Saturday, February 16, 2013

Follow-up: Yesterday's score in the cosmic shooting gallery -- a screamingly close near-miss scrape and a hit

It is worth clipping Ms Dunn of AP, as a follow up:
CAPE CANAVERAL, Fla. (AP) — A 150-foot asteroid hurtled through Earth's backyard Friday, coming within an incredible 17,150 miles and making the closest known flyby for a rock of its size. In a chilling coincidence, a meteor exploded above Russia just hours before the asteroid zoomed past the planet . . . .

Asteroid 2012 DA14 [the fly-by object], as it's called, came closer to Earth than many communication and weather satellites orbiting 22,300 miles up. Scientists insisted these, too, would be spared, and they were right . . . . 

NASA estimated that the meteor that exploded over Russia was tiny — about 49 feet wide and 7,000 tons before it hit the atmosphere, or one-third the size of the passing asteroid.

As for the back-to-back events, "this is indeed very rare and it is historic," said Jim Green, NASA's director of planetary science. While the asteroid is about half the length of a football field, the exploding meteor "is probably about on the 15-yard line," he said.

"Now that's pretty big. That's typically a couple times bigger than the normal influx of meteorites that create these fireballs," he said in an interview on NASA TV.

"These fireballs happen about once a day or so , but we just don't see them because many of them fall over the ocean or in remote areas. This one was an exception."
[--> I recall seeing one that never made the news, on an afternoon in the early 1970's, from the verandah of the rectory at my High School, looking eastwards over the Port Royal Mountains surrounding Kingston, Jamaica on the East: blue-white streak-trail, orange-ish airburst if I recall correctly at this distance in time; colours could be reversed. From my direction, the path was slightly canted S-wards from coming down straight from the sky, at an elevation of maybe 5 - 10 degrees angular view over the skyline. There may have been a slight kink in the path just before the ball-flash.]

As the countdown for the asteroid's close approach entered the final hours, NASA noted that the path of the meteor appeared to be quite different than that of the asteroid, making the two objects "completely unrelated." The meteor seemed to be traveling from north to south, while the asteroid passed from south to north — in the opposite direction.

Most of the solar system's asteroids are situated in a belt between the orbits of Mars and Jupiter, and remain stable there for billions of years. Some occasionally pop out, though, into Earth's neighborhood.

NASA scientists estimate that an object of this size makes a close approach like this every 40 years. The likelihood of a strike is every 1,200 years . . .  [Cf FAQ here.]
What is not being emphasised: objects as small as these in the Asteroid belt between Mars and Jupiter are inherently subject to essentially unpredictable orbital path disturbances, not just to go near-earth, but possibly to hit us.

Wake-up call, for those with ears to hear and hearts to listen. END