoming sunlight to create “winer”. After the dust settles, water vapor and CO2 remain in the atmosphere, causing a global-warming “summer”. Additionally, if the impact occurs in the ocean, tsunami of 1-to 3-km height can occur.
About 50 house-size bodies pass between the Earth and Moon each day, but the Earth is protected by its atmosphere. It is difficult to estimate how often large bodies impact Earth because plate tectonics and erosion destroy the evidence. However, looking at the Moon’s surface indicates Earth receives a crater greater than 15-mi diameter every 1.33 million years.
Statistically, your risk of being killed by a meteoroid impact is greater than that of dying by flood or tornado. We have the ability to locate incoming meteoroids and could possibly change their paths by sending explosives or a rocket out to redirect them.
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