The Interstellar Visitor You Should Hope Never Arrives

0:00 Meteors have the power to transform our planet,

0:04 to wipe out huge swaths of life on Earth in one impact.

0:08 But, not all of that dramatic.

0:11 We are hit by more than 100 tons of small sand-sized particles every day,

0:17 and they are essentially unnoticeable.

0:20 About once a year, a car-sized meteor comes crashing through our atmosphere,

0:25 but the resultant impressive fiery streak

0:28 burns up long before hitting the ground.

0:32 It's only on the scale of millions of years that we are

0:35 in danger of being hit by meteors a kilometer or two wide,

0:39 big enough to do some serious damage.

0:42 But, we've not seen one of those since the dinosaurs, lucky for us.

0:47 But, size isn't everything.

0:49 In fact, the biggest impacts may not even be from the largest objects.

0:54 If one particularly interesting theory is true,

0:58 some very rare meteors may be made of something a little more exotic than rock.

1:05 Externally, there would be not much to differentiate these rarer meteors.

1:10 In the vacuum of space,

1:11 they would appear exactly the same as any other space rock.

1:15 But, while regular meteors might create a fiery streak in the sky,

1:19 these outliers would have impacts that exceed the largest of nuclear bombs.

1:26 And those are just the small ones.

1:28 If a kilometer-sized meteor of this variety hit the Earth,

1:33 similar in size to the normal meteor that killed the dinosaurs,

1:37 we might not have a planet anymore.

1:40 That is the power of a meteor made of antimatter.

1:46 Could antimatter meteors really exist?

1:49 What clues would help us identify them from regular matter meteors?

1:54 And how big would they have to be to become a major problem?

1:59 I'm Alex Holligan, and you're watching Astrum.

2:02 Join me today as we test the scientific theory behind antimatter meteors,

2:07 and explore the odds of such objects lurking in our solar system.

2:13 Antimatter is a funny substance.

2:16 The fact that it exists means that we shouldn't be here.

2:20 It is almost identical to regular matter with a few key differences.

2:25 One is that it has an inverted charge.

2:28 Another is that when antimatter meets regular matter,

2:32 the two annihilate each other completely,

2:35 converting almost entirely into energy.

2:40 Now, in the early universe, it wasn't just matter that was created.

2:44 In theory, an equal amount of antimatter came [music] into being, too.

2:49 All the matter should have bumped into the antimatter,

2:52 and everything would have canceled each other out.

2:56 This would have left no universe for us,

2:58 as there would be nothing to make the universe out of.

3:02 It is one of the mysteries of science that this did not happen.

3:06 And for some reason,

3:07 a slightly larger amount of matter coalesced into existence than antimatter,

3:12 perhaps as small a discrepancy as a billion

3:15 and one matter particles to every billion antimatter ones.

3:20 Scientists are still trying to figure out why this might have occurred,

3:24 but the mystery remains unsolved for now.

3:28 [music] Perhaps there is some rule at play that we've not yet identified.

3:31 Whatever caused it, this imbalance is the reason the universe

3:34 we see around us is almost entirely made of regular matter.

3:39 And the only place we reliably see antimatter is when

3:42 they make tiny amounts of it in experiments at CERN,

3:46 and in other particle accelerators.

3:48 Some hospitals even have small particle

3:50 accelerators to create positrons for PET, or positron emission tomography scans.

3:58 However, just because we don't see it,

4:01 doesn't mean that tiny pockets of antimatter [music] couldn't exist.

4:06 When the raw primordial soup quark-gluon plasma

4:10 of the Big Bang began to form into particles,

4:12 while overall there would have been more matter than antimatter,

4:17 in local areas there were fluctuations.

4:18 [music] So, it's logical that clumps of antimatter could

4:22 have emerged and dominated as gravity pulled them together.

4:27 After all, if you flip a coin enough times,

4:30 you'll inevitably end up with runs where you

4:32 flip nothing but heads or nothing but tails.

4:36 If these clumps were large enough in scale,

4:38 they wouldn't annihilate away in a burgeoning solar system.

4:42 Instead, they would be the solar system,

4:45 and it would be pockets of matter that would eventually annihilate out,

4:50 leaving behind stars and protoplanetary disks made entirely of antimatter.

4:57 This seems highly theoretical,

4:59 but could such solar systems [music] actually exist?

5:03 I personally think it would be really cool if they do,

5:06 and should we ever find one, it will certainly be breaking news.

5:10 If you want to be the first to know when a story like this does [music] break,

5:14 and keep up to date with other slightly more likely discoveries,

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5:37 Ask us a space question, and we'll do our best to answer them.

5:40 For now, though, let's get back to the antimatter at hand.

5:46 For the most part, an antistar would be visually identical to a regular one,

5:52 [music] as antimatter behaves in all the ways you might expect matter to.

5:55 It obeys the same laws of gravity, and mostly looks the same.

6:00 The only telltale giveaway would be when regular matter interacted with it,

6:05 such as when the interstellar winds met the edge of the fledgling solar system,

6:10 and resulting annihilations would emit gamma radiation.

6:13 And curiously, there are some systems that seem to do this.

6:18 14 such gamma-ray emitting star candidates were found in the Milky Way,

6:23 thanks to the Fermi Large Area Telescope in 2021.

6:28 If these are antistars,

6:31 and their profiles do match what we would expect out of antistars,

6:35 so this is not ruled out, and [music] they're not other objects that emit

6:39 gamma rays like pulsars or black holes,

6:43 then systems made of antimatter with planets and asteroids do exist.

6:49 The ratio of antistars to stars would be about one in 400,000.

6:55 So, the stage is set.

6:57 If antistar systems could exist,

7:00 it's not illogical to think that antimatter meteors do, too.

7:04 And that leads us to the question, what are the chances of them coming to Earth?

7:11 The idea of antimatter meteors striking our planet is not a new one.

7:16 Even back in 1940, only a decade or so

7:19 after the discovery of antimatter as a concept,

7:22 Russian-American physicist Vladimir Rojansky began

7:25 to speculate about their existence.

7:28 All it would take was for our solar system to have passed

7:31 one of these antimatter solar systems at some point in the past.

7:35 The sun's gravity would then knock a few outlying

7:38 antimatter meteors out of their precarious orbits and into ours.

7:43 Antimatter meteors may not have been able to form in our solar system.

7:47 Their particles would have been annihilated by interaction

7:49 with matter far too early for that.

7:51 But, in space, just an empty vacuum somewhat devoid of matter,

7:56 there would be nothing for them to annihilate with.

8:00 So, there's a chance they could be among us.

8:03 And if they were, would we even notice?

8:07 Soon after Rojansky,

8:09 American astronomer Lincoln LaPaz began to wonder whether any

8:13 of the craters on Earth could be attributed to antimatter meteors.

8:17 So, perhaps this is the time to consider what an antimatter

8:20 meteor could do if it came in contact with the Earth,

8:24 so we know what to look out for.

8:26 Thankfully, it's not necessarily a simple journey.

8:31 The first issue such an antimatter meteor would

8:33 encounter before reaching Earth would be our atmosphere.

8:37 To be fair, this is a problem for regular meteors, too.

8:41 When one of those trades vacuum for air,

8:44 the speed at which it's traveling causes it to generate incredible friction,

8:48 causing some or all of the meteor to burn up on the way down,

8:53 depending on its starting size,

8:54 leading to the fiery streak I mentioned at the start.

8:58 However, antimatter meteors would have it much worse.

9:02 Each particle of atmosphere that the antimatter meteor encountered

9:05 on the way down would annihilate a similar amount of the meteor.

9:09 So, to understand what happens next,

9:11 we need to turn to Einstein's famous equation, E= mc².

9:17 The meteor's mass, multiplied by the speed of light squared,

9:21 tells us how much energy would be released by the meteor on the way down.

9:25 Technically, twice that.

9:27 As for each particle of the meteor that's annihilating,

9:30 a particle of atmosphere is doing so, too.

9:34 This is potentially a huge amount of energy being released.

9:38 Let's do a bit of a thought experiment to work out how much.

9:43 While the dividing line between the atmosphere and space is either 100 km up,

9:48 if you're talking to Europeans, or 80 km up, if you're talking to Americans,

9:52 as the two haven't reached a consensus on that point yet,

9:55 over 90% of the mass of Earth's atmosphere is actually clumped below 16 km,

10:01 clinging to the planet as closely as possible thanks to the pull of gravity.

10:05 So, by working out how much air

10:07 exists between this line and the Earth's surface,

10:10 we can get a rough idea of how much antimatter

10:12 you'd need to have before an antimatter meteor hits the ground.

10:17 This is a little tricky to calculate, but thanks to a chart

10:20 released by the International Standardization Organization,

10:23 I was able to add up the sum total of the atmosphere

10:26 at different elevations between the surface and 20 km high,

10:30 and found that in a 1 m by 1 m corridor between space and the surface,

10:35 you'd have roughly 10,132 kg worth of atmosphere.

10:40 A meteor would need to be roughly this large to even hit the surface,

10:44 assuming it traveled the most direct route straight down.

10:49 Now, antimatter is similar in mass to matter,

10:52 so we can assume that they would have comparable compositions, too.

10:56 Most meteors are made of chondrites,

10:59 so assuming an average antimatter meteor made

11:02 of the antimatter version of the same stuff,

11:04 we can put the density of our antimatter

11:07 meteor at around 3,400 kg per cubic meter.

11:11 Of course, there's then a balancing act you need to do.

11:15 The bigger the meteor, the larger the surface area,

11:17 and the more air it thus encounters before it reaches the surface.

11:21 However, as volume scales up in cubes while surface area is only squared,

11:26 there is a sweet spot you can hit where the amount of air being

11:28 annihilated by the meteor would theoretically perfectly

11:32 match the amount of mass the meteor possesses.

11:35 And then we know that any mass of meteor above

11:37 that would make it through the atmosphere to hit the ground.

11:41 Using very rough math, I found that a 3 by 3 by 3 m meteor, or 27 cubic meters,

11:48 worked best for this calculation, which had a mass of 91,800 kg,

11:54 or 3,400 kg per cubic meter times 27 cubic meters.

12:00 This would only encounter 91,191 kg worth of air on the way down,

12:07 meaning 608 kg worth of meteor would actually hit the surface.

12:13 That's approximately the mass of a large grand piano.

12:17 How much damage could 600 kg of antimatter actually do?

12:22 It's time for our equation, E= mc².

12:26 Using this calculation,

12:27 we learn that 600 kg of remaining meteor releases 5.4* 10^ 19 J of energy,

12:37 or 54 quintillion joules.

12:41 Then double that, as the ground being annihilated releases that amount, too.

12:46 So, 108 quintillion joules.

12:49 For a point of reference, a 1 megaton nuke gives off 0.18* 10^ 15 J of energy.

12:58 Even if we scaled up to the largest nuke ever detonated,

13:02 the Tsar Bomba, which had a yield of 50 megatons,

13:07 we're still only looking at 2.09* 10^ 17 J,

13:12 a full 5,000 times weaker than our antimatter grand piano.

13:17 And the Tsar Bomba blast was so great,

13:20 towns within 55 km, like 70, were leveled.

13:26 Wooden buildings 160 km away were reportedly damaged.

13:31 The light from the blast was seen 1,000 km away.

13:35 Windows in Norway and Finland were shattered by the explosion.

13:40 If just 600 kg of our antimatter meteor

13:44 impacted in the middle of a state like Texas,

13:47 the whole state would be destroyed, the center vaporized, the rest devastated.

13:55 This is just the energy released

13:56 from our antimatter meteor annihilating on the ground,

14:01 not even going into things like kinetic energy.

14:04 But even then, it's actually not just the 600

14:07 kg that hits the ground we need to worry about.

14:10 When you consider the rest of that 91,200

14:14 kg of mass that was annihilated in the atmosphere,

14:18 the blast radius becomes a lot bigger.

14:22 While some of that energy would travel upwards into space,

14:25 minimizing the damage below, suddenly you're not just worrying about Texas.

14:31 You're worrying about the entirety of the USA.

14:35 All that's just from an antimatter meteor that's comparable in size to a car.

14:41 We really do not want to get hit by an antimatter meteor.

14:47 So, what actually are the risks here?

14:49 Let's say that an antimatter meteor had got swept up

14:52 in the sun's gravity well millions to billions of years ago.

14:56 Could it now be one of the 40,155 near-Earth asteroids that NASA tracks?

15:03 The good news is, no.

15:06 For one simple reason.

15:09 Space isn't actually empty.

15:12 While we talk of space being a vacuum, even in space,

15:16 there are trace amounts of dust floating in the void.

15:20 As such, an antimatter asteroid traveling

15:23 even through the interstellar medium would

15:25 not likely have a survival rate of longer than around 300 years.

15:30 As we last clipped another star 70,000 years ago,

15:34 Scholz's star, in case you're interested,

15:36 it would have to have been an exceptionally lucky antimatter meteor

15:41 to not only dodge all the other asteroids in that time,

15:44 but also to have not encountered enough dust since

15:48 then that it would have disintegrated into gamma radiation.

15:52 For this same reason,

15:54 an interstellar antimatter comet coming our solar system would be unlikely.

15:59 Small ones would burn up before reaching us,

16:02 and larger masses would be noticeable.

16:04 They would emit a steady stream of gamma rays as they traveled,

16:07 making them detectable to our telescopes.

16:10 No such sparkling asteroids have ever been detected.

16:14 So, all in all, while it would be devastating to be hit by an antimatter meteor,

16:20 it is unlikely that one would survive long enough to reach our planet,

16:24 assuming they and antimatter stars exist in the first place.

16:29 We are probably quite safe.

16:31 Besides, if antimatter meteors existed,

16:34 we might have seen some evidence of them before.

16:36 Meteor impacts with unusual destructive capacity,

16:40 but leaving no traces of the meteor that caused it.

16:43 We've not seen anything like that.

16:46 Have we?

16:48 In June 1908, a fireball lit up the sky in a remote part of Siberia.

16:54 The meteor exploded before hitting the ground,

16:56 its detonation causing massive forest fires and sending trees crashing

17:01 to the ground like bowling pins in an area of destruction kilometers wide.

17:06 Witnesses more than 30 km away reported seeing a flash brighter than the sun,

17:12 followed by a roar of thunder.

17:15 Due to its remoteness, scientific teams did not arrive at the site until 1927,

17:20 but even then, the destruction caused by the blast was easy to see.

17:25 Strangely, for an object that caused such destruction,

17:29 almost no trace of the meteor was ever found beyond a few microparticles.

17:36 But the Tunguska event couldn't have been

17:38 caused by an antimatter meteor, could it?

17:43 Don't worry, we know that it probably wasn't an antimatter meteor,

17:48 but there was a lot of debate about the topic in the past,

17:50 and we couldn't resist being a little spooky.

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