An asteroid as big as a bus that flew past the Earth closer than the distance to our moon on May 3 arrived with little warning. Astronomers say its very existence was unsuspected until April 28.

NASA's Asteroid Watch project, at its Jet Propulsion Laboratory in Pasadena, California, spotted the asteroid as it approached the Earth.

In March an even larger asteroid passed close to the Earth but was detected just five days prior to its worryingly close approach.

And of course the Chelyabinsk meteor, resulting in substantial amounts of property damage plus injuries to around 1,100 people when it exploded over Russia's Ural Mountains region in February 2013, had gone completely undetected before it blew apart in a fireball low in our atmosphere.

Latest released study also revealed asteroid strikes where object have actually impacted on the Earth's surface, have been more common than we previously believed.

No more than one percent of the millions of such objects flying around and through the solar system have yet been found and identified.

Hoping to improve the situation, the space agency is conducting a series of competitions dubbed the Asteroid Grand Challenge, in hopes of garnering new ideas of how to find and track any asteroids whose solar system wanderings could bring them close enough and present a risk of collision with Earth.

"Asteroid hunting is an activity everyone can get involved with, whether it's writing computer code, building hardware, making observations through a telescope," a narrator says in a NASA video announcing the Asteroid Grand Challenge. "Survival is its own reward. It's up to each of us to protect our planet from asteroids."

"The dinosaurs would have cared if they knew about this problem," he says.

NASA says it will award $35,000 this year to people who contribute good ideas to the problem of finding ways to locate asteroids that have so far escaped our best efforts to uncover them

NASA plans 10 contests this year, spokeswoman Sarah Ramsey said, managed by the space agency's Center of Excellence for Collaborative Innovation.

"This is a big global problem that needs everybody to solve," Ramsey said. "We can't do it alone. That's the whole point of the grand challenge."

An answer to a question of how long the complete Asteroid Grand Challenge would run, Ramsey replied, "Until the problem's solved."