Asteroid day will draw eyes to the stars, but the more urgent threat may be under our feet

While an asteroid impact with Earth may make for great drama in the movies, no human in the past 1,000 years is known to have been killed by a meteorite or by the effects of one impacting our planet, according to NASA. That is just one reason Robert Mohr, Ph.D., instructor in the University of Alabama at Birmingham's College of Arts & Sciences, says energies might be better spent on the super volcano under Yellowstone.

"If the Yellowstone super volcano erupts, it will take out anywhere from 20-30 percent of the continent," Mohr said. "And the effects will be felt basically everywhere in the United States and in places beyond, potentially for years."

Aside from giant asteroid strikes, super volcanoes are considered to be the most devastating of all natural disasters. Super volcanoes have been known to cause mass extinctions and long-term climate changes.

The last known super volcano eruption, believed to have occurred around 70,000 years ago on the site of today's Lake Toba in Sumatra, Indonesia, caused a "volcanic winter" that blocked out the sun for six to eight years.

The super volcano that erupted in Wyoming 600,000 years ago, in what is now Yellowstone National Park, ejected more than 1,000 cubic kilometers of lava and ash into the atmosphere -- enough to bury a large city several kilometers deep. By comparison, the 1991 eruption of Mount Pinatubo in the Philippines, which caused a 0.4 degree drop in average global temperature for the following year, was 100 times less forceful than the Yellowstone eruption.

"A Yellowstone eruption would alter life as we know it for a long time," Mohr said. "Sunlight would be blocked for long periods of time, which would affect crop growth and food supply. Preparing for something like that, which is a lot closer to a likelihood than an asteroid's hitting Earth, would seem to me to be more prudent."

NASA knows of no asteroid or comet currently on a collision course with Earth. In fact, as far as the agency can tell, no large object is likely to strike the Earth any time in the next several hundred years. To be able to better calculate the statistics and narrow down concrete possibilities, astronomers need to detect as many of the near-Earth objects as possible -- an exercise that is quite hard to achieve with asteroids.

Mohr knows some will disagree with the notion that a super volcano is a more worrisome threat, and he admits it would be "nice to know" if an asteroid were heading straight for us. But he says the likelihood of discovering any asteroid far ahead of impact is quite small.

"There is no easy way to find an asteroid," he said. "It's not like looking for Easter eggs in a defined yard. There's a whole bunch of sky, and you're looking for something extremely small and that doesn't really give off a whole lot of light, so it doesn't show itself well. Where the asteroid is going to be in the sky and the odds of your actually being able to take a telescope, point it at the asteroid and pick it out with all the other stuff you're going to see in the telescope are very, very low -- even if it's right there."