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Impact on Earth

Collisions with our Planet

Artist's Drawing of Quaoar


Large Icy Bodies and particles down to the size of dust reside beyond Jupiter in the Kuiper Belt, a disk of debris left over from the formation of the Barringer Meteor Crater, Arizona solar system.


Could the Earth Be Hit
by an asteroid
during our lifetime?
The picture on the right is Barringer Meteor Crater near Winslow, Arizona.
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Tracking and Predicting Asteroid Encounters

Recently, some astronomers found some objects that were predicted to hit the Earth in 2028 and 2030. After further study, both objects were projected to miss by several million miles. A system has been designed to avoid public panic and fear over an asteroid or comet hitting the Earth.

The International Astronomical Union has a system to alert the public to such possible collisions by asteroids and comets. Developed by Richard Binzel of MIT, the Torino Scale is designed to rate the level of damage an object might do to the Earth if it hit. This method is similar to the Richter Scale used for earthquakes and scales used for severe weather and tornados. A summary description can be found below.

Some astronomers and other scientists are tracking asteroids. NASA has a Near-Earth Orbit project and Near-Earth Object Rendevouz spacecraft mission to study asteroids and other objects that might come close to Earth as they orbit the sun. There are three types of Near Earth Objects:

Mars-crossing but not Earth-crossing asteroids;
with perihelion distance 1.017 < Q < 1.3 AU.
Includes most Earth-crossing asteroids (except for the Atens);
with semimajor axis > 1.0 AU, and perihelion distance Q < 1.107 AU.
Asteroids with orbits largely inside the orbit of the Earth;
with semimajor axis < 1.0 AU and aphelion distance Q > 0.983 AU.


How does the Torino Scale Work?

The Torino Scale utilizes numbers that range from 0 to 10, where 0 indicates an object has a zero or negligibly small chance of collision with the Earth. (Zero is also used to categorize any object that is too small to penetrate the Earth's atmosphere intact, in the event that a collision does occur.)

A 10 indicates that a collision is certain, and the impacting object is so large that it is capable of precipitating a global climatic disaster.

The Torino Scale is color coded from white to yellow to orange to red.

Each color code has an overall meaning:

  • White - "Events having no practical consequences," meaning they are virtually certain to miss Earth or are so small that any impact would almost certainly dissipate in the atmosphere. White corresponds to category 0.
  • Green - "Events meriting careful monitoring" refers to objects that have predictable close approaches with some very small, but not seriously concerning, chance of a collision. Nonetheless, prudence dictates their orbits should be tracked closely so that the collision chance becomes refined, and probably in all cases, will ultimately be reclassified within Torino Scale category zero. Green corresponds to category 1.
  • Yellow - "Events meriting concern" are close approaches by objects that have higher collision chances than the Earth typically experiences over a few decades. These are object for which refinement of the orbit is of high priority. Yellow corresponds to categories 2, 3, 4.
  • Orange - "Threatening events" refers to close encounters with objects that are large enough to cause regional or global devastation, where the chance of collision greatly exceeds the level that typically occurs within a given century. These are objects for which refinement of the orbits are an extreme priority. Orange corresponds to categories 5, 6,7.
  • Red - "Certain collisions" refers to objects that are certain to collide with Earth having sufficient size to likely penetrate the atmosphere with the capability to cause either local damage, regional devastation, or a global climatic catastrophe. Red corresponds to categories 8, 9, 10.

The Torino Scale

Events having
No Likely
0 The likelihood of a collision is zero, or well below the chance that arandom object of the same size will strike the earth within the next few decades. This designation also applies to any small object that, in the event of a collision, is unlikely to reach the Earth's surface intact.
Meriting Careful
1 The chance of collison is extremely unlikely, about the same as a random object of the same size striking earth within the next few decades.
2 A somewhat close, but not unusual encounter. Collision is very likely.
3 A close encounter, with 1% or greater chance of a collision capable of causing localized destruction
4 A close encounter, with 1% or greater chance of a collision capable of causing regional devastation.
5 A close encounter, with a significant threat of a collision capable of causing regional devastation.
6 A close encounter, with a significant threat of a collision capable of causing global catastrophe.
7 A close encounter, with an extremely significant threat of a collision capable of causing global catastrophe.
8 A collision capable of causing localized destruction. Such events occur somewhere on Earth between
once per 50 years and once per 1,000 years.
9 A collision capable of causing regional devastation. Such events occur between once per 1,000 years and once per 100,000 years.
10 A collision capable of causing global climatic catastrophe. Such events occur once every 100,000 years or less often.

Research Projects for Students

You could do a project by describing the Torino Scale and discussing one or more of the following ideas.

  • Should more money be provided to NASA and others to study and find Near-Earth Objects?
  • Should the public be told about a close asteroid only at the mid or higher levels on the Scale or at the lowest scales?
  • What impact craters are found on the Earth? Include the size and location of some craters and where they might be listed on the Torino Scale.
  • Interview your classmates to make a list of 10 questions they might have about objects hitting the Earth. Then try to find out the answers.

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