Usually the government sticks to reality, but there are a number of times where agencies have investigated or weighed in on more mythical ideas. From mermaids to Santa Claus, here are 11 legends that the government has acknowledged, even if just to deny.

1. Mermaids

Late last month, the National Oceanic and Atmospheric Administration published a curious addition to its Ocean Facts section: "Are Mermaids Real?" Describing them as "half-human, half-fish sirens of the sea," the post goes on to describe the various appearances of mermaids in folklore, from cave paintings to The Odyssey. However, NOAA comes to the final conclusion that "no evidence of aquatic humanoids has ever been found." The agency says the post came in response to several requests from the public after Animal Planet aired a special called Mermaids: The Body Found that claimed to paint "a wildly convincing picture of the existence of mermaids."

Verdict: Not real

2. Mutants

While villainous government officials in the X-Men universe may have been fighting for mutant registration and restriction, a real-life lawsuit left the Department of Justice arguing that mutants are actually closer to humans. The bizarre case (described in a great Radiolab piece) centered on customs regulations and the definition of "dolls" versus "toys." According to the law, "dolls" represented humans and were taxed at a higher rate than "toys," which have non-human characteristics. A pair of enterprising lawyers working for a company producing figurines for Marvel realized that the company could almost halve their taxes by arguing that the "dolls" were actually non-human "toys." Citing features like Wolverine's claws, Cyclops' laser eyes and the blue fur of Beast, the company went to court to say that the mutants represented in the figurines could not be classified as human. The government, however, argued that the characters were essentially human. Ultimately, the United States Court of International Trade came down on the side of the toy company, declaring in their verdict that the mutants are "more than (or different than) humans" and adding that they "use their extraordinary and unnatural physical and psychic powers on the side of either good or evil."

Verdict: If they're real, they're not human

3. Zombies

After a Miami man was found eating a victim's face, a Baltimore college student admitted to killing his roommate and eating his body parts, and a New Jersey man threw his own intestines at police, rumors of a coming mass zombie attack started flying. In fact, the chatter got so heavy that the Centers for Disease Control and Prevention even had to respond. In a statement to the Huffington Post, CDC spokesman David Daigle wrote that the "CDC does not know of a virus or condition that would reanimate the dead (or one that would present zombie-like symptoms)."

Just in case, the CDC also has a helpful guide on preparing for a zombie apocalypse, published in May 2011. Among their tips: get an emergency kit ready, get your emergency contacts ready and plan multiple evacuation routes "so that the flesh eaters don't have a chance."

Verdict: Not real, but be prepared

4. Atlantis

Images published on Google Earth of the ocean floor have led several people to think that they've found the lost city of Atlantis, or at least evidence of some underwater civilization. The clue, they say, is a series of grid-like lines on the floor that had to be man-made. In response to several inquiries about the lines, NOAA has published posts debunking the Atlantis theories. The real reason the lines are there, they say, is because the mapping tools are layering several smaller maps on top of each other. "While the strange grid-like patterns they found were in fact created by humans, the patterns were only made of data," NOAA said.

Verdict: If it's real, you haven't found it yet.

5. Bermuda Triangle

The legend of the Bermuda Triangle (also known as the Devil's Triangle) describes a region of the Atlantic where ships and planes vanish. But on its website, the U.S. Coast Guard emphatically denies the existence of the triangle as a region of "specific hazard" to any ships and planes. In fact, the USCG says that a review of vehicle losses found "no extraordinary factors" relating to casualties or crashes. And NOAA -- noting that there are explanations for the supposed Devil's Triangle that are rooted in science -- cautions that there's no evidence for more disappearances in that region than anywhere else in the ocean.

Verdict: Not real

6. Santa Claus

Wondering where Santa Claus is every Christmas? The North American Aerospace Defense Command (NORAD) holds the answer with their annual Santa Tracker, which provides up-to-the-minute updates on where Father Christmas is delivering presents. The tradition started in 1955, when Sears posted an ad in a Colorado Springs newspaper with a number for children to call Santa. However, a misprint led to children actually calling a local Continental Air Defense Command (CONAD) Center, a military precursor to NORAD. The on-duty colonel told everyone at the base to give any children who called a location for Santa. Today the location is given out through a Google Earth map on the NORAD Santa Tracker website.

Verdict: He's right there!

7. UFOs

The FBI's online vault contains a treasure trove of documents for UFO enthusiasts, detailing various investigations and general interest into unexplained objects. The UFO page contains many reports of events between 1947 and 1954, including some that touch on the Roswell crash. Their verdict? Just a weather balloon.

Verdict: Not real, but worth investigating.

8. The Mayan Apocalypse

The Roland Emmerich disaster movie 2012 was one of the many recent takes on the legend that the world would end this December, when the Mayan calendar supposedly runs out. But don't tell NASA. The agency has an entire Q&A page dedicated to debunking those rumors. The page calmly states that the calendar does not end in 2012, but merely begins another period. And the scientists declare that there are no planets, asteroids or stars set to crash into the Earth, nor is there a threat of the Earth completely reversing its rotation. "Impressive movie special effects aside, Dec. 21, 2012, won't be the end of the world as we know," NASA wrote. "It will, however, be another winter solstice."

Verdict: Not true

9. Alien Attacks

Pretty much every alien invasion movie scenario was covered in a 2011 paper written by a NASA scientist along with colleagues from Penn State, including the possibility that aliens could attack humans because we're wasteful. The report considered a number of scenarios for alien contacts, everything from them coming in peace to their desire for destruction. Many of them fell on the slightly boring side -- they could come and be unable to communicate with humans, or they could accidentally carry a deadly disease. To make sure things will be okay, the researchers say that the best course of action is to not broadcast out our biological information and stick to communicating on a mathematical level until any alien intentions become clear.

Verdict: It's possible

10. Vampires

While not an official government position, the U.S. Army has tried to play on the existence of vampires in the past. According to passages of the book "Counter-Guerrilla Operations" by Philippine colonel Napoleon Valeriano and U.S. military adviser Charles Bohannan, U.S. soldiers in the Philippines fighting an uprising of the Huk rebels would try to scare their enemy using the legend of the monster. They would kidnap the last man in a Huk patrol, poke two holes in his neck and drain his body of blood. When the Huk rebels found him the next day, they would fear that vampires were around and would leave.

Verdict: Believe it if you want

11. ESP

Also tucked into the FBI Vault was a file on extra-sensory perception. One memo describes an agent going to see a display of ESP and mind powers put on by a man named William Foos, encouraging the FBI to follow up. If the powers turned out to be real, he wrote, "there is no limit to the value which could accrue to the FBI," including reading mail and seeing through walls. Ultimately, however, the file shows that an investigation showed up no evidence of ESP and the original display turned out to be a series of tricks.

Verdict: Not real