The Sentinel Mission

Full moon as seen from STS-103 orbiter Discovery.

There are no passengers on spaceship Earth. We are all crew.—Marshall McLuhan (1965)

Ed Lu wants to save the world. In a talk Thursday at the University of Hawai‘i, the former astronaut recalled looking at the moon while he was aboard the International Space Station. Its craters were dramatic visual evidence of the number and size of the asteroid impacts the moon had sustained. Lu knew that the more massive Earth is hit by asteroids even more often than the moon, although the evidence of those collisions is obscured by water, weather, and vegetation.

We know with a fair amount of confidence how often asteroids hit the earth. In the next 100 years there’s about a 30% chance that the planet will be hit by a “city-killer” asteroid like the one that exploded over the remote Tunguska River region of central Russia in 1908. That asteroid exploded with a force about 500 times greater than the nuclear bomb dropped on Hiroshima. If an asteroid that size were to hit a city or a densely-inhabited area, it would kill millions of people. There’s about a 1% chance in the next 100 years that the planet will be hit by an asteroid 20 times the mass of the Tunguska asteroid. An asteroid that size would hit with about five times the explosive force of all the bombs—nuclear weapons included—used in World War II. And there’s a 0.001% chance that in the next 100 years we will be hit by an asteroid large enough to wipe out human civilization entirely.

“The odds of a space-object strike during your lifetime may be no more than the odds you will die in a plane crash,” Nathan Myhrvold memorably said. “But with space rocks, it’s like the entire human race is riding on the plane.” A thousandth of a percent is not by itself a very large chance. But it’s still high for something that could mean the extinction of the human race and destruction of everything we know and love. As a species, we are—whether we’re aware of it or not—essentially playing a game of Russian roulette. Our number probably won’t come up this century or even the next century. But, as Lu said, in the long run “you can’t beat the house.”

If we knew well enough in advance that an asteroid were going to hit the Earth, it would actually be relatively easy to deflect it far enough from its course to make it miss. But because asteroids are so unreflective—they’re roughly the color of charcoal—it’s more difficult to identify possible threats before they enter the Earth’s atmosphere. While NASA has identified many of the most dangerous asteroids, it isn’t making a systematic effort to survey all the most potentially hazardous objects in the solar system, because cataloging asteroids doesn’t clearly fall within the agency’s mission of basic research. As Lu puts it, “Saving the planet is not considered science at NASA.”


So Lu proposes that we save the planet ourselves. His B612 Foundation—B612 is the name of the planet that was home to Antoine de St. Exupéry’s Little Prince—is working toward launching an infrared telescope designed to survey the asteroids that approach Earth’s orbit. The Sentinel telescope would orbit the Sun near Venus and look for the infrared light emitted from asteroids warmed by the light of the Sun. The B612 Foundation aims to raise $250 million so it can build the telescope and put it into orbit in 2018. It would be the first privately-funded interplanetary mission, although a number of the major ground-based telescopes were funded with private money. As Lu says, $250 million is comparable to the amount of money a museum might raise to build a new wing.

Asteroids are probably not the greatest threat to either the planet or to the human race. As I have argued, there’s a probably greater chance in the next century that we destroy our environment or ourselves than that Earth is hit by a major asteroid. But Lu is right to point out that compared to stopping climate change or preventing a nuclear war, detecting large asteroids is relatively easy. For the price of a museum wing, insurance against asteroid impacts would be a wise investment, especially when you consider some of the other things we collectively spend our money on. Lu noted that the movie Armageddon—about preventing an enormous asteroid from hitting the Earth—cost almost as much in real terms as the Sentinel Mission. “You can either make the movie Armageddon,” Lu said, “or prevent Armageddon.”

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Image of the moon seen from the Space Shuttle Discovery courtesy of NASA. Sentinel orbit diagram courtesy of the B612 Foundation.

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