Impact events

Impact events are caused by the collision of large meteoroids, asteroids or comets (generically: bolides) with Earth and may sometimes be followed by mass extinctions of life.

(...)

Meteorite impact

In the history of the Earth, it is widely accepted that several large meteorites have hit Earth. The Cretaceous-Tertiary asteroid, for example, is theorized to have caused the extinction of the dinosaurs. If such an object struck the Earth it could have a serious impact on civilization. It's even possible that humanity would be completely destroyed: for this, the asteroid would need to be at least 1 km (0.6 miles) in diameter, but probably between 3-10 km (2-6 miles). Asteroids with a 1 km diameter impact the Earth every 0.5 million years on average. Larger asteroids are more rare. The last large (>10 km) impact happened 65 million years ago. So-called Near-Earth asteroids are regularly being observed.

Some scientists believe there are patterns in the amount of meteorites hitting Earth. An interesting explanation of such a pattern is given by the hypothetical star Nemesis. This hypothesis states that a star named Nemesis regularly passes through a denser part of the Oort cloud, causing meteorite rains to collide onto Earth. However, the very existence of this pattern is not widely accepted, and the existence of the Nemesis star is highly controversial.

A star passage that will cause an increase of meteorites is the arrival of a star called Gliese 710. This star is probably moving on a collision course with the Solar System and will likely be at a distance 1.1 light years from the Sun in 1.4 million years. Some models predict that this will send large amounts of comets from the Oort cloud to the Earth. Other models, such as the one by García-Sánchez, predict an increase of only 5%.

• Large Synoptic Survey Telescope - Proposed telescope to monitor hazardous near-Earth asteroids and other objects.

-- GeirThomasAndersen - 16 Sep 2006