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Protecting Earth from asteroids

Asteroid impacts with Earth are a near-certainty, scientists say. The question is: What, if anything, should we do to track asteroids and protect Earth from them?

By Moises Velasquez-Manoff / January 25, 2010

This is an artist's depiction of a huge meteorite striking Earth 65 million years ago, which, scientists says, sent the dinosaurs and many other life forms into extinction.

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Last week, a meteorite reportedly crashed through the roof of a doctor's office in Virginia. No one was hurt when, traveling at some 200 miles per hour, a half-pound space rock smashed into an examination room, breaking into pieces on the concrete floor. But the incident highlighted the not-insignificant threat posed by asteroids and ice balls from space.

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The consequences of a sufficiently large asteroid or comet strike could be catastrophic, which is why you're reading this in a blog about the environment:. Depending on size, an amount of energy equivalent to tens of thousands and even many millions of nuclear bombs would be released on impact. Such a strike could be disastrous not just for civilization, but for the planet's entire web of life.

If it landed in the ocean, the impact would send walls of water in all directions, inundating continental margins. If it struck land, it could ignite continent-wide fires.

And while the destruction would be immediate around the strike zone, the problems would likely become global in the aftermath: Dust injected into the atmosphere could block sunlight. Photosynthetic organisms would stop growing. Everything else that depended on them would suffer the consequences of a reduced food supply. Mass starvation would ensue.

The last asteroid strike on this scale is widely thought to have contributed to the dinosaurs' end 65 million years ago. The asteroid, which left a 110-mile-wide crater off Mexico's Yucatan Peninsula, was only six miles in diameter, roughly the size of Manhattan Island. But three-quarters of life on Earth disappeared.

Scientists generally agree that asteroid impacts in the future are a near-certainty – smaller ones more often, larger and much more catastrophic ones less often. Scientists think that asteroids like the one that ended the dinosaurs' reign hit Earth every 100 million years or so.

That's why, in 2005, Congress mandated that NASA should try to detect 90 percent of near earth objects (NEOs) with a diameter of more 140 meters or more by 2020. Asteroids of this size hit earth roughly every 30,000 years.

Before that, in 1998, Congress asked that NASA find 90 percent of all NEOs measuring more than 1 kilometer in diameter within 10 years. These hit with less regularity, but could cause substantially more damage.

Late last week, the National Research Council released a progress report that found that NASA has been quite good at locating and tracking objects larger than 1 km in diameter. But, due to insufficient funding — only $4 million yearly for tracking NEOs — NASA wouldn't meet the goals set out by Congress in 2005.

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