An artist's image of an asteroid hitting Earth. The picture shows a celestial impact far larger than any that has taken place. (NASA)

We have been warned. Apophis is coming.

We even have the exact date: April 13, 2036, so there's no excuse not to be ready.

Apophis is a 320-metre-long asteroid with a slightly wonky orbit that brings it close to Earth every now and then. You guessed it. That April day 29 years from now is when our planet and Apophis might be in the same place at the same time.

The warning comes from scientists and ex-astronauts at the annual conference of the American Association for the Advancement of Science in San Francisco. The same group is also calling for the United Nations to co-ordinate a global response to incoming celestial flak. There's even an "Oregon-based risk analysis company" warning that entire cities could be annihilated by Apophis.

Scary stuff. Anyone who's watched Bruce Willis save the planet in the movie Armageddon or sat through the even sillier Deep Impact will get the point. The time for action is now.

Or is it? Is Apophis really going to squelch into Venice, flatten Los Angeles or leave Mumbai at the bottom of a deep crater?

A wary eye on space

Statistically speaking, it's probably not going to hit us. NASA's Ames Research Centre in California keeps a wary eye on objects that stray close to Earth's orbit. Several hundred asteroids, comets and other chunks of celestial matter are monitored pretty closely and many thousands more are thought to be out there.

But NASA recently downgraded the threat of a direct hit by Apophis from one in 42 to one in 45,000.

Those are pretty long odds. Getting four of a kind in a poker game is eleven times more likely, for example. Getting struck by lightning in the next five years is about as likely as Apophis hitting Earth in 2036, according to Prof. Fred Hoppe of McMaster University's mathematics department.

Long-suffering Toronto Maple Leaf fans will cringe to hear Hoppe's estimate that the chances of a collision with Apophis are about the same as the current Stanley Cup drought in Toronto lasting until 2324, presumably long after the impact of the asteroid wipes out our species. Not a nice thought.

Seriously though, we do get smacked by space rocks on a fairly regular basis. Almost every day, a meteorite streaks through the atmosphere and actually hits us — usually a harmless splash in the oceans that cover three-quarters of our planet. Every week or so, one hits land and occasionally thumps into a building or even a person.

Bigger, more potentially disastrous celestial body impacts happen much less frequently. In 1908, a comet or an asteroid apparently exploded over Tunguska in Siberia, a blast heard and seen for hundreds of kilometres. There's the famous Arizona meteor crater, a kilometre-wide hole thought to have been made by a piece of cosmic iron ore just 100 metres in diameter. Sudbury's nickel deposits come from one of the largest space objects to hit the Earth and a crater that lies under Mexico's Yucatan Peninsula is thought to have come from a meteor strike that is thought to have caused the extinction of most dinosaurs 65 million years ago.

The threats are out there

So it's no laughing matter, this asteroid business. Apophis orbits the sun roughly parallel to the Earth and it's much bigger than the meteor that left Arizona's famous hole. Its orbit intersects with Earth roughly every six years. An impact might be unlikely but it's not beyond the realm of possibility. And there are dozens, if not hundreds of other pieces of rock just like Apophis, out there, orbiting in relative darkness. Any number of them could be hurtling towards us and we just haven't noticed yet. We might not until it's too late.

There is merit in being prepared. But let's examine what they were calling for in San Francisco recently. Ex-shuttle astronaut Edward Lu says we need to build something called a "gravity tug," a space version of those stubbly little boats that pull massive ships in and out of port. It would only cost $300 million (US), he says.

The idea is to position a rocket ship or a satellite near the orbiting Apophis and use its tiny but significant gravitational pull to deflect the oncoming asteroid. I don't know about you but I'm not sure that's enough protection for me. Something a little more interventionist might be necessary, just to keep up morale on Earth.

Then there's the Bruce Willis option — blowing up the asteroid with a massive nuclear device. It may be a bit Hollywood to send up a Texas oil drilling team, as they did in Armageddon, to plant the nuke deep inside. A big space missile might just be enough. But wait, says Vancouver-based astronomer David Dodge, blowing up Apophis might just transform a single threat from space into a swarm of them.

"It's the last thing you want to do," he told CBC Newsworld.

Connect the dots

Denis Grey of the Royal Astronomical Society of Canada sounds a note of caution. Apophis isn't likely to hit us, he says. Much depends on the quality of information astronomers have, and when we first started hearing about this latest threat to our planet, we just didn't know enough to say for sure.

"It's like connect the dots," he says. "You can't call it a face with just a few dots. Now we know. We have all the dots on Apophis."

It is statistically almost certain that the asteroid won't hit us in 2036, or even six years after that when scientists are already warning of a rematch. Besides, all sorts of things could cause similar levels of havoc well before then — climate change, pandemic disease, nuclear war and toxic food come to mind.

We live in fearful times. Do we really need something else to be afraid of? Before we start a "war against asteroids," perhaps we need more information and a thoroughly informed debate. Not to mention the Leafs winning the Stanley Cup.