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Wondering what could cause the Mayan Apocalypse? Just look up at the stars.

For years, conspiracy theorists, numerologists, and armchair prophets have predicted the end of the world will take place on December 21, 2012. They point to several apocalyptic events: a long-period comet hurtling toward Earth, or a massive solar storm that causes complete power grid failure.

And they take the stories seriously. Rob Skelton, who runs Survive2012.com and has studied a possible Mayan doomsday event for 15 years, says there is a reason to be concerned. For the long-period comet, he admits we would normally have spotted one by now -- unless it had gone dark and lost its reflective ice. For the solar storms, he says the Mayans could have found a pattern in low-latitude auroras and predicted a coming disaster.

“Both are only predictable via periods of observation longer than the modern scientific era,” he told FoxNews.com. “All I’ve done is find a reason why it could happen this December.”

According to Skelton, a solar storm could wreak havoc in the U.S., knocking out the power grid for months. The U.S. relies on the grid to keep nuclear power plants safe, run factories, and communicate between fire and police forces. Without this key infrastructure, there will be mass pandemonium and destruction, he said.

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But will these events happen on December 21? That’s extremely unlikely, says one NASA scientist.

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“This is purely an Internet phenomena,” said David Morrison, an astrobiologist at NASA. Comets that cause destruction on Earth are extremely rare – they could happen once every 500 million years.

'There are no objects out there that will impact the Earth.'

— David Morrison, an astrobiologist at NASA

Mysterious objects have been known to strike planets in the past. In 1994, a series of comets struck Jupiter, the largest planet in our solar system. Most scientists agree that solar storms are relatively common events and can cause electrical disruptions. And comets do tend to be harder to track in our solar system until they pass by the sun. But nothing like that is imminent, Morrison said.

“There are no objects out there that will impact the Earth,” he told FoxNews.com.

As for the massive solar storms, Morrison says they do happen. “The power does go out, and that’s not a nice thing and it means people are not happy. But that doesn’t kill millions.” In most cases, even with a major outage, it can take weeks at most, not month, to regain power, he said.

“Solar storms are relatively common events,” agreed Chris De Pree, a professor at Agnes Scott College and author of The Complete Idiot's Guide to Astronomy. “Other than disrupting communications and putting on a great boreal light show, the long term effects would probably not be great.”

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NASA operates the Solar and Heliospheric Observatory (SOHO) to track comets and asteroids, and also runs the Spaceguard Survey, a ten-year project intended to track near-Earth objects in our solar system. There are no hidden secrets, De Pree said: NASA publishes the report online.

About those comets? Morrison says comets are well-known to have dark surfaces. NASA still tracks them, as well as asteroids – which are “dark as a lump of coal.”

Morrison is most skeptical about the Mayan predictions. “There is nothing special about that date,” he said. “The Mayans never predicted anything will happen. There are thousands of people who run Web sites and make YouTube videos about catastrophes who are not scientists.”

He says the Mayan calendar works a bit like our own calendar: When you reach the end, you flip over a page and start a new calendar. What will the doomsday predictors turn to next? That’s hard to say, but history has shown that there will be yet another catastrophic event to worry about.

“Claims about the end of the world are a time-honored way to sell things,” De Pree said.