173 Kiloton Explosion Over The Bering Sea Was Asteroid Breaking Up
On Dec. 18, 2018, a school bus-size meteor exploded over Earth with an impact energy of roughly 10 atomic bombs. According to NASA, the blast was the second-largest meteor impact since the organization began tracking them 30 years ago, bested only by the infamous fireball that exploded over Chelyabinsk, Russia, in Feb. 2013.
Despite this, hardly anyone noticed it was happening — and nobody saw it coming.
As to why one of the largest meteor impacts in recent history may have totally passed you by, that’s likely because the space rock in question shattered over the Bering Sea, a cold stretch of the Pacific Ocean between Russia and Alaska, miles from inhabited land.
NASA learned about the December impact thanks to the U.S. Air Force, whose missile-monitoring satellites were among the first to detect the blast. The rumble of the impact also registered on infrasound detectors — stations that measure low-frequency sound waves inaudible to human ears — around the world, giving scientists enough data to draw some basic conclusions about the sneaky meteor.
According to NASA, that meteor weighed about 1,500 tons (1,360 metric tons), had a diameter of about 32 feet (10 meters), and was traveling through the atmosphere at about 71,582 mph (115,200 kilometers per hour) when it exploded. The blast occurred about 15.5 miles (25 km) over the ocean and erupted with an energy equivalent to 173 kilotons of TNT — roughly 10 times the energy of the atomic bomb that the United States detonated over Hiroshima during World War II.
The world’s asteroid-monitoring groups failed to see the rock headed our way likely due to its smallish size. Alan Fitzsimmons, an astronomer at Queen’s University Belfast in Northern Ireland, told New Scientist that most modern telescopes are best able to detect objects measuring several hundred meters or more in diameter, making smaller objects like this one easy to miss.
NASA asteroid hunters are most concerned about identifying near-Earth objects measuring 460 feet (140 m) across, which have the potential to obliterate entire US states if allowed to pass through the atmosphere, Live Science previously reported.
The December 2018 impact only came to attention this week thanks, in part, to a presentation at the Lunar and Planetary Science Conference in Texas that was delivered by Kelly Fast, NASA’s near-Earth objects observations program manager. Fast told BBC News that the December event exploded with “40 percent the energy release of Chelyabinsk,” but didn’t show up in the news because of the impact’s relatively remote location.
The Chelyabinsk meteor, which measured 62 feet (19 m) wide, passed over mainland Russia and was recorded by many motorists. The resulting shockwaves injured more than 1,200 people.
What happened over the Bering Sea?
As spotted, among others, by meteor researcher Peter Brown, of the University of Western Ontario, a few weeks back – a fireball was spotted over the Bering Sea, near Russia’s Kamchatka Peninsula, on December 18th, 2018.
The location was too remote for anyone on the ground to spot the fireball, but in this case, monitoring stations spread across the world recorded the impact. Per the Guardian, the boom was picked up on by infrasound detectors, which have an ear for sound waves that humans can’t pick up on.
Using data from a myriad of satellites and sensors, NASA continuously updates its records of cometary and asteroid fragments that enter our atmosphere on its Near-Earth Object website. A quick browse of the catalog reveals that not-insignificant significant chunks of space debris combust in our skies fairly frequently, but it’s fair to say that the event on December 18th stands out.
Was this a meteoroid, meteor or meteorite?
As the object made it through the atmosphere but didn’t impact the surface, this is known as a meteor. It’s only a meteorite if it slams into the ground. At the same time, this was a fireball as it was an exceptionally bright meteor, and a bolide, as it was a fireball that exploded in our atmosphere.
Why did it explode in mid-air?
Air-burst events are fairly common for meteors over a certain size, moving at just the right angle and with the right about of momentum.
Essentially, if enough air gets in front of a speedy space rock, said air becomes incredibly compressed, which heats it up. This causes the outer layers of the meteor to ignite, creating the fireball. As the pressure on the front edge of the meteor builds to a critical point, the mechanical strength of the rock is overcome; it rapidly breaks up, releasing a huge amount of kinetic energy as it does so.
The meteor has to be of a certain size for this violent fragmentation to take place. If it’s too large, it may still burn up a little but it will resist the urge to shatter. If it’s far too small, it’ll simply be obliterated in the upper atmosphere. In this case, the Bering Sea fireball was, per Brown, just 10 meters (33 feet) across, although it did weigh about 1,400 tons – as much as 20-and-a-half M1 Abrams battle tanks.
Why do powerful meteor air-bursts keep happening over or near Russian territory?
It’s just a coincidence. Russia is the world’s largest country by far in terms of area, covering 17.1 million square kilometers (6.6 million square miles). There’s a good chance that, with all over things being equal, meteors and space debris are going to fall over Russia at a greater frequency compared to other parts of the planet.
Russia only makes up 3.3% of the entire planet’s surface area. Most of our planet is water, which is why most space debris explodes over or ends up in, the soggy depths – just like December’s fireball over the Bering Sea, which, to be fair, is pretty close to Russia.
Did any satellites see the meteor other than the infrared trail?
Why yes, they did! Simon Proud, an aviation safety expert and meteorologist at the University of Oxford, was having a peruse through the Himawari-8 weather satellite. Owned by the Japan Meteorological Agency, this collection of tech is geostationary, which means it hangs above the same point of the planet at all times so it can keep an uninterrupted eye on things.
It appears Himawari-8 recorded the smoke trail of the Bering Sea meteor, created as it began to burn up in our atmosphere. The smoke trail is pretty much perpendicular to Earth’s surface, which matches with NASA’s data showing that the object entered the atmosphere at a steep 7-degree angle.
How commonplace are meteors like this?
Space debris hits Earth’s atmosphere (and the lunar surface) pretty much all the time. However, for impacts of this energy, Brown tweeted that they occur somewhere on the planet once every few decades.
As it happens, a recent study indicated that, from about 290 million years ago, the number of impacts on both the Moon and Earth tripled compared to the 710 million years prior, and there’s no sign that this bombardment has slowed down yet. It’s not clear why this happened, but a cascade of destructive events in the asteroid belt is likely to blame.
Is this fireball as descendent of that ancient cataclysm? It’s hard to know, but it’s certainly safe to say that Earth serves as target practice for the rocky remnants of the inner solar system.
Is this type of meteor anything to worry about?
There’s not much you personally fretting is going to do about it, but space debris of a certain size crossing Earth’s path is something various space agencies are of course very concerned about. NASA’s very own Planetary Defense Coordination Office, for example, is tracking the sky hoping to spot a range of potentially hazardous objects, or PHOs, that will come within 8 million kilometers (5 million miles) of Earth’s orbit – which, by the way, is close by astronomical standards.
In general, the office tracks objects that are at least 30 meters (about 100 feet) across, which at that size will cause “significant damage” if they impact the planet. The Bering Sea event, although energetic, was about a third of that size; the Chelyabinsk meteor was about two-thirds. Technically, both wouldn’t make the cut even though, as we can see in the case of the latter, it can cause plenty of injuries even by exploding in mid-air. That’s not because NASA isn’t bothered by them, but because they are far harder to spot – more on that in a moment.
Those 30-meter-long objects, by the way, aren’t enough to cause planetary devastation. The Chicxulub impactor that heralded the end of the age of the dinosaurs, for example, was 12.1 kilometers (7.5 miles) across.
At 30 meters or above, though, they could of course cause major damage to a populated area. As Megan Bruck Syal, a planetary defense researcher at the Lawrence Livermore National Laboratory tweeted after we previously spoke about blowing up sizeable asteroids, it’s these “city-killers” that her colleagues worry about. These include the next Tunguska, a 60-100-meter (200 to 330-foot) rocky meteor, or a similar, 50-metre (164-foot) iron collider that creates something similar to Meteor Crater upon impact, which left a 1.25-kilometer (4,100-foot), 174-metre (570-foot) hole in the ground.
Could we stop a Bering Sea meteor city-killer asteroid from hitting us?
More apocalyptic asteroids like the Chicxulub impactor will likely need to be nudged out of the way. If we try and obliterate them with nuclear weapons or a kinetic impactor of some sort, then based on recent computer simulations it will break up and then quickly reform, a bit like the shapeshifting antagonist from Terminator 2. Conversely, city-killer-sized asteroids, per Syal’s tweets, could be easily “disrupted and well-dispersed” – as in, shattered into pieces – in a way that no sizeable fragments slam into Earth.
The key factor here is to be able to spot them coming in the first place, regardless of size. NASA is doing the best they can with the resources they have, and they are doing an indubitably stellar job tracking a huge number of big, scary objects out there in the darkness. But, as with all hazards, every little helps when it comes to mitigating them.
Syal points to the Near-Earth Object Camera or NEOCam. This is a proposed mission whose infrared telescope and the wide-field camera is designed to, among other things, discover all kinds of menacing objects lingering near our planet. Missions like this, Syal explained, “are critical for finding the hundreds of thousands of objects in the tens to hundreds of meter size range that remain invisible to us today.”
Like Chelyabinsk before it, the Bering Sea meteor is a timely reminder that we need to do all we can to keep our eyes on the skies. After all, they aren’t always going to explode above, or slam into, the ocean.