(ABC News) -- It was 10 years ago that veteran NASA scientist David Morrison began to answer a question a day from the public about the origin of life on Earth, evolution and the mysteries of the cosmos.
Lately, though, Morrison, senior scientist at the NASA Astrobiology Institute, has been inundated with questions about both Doomsday 2012 and the Nibiru cataclysm, a supposed apocalyptic event in which Earth will collide with a massive rogue planet.
Some of these questions, he says, are increasingly alarming, and include threats of murder and suicide.
"I think it was about 4 years ago, early in 2008, I started getting 5 questions a day about 2012, and now it has increased," Morrison told ABCNews.com. "The most common question is, 'Will the world end on December 21, 2012?' I find that strange because the idea of the world ending is absurd. Do they really think, 'The world is ending, but if I build a bomb shelter in my back yard, I'll survive'?"
The frequency of the queries has even led Morrison to add a disclaimer to the NASA "Ask an Astrobiologist" page, noting that he has now answered 400 questions about Nibiru and 2012, and to please read these before submitting a new query.
"The most specific questions are about this rogue planet Nibiru," he said. "I think, if it were four years ago, you could say, 'maybe.' If it were real at this point, it would be the brightest thing in the sky."
But over the past few years, some of the questions he's receiving are increasingly alarming, and include a number of children who, faced with a perceived threat of impending doom, say they are planning their own deaths.
"I get 1-2 a month from a person who self-identifies as 11-12 years old, who is contemplating suicide," he said. "It happens often enough to disturb me … to hear that children are considering ending their lives."
Morrison said that one letter was from a middle school teacher in Stockton, Calif., who said that the parents of a student said they were planning to kill their kids and themselves. Another was from an elderly person, who said that her best friend was a little dog. The writer asked when the dog should be put to sleep, so it doesn't suffer when the world ends.
Though he finds these messages alarming, Morrison said that he only has limited information on the people writing in. He said he does whatever he can to soothe their fears, but at the end of the day, people's beliefs and fears are out of his hands.
"I can tell them there is absolutely nothing to be worried about. But I am in no position to provide psychiatric advice," he said.
From theories about pole shifts to the black hole at middle of the Milky Way to galactic planet alignment, Morrison says he has heard a number of doomsday theories -- the most popular of which relate to the Mayan calendar – a modern hoax. The Mayan calendar, which is made of cycles of day counts, does not end this year, he says. Rather, one cycle ends and the next cycle begins.
"It's purely a fantasy," he said. "It amazes me you can get so much … I sense that some of these people are into the conspiracy issues."
Morrison says that he will give up from answering the public's questions next year. But in the meantime he is carrying on, weathering the public's theories and phobias. Although some of the queries border on the nasty -- suggesting government conspiracy and NASA cover-ups, he said he doesn't let it get to him.
"I'll ask for apology on Dec 22," he said, "when none of this happens."