【eroticism in the 80s】

This post is eroticism in the 80spart ofScience of Sci-Fi, Mashable's ongoing series dissecting the science (or lack of science) in our favorite sci-fi movies, TV shows, and books.

Some days are so damaging to your faith in humanity, you may find yourself idly wishing for the cleansing global firestorm that would follow an impact from the kind of asteroid that killed off the dinosaurs 65 million years ago.

If that's the case, then astrophysicist and planetary scientist Michael Busch has some bad news. Over the last couple of decades, telescope-watchers like him have done such a good job of detecting and tracking the orbits of all possible extinction-level rocks out there that we can now say with confidence that none will hit us, at least not in the next 860 years.

"We think we've discovered everything out there that's larger than 1 km across," Busch, who has been tracking asteroids since 2005, told me from his office in Mountain View, California. "Anything smaller than a kilometer would only cause regional destruction."

For comparison, the dinosaur killer that landed in Mexico was a whopping 10 to 15 kilometers wide.

C'mon, really, everything has been logged? Well, Busch concedes, "it's possible there may be one or two behind the sun" where we can't see them with current telescope technology. But the rocks would have to have been hiding there for the past decade, which is highly unlikely.

And what do we get in 860 years' time? A puny rock called 1950 DA, which is a mere 1.1 kilometers across, and according to NASA models has at best a 0.3 percent chance of hitting the Earth in 2880. We don't know exactly where yet, because climate change is altering the Earth's rotation by tiny amounts -- and on a timescale of 9 centuries, that change matters.

The next frontier for scientists like Busch is finding all space rocks larger than 100 meters in diameter -- the kind that "if it fell on a city, there's no more city," he says.

But even if a potential city-buster lurks out there in the darkness, that still means we have to reset our cultural expectations of total planetary apocalypse -- which have been stuck in the same place for the last 20 years, largely thanks to Hollywood.

In 'Deep Impact', astronauts attempt to plant nuclear bombs aboard a comet heading for Earth --  utterly unnecessary, according to experts. Credit: paramount pictures/Getty Images

Old-school end of the world

In 1998, two asteroid disaster movies collided on the screen at roughly the same time. First came Mimi Leder's Deep Impact, which we might best describe as blue-state America's vision of an impact event. It was the somber, serious version, starring an MSNBC reporter and lots of government officials, including President Morgan Freeman.

And then there was Michael Bay's Armageddon-- an asteroid movie for the red states. Ignoring science, Bay casually devastated New York and Paris with a meteor shower (take that, liberal elites!). The rest of the movie focused on Bruce Willis, Ben Affleck and a couple Space Shuttles' full of roughnecks, who blast off to kick some asteroid ass with an all-American H-bomb.

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"Every time I give a public talk about asteroids, someone jokes about Bruce Willis."

This was so unrealistic that Bay had to add a disclaimer in the credits that though he had consulted with NASA, the space agency did not endorse his story. Many years later, scientists calculated that for the movie's plot to work -- the H-bomb splitting the Earthbound asteroid in two with enough energy to completely change the course of the two chunks -- it would have to be a billion times more powerful than the largest H-bomb ever built.

Not surprisingly, it is the unserious Armageddonvision that persists in our cultural imagination.

"Every time I give a public talk about asteroids, someone jokes about Bruce Willis," Busch laments.

When it comes to deflecting those smaller city-busting asteroids, it turns out, an H-bomb can be a useful tool. But "blowing an asteroid in half is not how it's done," Busch says. "It's a poorly-controlled process" -- you wouldn't be able to designate where the chunks of rock went.

If you're going to make a fusion bomb do the work of predictable asteroid deflection, what you want to do is detonate it nearone. Because it isn't about the explosion, it's about the waves of radiation that come in its wake. "What matters for an asteroid is the X-rays," Busch says. "They'd vaporize one whole side of the asteroid, just turn it into a cloud of gas" -- and nudge the bulk of the rock off course.

But nobody's going to make a Hollywood thriller about the sensible method of bending asteroid orbits to our will

That's kind of a last resort option. Busch's preferred method for asteroid deflection is what he calls a "gravity tractor." If you simply park a spacecraft near an object like 1950 DA, then over a number of years the weak gravitational pull of the spacecraft itself would change an asteroid's course enough to save the Earth.

But nobody's going to make a Hollywood thriller about the sensible method of bending asteroid orbits to our will, Busch laments: "A gravity tractor wouldn’t look that exciting, because you’re basically sitting there with the motor running for 10 years."

Morgan Freeman as president announces an extinction level event, which now unfortunately will never happen. Also unfortunate: Morgan Freeman is not the president. Credit: paramount pictures/Getty Images

Space rocks, the next generation

The fact that Busch is involved in the anti-asteroid effort at all says a lot about how we got to this terribly safe juncture. Technically he works for the SETI Institute, the goal of which is to use telescope time to look for alien signals from the stars.

But at a certain point, everyone's just looking for stuff from the sky. And there's been so much cross-pollination of asteroid science and research around the world in the last couple of decades, so much telescope-sharing, that it's hard to say exactly how many people are involved in the effort to log and track dangerous rocks.

Back in the Armageddonyears, there were "fewer people working on this full-time than work in the average McDonald's," Busch says. These days, "there's a large international effort that happens to be below the radar of the daily news." Some of it even recruited members of the public, as in the game-like project known as Asteroid Zoo.

A big part of that effort, and a lot of the funding behind it, came in 2013. That was the year a meteorite hit Russia, landing near Chelyabinsk, 930 miles east of Moscow, and injuring 1,000 people. You probably remember the viral dash cam videos of the meteorite's path across the sky.

Most of the injuries were caused by a shockwave of shattered glass after impact -- which is why the smartest thing you can do if you happen to see a rock streaking through the sky is to get away from the windows.

The Chelyabinsk rock was a mere 20 meters wide. Which helps to make Busch's point that the rocks that remain still pose a threat, even if they aren't going to be ending human civilization any time soon.

In fact, he thinks it's high time Hollywood made a more realistic film -- perhaps one about a 100-meter-wide city-killer landing on a major metropolis. "If we can get someone interested in that, I'm happy to advise," Busch says.

Your move, Michael Bay.

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