On a mission to save Earth

Armed with startling new data about the scale of the threat Earth faces from asteroid strikes, a group of former Nasa astronauts is on a mission to save the world.

Fourteen months after a meteor exploded over Chelyabinsk, Russia, exploding with a violence equivalent to that of 30 Hiroshima atomic bombs, the B612 Foundation is warning that only "blind luck" has so far saved our planet from much worse devastation.

The foundation is a non-profit group founded by Apollo 9 astronaut Rusty Schweickart and space shuttle astronaut Ed Lu.

"It's a giant game of chance we're playing . it's cosmic roulette," said Lu, whose group is working towards building and launching Sentinel, a $250-million (R2.6-billion) telescope that would spot space rocks on a collision course with Earth, giving years or decades of notice in which to deflect disaster.

"You can't just keep playing a game of chance and expect to keep winning," said Lu, the group's chief executive officer.

"Data obtained since the Chelyabinsk incident by Peter Brown, a planetary scientist and asteroid expert at the University of Western Ontario, in Canada, reveals that, since 2001, Earth has been rocked by atomic-bomb-scale asteroid impacts 26 times; up to 10 times more frequently than previously thought."

Today, which is Earth Day, the f oundation will reveal more details of the threat, including a video presentation showing for the first time the locations and sizes of the multikiloton impacts.

"We are in a shooting gallery," said Schweickart. "That's the message we want people to understand. It's happening, it's continuing, and the big ones will come. It's just a matter of when."

The video is based on information from the International Monitoring System, a network of sensors set up around the world to verify compliance with the global ban on nuclear weapons testing. The technology detects sound waves and shock waves above and below Earth's surface.

Because only 28% of the planet's surface is land, and only 1% is populated, most asteroid strikes are in remote areas, deserts and oceans.

"That none of these asteroid impacts represented in the video was detected in advance is proof that the only thing preventing a catastrophe from a city-killer-sized asteroid is blind luck," said Lu.

The Chelyabinsk asteroid ripped through Earth's atmosphere as a 57600km/h fireball, exploding nearly 30km above the ground.

It damaged 7200 properties in six cities and injured 1500 people within a 49km radius.

Sentinel, which the foundation wants to launch in 2018, will be positioned 274million kilometres from Earth, near Venus.

In its first month of operation it is expected to detect and track more than 20000 near-Earth asteroids, exceeding the discoveries made by all other telescopes combined over the past 30 years.

The group has designed technologies to deflect asteroids from collisions with Earth.

It has to raise the $250-million to build Sentinel and the $200-million needed to operate it.