Doom from the sky

People laugh about the story of Chicken Little who cries out that the sky is falling. But a group of astronomers has warned that something like that may very well happen before this half-century is out. They have discovered an asteroid nearly a quarter-mile wide that they think might slam into the earth 30 years from now and are urging immediate action by governments around the world to start planning programs to avert that happening.The group is made up of people who are experts in near-Earth objects, for which they make the acronym NEO. They had a conference in London recently and compared notes on their findings.The asteroid in question was identified in 2004 and studied in 2005 for its trajectory. At first they were scared enough to believe that it could hit the earth in 2029. Then they did some more fine-tuning of their computer data and decided that it would come close to the earth in 2029, but wouldn't be on a possible collision course until 2036.They're worried. As one of the conferees said: "It's question of when — not if — a near-Earth object collides with Earth."

The conference pointed out that the geologic record shows that an object a half-mile or more in width has collided with the earth every few hundred thousand years. An object three miles wide, which could cause mass extinction, has hit the earth every hundred million years.Given the geologic record of the last time something like that happened, one scientist at the conference said: "We are overdue for a big one."This particular asteroid orbits the sun every 324 days. It will be visible enough to be studied by radar in 2006, and the next time that condition will come about will be 2013. But the conference said nations should start planning on counter-action soon, because the strategy for such counter-action is sketched out in theory but no hardware is ready to do the job.
Computer technology has given immense help to the study of this asteroid. It can simulate where its orbit will take it in space, by comparison to where the earth will be, and the scientists in the study have come up with this scenario:

In 2029 the asteroid will be closer to the earth than the moon is. It will be seen in the sky with the naked eye. And that will bring it close enough to Earth's gravity to cause its orbital trajectory to alter. The next time it gets that close to our neighborhood will be 2036, and the scientists think its trajectory change could well have put it on a collision course with Earth.

While most objects that fall from the sky burn up in the earth's atmosphere, often appearing as brilliant meteors, there have been some major collisions in the past. Something big brought an end to the Cambrian geologic era. The later Permian era came to an end when an object as big as Mount Everest slammed into the earth at a spot that is now off the northwest coast of Australia. And scientists now generally agree that the age of the dinosaurs was ended by the crash of a large object off what is now the Caribbean off Yucatan.

Smaller strikes have been recorded frequently. One descended with a fiery streak into the Atlantic in the 1930s. In the early 1900s one hit an uninhabited spot in Siberia, leveling forests for miles around. There's a big crater in Arizona that is the record of a hit in that spot in ancient times.

So what to do to keep the present danger from hitting? The European Space Agency has designed a plan to send two missiles to a space object large enough for practical study, probably another asteroid. One satellite will hit the object at high speed, and the other will measure any change in the orbit of the object.

Those at the London conference didn't think it would be a good idea to try to blow the asteroid up. If an object a quarter-mile wide were broken into 10 or a dozen pieces, they said, those pieces would still be big enough to slam into the Earth over a wider area. There's no technology for reducing an entire asteroid to sand particles that would burn up before hitting the ground.

Computer studies show that if the asteroid hits in 2036, it will be somewhere in the eastern hemisphere, releasing energy 100,000 times the energy released by the atom bomb dropped on Hiroshima. Debris and dust kicked up by this blast would cloud the entire earth, probably for months.

Since discovering this potential danger, the scientists sought to find a name for the asteroid. They settled on "Apophis." The ancient Egyptian myths gave that name to a demon seeking to plunge the earth into darkness — a very appropriate name for this heavenly body.

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