Death by asteroid may come in unexpected ways
Every now and then a really big rock from space comes careening through Earth’s atmosphere. Depending on its size, angle of approach and where it lands, few people may notice — or millions could face a risk of imminent death.
Concern about these occasional, but potentially catastrophic, events keeps some astronomers scanning the skies. Using all types of technologies, they’re scouting for a killer asteroid, one that could snuff out life in a brief but dramatic cataclysm. They’re also looking for ways to potentially deter an incoming biggie from an earthboard path.
But if a big space rock were to make it to Earth’s surface, what could people expect? That’s a question planetary scientists have been asking themselves — and their computers. And some of their latest answers might surprise you.
For instance, it’s not likely a tsunami will take you out. Nor an earthquake. Few would need to even worry about being vaporized by the friction-heated space rock. No, gusting winds and shock waves set off by falling and exploding space rocks would claim the most lives. That’s one of the conclusions of a new computer model.
It investigated the likely outcomes of more than a million possible asteroid impacts. In one extreme case, a space rock 200 meters (660 feet) wide whizzes 20 kilometers (12 miles) per second into London, England. This smashup would kill more than 8.7 million people, computers estimate. And nearly three-quarters of those expected to die in that doomsday scenario would lose their lives to winds and shock waves.
Clemens Rumpf and his colleagues reported this online March 27 in Meteoritics & Planetary Science. Rumpf is a planetary scientist in England at the University of Southampton.
In a second report, Rumpf’s group looked at 1.2 million potential smashups. Here, the asteroids could be up to 400 meters (1,300 feet) across. Again, winds and shock waves were the big killers. They’d account for about six in every 10 deaths across the spectrum of asteroid sizes, the computer simulations showed.
Many previous studies had suggested tsunamis would be the top killer. But in these analyses, those killer waves claimed only around one in every five of the lives lost.
Even asteroids that explode before reaching Earth’s surface can generate high-speed wind gusts, shock waves of pressure in the atmosphere and intense heat. Space rocks big enough to survive the descent pose far greater risks. They can spawn earthquakes, tsunamis, flying debris — and, of course, gaping craters.
“These asteroids aren’t an everyday concern,” Rumpf observes. Yet clearly, he notes, the risks they pose “can be severe.” His team describes just how severe they could be in a paper posted online April 19 in Geophysical Research Letters.
Previous studies typically considered individually each possible effect of an asteroid impact. Rumpf’s group instead looked at them collectively. Quantifying the estimated hazard posed by each effect, says Steve Chesley, might one day help some leaders make one of the hardest calls imaginable — work to deflect an asteroid or just let it hit. Chesley is a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. (NASA stands for National Aeronautics and Space Administration.) Chesley was not involved with either of the new studies.
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Land hits would pose the biggest risks
The 1.2 million simulated asteroid impacts each fell into one of 50,000 scenarios. They varied in location, speed and angle of strike. Each scenario was run for 24 different asteroids. Their diameters ranged from 15 to 400 meters (50 to 1,300 feet). About 71 percent of the Earth is covered by water, so the simulations let asteroids descend over water in nearly 36,000 of the scenarios (about 72 percent).
The researchers began with a map of human populations. Then they added in data on the likely energy that a falling asteroid would unleash at a given site. Existing casualty data from studies of extreme weather and nuclear blasts helped the scientists calculate death rates at different distances from a space rock’s point of impact. All that was then combined into the computer model to gauge how deadly each modeled impact would likely be.
The most deadly one would have killed around 117 million people. Many asteroid hits, however, would pose no threat, the simulations found. More than half of asteroids smaller than 60 meters (200 feet) across caused zero deaths. And no asteroids smaller than 18 meters (60 feet) across led to deaths. Rocks smaller than 56 meters (180 feet) wide didn’t even make it to Earth’s surface before exploding in the atmosphere. Those explosions could still be deadly, though. They would generate intense heat that could burn skin, the team found. They also would set off high-speed winds that would hurl debris and trigger pressure waves that could rupture internal organs.
Where asteroids fell into the ocean, tsunamis became the dominant killer. The giant waves accounted for between seven and eight of every 10 deaths from these asteroid splashdowns. Still, the casualties from water impacts were only a fraction as high as those due to asteroids that smashed into land. (That’s because asteroid-generated tsunamis are relatively small and quickly lose steam as they plow through the ocean, the computer model showed.)
Heat, wind and shock waves topped the impacts from land smashups, especially if they hit near large population centers.
Bottom line: For all asteroids big enough to hit Earth’s surface, heat, wind and shock waves caused the most casualties overall. Other land-based effects, such as earthquakes and blast debris, resulted in fewer than 2 percent of total deaths, the computer projected.
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While asteroids have the potential to kill, deadly impacts are rare, Rumpf says. Most space rocks that bombard Earth are tiny. They burn up in the atmosphere, causing little harm.
Consider the rock that lit up the sky in 2013 and shattered windows around the Russian city of Chelyabinsk. Such 20-meter- (66-foot-) wide meteors strike Earth only about once a century. Far bigger impacts are capable of wiping out species. An asteroid at least 10 kilometers (6 miles) wide that smashed into Earth 66 million years ago has been blamed for wiping out the dinosaurs. Such mega-events are especially rare, however. They may occur only once every 100 million years or so.
Today, astronomers scan the skies with automated telescopes scouting for those potential killer space rocks. So far, they’ve cataloged 27 percent of those 140 meters (450 feet) or larger whizzing through our solar system.
Other scientists are analyzing how they might divert or catch an earthbound asteroid. Proposals include whacking the asteroid like a billiard ball with a high-speed spacecraft. Or perhaps part of the asteroid’s surface might be fried with a nearby nuclear blast. The vaporized material should propel the asteroid away like a jet engine.
Understanding the potential threats — and options available to deal with them — could offer guidance on how people should react to a warning that an asteroid was heading Earth’s way. It might help people decide whether it’s better to evacuate or shelter in place — or even mobilize space troops to try and divert the asteroid.
“If the asteroid’s in a size range where the damage will be from shock waves or wind, you can easily shelter in place,” Chesley says. He says this should work for even a large population. But if the heat generated as it falls, impacts or explodes “becomes a bigger threat,” he says “and you run the risk of fires — then that changes the response of emergency planners.”
Making such tough calls will require more information about what the asteroids are made of, says Lindley Johnson. He serves as the “planetary defense” officer for NASA in Washington, D.C. Those properties in part determine an asteroid’s potential for bringing devastation. Rumpf’s team couldn’t consider how those characteristics might vary, Johnson says. But several asteroid-bound missions are planned to provide some answers to such questions.
For now, making decisions based on the average deaths presented in the new study could be misleading, warns Gareth Collins. He’s a planetary scientist at Imperial College London. A 60-meter- (200-foot-) wide incoming space rock, for instance, would cause an average of 6,300 deaths in the simulations. But just a handful of high-fatality events inflated that average. These included one scenario that resulted in more than 12 million casualties. In fact, most space rocks of that size struck away from population centers in the simulations. And they killed no one. “You have to put it in perspective,” he advises.
Death from the skies
A new project simulated 1.2 million asteroid strikes on Earth. That let scientists estimate how many deaths could result from each effect of a falling space rock. (Averages for three of the classes of asteroids that were evaluated are shown in the interactive below. People who could have died from two or more effects are included in multiple columns.)
Click the graphic to explore the asteroid simulation data.
angle The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
asteroid A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
atmosphere The envelope of gases surrounding Earth or another planet.
cataclysm An enormous, violent, natural event. A meteor hitting Earth and wiping out most living species would qualify as a cataclysmic event.
climate The weather conditions prevailing in one area, in general, or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and the clearing of forests.
colleague Someone who works with another; a co-worker or team member.
computer model A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
crater A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.
data Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning.
death rates The share of people in a particular, defined group that die per year. Those rates can change if the group is affected by disease or other deadly conditions (such as accidents, natural disasters, extreme heat or war and other sources of violence).
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
deter An event, action or material that keeps something from happening. For instance, a visible pothole in the road will deter a driver from steering his car over it.
diameter The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.
dinosaur A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago.
extinction The permanent loss of a species, family or larger group of organisms.
friction The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage a surface of some material as it rubs against another.
mechanism The steps or process by which something happens or “works.”
meteor A lump of rock or metal from space that hits the atmosphere of Earth. In space it is known as a meteoroid. When you see it in the sky it is a meteor. And when it hits the ground it is called a meteorite.
National Aeronautics and Space Administration (or NASA) Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.
numerical Having to do with numbers.
online (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.
organ (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
planetary science The science of planets other than Earth.
population (in biology) A group of individuals from the same species that lives in the same area.
pressure Force applied uniformly over a surface, measured as force per unit of area.
propulsion The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.
range The full extent or distribution of something.
risk The chance or mathematical likelihood that some bad thing might happen.
scenario An imagined situation of how events or conditions might play out.
shock waves Tiny regions in a gas or fluid where properties of the host material change dramatically owing to the passage of some object (which could be a plane in air or merely bubbles in water). Across a shock wave, a region’s pressure, temperature and density spike briefly, and almost instantaneously.
simulation (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might vary over time or in response to different anticipated situations.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
telescope Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
tsunami One or many long, high sea waves caused by an earthquake, submarine landslide or other disturbance.
wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.
Journal: C.M. Rumpf, H.G. Lewis and P.M. Atkinson. Asteroid impact effects and their immediate hazards for human populations. Geophysical Research Letters, in press, 2017. doi: 10.1002/2017GL073191.
Journal: C.M. Rumpf, H.G. Lewis and P.M. Atkinson. Population vulnerability models for asteroid impact risk assessment. Meteoritics & Planetary Science. Published online March 27, 2017. doi: 10.1111/maps.12861.