Collision with a cometBOULDER, Colorado Deep Impact
On Sunday night, NASA fired a 3-foot-wide, 820-pound copper barrel directly into the path of a 9-mile-long, potato-shaped comet by the name of Tempel 1. The two successfully collided at 23,000 mph while a mother craft photographed the action from a safe distance and sent the pictures home to us.
Why? So we can learn about impact cratering, one of the major forces that has shaped all the worlds of our solar system. We will also have the chance to peer into the newly formed crater and observe the ice and vapor blasted back into space, thereby learning what lies within this frigid little world.
When I describe the mission to people outside the community of space scientists and enthusiasts, it receives mixed reactions. Some feel that this is a fine hello to a new world, blasting away at it just to see what happens, like greeting a stranger by shooting first and asking questions later. Aren't we going too far to satisfy our curiosity here?
Well, no. This explosion is not going to hurt anyone or anything.
Here's an analogy. You would be justifiably concerned if, in order to learn about shorelines, some scientist decided to dig up your favorite beach. But you wouldn't object if the scientist took a few grains of sand to study. There are something like one trillion comets larger than 1 mile in diameter, several hundred for each human on Earth in this solar system alone, and countless more in the wider universe. So even if we destroy Tempel 1 entirely, we would not be making a dent in the cometary sandbox.
What's more, this mission will not demolish the comet, alter its course, or otherwise affect the cosmic scheme. Comets collide with other celestial objects all the time. The only thing extraordinary about this particular impact is that we engineered it. Deep Impact will simply make one more small hole in an object that, like all planets large and small, has been repeatedly dinged by colliding space debris since our solar system's origin 4.6 billion years ago.
It is those dusky beginnings that this experiment can illuminate.
Beneath the dirty ice crust of a comet like Tempel 1 is material that has been in deep-freeze since the birth of our solar system. Mixed into this timeless frozen treat are organic molecules like those that seeded the young Earth with raw materials for making life. That ice may hold some buried chapters of the story of our origin.
As H.G. Wells, once wrote: "There is no way back into the past. The choice is the Universe - or nothing." It has been said that the dinosaurs ultimately got snuffed because they lacked a space program. Sooner or later a killer comet will again cross Earth's path, threatening all life. Only next time, armed with knowledge about comets and space engineering, life on Earth will have a fighting chance.
Given the recent reckless talk from the Department of Defense about introducing offensive weapons into space, Deep Impact will probably be seen in some quarters as more evidence of American aggression.
In reality, it is the opposite: a peaceful gift from our nation to the world. Deep Impact is pure exploration. In that sense, we have evolved. Unlike Apollo, which was meant in part as a Cold War threat to the Russians, Deep Impact really is for all humankind: It could further our understanding of where we came from.
Of course, explosions are cool (when they aren't hurting anyone). They're also often quite beautiful. Why, after all, do we love to watch fireworks? First images of the approaching comet, the brilliant impact, the new crater and the receding icy nucleus should be available soon.
The scientific analysis that reveals the true meaning will be slower in coming, but once it arrives, the knowledge will be here as long as we are.
(David Grinspoon, a planetary scientist at the Southwest Research Institute, is the author of ''Lonely Planets: The Natural Philosophy of Alien Life.'')