HUGE Asteroids on a Collision Course with Earth? - NASA: "Eyes Wide Shut" (+Video)

If we don’t do something, sooner or later Earth will be hit by an asteroid large enough to kill all or most of us. That includes the plants and animals, not just people. Maybe this won’t happen for millions of years. Maybe in 15 minutes. We don’t know. 

We have been warned. On 23 March 1989, asteroid 1989FC (with the potential impact energy of over 1000 megatons, roughly the equivalent a thousand of the most powerful nuclear bombs) missed Earth by about six hours [Freedman 1995]. We first saw this fellow after closest approach. If 1989FC had come in six hours later most of us would have been killed with zero warning. We are hit by thousands of smaller asteroids every year and we don’t see any of them before the collision.

In October of 1990 a very small asteroid struck the Pacific Ocean with a blast about the size of the first atomic bomb (the one that leveled Hiroshima, Japan, killing roughly 200,000 people in seconds). If this asteroid had arrived ten hours later it would have struck in the middle of more than a million U.S. and Iraqi soldiers preparing for war. How would America have reacted to what looked like an Iraqi nuclear attack? Hiroshima-sized explosions due to asteroids actually occur in the Earth’s atmosphere about once a month [Lewis 1996b], but are seldom seen because most of the Earth is unpopulated.  The data comes from Air Force satellites designed to look for nuclear explosions.

In 1908 a small asteroid (perhaps 50 meters across) hit Tunguska, Siberia and flattened 60 million trees. That asteroid was so small it never even hit the ground, just exploded in mid-air. If it had arrived four hours and fifty-two minutes later it could have hit St. Petersburg [Lewis 1996b]. At the time St. Petersburg was the capital of Russia with a population of a few hundred thousand. The city would have ceased to exist. As it was, dust from the blast lit up the skies of Europe for days. Asteroid strikes this size probably happen about once every hundred years. However, this is just an average. Just because we got hit once doesn’t mean we’re safe for another hundred years. Indeed, there was another Tunguska-class strike in the Brazilian rain forest on 13 August 1930 [Lewis 1996b].

There are about 1,000 asteroids a kilometer or more in diameter that cross Earth’s orbit (the path Earth takes around the Sun). About a third of these will eventually hit Earth [Lewis 1996a]. An asteroid strike this large can be reasonably expected to kill a billion people or so, depending on where it hits. A strike in China or India would kill more, in Antarctica less. Even a strike in the ocean would create a tsunami so enormous most people living near the coast would be drowned. A strike of this size is expected about once every 300,000 years or so.

Read more here: Planetary Defense -Asteroids can make us extinct (the threat)

http://www.nss.org/resources/library/planetarydefense/planetarydefense.html

The Threat to Earth from Asteroids & Comets  http://panstarrs.ifa.hawaii.edu/public/asteroid-threat/asteroid_threat.html