According to physicist and former NASA astronaut Ed Lu, the Earth has been hit by "26 multi-kiloton explosions since 2001, all of which are due to asteroid impacts."

This evidence -- gathered by the asteroid-hunting B612 Foundation -- demonstrates that "asteroid impacts are not rare, but actually 3-10 times more common than we previously thought."

Just last week over the Russian city of Murmansk, a fireball came screaming across the sky around 2:10 a.m. local time:

Russian astronomers believe it was an early arrival from the annual Lyrid meteor shower, but its sudden and unexpected appearance underscores Lu's point: "The only thing preventing a catastrophe from a 'city-killer' sized asteroid is blind luck."

Lu and fellow former astronauts Bill Anders and Tom Jones will make a presentation on Earth Day tomorrow, in which they will endorse the construction of a sophisticated asteroid warning system around the Sentinel Infrared Space Telescope (SIST).

The SIST will be launched on a privately funded SpaceX Falcon 9 rocket in 2019, and will scan the solar system via infrared wavelengths to identify the trajectory of any near-Earth objects larger than 500 feet. The team hopes it will discover many currently undetectable near-Earth objects that could pose a threat to the planet.

The potential risk to the planet posed by impacts was magnified by the arrival of a near-Earth object in the skies above Chelyabinsk, Russia in February of last year.

The resulting explosion had a power nearly 20 to 30 times that of the atom bomb detonated over Hiroshima, and many scientists consider it fortunate that only 1,500 people were injured by the blast.

["Asteroid striking Earth" on Shutterstock]