NASA estimates 4,700 'potentially hazardous' asteroids

[alp227]

About 4,700 asteroids are close enough and big enough to pose a risk to Earth, NASA estimated Wednesday after studying data beamed back from an orbiting telescope.

The figure -- give or take 1,500 -- is how many space rocks bigger than 100 meters (330 feet) across are believed to come within 5 million miles (8 million km) of Earth, or about 20 times farther away than the moon.

"It's not something that people should panic about," said Amy Mainzer, an astronomer at NASA's Jet Propulsion Laboratory in California. "However, we are paying attention to the issue."

NASA defines a potentially hazardous asteroid as one large enough to survive the intense heat generated by entry into the atmosphere and cause damage on a regional scale or worse. The figure released Wednesday is lower than a previous rough estimate had projected, but more are now thought to be in orbits inclined like Earth's, making them more likely to cross its path.

full: http://www.cnn.com/2012/05/16/us/nasa-asteroids/index.html

[pokerfan]

1. Neil deGrasse Tyson said it best

Venus has a runaway greenhouse effect. I kind of want to know what happened there because we're twirling knobs here on Earth without knowing the consequences of it. Mars once had running water. It's bone dry today. Something bad happened there as well. Asteroids have us in our sight. The dinosaurs didn't have a space program, so they're not here to talk about this problem. We are, and we have the power to do something about it. I don't want to be the embarrassment of the galaxy to have had the power to deflect an asteroid, and then not and end up going extinct.

[longship]

2. Tunguska was smaller than 100 m.

And it would have wiped out a major city.

There is no consensus for its size but there is general agreement that it was tens of meters in diameter.

See Wiki for details.

[FogerRox]

3. And was of a composition that it likely did not break up on the way in.

That asteroid that we passed a month or so ago, was a loose amalgamation of carbon like material and would have quickly broken up.