Wednesday, December 19, 2007


Okay, this isn't a standard Oread Daily sort of article, but since an asteroid impact just might be a bad thing for you, me, and your little dog, too, I'm going to plow right on with it.

It turns out that a much smaller asteroid then previously thought likely caused the huge explosion that tore apart a large part of Siberia just about one hundred years ago. At least, that what scientists at the Sandia National Laboratories in New Mexico are telling us today (see article below).

Now I know we can't go through life worrying about things falling from the skies, but in an age when we really could do something to increase our chance of survival if a big one came a'callin, you'd think some big shot somewhere might be thinking about it.

It turns out some people are, but they're not people with any real power (just like in global warming).

Michael Gaffey, professor of space studies at the University of North Dakota, and widely recognized by his peers for his studies on asteroids and meteorites, says the risk of dying from an asteroid strike is about 1 in 2 million. The problem is that the consequences are tremendous; a half-mile-wide asteroid or larger, of which there are more than 700 that come close to Earth’s orbit, could have an impact equal to 60 billion tons of TNT. While it is not likely to happen, you still want to be prepared he thinks. “You don’t panic, you don’t have to run around screaming and waving your hands,” Gaffey says. “But you do need to devote resources to it."

Gaffey explains: a 1-kilometer (5/8 mile) object hitting the Earth would explode with a force of 50,000 megatons, the equivalent of about twice the entire arsenal of atomic weapons held by the United States and the Soviet Union at the peak of the Cold War.
But, come on, is there really that much danger out there?

“In 1995, there were about 350 known objects approaching the Earth,” Gaffey says. “Now, we know that there are at least 4,000, and more are being discovered each month.”

It was such a large object that basically sterilized the planet 65 million years ago. “It was a real bad day for dinosaurs,” Gaffey quips.

According to an accepted hypothesis, a hit by an asteroid at least 10 km in diameter circa 65 million years ago excavated a mammoth crater measuring 180 km across and 100 km deep. Pieces were thrown into space, and those with insufficient escape velocities ignited upon reentering the earth's atmosphere and kindled a global firestorm. Dark clouds of dust and smoke enveloped the earth, blocking solar radiation and prompting murky nights that lasted for weeks. Several life forms, including the dinosaurs, became extinct.

But then, as far as we know, there wasn't much the dinosaurs could have done. Tough cookies for them though.

We could though.

But we're not.

NASA, with many other mandates on its plate already, did not jump at the chance to develop ways to deflect approaching asteroids even though there is an unfunded (no money) 2005 mandate telling them to do so.

As NASA's head of Program Analysis and Evaluation Scott Pace put it, we can't do more to detect Near Earth Objects "given the constrained resources and the strategic objectives NASA already has been tasked with."

Still, it seems somebody ought to do it. Some agency has to decide to do this and fund it. This isn't about ducking a bullet going past your head; this is about seeing what is coming your way decades ahead and believing in the laws of gravity.

And it turns out there are folks with reasonable ideas to prevent such a calamity.

Edward T. Lu is a NASA astronaut and he has developed a plan of action for deflecting an asteroid. He and fellow astronaut Stan Love have come up with the concept of a space tug. A space tug is a rocket that would launch to the same orbit as an asteroid threatening to hit the Earth and alter the asteroid's orbit by pushing in the direction of its orbital motion.

Lu told ABC News, "You don't have to change much -- one hundred thousandth of a mile an hour is enough, 10 years ahead of time, to cause an asteroid to miss the rendezvous with Earth."

Massimiliano Vasile, a lecturer in aerospace engineering at the University of Glasgow, recently concluded a two-year study comparing nine asteroid-deflection methods, rating them for efficiency, complexity and launch readiness.

The best method, he found, called “mirror bees,” entails sending a group of small satellites equipped with mirrors 30 to 100 feet wide into space to “swarm” around an asteroid and trail it, Vasile explains. The mirrors would be tilted to reflect sunlight onto the asteroid, vaporizing one spot and releasing a stream of gases that would slowly move it off course. Vasile says this method is especially appealing because it could be scaled easily: 25 to 5,000 satellites could be used, depending on the size of the rock.

Again, I'm not telling you to lose sleep tonight worrying about an asteroid strike, but still I'd like to think we had leaders who once in a while thought in the long term.

Yeah, right, that'll be the day.

Our leaders are more concerned that undocumented workers might get a driver's license.

Oh my.

The following is from the Sandia National Laboratories.

Sandia supercomputers offer new explanation of Tunguska disaster

Smaller asteroids may pose greater danger than previously believed.

ALBUQUERQUE, N.M. — The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as previously published estimates, Sandia National Laboratories supercomputer simulations suggest.

“The asteroid that caused the extensive damage was much smaller than we had thought,” says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908. “That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed.”

Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, “We should be making more efforts at detecting the smaller ones than we have till now.”

The new simulation — which more closely matches the widely known facts of destruction than earlier models — shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball.

This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion limited to the height at which the blast was initiated.

“Our understanding was oversimplified,” says Boslough, “We no longer have to make the same simplifying assumptions, because present-day supercomputers allow us to do things with high resolution in 3-D. Everything gets clearer as you look at things with more refined tools.”

Sandia is a National Nuclear Security Administration laboratory.

The new interpretation also accounts for the fact that winds were amplified above ridgelines where trees tended to be blown down, and that the forest at the time of the explosion, according to foresters, was not healthy. Thus previous scientific estimates had overstated the devastation caused by the asteroid, since topographic and ecologic factors contributing to the result had not been taken into account.

“There’s actually less devastation than previously thought,” says Boslough, “but it was caused by a far smaller asteroid. Unfortunately, it’s not a complete wash in terms of the potential hazard, because there are more smaller asteroids than larger ones.”

Boslough and colleagues achieved fame more than a decade ago by accurately predicting that that the fireball caused by the intersection of the comet Shoemaker-Levy 9 with Jupiter would be observable from Earth.

Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth’s atmosphere. As it penetrates deeper, the more and more resistant atmospheric wall causes it to explode as an airburst that precipitates the downward flow of heated gas.

Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.

“Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion,” says Boslough.

One of most prominent papers in estimating frequency of impact was published five years ago in Nature by Sandia researcher Dick Spalding and his colleagues, from satellite data on explosions in atmosphere. “They can count those events and estimate frequencies of arrival through probabilistic arguments,” says Boslough.

The work was presented at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon, co-authored by Sandia researcher Dave Crawford and entitled “Low–altitude airbursts and the impact threat” has been accepted for publication in the International Journal of Impact Engineering.

The research was paid for by Sandia’s Laboratory-Directed Research and Development office.

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