Assessing Asteroid Risks


By Cody Fenwick

Photo courtesy of Wikimedia Commons.

Sometimes, under the light-polluted glow of New York City’s night sky, I look up at the few visible stars and wonder, “Is anything up there going to kill me?”

Perhaps this is a bit paranoid–but only a bit. As recently as 2013, a meteor exploded in the air above the Russian city Chelyabinsk, injuring over 1,000 people. Some were injured in the shockwave that shook buildings and shattered glass, while others were burned by a blast 30 times brighter than the sun.

More frightening still, in 1908 a meteor exploded over the Podkamennaya Tunguska River in Central Siberia, flattening trees in an approximately 800 square mile area. It’s difficult to estimate the human damage such an event could cause if it occurred over a densely populated area. Downstream consequences of this kind of natural catastrophe occurring in a large metropolitan region on the global economy are even more uncertain, though undoubtedly dire.

The worst-case scenario is one everyone knows. Scientists believe that 65 million years ago, a meteor hit near the present-day Yucatan Peninsula, leading to the extinction of the dinosaurs. Some argue that an asteroid of similar size wouldn’t necessarily kill all humans, but it would certainly come close.

How likely are any of these scenarios? Gerhard Drolshagen of the Netherlands, co-manager of the European Space Agency’s (ESA) Near-Earth Object activities, explains to me the danger of meteors and what is being done to mitigate such risks.

Drolshagen says larger asteroids are much less common than smaller ones, such that the size of the object is conversely related to the probability of a collision with Earth. Objects the size of the Chelyabinsk meteor, about 18 meters, can be expected to hit earth approximately every 20 to 50 years, while objects comparable to the Tunguska meteor hit with far less frequency, in the 200 to 1,000 year range.

“A really big object, like the one that killed the dinosaurs, will only [impact Earth] every 80 million years or so,” Drolshagen says.

So despite what many might have judged on the basis of popular ‘90s disaster movies, the likelihood of extinction-level impact is vanishingly small. This shouldn’t be much of a surprise–if such events were frequent, humanity would likely not have survived as long as it has.

But damage from smaller asteroids is still concerning. “We should be prepared, because it’s the first time we could do something if we see an object coming,” Drohlshagen explains.

For this reason, the ESA and NASA have teamed up for the Asteroid Impact and Deflection Assessment mission (AIDA), which is still in its early stages. They hope to crash a probe into the smaller of two asteroids, held together by gravity in a binary system called the Didymos asteroids. Though these asteroids are not a risk, researchers hope that by studying the results of impact of the trajectory of the system, we will better understand our ability to alter the course of asteroids and potentially avert future disasters.

Photo courtesy of Wikimedia Commons.

Two alternate possibilities for deflecting asteroids have also been discussed. We might also use a nuclear explosion near the asteroid to modify its path. But the B612 Foundation, a non-profit whose purpose is to investigate asteroid threats and possible response strategies, has suggested the subtler method of using a spacecraft’s gravity to divert an asteroid away from a path of impact.

Even if these contingency plans are expertly designed and executed, they are useless if we cannot predict the next impact. NASA’s Chief Technologist, Dr. David Miller, tells me how we are able to monitor these astronomical threats.

In terms of the most dangerous asteroids–the dinosaur-killing variety–Miller explains, “We know where those are, we know their characteristics, and we know that there’s none that threatens us in the foreseeable future.”

Naturally, the smaller (and as noted above, more numerous) asteroids are much harder to track. “Those are the one’s we’re trying to fill out our knowledge on,” Miller says.

“We’re doing a lot; the question is, is it enough?” he points out. Current methods have certain drawbacks. For example, because the Southern Hemisphere is mostly covered with ocean, there are not nearly as many ground-based telescopes monitoring the southern sky, though there’s been a recent push to address this gap.

The B612 Foundation plans to launch an infrared telescope called Sentinel into space, the first deep space mission to be carried out by a private organization. Sentinel would be better positioned to monitor smaller asteroids that are otherwise blocked from view by the sun’s light.

Addressing these concerns is not cheap. The Sentinel Mission, for instance, is estimated to cost $450 million.

Such costs are minuscule, of course, compared to the potential for danger from a medium-sized asteroid. But asteroids are not the only threat we have to worry about, indeed, they are not even the only astronomical threat.

As Miller relates, there was a solar storm in the 1800s that sent a powerful electromagnetic pulse to Earth, which caused fires at telegraph stations. A similar storm occurring now could cause immeasurable damage to electronics, satellites, and power grids that we depend upon.

“That’s something that’s much more likely and we need to be ready for that,” Miller warns. “We don’t want to one day be in the early 2000s, and then end up in the mid 1800s because a lot of our electrical systems went down.”

When we assess the risks and rewards of funding potential interventions certain against natural (and artificial) disasters, such as the asteroid hazard, we must also be aware of what we’re not preparing for. Humans are not known for our rational assessment of potential threats, and we risk ignoring more pressing concerns if we focus too much on particular dangers. We would be well advised to take a more calculated, wide-reaching approach to understanding the global hazards we face.