Somewhere out there, a big rock is hurtling this way
You may laugh at Nostradamus for predicting that a great meteor will someday slam into the Earth, but scientists are on the seer's side.
By TOMOHIRO MURAYAMA
AERA
Today, the prophesy by 16th-century French astrologer Nostradamus that a meteor--the "Great King of Terror," he called it--will devastate the Earth prompts little more than laughs.
Yet scientific evidence suggests that an asteroid is sure to collide with the Earth one day. And in Japan, at least, efforts are finally being made to determine when that day might come.
According to Junichi Watanabe, head of the publicity department of the National Astronomical Observatory, it will not be October 2028.
That is the date named in a news report on March 12 last year: "In October 2028, an asteroid will draw dangerously close to the Earth." Since the source was the respected International Astronomical Union (IAU), the media gave it prominent coverage worldwide.
The minor planet or asteroid "1997XF11" was discovered in 1997 by a specialist at the University of Arizona who calculated its orbit and concluded that "the asteroid will hurtle past the Earth at a distance of 0.00031 astronomical unit (AU) from the center of the Earth 30 years from now." (An equivalent to the distance between the sun and the Earth, an AU is about 150 million kilometers.)
The asteroid was predicted to pass by at an altitude of approximately 40,000 kilometers from the Earth's surface. Since the height matched that of the orbits of stationary satellites, including communications and weather satellites, it was feared that the asteroid was in range to potentially collide with the Earth.
The piece of rock, with a diameter of one to two kilometers and a furious speed of tens of kilometers per second, was believed capable of releasing energy a million to 10 million times greater than that of the atomic bomb dropped on Hiroshima. If it hit land, it could create a crater measuring tens of kilometers in diameter. If it hit the ocean, a tsunami hundreds of meters high devastate area more than 1,000 kilometers from the point of impact.
In the end, however, the commotion over 1997XF11 subsided after just one day. Specialists at the Jet Propulsion Laboratory of the National Aeronautics and Space Administration calculated the asteroid's orbit based on new findings. They found that it will pass by the Earth at a safe distance of 0.0064 AU (approximately 960,000 kilometers).
"It happens all the time," said Watanabe, of the asteroid scare.
Calculated figures of an asteroid's orbit often change as time passes, he said. As additional data are gathered, the clearer information about the orbit becomes. Many astronomers believe it is better to wait until the asteroid's orbit is better known before making news.
Subject of movies
But the interest in asteroids is not confined to last year's "close call." Recently, collisions with asteroids and comets have become the subject of blockbuster movies, such as "Deep Impact" and "Armageddon." And even Nostradamus' doomsday prophecy has been attracting attention.
Watanabe of the National Astronomical Observatory said one reason for the surge in interest is an unprecedented incident that took place five years ago. In July 1994, Comet Shoemaker-Levy 9 which had split into about 20 fragments collided with Jupiter.
"It was the first time for mankind to observe such an incident in real time. The impact of the event was great," said Watanabe.
The collisions left impact craters with diameters that measured a distance equal to 60 percent of that of the Earth (7,500 kilometers) and created mushroom-shaped clouds as high as 3,000 kilometers. The images were striking for those who have imagined a comet colliding with the Earth.
Celestial bodies that are at risk of colliding with the Earth are asteroids and comets called "near Earth objects" (NEO) that draw close to the Earth's orbit.
The numerous craters on the moon testify to the NEO collisions. Although the objects must have also hit the Earth, their craters have become inconspicuous after being buried under earth and sand, or having collapsed due to erosion or the movements of the Earth's crust. In 1991, one such massive crater was discovered beneath the ground in a jungle on the Yucatan Peninsula of Mexico.
"From its diameter (180 kilometers), the crater must have been created by a NEO which measured around 10 kilometers across," said Takafumi Matsui, assistant professor of science at the University of Tokyo, who is studying the site. "It is scientifically convincing to say that this particular collision, which occurred 65 million years ago, wiped out the dinosaurs."
Matsui's recent studies have shown that as a result of the collision, tsunami several hundred meters high crashed against what is known today as the North American continent, flooding hundreds of kilometers inland. An earthquake registering a magnitude of 10 on the Richter scale is thought to have shaken the Earth. The ensuing long-term destruction of the atmosphere's ozone layer, acid rain and global warming reportedly eliminated 70 percent of all living things on the Earth.
So far, a total of 150 massive craters have been found around the world. Some researchers say that a number of the collisions are linked to the extinction of some species of the past.
The risks of NEO colliding with the Earth depend on their size. Matsui said that a collision with a huge NEO, like the one which wiped out the dinosaurs, occurs once every 30 million to 100 million years. A collision with a NEO whose diameter is in the one-kilometer range occurs every 100,000 to a million years; if the NEO measures around 100 meters in diameter, the frequency of a collision is every thousand to 10,000 years.
"The smaller the NEO, more frequently they come," said Matsui.
A NEO measuring several dozen meters in diameter, a size which is likely to collide with the Earth once every hundred years or so, actually reached the Earth in June 1908. A tremendous explosion occurred in Tunguska, Siberia, the place of impact, and the surrounding forest within a 20- to 30-kilometer radius was annihilated by fire and the blast.
Some researchers have commented that had the asteroid fallen some distance to the west, on St. Petersburg, Vladimir Lenin may have died and history may have taken a completely different course.
As for the "great collision" that occurred 65 million years ago, the NEO may have missed the Earth had it passed minutes earlier or later. In that case, the dinosaurs would not have died out and whether mankind could have evolved as it did is questionable.
"The collisions with NEO have influenced the history of the Earth," said Matsui.
There is even possibility of mankind facing the same fate as the dinosaurs one day. In fact "near-misses" with the NEO occur quite frequently.
According to the Minor Planet Center of the Smithsonian Astrophysical Observatory in the United States, asteroids that draw close to the Earth within the 1.5-million-kilometer (0.01 AU) range have been observed 19 times as of January this year. The closest encounter occurred in December 1994, when the distance between the asteroid and the Earth was 105,000 kilometers. The asteroid passed by the Earth at a point which was a quarter of the distance between the Earth and the moon. Such incidences of the NEO passing by the Earth at points closer than the moon occurred four times in the past.
The figure should not be dismissed as "low." Of the 19 observations mentioned, 15 have taken place during the 1990s, as a result of the advance in precise machinery. Therefore, a similar number of near-misses is thought to have occurred in the past.
If an asteroid with a diameter in the 10-kilometer range collides with the Earth, a large number of species are in danger of becoming extinct. If the falling asteroid is around one kilometer in diameter, modern civilization will teeter on the brink of collapse; if it has a diameter in the 100-meter range, Japan will be ruined. "Therefore, it makes sense to collect data on the NEO," maintained Atsushi Nakajima, chief researcher at the National Aerospace Laboratory.
Asteroids with diameters in the 10-kilometer range have for the most part been discovered and are known. Yet, many of those with diameters in the one-kilometer range have not been identified. As for comets, the number of existing comets is said to be several times greater than those that have been identified. And NEO are sure to exist among these unidentified asteroids and comets.
According to Koichi Matsushima, an administrative member of the Japan Spaceguard Association, which has been alerting the public on the NEO issue, the NEO whose orbits are already known are unlikely to hit the Earth during the next 1,000 years. "But we don't know whether unidentified NEO will come our way tomorrow or 1,000 years from now."
Steady observations
The only way to fully comprehend NEO is to carry out steady observations. Although past observations have been carried out mainly in the United States, there is a move to follow suit in Japan.
In January, the construction of a facility to survey the asteroids and space debris began in the town of Bisei in Okayama Prefecture.
An incorporated foundation called the Japan Space Forum will spend about 700 million yen to construct one-by-one-half-meter telescopes that are expected to begin operating in the fiscal 2002.
Nakajima of the National Aerospace Laboratory said that the telescopes are capable of observing dark, difficult-to-detect celestial bodies.
"They will be able to detect asteroids that are one kilometer or larger in diameter," Nakajima said.
If more than 10 telescopes of such scale exist around the world, it is possible to identify all minor planets, which have diameters in the one-kilometer range and which could strike a devastating blow to modern civilization.
But we have to wait many years for that to happen. Although the Spaceguard Foundation, an international group consisting of researchers interested in the NEO, has been appealing to governments to reinforce their observation programs, its effort has not really been rewarded.
In case an unidentified NEO is heading toward the Earth, early discovery will be difficult if the sun is behind it. As for the NEO with diameters in the range of 100 meters, they are too dark and complete detection is impossible.
"To solve these problems, it is ideal to observe them using telescopes placed in space, as is the case with the Hubble Space Telescope," explained Masayoshi Utashima of the National Space Development Agency of Japan. He added that researchers are discussing a plan to place a telescope on the moon to obtain more accurate observation data.
What should be done if an approaching NEO is discovered?
One idea is to push the NEO out of its orbit by shooting it with laser beams or hurling something at it.
One of the more realistic ideas would be to use a nuclear warhead. In the films "Deep Impact" and "Armageddon," characters try to prevent a collision with Earth by burying nuclear warheads in the NEO. But since such a method is technically difficult to execute, a rocket would likely have to be used.
"If we just flung a rocket at the NEO, there is the danger of fragments of it hitting the Earth. A more subtle technique which triggers a nuclear explosion on the surface of the NEO and changes its orbit without destroying the NEO itself is called for," said Matsushima of the Japan Spaceguard Association.
Naturally, it requires money to establish all the observation facilities and defense programs.
Although critics stress that the budget should not be spent on preparing for unforeseen occurrences, Matsushima maintained that we should at least continue to make the observations.
"We should feel uncomfortable about not knowing what is going on around our house," he said.
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