NEAR-EARTH OBJECTS (NEOs) and TORINO SCALE

NEAR-EARTH OBJECTS (NEOs) and TORINO SCALE

Near-Earth objects (NEOs) are meteoroids, asteroids, and comets whose orbits lie close to -- and sometimes cross -- Earth's. Impact craters on Earth bear witness to the destructive potential of NEOs. The hazard posed by NEOs has captured the professional attention of not just astronomers but also geologists, biologists, mission planners, aerospace engineers, and even the United States Department of Defense. The public is increasingly aware that Earth resides within a cosmic shooting gallery. The crash of Comet Shoemaker-Levy 9 into Jupiter in 1994 provided proof that cosmic collisions do occur. 

Yet NEOs also represent a hitherto untapped resource for the future exploration of our solar system. Lying close to Earth in space and having negligible gravity, NEOs represent an abundant source of raw materials such as metals and water waiting to be harvested for space-based construction.

Asteroid Belt

An Asteroid

a graphic image of NEO impact

On a daily basis, about one hundred tons of interplanetary material drifts down to the Earth's surface. Most of the smallest interplanetary particles that reach the Earth's surface are the tiny dust particles that are released by comets as their ices vaporize in the solar neighborhood. The vast majority of the larger interplanetary material that reaches the Earth's surface originates as the collision fragments of asteroids that have run into one another some eons ago.

With an average interval of about 100 years, rocky or iron asteroids larger than about 50 meters would be expected to reach the Earth's surface and cause local disasters or produce the tidal waves that can inundate low lying coastal areas. On an average of every few hundred thousand years or so, asteroids larger than a kilometer could cause global disasters. In this case, the impact debris would spread throughout the Earth's atmosphere so that plant life would suffer from acid rain, partial blocking of sunlight, and from the firestorms resulting from heated impact debris raining back down upon the Earth's surface. Since their orbital paths often cross that of the Earth, collisions with near-Earth objects have occurred in the past and we should remain alert to the possibility of future close Earth approaches. It seems prudent to mount efforts to discover and study these objects, to characterize their sizes, compositions and structures and to keep an eye upon their future trajectories. 

The below link is very useful in understanding more about Near Earth Objects

http://www.jpl.nasa.gov/multimedia/neo/spaceRocks.html

Meteor Crater in the state of Arizona was the first crater to be identified as an impact crater. Between 20,000 to 50,000 years ago, a small asteroid about 80 feet in diameter impacted the Earth and formed the crater. The crater is the best preserved crater on Earth and measures 1.2 km in diameter.

a crater site in Arizona (USA)

NEO impact is measured in terms of TORINO SCALE

Torino Scale is a "Richter Scale" for categorizing the Earth impact hazard associated with newly discovered asteroids and comets. It is intended to serve as a communication tool for astronomers and the public to assess the seriousness of predictions of close encounters by asteroids and comets during the 21st century

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:

TORINO SCALE (similar on lines with Richter Scale)

Courtesy: NASA