NASA photo

The asteroid 2012 DA14, which will come within about 17,000 miles of Earth on February 15, is about half the size of a football stadium, and in a collision would generate an explosive energy equivalent to 2,500 kilotons of TNT. In comparison, the atomic bomb over Hiroshima that instantly killed more than 70,000 people released “merely” the equivalent of 17 kilotons of TNT. Seventeen-thousand miles seems like plenty of room, but in cosmic terms, it’s an awfully close shave. “Remember, the Earth is a moving target, traveling around the sun at 65,000 miles per hour,” former astronaut Ed Lu said in a public appearance at the Stanford Institute for Economic Policy Research earlier this month. “So [the asteroid] is missing us by only about 14 minutes.”

2012 DA14
highlights Earth’s vulnerability to mid-sized asteroids capable of delivering nuclear-sized blasts.To be clear, the asteroid is not going to collide with Earth. But if it did, it’d have a devastating impact — one that highlights Earth’s vulnerability to a tough-to-detect mainstay of the cosmos: mid-sized asteroids capable of delivering nuclear-sized blasts. Comparable in size to the asteroid that destroyed 1,000 square miles of trees and reindeer in Tunguska, Siberia in 1908, 2012 DA14 would be very bad news in a direct collision with a populated area. Imagine a giant explosion in the sky, followed by a blast wave that would level buildings, knock the Golden Gate Bridge into the sea, and subject an area between San Francisco and San Jose to total destruction. A Spanish dental surgeon and amateur astronomer named Jaime Nomen first spotted 2012 DA14 last year –- hence the “2012” in its name –- so you might think that would give officials ample time to come up with an asteroid-deflection plan. But no. “With one year’s notice, there’s absolutely nothing we can do,” Lu said. “There’s no launch opportunity –- the asteroid is orbiting back around the sun. Had it been coming back to hit us, the only option would have been to evacuate. That’s not a good option.”

The good news: With enough warning — preferably decades — an asteroid headed for Earth could be deflected. Ramming a remotely controlled spacecraft against an asteroid to change the velocity by just millimeters per second can avert a collision with Earth. If, that is, we have at least 10 years notice before a collision. With less time, the change in velocity needs to be far greater. “The curve goes from millimeters per second to meters per second pretty quickly,” Lu told Popular Science. “The job rapidly goes from ‘easy- easy’ to almost impossible starting at about a decade.”

There are about one million asteroids larger than 40 meters that scientists consider “near Earth objects,” because their paths around the sun criss-cross the Earth’s orbit. NASA’s near-Earth object office in Pasadena, California, reports that humans have spotted about 94 percent of the really large, civilization-ending near-Earth asteroids – in the 1- to 10- kilometer range, like the monster that wiped out the dinosaurs 65 million years ago – and concluded that none so far discovered will hit Earth in the next hundred years. But due to budgetary constraints, Lu points out that we have identified the orbits of only 1 percent of the still potentially dangerous medium-sized asteroids of at least 40 meters – like 2012 DA 14 or the Tunguska asteroid.

Though amateur and professional astronomers on Earth have spotted the NEOs that we do know about, there are limits to what terrestrial telescopes can accomplish. Telescopes only work at night, which prevents us from seeing asteroids approaching the planet from the inside of Earth’s orbit. Also, many asteroids are dark black and reflect less than 10 percent visible light, making them hard to spot from Earth. They do emit infrared light, but many infrared wavelengths do not make it through the Earth’s atmosphere. Lu has raised several million dollars toward a final goal of roughly $400 million through his B612 Foundation to launch a telescope called Sentinel into orbit near Venus. During a proposed 6.5 year mission, Sentinel will spot asteroids that cannot easily be identified from Earth. If successfully launched in 2018, Lu promises that Sentinel will spot about 500,000 NEOs, including 90 percent of all NEOs that are more than 140 meters, and 50 percent of the Tunguska-sized 40-meter rocks.

The only warning sign is a flash in the sky and a tidal wave.In making his fund-raising pitch, Lu likes to compare the asteroid threat to the risks we face every day. Our planet has about a 30 percent chance of getting hit by a Tunguska- sized 40 meter asteroid in the next 100 years — compare that to the 23 percent chance an American has of dying of cancer. There’s about a 1 percent chance of getting hit by a 140-meter asteroid in the next century, which would unleash the power of 100 megatons of TNT — twice as large as the largest nuclear bomb ever exploded, the Soviets’ Tsar Bomba detonation in 1961. As a comparison, a person has about a 1 percent chance of being killed in a car crash. And in the next 100 years, there is roughly a .01% percent chance of getting hit by a 1-kilometer or greater asteroid that would destroy all of human life on Earth. A 1-kilometer and up asteroid would blanket the hemispheres with enough dirt and dust to destroy several years of food growing season, leading to a Mad Max-like scenario in which survivors would quickly exhaust the world’s three-month food supply. As a comparison, any given American has about a .01% chance of dying in a plane crash. “I think the governments of the world are very good at confronting a threat that is quantified: real time, date, place,” Lu says. “When things are probabilistic? We’re just not good at that.”

Lu compares the Sentinel project to a safety-precaution against a small but real threat of disaster, like putting on a seat belt before driving. And he stresses that the asteroid problem can be easily handled –- so long as we know where the asteroids are well in advance. “If you don’t know where they are, the only warning sign is a flash in the sky and a tidal wave.”