Last week, we saw quite an array of celestial events. First, lightning struck St. Peter’s Basilica only hours after the Pope shocked the world by announcing his retirement, suggesting that Someone preferred to keep such decisions to Himself.

Then, on the same day that we smugly expected an asteroid that we knew would come closer than some man-made satellites, but miss us, a smaller one that we weren’t anticipating didn’t. Miss us, I mean. It put on a light show and did spectacular damage in Siberia, injuring more than a thousand people. (Apparently, meteors hate Siberia more than tornadoes hate trailer parks.)

It’s like the heavens were mocking us and our belief that we have a handle on things.

Speaking of which, I thought I’d pass on this interesting piece that I saw in The Guardian from ex-astronaut Rusty Schweickart. He said that we need to know more about these smaller asteroids, and that we can, if we invest in new telescope technology. But the most surprising thing he said was that if we spot these rogue rocks early enough, we can actually do something to keep them from hitting us. Excerpts:

Spaceship Earth just took two celestial shots across its bow as, first, a meteor struck Russia, showering the Chelyabinsk region with fragments and reportedly injuring several hundred people, and second, as Asteroid 2012 DA14 whizzed past on 15 February. Traditionally, a torpedo across the bow is fired as a warning to change one’s behavior – and this coincidence of events should be a warning to humanity that meteors are not always as benign as “shooting stars” and that the next asteroid might not miss! Will we, the crew of SS Earth heed this warning?…

Nevertheless, the Earth is hit by one of these relatively small DA14-sized asteroids about once every 300 years, on average. And “small” is far, far from insignificant. The DA14-like asteroid that hit Earth in 1908 did so in a remote region of Siberia, where the explosion (the equivalent of about 250 Hiroshima nuclear bombs going off at one time) destroyed over 800 square miles of the countryside. This disaster zone, superimposed on any city in the world, would have wiped it and all its residents from the face of the Earth. I refer you, as a graphic reminder of the power of such explosions, to the post-facto Hiroshima bomb pictures readily found online.

The second way to view DA14 is to realize that, until just about a year ago, it was one of about 1 million similarly sized, near-Earth asteroids, which we know are out there, statistically, but that we haven’t yet seen. Consequently, until we find them in our telescopes, we are like sitting ducks in a shooting gallery with nothing more than luck to prevent a disaster. Regrettably, the Earth-based telescopes we’ve been using to discover and track these objects have, practically speaking, reached their limitations for finding the vast majority of these cosmic torpedoes.

Why do we care about finding them if there’s nothing we can do about it? Because, unknown to most people, is that if we have adequate early warning, our current space technology is sufficiently advanced to deflect these asteroids. For smaller impacts, even a last-minute warning of several days could enable a local evacuation and save many lives.

Deflection, however, will generally require several decades of warning. Fortunately, due to the relatively pure nature of space dynamics, forecasting an asteroid impact 100 years in advance is possible once its orbit is well known. The sine qua non, therefore, is finding them…

He goes on to make a pitch for the Sentinel telescope. He’s involved with a nonprofit that wants to build this thing and save the planet. Which is good of him.

What he does not to, to my frustration, is explain his claim that we can deflect these things. However, Stuart Clark, also writing in The Guardian, answers my question:

“There are three ways to deflect a dangerous asteroid: the gently pull, the swift kick and nuking it,” says Fitzsimmons. Which method is best depends on the asteroid’s size, composition, orbit, and crucially, how much warning we get. Typically, warning times of a decade or so would be required.

With plenty of warning, the gentle pull may be all that is needed. In this scenario, you send the heaviest spacecraft you can launch to “hover” close to the dangerous asteroid. The tiny gravitational pull that the spacecraft produces on the asteroid then adds up over many years to shift it off collision course. It’s a concept known as the gravity tractor.

The swift kick actually involves a collision. You hit the asteroid with a heavy spacecraft that instantaneously changes its orbit. The more warning you have, the smaller the kick you need to give it. Observations can quickly show whether the method has worked or whether another kick is needed.

Finally, if things are desperate, nuke it. This can provide the biggest kick of all. But don’t shatter the asteroid. The last thing you want to do is break it up. That turns a cannonball into buck shot without significantly changing its orbit.

Instead, a nearby nuclear explosion would evaporate the surface layers of the asteroid. As the vaporised rock jets into space, the asteroid would be pushed in the opposite direction.

But — correct me if I’m wrong — in order for us to do any of that, our space program needs to be more advanced than it is now. The gentle pull, anyway. To be able to intercept an asteroid decades away from us in time to gradually pull it off course sounds to me well beyond our current technology. Seems that we might want to step up our game a bit. As Clark quotes Larry Niven as saying, “The dinosaurs became extinct because they didn’t have a space programme.”