Scientists Assess Danger of Earth’s Demise by Asteroid
Is this something else you really need to worry about?
An asteroid the size of Los Angeles slams into the Earth and explodes with the force of 10 million megatons of TNT, ending life on the planet as we know it.
That end-of-the-world scenario is being discussed by sober-minded scientists from around the world during an extraordinary conference here this week. Many of them have been working in the back waters of astronomy for years, studying the cold, black rocks that orbit the sun to the disdain of other astronomers who favor the more exotic members of the celestial zoo.
“Some of the people here used to make fun of me for studying these things,” said Eleanor Helin of the Jet Propulsion Laboratory, who has discovered more near-Earth asteroids than any other scientist in the world.
Today, she is a star.
What changed for Helin, as well as many others who have labored in the shadows of astronomy’s more glamorous endeavors, is the growing evidence that an asteroid slammed into the Earth 65 million years ago with enough force to wipe out the dinosaurs that had reigned supreme for 150 million years.
Scientists have reason to believe another asteroid that size will hit the Earth again, and there is ample evidence that such an impact would be catastrophic. But they have no reason to believe such a collision is imminent.
The mere fact that it almost certainly will happen sometime before the sun blinks out a few billion years from now has given a sense of urgency to a field that has been largely ignored in the past.
But are they worried, these gentle folks who comb the heavens looking for approaching doom?
“No one here will go to bed tonight wondering if an asteroid will kill them before they wake up in the morning,” one scientist mused during a break from the long technical sessions of the conference, which is sponsored by the Pasadena-based Planetary Society and the San Juan Capistrano Research Institute. “What this meeting is all about is funding.”
Indeed, one scholar, Eugene Shoemaker of the U. S. Geological Survey warned his colleagues attending the conference that the fear factor ought not be overblown.
Shoemaker believes that if an asteroid of a few miles diameter were speeding toward the Earth, it probably would have been detected by one of several searches now under way.
“The odds are there isn’t anything out there bigger than (half a mile in diameter) that’s going to hit us,” he said.
Even a much smaller object of only a few hundred feet in diameter could devastate a large region. Such an asteroid would be very dim in the evening sky and could easily escape detection.
Although the scientists attending the conference, which ends today, had varying views on the seriousness of the heavenly threat, there was agreement on one point:
If a large asteroid were to strike tonight, or sometime in the next few million years, it would be one spectacular show.
Such an impact would kick up so much dust that “it would cover the entire planet several feet deep,” said David Morrison, chief of the space science division of NASA’s Ames Research Center in Mountain View.
Morrison has emerged as the most eloquent evangelist for the doomsday scenario, and this veteran of some of NASA’s most successful programs roams the planet like a guru descended from the mountain top in a three-piece suit.
Dust from such an impact would “turn off the sun and we would have hot rocks falling out of the sky,” Morrison told several hundred people who turned out for a public meeting on the issue. Even a relatively small asteroid would cause climatic changes that could destroy one year’s crops around the planet, and “that would probably lead to the death of most of the population,” he said.
About 75,000 years ago, a modest asteroid about the size of the Los Angeles Coliseum slammed into what is now eastern Arizona and blasted out Meteor Crater, which is about a mile wide. That crash undoubtedly had a profound impact on the local region, and it proves that such things do happen, although not too frequently.
Morrison admits it is not easy to get people to take his warning seriously because of one little statistic:
“Nobody has ever been killed in human history” by a meteoroid or an asteroid, he said.
But that doesn’t mean it won’t happen. Morrison has compiled statistics he says show that, because everyone would be killed by a catastrophic impact of an asteroid and relatively few people die in plane crashes, you are about as likely to die from an asteroid as you are in a plane crash.
So, what’s a body to do?
Many scientists attending the meeting believe that if an asteroid were found to be on a collision course with the Earth, it would be possible to send rockets up and give it a little nudge, thus sending it out of harm’s way.
“If we found one to be on a collision course, let’s say (it would hit) 83 years from now, we would be highly motivated to go out there and change its orbit,” he said.
The hope of doing something about it is one of the reasons why people such as JPL’s Helin has begun to emerge out of the darkness and into the limelight.
“I’ve been working at this for 20 years,” said Helin, a geologist. Using a small telescope at the Mt. Palomar Observatory, Helin and her co-workers have discovered about 85% of the near-Earth asteroids known to pass close enough to the planet to cause concern.
The ones she has found are errant members of a great group of asteroids that orbit the sun. They are believed to be debris left from the formation of the solar system--chunks of rock and ice that never combined to form large planets. But some of them are big enough to be considered “minor planets.”
Some collide with other bodies, such as the Earth and the moon. The moon has no atmosphere, so it preserves the impact record far more clearly than the dynamic Earth, although both should have been subject to similar impacts.
The record frozen in the surface of the moon suggests that the Earth probably has been hit by an asteroid large enough to create a 30-mile-wide crater “on an average of every 10 million years,” Morrison said. Smaller asteroids of about 100 feet in diameter are believed to hit the Earth about once every 200 years, but they usually hit in the ocean or unpopulated areas.
The possibility of a large asteroid strike has compelled organizations such as the Planetary Society to fund the work of such scientists as Helin, allowing them to upgrade their equipment so that the search for asteroids might be improved.
Helin, who earlier was happy with two or three discoveries per year, is finding that many asteroids every month. She has found most of the 128 asteroids that are on orbits that cross the path of the Earth.
However, that is believed to be only about 5% of such asteroids, and that great void in the record is what disturbs many scientists. There could be a beast speeding toward the Earth at this very moment, and no one knows it.
Only about $1 million a year is being spent on the effort, a puny sum in terms of space research. Many scientists would like to see that at least tripled. But not all scientists are comfortable with seeking funds on the basis of fear.
Shoemaker, of the U. S. Geological Survey, is among those who believe that it is a mistake to dwell on the fear. Asteroids are pristine remnants of the early solar system, and could be mined for fuel for future space flights. They also could hold all kinds of precious minerals.
Scientists hope to send spacecraft out to intercept a near-Earth asteroid in the next decade to see just what wonders it may be hiding. But that will take money that will be hard to get, especially without the fear factor.
Terry Dawson, an adviser to the House Committee on Space, Science and Technology, told the scientists that concern over an asteroidal impact finally has the attention of Congress.
“The probabilities are very low, but the consequences are very dire,” said Dawson, who then spent about 20 minutes telling them that with all the other expensive ventures on NASA’s plate, they should not expect to see their funding grow much.
After hearing similar comments in an earlier technical session, one scientist rose to his feet and wondered allowed:
“Does all this mean an asteroid will land on us before we land on an asteroid?”
