Artist’s impression of an asteroid approaching the Earth. Image Credit: Jeff Darling

NEOs: Too Close For Comfort?

By David Darling

Be afraid – but not too afraid. It’s true that at some point, if we don’t take steps to prevent it, a big dumb object is going to smash into the Earth so hard that civilization as we know it will be seriously inconvenienced, or even wiped out (see? No reason for too much fear). But the odds are that such a cataclysm lies way, way in the future.

Still, you never know…

The chunks of cosmic debris we need to keep a keen eye on are so-called near-Earth objects (NEOs) – asteroids and (a few) comets whose orbits can sometimes bring them close to the Earth. Around 9,000 NEOs have been discovered to date, the vast majority of them asteroids. Of these, about 1,350 are considered potentially hazardous asteroids (PHAs).

A PHA is defined as an asteroid that can approach the Earth closer than 0.05 astronomical unit (7.5 million kilometers) and has a diameter of at least 100 to 150 meters. As one might imagine, an object of that size is big enough to cause a lot of damage. The latest estimate, based on a survey known as NEOWISE, was carried out using NASA’s WISE (Wide-field Infrared Survey Explorer) satellite. To date, it is estimated that we’ve found between 20 and 30 percent of all these threatening objects.

Read more: NEOs: Too Close For Comfort? « AmericaSpace.

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