Illustration of asteroid Toutatis nearing Earth. Toutatis is expected to pass within 4 million miles of Earth tomorrow (12/12/12). But another smaller asteroid passed much closer today. (E. De Jong and S. Suzuki, JPL, NASA)

But if you think that’s too close for comfort, how about an asteroid passing within just 140,000 miles (only 60% of the distance between the Earth and moon) of our planet? Guess what?... already happened earlier this morning.

Discovered only two days ago, XE54 came about as close to crashing into Earth as an asteroid can without actually doing so - close enough to be “eclipsed by Earth’s shadow, causing its shadow to ‘wink out’ for a short time,” according to Universe Today.

With a diameter of just 72-160 feet, XE54 is a far cry from the over six-mile wide asteroid that wiped out dinosaurs (and about 50% of all life’s species) 65 million years ago. But, while it’s possible an asteroid of this size would produce nothing more than a brilliant fireball as it disintegrated after entering the atmosphere, a direct hit by remaining rock chunks on a populated region could be disastrous.

Believe it or not, a surprise near miss of this sort is not especially unusual. In June 2011, an asteroid estimated about 30 feet in size (“2011 MD”) passed by Earth and missed a direct hit by only 7,500 miles. An even closer encounter occurred earlier in 2011 when another small asteroid missed Earth by just 3,400 miles.

Asteroids coming this close cross through the zone of geosynchronous satellites (such as the GOES series). The chances of an asteroid-satellite collision are extremely small, though not zero.

Small asteroids such as these are difficult to discover, usually detected within a week of their closest encounter, and that’s much too little time to do anything but issue a warning about the likely locations of impact. In most, but not all cases, impacts would focus on oceans or relatively unpopulated regions.

Fortunately, asteroid strikes by ones of the size that wiped out dinosaurs are few and far between. An impact with more common intermediate-sized asteroids - dimensions larger than about 500 feet – would explode with the power of a large atomic bomb. However, large and intermediate-sized asteroids can be detected and tracked years before any close encounter with Earth.

At this time, there are no sure collisions on the horizon even over the next few hundred years. That said, much of the sky, especially that viewed from the southern hemisphere, is not being monitored!

Related: Close asteroid encounter - September 2012

What could be done if a large- or intermediate-sized asteroid strike on Earth were deemed likely? Although no U.S. or international government agency has assumed responsibility for stopping a potential collision, there have been a number of academic and some technical studies, not to mention numerous movies, on how a devastating asteroid impact might be avoided. Among the solutions are deflecting the asteroid trajectory by nudging it with robot space vehicles, or destroying the asteroid with a nuclear-armed rocket.

One of the most intriguing ideas is to deflect an approaching asteroid with paintballs. While this sounds pretty far out there at first, the approach formulated by an MIT graduate student won the top spot of a competition sponsored by the United Nations Space Generation Advisory Council (2012 Move an Asteroid Technical Paper Competition).

Video: Deflecting an asteroid, with paintballs

Essentially, the strategy would be to blast the asteroid with paint pellets launched from a spacecraft and filled with white powder. The initial force of the pellets would deflect the asteroid, and the albedo of the white painting would reflect the sun’s rays, thereby exerting a force that would deflect even more.

The caveat to this strategy, like most others, is that it requires about 20 years of advanced warning.