Sunday, May 2, 2010

Asteroids and Earth: Time for the Space Patrol?

"New And Old Observations Bolster Asteroid Worries"
Space News, Discovery News (May 1, 2010)

"Cornell University astronomers announced last week that they tracked a near-Earth object (NEO) named 2005 YU55 as it skimmed within 1.5 million miles of our planet last April 19. The giant radio antenna at Arecibo, Puerto Rico measured the intruder's size at a planet-walloping 1,300 feet in diameter.

"The speedy visitor is on a wanted list of 'potentially hazardous asteroids' maintained by the Minor Planet Center, of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass...."

"...Unsettling clues that underscore our lack of knowledge about the asteroid threat can be found as far as 500 million miles away and a few centuries back in time.

"On the night of July 19, 2009 Australian amateur astronomer Anthony Wesley photographed a mysterious dark spot that appeared low in Jupiter's southern hemisphere...."

Whatever fell into Jupiter's atmosphere last year was probably a few hundred feet across. As it fell below Jupiter's cloud deck, it heated up - a lot. Then, released the energy it had collected: about as much as you'd get, setting off a few thousand megatons of TNT.

That's a big explosion. By comparison, the Ivy Mike thermonuclear device released about 10.4 megatons of energy. (video embedded in January 13, 2010 post) Ivy Mike turned an island in the pacific into a hole in the seafloor, about 6,240 feet across by 164 feet deep. ("Operation Ivy," The Nuclear Weapon Archive) That's a tad over 1.9 kilometers across and almost 50 meters deep.

One thousand megatons is a little over 95 times the energy of the Ivy Mike explosion. Multiply that several times, and you've got what happened when something a few hundred feet across fell into Jupiter.

Something like that falling on Earth - anywhere - would be bad news.

A Ball of Rock Falls Down: How Bad Can it Be?

I did a little checking, using the Earth Impact Effects Program on the Department of Planetary Sciences' Lunar and Planetary Laboratory (University of Arizona). A ball of porous rock 300 feet across, hitting Earth at a 45 degree angle, at 17 kilometers per second (typical for an asteroid impact) would involve about 20.7 megatons of energy.

If it hit land, where we had sedimentary rock under the soil, and you were standing a hundred kilometers (62.1 miles) away, you'd see quite a show. The object would start breaking up at about 72,500 meters, or 238,000 feet; and explode at about 4,030 meters, or 13,200 feet. Since the object would have shed quite a lot of energy by then, the yield would be a modest 20.2 megatons.

You'd hear the blast just over five minutes later, and it'd be as loud as heavy traffic.

If you were closer, say 10 kilometers (6.21 miles) away: you'd hear the blast sooner, about 32.7 seconds after the explosion. Your ears would hurt, most likely, but you'd survive. Provided that you were in the open, and weren't hit by one of the fragments.

There'd be a bit of wind: 334 miles an hour for a short time. You'd better hope your property insurance was paid up, because this is what would be happening around you:
  • Multistory wall-bearing buildings will collapse
  • Wood frame buildings will almost completely collapse
  • Glass windows will shatter
  • Up to 90 percent of trees blown down; remainder stripped of branches and leaves
On Earth, this sort of thing happens, on average, once every 1,100 years or so. That's an average, of course: chunks of rock like that don't arrive on a fixed schedule.

Well, how bad could that be? Look at it this way: If that rock exploded 4,030 meters over Dallas, Texas, and you were in Cockrell Hill - you'd better hope you're standing in a big open space. Like that plot of land between North Plymouth Road and Sheffield Drive, near Mountain View College.

Not the college campus: that'll be smashed flat. If you lived in the area, your neighbors would most likely be dead. I'm not sure what an urban firestorm would be like - but I'm pretty sure you wouldn't enjoy the next few minutes.

Downtown Dallas? There wouldn't be a crater - but I don't think there would be much of the city center under ground zero, either.

Every Thousand Years or So?

I think one reason that we aren't as aware as we could be, of what's been happening is that in the 'good old days,' news didn't travel as fast. And there weren't as many people around.

Back then, the odds were pretty good that a rock like that would land between population centers. A few people would probably be killed, and a lot of damage done to the landscape - but there wouldn't really be all that much impact on surrounding cultures. Of course, if a rock like that made a direct hit on some small civilization's center - well, they'd be gone, with nothing left by some fairly wild travelers' tales to mark their passing.

Time to Launch the Space Patrol?

Science fiction shows from the fifties didn't, probably, do much to make space travel seem plausible.

That was then, this is now. America is building its seventh spaceport, robot spaceships are exploring the Solar system, and Earth's leaders are beginning to catch on that this planet isn't the safest spot in the universe.

Back to that article:

"...Though 2005 YU55 is scheduled to swing closer the Earth than the Moon on Nov 8, 2011 (just 13 months before the Mayan Calendar ends –- oh my!), the latest observations rule out any collisions with Earth for another century, say Cornell astronomers.

"But what else is lurking out there that we don't know about? President Barack Obama has proposed that NASA's NEO program be increased from $3.7 million in 2009 to $20.3 million in 2011. And, 63 percent of the American public feel that NASA's most important task is to keep an eye on asteroids according to a recent opinion poll."

I'm a bit relieved to read that Cornell astronomers say we have maybe a century to get our ducks in a row. For 2005 YU55. On the other hand, there's Asteroid 99942 Apophis. But I've written about that before. And 2012, too, for that matter. (November 16, 2009, for starters)

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