Near-earth objects: monsters of doom?

Asteroid! Asteroid! Speeding through the sky. Will it strike or graze the earth? Will everybody die?

- Armand T. Ringer

Last March astronomer Brian Marsden, at the Harvard-Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, issued a spine-chilling announcement. based on eighty-eight days of observing asteroid 1977 XF11, his computer calculated that this massive rock would come perilously close to Earth at 1:30 P.M. Eastern time, on Thursday, October 26, 2028. It could miss Earth by a mere 30,000 miles, only about one-eighth our distance from the moon. Almost a mile wide, if the rock struck the earth the devastation would be too awful to contemplate.

The next day, before fundamentalist cult leaders had time to integrate this possible cataclysm into their Second Coming prophecies, Marsden was humbly apologizing. Eleanor Helin and her associates at NASA's Jet Propulsion Laboratory located a seven-year-old photo of XF11 that permitted a more precise calculation of its path. The asteroid circles the sun every twenty-one months. On its 2028 crossing of Earth's orbit it will miss us by 600,000 miles, about two-and-a-half times the moon's average distance from Earth.

"Near-Earth Objects" (NEOs) is today's term for massive objects that periodically cross Earth's orbit not far from our planet. They include asteroids, meteoroids that are mostly asteroid fragments resulting from collisions, and comets which come from regions far beyond Pluto. Disasters caused by NEOs striking Earth were common themes in early science fiction as well as in some modern disaster movies.

As usual, H. G. Wells pioneered the theme.' His novel 'In the Days of the Comet concerns the effects on Earth of a near miss by a giant comet. His short story "The Star" is a vivid account of devastation caused by a mammoth NEO. An asteroid (Wells calls it a "planet") from the outskirts of the solar system is Shifted from its orbit. It collides with Neptune. The two coalesce to form a flaming "star" that almost demolishes the Earth before it plunges into the sun.

Wells's story first ran in the 1887 Christmas issue of the London periodical The Graphic. I have framed in my study the magazine's full-page, full-color illustration showing Londoners staring upward at the star and shouting "It is brighter!" A newsboy holds a paper with a headline, "Total Destruction of the Earth," in huge scarlet letters.

Here is how Wells describes what happens as Earth and star swing around each other:

And then the clouds gathered, blotting out the vision of the sky, the thunder and lightning wove a garment round the world; all over the earth was such a downpour of rain as men had never before seen, and where the volcanoes flared red against the cloud canopy there descended torrents of mud. Everywhere the waters were pouring off the land, leaving mud-silted ruins, and the earth littered like a storm-worn beach with all that had floated, and the dead bodies of the men and brutes, its children. For days the water streamed off the land, sweeping away soil and trees and houses in the way, and piling huge dykes and scooping out Titanic gullies over the countryside. Those were the days of darkness that followed the star and the heat. All through them, and for many weeks and months, the earthquakes continued.

I still recall as a boy reading in Hugo Gernsback's Science and Invention, then my favorite magazine, the six installments of a preposterous novel that ran in issues July through December 1923. The author was Ray Cummings, and his novel was titled Around the Universe: An Astronomical Comedy. It was about a spaceship that carried Tubby, his girlfriend, and an astrophysicist called Sir Isaac. After exploring the universe, they learn that evil Martians are planning to invade the earth. To prevent this, Sir Isaac steers his spaceship in circles around a tiny asteroid, causing it to shift its orbit slightly. This results in a series of collisions with larger asteroids, all precisely calculated by Sir Isaac, that finally create a giant fireball which collides with Mars and obliterates its inhabitants.

This is not as crazy as it seems. The orbits of asteroids are chaotic. A minute change in one orbit could start a "butterfly effect" of the sort triggered by Sir Isaac. Even our solar system is unstable. A giant NEO coming close to a small planet or striking it could set off a chain reaction that could conceivably kick a planet out of the solar system. (See "Crack in the Clockwork," by Adam Frank, in Astronomy May 1998, pp. 5459.) Newton was well aware of this instability. He believed it was necessary for God to intervene at times to readjust planetary orbits to keep the system running smoothly.

Later science-fiction novels about NEOs that wreck Earth are far too numerous to list. On the movie screen New York City has twice been destroyed by NEOs. It was demolished in a dreary 1979 film, Meteor, which wasted the talents of Sean Connery, Natalie Wood, Henry Fonda, and Trevor Howard. In an earlier and even more absurd film, When Worlds Collide (1951), a wandering star called Ballus flattens New York City with a gigantic tidal wave. The recent XF11 scare has been great publicity for two new disaster films about NEO impacts released this year just after the time I am now writing: Disney's Armageddon, starring Bruce Willis and Paramount's Deep Impact featuring Robert Duvall. It's a good bet that the visual effects of both films will be superior to their scientific accuracy.