Bullets from Outer Space

In June 1908, a stray space rock—now thought to be a comet—hurtled toward the Tunguska River in Siberia and exploded about five miles above the ground. Observers tens of miles away from ground zero reported that the “sky split in two,” the air became unbearably hot, and a shock wave threw people against the ground. The force of the explosion leveled 500 square miles of forest.

The rock, by current estimates, was only 50 meters wide, about the length of Annenberg Hall.

The so-called Tunguska event dramatically illustrates what the dinosaurs painfully learned 65 million years ago: asteroids and comets do collide with earth. Geologists and astronomers believe that an asteroid several miles across crashed onto land then, kicking up enough dust to block out sunlight worldwide for years, leading to reduced agriculture and mass starvation. The same could happen to humans today should a “near-earth object,” or NEO, of that size crash into, say, Massachusetts.

Even smaller NEOs could prove troublesome at best, whether they crash into land or ocean. “There’s some modeling to indicate that objects of a few hundred meters across would [cause damage] comparable to what we saw in the tsunami in the Indian Ocean a few years ago,” said Brian G. Marsden, the director emeritus of the Minor Planet Center (MPC) at the Harvard-Smithsonian Center for Astrophysics in a phone interview. And they’ll come eventually: kilometer-wide NEOs strike the earth every few hundred thousand years, with Tunguska-size NEOs striking about once per century.

What’s different from a century ago is that we now have the ability to spot many of the 20,000 or so dangerous NEOs long before they approach earth. Of course, we’ll only spot them if we’re looking for them. But in a report it previewed Monday, NASA declined to allocate any additional funds from its $17 billion annual budget for this task.

What’s unique about this scientific task—identifying and cataloguing the orbits of NEOs—is that can be accomplished without using tremendous resources. In the past decade, 20 professional and 100 amateur astronomers across the globe, led by the Garden Street-based MPC, have identified three-quarters of asteroids at least one kilometer across, and all on a budget of a not-so-gargantuan $4 million per year (in 1996 dollars). Within the next two years, he expects that the MPC-led teamlet will have identified 90 percent of the 1,200 or so kilometer-wide asteroids. But smaller NEOs are still potentially dangerous.

“We are woefully unprepared for this right now,” said Rep. Dana Rohrabacher (R-Calif.), the former chairman of the Subcommittee on Space and Aeronautics, in a phone interview. What we need, in his opinion, is “a little money, a little attention, and a little organized structure”—that is, a structure for a response to an earthbound NEO. A search for objects in the 140-meter to one-kilometer range would require more people and more telescopes since the objects would be too small for amateurs’ more modest telescopes to routinely spot. But the cost would be only about $1 billion over 20 years, which is a pittance as scientific research goes.

Of course, what exactly to do about a Harvard Square-sized boulder bearing down on earth is an entirely different challenge. Currently, there are several hypothetical options, which fall into two broad categories. One, give the asteroid a very gentle nudge away from the earth. This could be accomplished either with a tiny rocket attached to the side of the asteroid or by a minute gravitational tug from a nearby spaceship. Two, detonate a nuclear bomb next to the asteroid, vaporizing one side of it, and sending it careening in another direction. Either option requires a good deal of advance notice. Engineering and launching an interceptor might take years, and any sort of nuclear weapon in outer space would require years of international debate.

But first, the challenge is spotting the buggers. NASA needs to reshuffle its cash to fund the larger project, or Congress—which two years ago asked NASA to come up with a comprehensive search-and-destroy plan—needs to boost the space agency’s budget accordingly. And NEO-spotting is still a long-term project. We can catalog all the dangerous asteroids in the next few decades, but comets are more troublesome, since they come shooting from the dark reaches of the outer solar system. We’d have substantially less warning—a few years, maybe months—about a comet on track for earth.

In the meantime, the United Nations needs to start talking about nukes in space and should encourage member nations assist the research effort, since any large collision would have global consequences. Congress needs to designate an entity that would lead the response to an NEO, Rohrabacher says; and we need to do it now, not when an NEO is about to hit. “Everyone always wants to ignore the worst-case scenarios,” he says. “That’s not the way to be safe.”



Matthew S. Meisel ’07 is a chemistry concentrator in Currier House. His column appears on alternate Fridays.