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00:00Life on Earth has already suffered a number of mass extinctions throughout its history.
00:05The world-ending events of the past have brought everything from volcanic eruption,
00:09to slow-build climate change, to fundamental shifts in the makeup of our atmosphere.
00:14An asteroid strike, though, brings much more sudden death and destruction,
00:19as well as all of those other factors.
00:21So could a rock from space one day trigger our next mass extinction?
00:26This is Unveiled, and today we're taking a closer look at the asteroids that could one day kill us all.
00:32And we're exploring exactly how much of a warning we'll get.
00:36Do you need the big questions answered? Are you constantly curious?
00:39Then why not subscribe to Unveiled for more clips like this one?
00:42And ring the bell for more thought-provoking content.
00:45Though large asteroid strikes are a rare occurrence, smaller ones happen far more frequently.
00:59According to NASA, Earth is bombarded with an average of 100 tons of space dust on a daily basis,
01:05and small asteroids, which are still roughly the same size as small cars, enter Earth's atmosphere every year.
01:13Thankfully, the vast majority of rocks like these burn up before they hit the ground.
01:18But occasionally, our planet is pelted by something bigger.
01:22The amount of damage a larger asteroid could cause depends on a variety of factors, including the speed and angle of impact.
01:29But were an asteroid with a width of, say, 50 feet to land in a rural and unpopulated area,
01:35it's thought the force would still be enough to shatter windows and release light bright enough to cause instant sunburn.
01:42A rock the size of a house could detonate on Earth with as much power as a nuclear bomb.
01:47Meanwhile, asteroids the size of football fields impact on Earth roughly every 2,000 years.
01:53However, for something to truly threaten the entire planet, it has to have a diameter of at least half a mile.
02:00Fortunately, rocks this size ramming into us are exceptionally rare.
02:04But that's not to say that the solar system as a whole doesn't contain thousands of asteroids big enough to pose a problem.
02:11In fact, a width of half a mile is actually very small compared to some of what's lurking in the asteroid belt.
02:18The rocks there can be as large as 550 miles across, and more.
02:23As far as we know, we've never been hit with anything quite that big.
02:27But arguably the most famous asteroid strike in history came via the Chicxulub impactor some 66 million years ago.
02:34A fateful rock thought to have been more than six miles wide,
02:38it was also held by many as the event which triggered the K-Pg mass extinction, which wiped out the dinosaurs.
02:44There's no real reason to expect another impact on this scale any time soon.
02:49But such monumental events do happen, and could theoretically happen at any moment, were an asteroid to go unnoticed.
02:57Missing something that big, though, does it ever really happen?
03:00Surprisingly, yes it does.
03:03In the summer of 2019, for example, we had a reasonably close call with an asteroid named 2019 OK,
03:10a football-field-sized rock which flew right by Earth with little to no warning beforehand.
03:162019 OK came within 45,000 miles of our planet, meaning it was less than one-fifth the distance to the moon from us.
03:24Still a long way away, but cosmologically speaking, uncomfortably nearby.
03:29In fact, it was the largest asteroid to pass by Earth in a century, and yet it was only spotted on the very same day that it flew past us.
03:38Say 2019 OK had veered just a fraction off course and headed towards Earth,
03:43it would have made an impact to devastate an area of at least 50 miles across.
03:48Generally speaking, NASA and the world's other space agencies are on top of things, however,
03:53keeping track of thousands of asteroids flying through space at any given time.
03:58Sure, there are some that slip through, but for the most part, we're already well aware of the most threatening asteroids out there,
04:04and we've calculated the likelihood that they'll ever cross our path.
04:08Prior warning, asteroid naming practices aren't exactly what you'd call creative.
04:13The monikers don't exactly roll off the tongue.
04:16One of the most threatening to us is named 85713-1998-SS-49.
04:22This particular asteroid is part of the Apollo Group, a band that are all expected to pass close to Earth at multiple times in the future,
04:29with this one projected to also eventually pass closer than the moon.
04:33While it is only around one-third the size of the Chicxulub impactor that did in the dinosaurs,
04:38were it to veer off course and hit us, then it would still inflict major damage.
04:43Interestingly, 85713-1998-SS-49 is also expected to pass by both Mars and Venus,
04:51making it a multi-planet threat, although so far there is no solid evidence that a collision will happen.
04:57It's difficult to precisely track objects like these because of their low reflectivity and relatively small size compared to things like planets and moons.
05:06But, such rocks are also listed as PHAs, or Potentially Hazardous Asteroids, for a reason.
05:12Because researchers believe they have the potential to change direction, to become even more threatening than they already are.
05:19And no matter how tricky it is to keep rocks like these in our sights, scientists are doing everything they can not to lose them.
05:26Another listed as a PHA is 4179 Toutatis, one of the largest and most lethal objects currently expected to pass close by us.
05:36With a diameter of three miles, it's more than big enough to end the large majority of life and trigger worldwide effects on our planet, if it strikes.
05:45Toutatis is especially notorious, though, because it has a highly eccentric orbit, meaning that it's also one of the most unpredictable asteroids out there.
05:54It's a frequent visitor to our particular region of the solar system as well, having had various close encounters with Earth in the past, including in 2012, when it sped within 18 lunar distances of us.
06:06It's currently projected to pass Earth again in 2069, but this time it will be twice as close.
06:13We should be comfortably safe, but if its orbit proves more chaotic than we think, then maybe not.
06:19The outright largest known asteroid with the potential to impact Earth is another prospect entirely.
06:24It's named 53319 1999 JM8, and it's a whopping 4.3 miles wide, making it only slightly smaller than our dinosaur killer of yesteryear.
06:37It's another frequent flyer around these parts, having passed within 0.2 astronomical units of Earth at least five times in the last century, with its next approach at a similar distance, slated for 2075.
06:50JM8 is also extremely dim, it has exceptionally low reflectivity, and a chaotic orbital path… all of which makes it especially difficult to track through a telescope, and therefore a likely candidate for one day passing by without our knowing.
07:06In the event that it eventually comes close enough to smash into us, well, our world would be plunged into a wholly apocalyptic scenario, facing multiple extinctions and total ecological disruption.
07:18But, and this is important, not one of these asteroids is actually expected to hit Earth.
07:24Rather, these are the ones scheduled to pass unusually close by.
07:28Right now, their orbits are subject to change, which is why they're monitored as a potential threat.
07:33But that doesn't mean that any of these rocks really will crash into us any time soon.
07:38It's just that if any of them did change course, defy predictions, and make straight for us, then they'd all have the potential to trigger worldwide chaos.
07:48And, coming up next, we'll take a closer look at exactly how much time we'd have on our hands if the worst ever were to happen.
07:56Ever since we discovered in the 1980s that a monstrous asteroid wiped out the dinosaurs, we've been obsessed with the idea that the same thing could happen again.
08:05After all, the solar system contains hundreds of millions of asteroids, and it seems like at any moment, one could tumble out of orbit and hurtle towards us.
08:14But how much time would we have to prepare if that happened?
08:27How long would it take an asteroid to hit Earth?
08:30No asteroid could ever destroy Earth, thankfully, because none of them are big enough to cause planet-shattering impact.
08:36But many could wipe out life as we know it in the short term, much like the asteroid that killed the dinosaurs 66 million years ago.
08:44That asteroid, the Chicxulub impactor, which landed on the coast of what is now Mexico's Yucatan Peninsula,
08:50was only about six miles wide, going by the size of the crater.
08:53Which is frighteningly small, considering just how many asteroids of this size, or significantly bigger, there are out there.
09:00And some of the potentially hazardous asteroids watched by NASA, in particular one called Apophis,
09:06which has made headlines more than once for approaching Earth uncomfortably closely, is only 1,100 feet wide.
09:13That's just 0.2 miles. NASA says there's no danger of Apophis hitting us in the next 100 years.
09:19But it's true that a large asteroid definitely will hit Earth again one day.
09:24But where might this asteroid come from?
09:26Well, excluding objects from beyond the solar system, the absolute furthest point that an asteroid could originate from is the Oort Cloud.
09:34The Oort Cloud is a theoretical sphere of planetesimals beyond even the heliosphere, surrounding the solar system like a shell of debris.
09:43Most long-period comets come from the Oort Cloud, and can take thousands or even millions of years to complete their orbits around the sun.
09:50The Oort Cloud primarily contains ice and comets, but it does contain some heavy asteroids.
09:56The inner edge of the Oort Cloud is thought to begin anywhere between 2,000 and 50,000 astronomical units from the sun,
10:03and extend between 100,000 and 200,000 astronomical units from the sun.
10:08One astronomical unit is the average distance between the sun and Earth, which is roughly 93 million miles.
10:15200,000 astronomical units is over three light-years away.
10:19So, how long would it take an asteroid coming from the outer edge of the Oort Cloud to crash into us here on Earth?
10:25Well, asteroids orbit the sun on average at around 15.5 miles per second, or 55,800 miles per hour.
10:34Since, again, one AU is 93 million miles, it would take an asteroid travelling at 55,800 miles an hour, 1,666 hours or 69 days to go one AU.
10:47That means it would take 6.9 million days to travel from the edge of the Oort Cloud if it's 100,000 AU away, or 18,891 years.
10:59If the edge of the Oort Cloud is 200,000 AU away, then doubling that number gets you the most extreme estimate, 37,782 years.
11:08That's a very long time for us to prepare, and by that point it's easy to imagine humans could have died out from something else, or even left Earth completely.
11:17At the nearest possible edge of the Oort Cloud, just 2,000 AU away, it would take a comparably fast 378 years.
11:25But that's still plenty of time for us to develop a countermeasure.
11:28So, if an asteroid fell out of its orbit in the Oort Cloud today, and was travelling at an average speed, it would still take anywhere between 38,000 years and 380 years to reach Earth.
11:39Admittedly, it could travel faster or slower than this, though more likely faster if you account for how acceleration speeds up the closer an object is to the sun.
11:49Far closer to us is the Kuiper Belt.
11:51Unlike the Oort Cloud, the Kuiper Belt, like the planets, orbits the sun on a relatively flat plane, rather than being a spherical cloud of celestial bodies.
12:00It's also significantly closer, ranging between 30 and 1,000 AU from the sun.
12:05This means that at most, it'll take 189 years for a Kuiper Belt asteroid to reach us, and at the shortest, less than six years.
12:14Considering the Kuiper Belt is beyond Neptune, that's very worrying when we take a look at the solar system's primary source of asteroids, the asteroid belt between Mars and Jupiter.
12:25The asteroid belt is between 2.2 and 3.2 AU from the sun, making it 1.2 and 2.2 AU away from Earth, on average.
12:34At the shortest, that's about 83 days, and the longest, 152 days, or five months.
12:41That's a lot more frightening than even the Kuiper Belt's six years, which is starting to look like a very reasonable amount of time to prepare for an asteroid impact.
12:49We also need to take into consideration exactly where Earth is in its orbit relative to where the asteroid's journey begins.
12:55For instance, if an asteroid 2.2 AU away from the sun begins to head toward us, it's possible that when it crosses Earth's orbit, Earth might be on the far side of the sun, an additional 2 AU away, and it would keep going straight into the sun.
13:09It's also worth noting that Earth's orbit is huge. Each year, Earth travels 584 million miles, and more than 99.99% of Earth's orbital path is empty at any given moment, which gives an asteroid millions of miles of leeway.
13:25It's been estimated that we'd need an asteroid with a diameter of 60 miles to completely wipe out life on Earth.
13:32But the Chig-Chelub impactor was only six miles wide, so even a much smaller asteroid would do incredible damage to the planet.
13:40And unfortunately for us, there are lots of asteroids floating around large enough to do this.
13:45NASA estimates that there are as many as 1.9 million asteroids in the asteroid belt with a diameter larger than 0.6 miles.
13:54And bear in mind, once again, that the tabloid's favourite deadly asteroid, Apophis, is three times smaller than NASA's lower limit.
14:03The asteroid belt also has many objects that are hundreds of miles wide, including Ceres, the dwarf planet, though it's not likely that Ceres is going to fall into the sun anytime soon, or even ever.
14:15With so many asteroids out there, we will have another large impact one day, even if it's not anytime soon, and we'll need to be prepared when it happens.
14:24Luckily, not only are NASA and other space agencies tracking asteroids, but there are lots of publicly funded, non-profit projects aiming to fill in the gaps, like the Sentinel mission.
14:35Sentinel uses an infrared telescope and boasts many people who previously worked for NASA and prestigious colleges.
14:43Somebody will spot a world-destroying asteroid ahead of time, but one coming loose from the Kuiper Belt still wouldn't give us much of a heads-up if it came straight for Earth.
14:52Many scientists are working on predictions of what would happen if an asteroid hit, and developing designs for countermeasures.
14:59But at the moment, the only realistic countermeasure that we could pull off in the shortest time span, 83 days, involves nuclear bombs.
15:08Blowing up a hazardous asteroid with enough nuclear weapons is the only asteroid countermeasure currently in our wheelhouse, and that could be deployed in such a short amount of time.
15:18For once, Earth's stockpiles of nuclear weapons will be beneficial.
15:22The world has, in total, close to 14,000, and since an asteroid impact would affect everybody, it's not hard to imagine that the planet's nuclear superpowers would work together to deal with the threat.
15:34We even already have plans for absolutely huge nuclear devices solely for the purpose of blasting a dangerous asteroid away.
15:41Other methods are more science fiction, with many researchers actually advocating for the use of a gravity tractor.
15:47We haven't yet developed any gravity tractors, which are large, artificial objects that would use their own gravitational field to redirect a problem asteroid.
15:56But, with enough R&D, they could become a viable option.
16:00Despite the vast distances in space, many of the asteroids close to Earth could find our planet worryingly quickly, and we don't have much of a plan for when the inevitable happens.
16:10What do you think? Is there anything we missed? Let us know in the comments, check out these other clips from Unveiled, and make sure you subscribe and ring the bell for our latest content.