What's really frightening is no one knows where they all are...

(CHICAGO) - Three huge asteroids are barreling through space on a rendezvous with Earth and there's not a damn thing anyone can do about it.

Motion pictures like Armageddon have depicted Earth threatened with annihilation by a giant asteroid traveling many thousands of miles per hour. Because of its speed and mass a large asteroid impact would release the energy of 100s or 1,000s of thermonuclear bombs.

Although the Earth is always saved in the movies, in real life the threat is more than just special effects on a piece of celluloid. There are rocks out there the size of mountains—some even larger—miles across.

Although asteroid tracking programs of Near-Earth Objects (NEOs) have been established, it's still an inexact science. And some astronomers admit if one of the really big NEOs blindsides us and approaches from behind the sun, on a collision trajectory with Earth, by the time the thing's discovered only weeks will remain to stop it.

Of course, with so little time remaining nothing could be done except to make final arrangements for the end of the world and the abrupt passing of the human race.

Tens of thousands of asteroids and comets haunt the space ways, some changing their orbits every time they pass near a large gravitational field like one of the outer gas giants or swing close by the sun. Their orbits are often changeable and unpredictable. The ones marked as possibly hazardous to the health of the human race are tagged as Potentially Hazardous Asteroids (PHA).

Many PHAs exist out there, completely unknown and invisible. Some of those could be the size of Pluto…or larger.

What's really frightening is no one knows where they are, how many exist or when they might show up unannounced.

What is known? Three asteroids—all PHAs—are heading towards Earth and we have no technology available to stop them.

1. Asteroid 2002 NT7 arrives February 1, 2019: The continent killer…1.5 miles long

The most threatening asteroid ever detected is 2002 NT7 arriving 2019.

Initial calculations of its preliminary orbit reveals it's on a collision course with Earth. Although the permutations of its orbit could change, nothing is certain in this game of cosmic billiards.

When it was discovered, astronomers assigned the killer a threat rating of +0.06. That rating on the Palermo technical scale—a risk assessment of asteroid and comet impact with Earth—awards NT7 the dubious distinction of being the first asteroid ever to be given a positive value.

Positive for the asteroid, a big, big negative for Earth. It's size and speed are calculated as meeting the threshold needed to vaporize an entire continent.

The asteroid's orbit takes 837 days traveling from the distance of the Martian orbit to just within the Earth's orbit.

As of this writing, it's due to meet up with Earth in less than 8 short years.

Will it hit? Although the likelihood's shrinking, it's still possible.

2. Asteroid Apophis arrives 2036: The city killer…1,000 feet across

Approximately the size of the asteroid that exploded in the sky above the Siberian Tunguska forest during 1908, Apophis is a city-killer. If it hit London or Moscow or New York, the city would be vaporized.

Russian scientists are convinced that Apophis is going to hit Earth in 2036. NASA says no.

But the Russians think NASA's wrong and have called for a major conference in July 2011 to address the problem of Apophis and other PHAs like NT7. The Russians are hoping that the European Space Agency will work with them...

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