It seems like every few weeks, the tabloids tell us we’re all going to die. The culprit of this frequent apocalypse: Asteroids.
So, let’s talk about asteroids for a bit. The word “asteroid” means “star-like,” although asteroids don’t have anything to do with stars. An asteroid is a small celestial body, basically a chunk of rock, metal, or both. Most asteroids hang out in the Asteroid Belt, which is located between the orbits of Mars and Jupiter. The largest asteroid is a dwarf planet named Ceres.
However, not all asteroids hang out in the belt (which, by the way, does not appear to be a former planet which exploded, but is just a place where the various interplaying gravitic forces from the Sun and the gas giants tend to put debris). Some asteroids wander around. And a subset of those are what we call “Earth-crosser” asteroids and “Near-Earth asteroids.” Those are the ones we’re worried about.
What are Near-Earth Asteroids?
These asteroids cross Earth’s orbit while on their own route around the sun. Which means that if things go wrong, they may collide with the Earth. And this actually happens fairly often. 64 million years ago, a huge one hit and wrecked the Earth’s ecosystem. If it hadn’t happened, then this article might be being typed by a descendant of velociraptors! Okay, so that’s pure speculation, but the point is: We have a reason to worry about asteroids.
But how much of a reason do we have? Because I just said it happens fairly regularly and we’re all still here.
Well, here’s the thing. Asteroids vary in size, a lot. Our best estimate of the size of the rock which destroyed the dinosaurs was that it was somewhere between 7 and 8 miles wide. That would destroy our civilization and possibly our species, but life would rebound, as it did before. Additionally, most of the near-earth objects aren’t classed as asteroids, but as meteoroids. Of the 19,470 NEOs we have discovered and charterd, only 1,955 are classed as “potentially hazardous asteroids.” This means there’s a non-zero chance they will hit us, and that they are large enough to do some damage if they do. We’ve charted 879 near-earth asteroids that are at least 1 kilometer (0.6 miles) across. A 1-kilometer wide space rock would indeed be a major problem. It would cause an “asteroid winter” that would last a year or two, temporarily weaken the ozone layer, reduce rain and cause widespread food shortages, possibly even famine. But our civilization would probably adapt and survive. And you wouldn’t want to be under it.
But precisely zero of the charted large rocks pose any kind of imminent threat.
But, “this happens regularly?”
Most of the rocks that actually hit us are meteoroids (less than 100 meters across). And we get meteor swarms we can practically set a calendar by. This article was written just a few days after the regular Leonid Meteor Shower hit. (The meteor showers are named for the constellation they appear to emanate from). These are sprays of small rocks that burn up in the atmosphere, making them nature’s fireworks. Enjoyable to watch and not a threat. How small? They’re the size of pebbles. Those massive fireballs are created by tiny, tiny objects moving very quickly.
Larger meteoroids break up when they hit the atmosphere. Chunks of them are the meteorites people sometimes come across, or which sometimes make a hole in somebody’s roof. They’re not dangerous unless you are literally standing under one when it lands. Which has happened! How many times you ask? Once. A lady named Ann Hodges was asleep on the couch when a nine-pound meteorite came straight through her ceiling, bounced off her radio, and hit her on the thigh. Quite the rude awakening. She was not significantly hurt.
What About Larger Rocks?
Chelyabinsk is a sleepy city in Russia that offers very little to do and was a dot on the map (I’m told the tractor museum is worth an afternoon) until February 15, 2013, when it gained the distinction of becoming the only city to be hit by an asteroid in modern times. The rock that hit was about 17 meters (56 feet) across, weighing about 11,000 tons. So, did it leave a massive crater? Nope. The Chelyabinsk meteor broke apart in the air well above the town, causing an air burst explosion thirty to forty times stronger than Hiroshima. Ack! So, what happened to Chelyabinsk?
1,100 people were injured (a bit over1 million people live in the Chelyabinsk district). Nobody was killed. Most of the injured people were hurt by flying glass after rushing to windows to see the fireball. A lot of windows were broken. Some buildings were damaged, with the worst damage to a zinc factory that was struck by a fragment that caused a partial collapse. The air burst broke the pots of people’s house plants, set off car alarms, and scared the wits out of the good people of Chelyabinsk…
…and that was it. Quite anticlimactic if you read all the alarmist headlines. (Pro tip: If you see a massive fireball, get away from windows…)
What about 2009 JF1?
That’s the one all the tabloids are whining about in November, 2019. Supposedly it’s going to hit on May 6, 2022 and destroy a city. 2009JF1 has a stated estimated size of 130m. So, let’s take a look at 2009JF1. First of all, per ESA, the next closest approach is May 10, 2022. That’s a reasonable margin of error, but the tabloids (and some more reputable business outlets) are all giving a specific date. The Sentry database of possibly hazardous objects is hard for a layman to read, and gives it’s estimated size at 0.013km. 1013. That’s. 13. Meters. Yes, somebody added a zero. Meaning 2009 JF1 is smaller than the Chelyabinsk meteorite, meaning the worst case scenario is it hits a larger city and…blows out a few windows. Not exactly a citykiller.
So, should we worry about an asteroid strike? The short answer is: Yes. A large asteroid could do a lot of damage. However, the longer answer is: Not that much. There are simply no citykillers, let alone planet killers, threatening us in the near future.
The worry should be enough to fund planetary defense initiatives, and those are in the works. The first test of asteroid diversion will take place in 2022, diverting a small rock that won’t do damage if they drop a decimal point and send it in the wrong direction. But it should not be enough for any of us to lose sleep over an asteroid hitting the planet.
We are not all going to die.
Well, not from an asteroid strike anyway…