- The Washington Times - Thursday, March 8, 2001

"Mir has lived a wonderful life and must end it in a graceful way,"said Russian Space Agency chief Yuri Koptev on television last month, defending the decision to bring the 15-year-old space station "Mir" down from orbit between March 13-18. "We must discard it while we are still capable of controlling it, not turn its descent into a roulette that threatens the whole global community."

There's still an element of Russian roulette about the enterprise:up to 40 tons of material from the station's original 130 tons will survive the heat of re-entry and smash into the Earth's surface in chunks that could weigh up to 1,500 pounds each. The Russians are aiming for an empty strip of the Pacific Ocean halfway between New Zealand and Chile, but they admit that if they lost control during re-entry it could hit anywhere on two-thirds of the planet's surface.

Given the craft's bizarre shape (it has been compared to two dragonflies mating), anything could happen when it hit the upper atmosphere. Indeed, when the United States brought the much smaller space station Skylab down in 1979, aiming for the Indian Ocean, it ended up crashing into an uninhabited area of Western Australia. The Russians calculate the odds on shrapnel from Mir hitting any major city at only 0.02 percent, but Chicken Little was right: Things falling out of the sky are inherently dangerous.

Meanwhile, in another corner of the Solar System, object 2000 SG344 is quietly orbiting the sun in an orbit that won't intersect Earth's until 2030. It's no bigger than a large office building, but if it did strike the Earth, the impact could be equivalent to a hundred Hiroshima-sized explosions. "This is the highest probability of impact we have ever calculated for an object," said project engineer Paul Chodas of NASA's Near-Earth Object Program Office last November. "In that sense, it's eye-opening."

Mr. Chodas added, however, that it could be an old Apollo rocket booster, which weighs very little and would burn up entirely on re-entry, rather than a far more dangerous rocky asteroid. As it gets closer the orbital calculations will get more precise, and it will probably turn out to be on a trajectory that narrowly misses Earth in any case: Most alarms are false alarms.

Objects of around this size strike the Earth about once a century. The last one, in 1908, exploded over an uninhabited region of Siberia and destroyed nothing except animals and trees. But we are now fairly certain that a much bigger asteroid, hitting the Gulf of Mexico 65 million years ago, killed off the dinosaurs. Suspicions are mounting that the "Great Dying" 250 million years ago, when 90 percent of all marine species and 70 percent of land animals became extinct, was also caused by a huge asteroid colliding with our planet.

What has all this to do with an aged space station falling out of the sky? Only that Mir's demise is being held up as the shabby, corroded proof that the era of manned flight beyond Earth orbit, of larger ambitions and broader horizons, is over. It might be true, too, at least for this generation if it were not for the growing recognition that the human race needs protection against mass death from space.

Late last month, the British government announced that it favored fitting all European space probes with asteroid detectors, building a giant telescope dedicated to finding them, retrofitting existing telescopes with special asteroid detection software, and creating an international flotilla of space probes to study the nearby asteroids. "The potential threat of asteroids to our planet is an international problem requiring an international solution," said Science Minister Lord Sainsbury.

"I think there will be great relief in the United States that we are joining in," a British astronomer remarked: "They were beginning to feel a bit silly about being the only ones to take the asteroid threat seriously." But NASA is right to take it seriously: It's a low-probability risk which, if it came to pass, could kill hundreds of millions of people, or even all of us. If the insurance only costs a few billion dollars a year, the premium is well worth paying.

On Feb. 12, the Near-Shoemaker probe, which had been orbiting the 20-mile-long asteroid Eros for the past year, was landed on it. It was a last-minute addition to a completed mission, meant mainly to test the hypothesis that Eros perhaps like many other asteroids was made not of solid rock but of dense aggregates of stones and pebbles with some spaces in between. It would be much harder to shift the orbit of that sort of asteroid than a solid stone one, since it might just break up.

This is the sort of work we need to be doing. As Helen Worth of Johns Hopkins University's applied physics lab, which ran the Near-Shoemaker project for NASA, put it: "We will have a much better idea what not to do the next time we want to put something on an asteroid like a bomb. And that could prove to be awfully important."

Mir is coming down, but the international space station Alpha is already up and running. It wasn't designed specifically for this role, but it is from there that the defense of Earth will initially be mounted. Even if it never accomplished any other task, that alone would justify its cost a hundred times over.

Gwynne Dyer is a London-based independent journalist.

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