Saturday, April 16, 2011

N is for ... NEO



Oops! Not Nemo...



Not you, either. Sheesh!

A NEO is a Near Earth Object. Astronomists define these as any astronomical body within 1.3 Astronomical Units (AU) of Earth, and, even though an AU is really really big - around 150 million kilometers, or about 90 million miles - there are literally thousands of them. They include man-made satellites, obviously, but also a whole bunch of asteroids and such. In some cases, the orbits of these bodies put them on a potential collision course with Earth; others are virtually stationary relative to Earth, or their orbits are out of synch with ours.

An international project called Spaceguard exists to identify the rest, which are officially designated Potentially Hazardous Objects - ones that could conceivably strike the Earth and do some hefty damage in the process. Anybody who's read Greg Bear's Eon, or seen Armageddon, appreciates the idea here.

So far, almost 1000 have been identified. Cheery thought, no?

The Spaceguard initiative still has a considerable amount of sky to examine. Cheery thought, no?

The most recent near-miss happened within the last five years: a fireball over Indonesia in 2009 with an estimated blast energy of 50 kilotons of TNT. That's twice the power of the Nagasaki atom bomb.

Although there were no reported casualties from that event, there has been extensive damage as a result of NEO impacts in the past. In 1908, around 5 miles above Tunguska, Siberia, a NEO detonated with an energy of 10 megatons - that's 200 times the strength of the Indonesia blast of 2009. Even at that height, it is estimated to have felled eight million trees. The shock wave is believed to have been the equivalent of a 5.0 earthquake. Eyewitness accounts were vivid - "the sky split apart" according to one report - but there was little scientific interest at the time.

Predictive computer models indicate the next Tunguska-sized NEO is most likely to impact China or the US. There is considerably more interest in that one...

4 comments:

Roland D. Yeomans said...

Love your sense of humor. And if a NEo impacts the U.S., we all might need a good sense of humor and resiliancy! Roland

Heather Henry said...

Mojo, you are truly a constant wealth of interesting information. I didn't know that's what NEO meant. I may have learned it at one time, but really I can't recall. I guess I should keep my eyes on the sky.
Never a dull moment! :)
I'm looking forward to the next letter.

Karen Walker said...

Well this post is certainly different - and interesting. Found you thru the a-z challenge. Nice to "meet" you.
Karen

Arlee Bird said...

I guess the Earth has been pretty fortunate considering the numbers we're up against. It's only a matter of time before something happens--let's hope it hits a very desolate area and doesn't create much havoc.


Lee
Tossing It Out
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