It's a fear that has hung over humans for hundreds of years: what would happen to life on Earth if a large asteroid collided with our planet?

Tuesday marked Asteroid Day– a day when scientists hope to raise awareness that we don't know all there is to know in the cosmos. June 30 is a big day in asteroid history because it was on that date in 1908 that the largest impact event in modern history happened, the Guardian said. The comet or asteroid that exploded above Siberia had the force of 1,000 atomic bombs, the report added. It wiped out a forested area nearly the size of Tokyo, NBC News reported.

Of the near-Earth asteroids that are at least a kilometer wide, which is large enough to end civilization as we know it, NASA says it has found 90 percent of them. That meets a congressional goal set in 1998, but there's still that other 10 percent that may leave Earthlings worried.

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"Asteroid impacts are one of the few threats we can quantify," British astronomer Martin Rees told the Guardian. "Every 10 million years or so, a body a few kilometres across will hit the Earth, causing global catastrophe – there are a few chances in a million that this is how we will die. However, there are larger numbers of smaller asteroids that could cause regional or local devastation."

A slew of supporters, including Rees, Apollo 9 astronaut Rusty Schweickart, biologist Richard Dawkins and British astronaut Helen Sharman, are hoping Asteroid Day will help raise awareness for the need to continue mapping these threats to our planet. They say we need more funding to build satellites that will track near-Earth asteroids, and not just the ones that could wipe out an entire civilization.

"We really have a gap in the knowledge that can assure us that we're not going to be struck," planetary scientist and former NASA astronaut Tom Jones told NBC News.

As it stands now, scientists can detect about 1,000 near-Earth objects per year, but Jones would like to see that total increased to 100,000 per year. Knowing about the threats could give us options to plan for impact or send weapons into orbit, like lasers or nuclear weapons, to either push the space rock into a different orbit or blast it apart, Jones added.

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