How Prepared Are We For An Earth-Bound Asteroid?
published during a waxing gibbous moon.

Of all the reasons to approach 2017 with caution, here’s one that might not be on your radar: apocalyptic asteroids.

At the recent American Geophysical Union meeting, NASA scientist Joseph Nuth raised concerns over humanity’s lack of preparedness for a devastating celestial event, such as an asteroid or comet that slams into Earth. Wait, you might be saying to yourself. I saw Armageddon—we’re totally prepared. Well…maybe not. If we spotted an asteroid on a collision-course with Earth, Nuth says, “there’s not a hell of a lot we can do about it at the moment.”

How much of a worry are asteroids or comets? We’ve all heard that an asteroid wiped out the dinosaurs, but in recent years scientists have challenged the idea that a massive asteroid strike in the Yucatan wiped out our prehistoric predecessors. Scientists think there was more than one asteroid strike (the one in the Yucatan may have occurred too early to have caused the dinosaurs’ demise), and that volcanic eruptions contributed greatly to the fall in temperatures. Regardless, there’s no doubt that a massive asteroid could wreak havoc across the globe, leveling cities and causing everything from climate change to tsunamis. We want to avoid such an event—if we can.
Earth-Bound Asteroid

OSIRIS-REx Will Map Asteroid Bennu. Credit: NASA

“You could say, of course, we’re due…”

Nuth estimates that an extinction-level strike occurs every 50-60 million years. But the asteroid that hit the Yucatan struck 65 million years ago. “You could say, of course, we’re due,” says Nuth, “but it’s a random course at that point.” So there’s no immediate cause to freak out, but we probably shouldn’t assume that something like this won’t happen again.

We haven’t had a close encounter with an asteroid or comet in a while. Twenty years ago, a comet slammed into Jupiter; two years ago, one passed close to Mars. That’s about as close as they’ve gotten to Earth, but the more hunting we do—NASA has a satellite, NEOWISE, devoted entirely to spotting asteroids—the more we find.

Earth-Bound Asteroid

Lightness-reversed cropped plot of orbits of all the known Potentially Hazardous Asteroids (PHAs), numbering over 1,400 as of early 2013. These are the asteroids considered hazardous because they are fairly large (at least 460 feet or 140 meters in size), and because they follow orbits that pass close to the Earth’s orbit (within 4.7 million miles or 7.5 million kilometers). Credit: NASA/JPL-Caltech

Scientists have found more than 600,000 asteroids in the solar system, nearly 15,000 of which are classified as “near-Earth objects” (NEOs), which means they orbit the sun and are relatively close to Earth (relative being a…well, a relative term). Of those, NASA has spotted 1,748 “potentially hazardous” asteroids in relatively close proximity to Earth, 874 of which are at least one kilometer wide. Suffice it to say; these objects are out there.


What if we spot one of these bodies heading for Earth? The comet that passed near Mars in 2014 was discovered roughly 22 months before its fly-by, and while 22 months might seem like a long time to prepare when dealing with massive chunks of flying space rock, it’s not long enough to employ either of the major strategies NASA has identified: nuking or intercepting.

Science fiction shows us two of the possible consequences of sending a nuclear warhead to meet an incoming asteroid. It might work, as it eventually does in Armageddon (although the 18 days lead time in the movie is laughable). Or, as in Deep Impact, the nuke might split the asteroid into two huge rocks (and shrapnel) that could cause even more damage. Nuth favors the interception approach, which involves deflecting an incoming asteroid with a rocket. Knocking an asteroid or comet out of Earth’s path has fewer possible negative consequences and is potentially more effective, but it’s even harder to pull off. Scientists would have to calculate the trajectory, mass, and speed of the incoming object, and then figure out when, where, how, and at what speed to launch the intercepting rocket. Those calculations require accurate data, as well as complicated math. Unfortunately, scientists know little about the composition of asteroids and comets beyond the basic rock and ice. Any unknown variable could render calculations inaccurate, and when it comes to something like this, there’s no room for error. Pulling off such a maneuver could take as many as five years of building and planning.

Earth-Bound Asteroid

Comet 67P/Churyumov-Gerasimenko from Rosetta. Credit: NASA

However, not all the news is bad. NASA has a planetary defense office (PDO), which has been working on identifying asteroids and developing an “asteroid redirect mission.” NASA’s OSIRIS-REx will bring back a sample from the asteroid Bennu in 2018, which will provide more information and insight. Nuth suggests that the PDO develop, test, and maintain an interceptor rocket just in case, as well as an accompanying spacecraft that would observe an interception mission. With proper preparation well ahead of time, it may be possible to stage an asteroid interception in as little as three years.

In the meantime space agencies from around the world will work together to continue monitoring NEOs. We certainly have enough to worry about in 2017 without obsessing about killer asteroids—perhaps it’s best to deal with only one extinction-level event at a time—but eventually we’ll want to be sure that the plotlines of Armageddon and Deep Impact remain fiction.