What are the odds of an asteroid or comet hitting the Earth? Has this happened in Earth’s past? What would happen to Earth’s civilization in the event of a collision? What can be done to protect Earth? Artist’s impression of an asteroid impact with Earth (ESA)

Meteoroids enter the Earth’s atmosphere every day Most are micro-sized but occasionally larger ones enter from space Some of these hit the ground, some explode in the atmosphere, and some deflect off the Earth’s atmosphere

During a period between 4.0 and 3.8 billion years ago, called the Late Heavy Bombardment, the newly formed Earth was being constantly bombarded by asteroids, comets, and debris left over from the formation of the solar system Since then the number of asteroids that have hit the Earth has dramatically decreased An artist’s image of early Earth being bombarded by asteroids

Probably the most famous object that hit the Earth is the one that created the Chicxulub crater and caused the extinction of the dinosaurs 65 million years ago Closer to home, Meteor Crater in Arizona was created 50,000 years ago by a large object slamming into the Earth Location of Chicxulub crater Meteor Crater near Flagstaff, Arizona

Sentry, a computer system developed by NASA’s Jet Propulsion Labs, calculates the odds of Near-Earth Objects (NEO’s) coming close to or hitting the Earth within the next 100 years It figures the object’s coordinates, distance, velocity, and gravitational influences to calculate its trajectory This sometimes requires months or years for the calculations to be accurate Known asteroid impact sites on Earth

JPL’s Impact Risks List shows the Near Earth Objects (NEO’s) most likely to hit the Earth For example, a 2- kilometer wide asteroid called 2002 NT7 has a 1 in 200,000 of striking Earth on Feb. 1, 2019 (a very, very low probability) If it would strike Earth it would release 1 billion tons of energy (the equivalent of 20,000 H- bombs) Orbit of asteroid 2002 NT7 (in blue)

Currently there are over 1,000 large NEO’s of one kilometer or more with only about 50% discovered so far If such an object collided with Earth, debris from the impact would cause worldwide effects that would endanger much of the life on Earth The blue circles are the orbits of the planets, the green dots are the Main Asteroid Belt between Mars & Jupiter, the red dots are NEO’s

A crater will form from the impact of the object If the object hit in the ocean a tsunami will devastate coastal areas As debris rains down after the collision, friction with the atmosphere can cause global firestorms Acid rain will damage foliage, harm ocean organisms and destroy the ozone layer Effects on Earth of a collision with a large NEO:

Dust from the impact will block the sunlight from reaching Earth and cause nuclear winter. Plant photosynthesis will stop and the food-chain would collapse After the planetary cooling, a greenhouse effect will increase the Earth’s temperature because of the increase of carbon dioxide in the atmosphere Effects on Earth of a collision with a large NEO:

The primary objective is to set up optical telescopes to discover all NEO’s and calculate their orbits NASA has two programs: NEAR (Near Earth Asteroid Rendezvous) and NEAT (Near Earth Asteroid Tracking) Internationally there is ESA’s Spaceguard Foundation Telescope at Mt. Palomar used in Near Earth Asteroid Tracking Survey NASA’s NEAR Shoemaker orbited and landed on an asteroid

If an asteroid is predicted to hit Earth there are some proposals to alter the orbit of an asteroid in a controlled manner: Give the asteroid a “shove” to move it out of Earth’s way, but there is a risk of breaking the asteroid into many pieces which will increase the threat Use gravitational effects by putting a spacecraft alongside and using gravitational attraction between the two to pull the asteroid off course Artist’s image of an asteroid being destroyed

The Earth moves in space the equivalent of its own diameter in just six minutes So to move an NEO off target, it would be enough to delay its arrival time by six minutes allowing it to harmlessly pass by

Right now there are no objects on a collision course with Earth The chance of a collision in the next century is about 1 in 1000, but an uncharted object can collide with Earth at any time We would need about 4-5 years warning to prevent an impact COSMIC IMPACTS ARE THE ONLY NATURAL DISASTER THAT CAN BE AVOIDED Image of a spacecraft fired into an asteroid (ESA)