We are back for season 2 and we start with a question every supervillain wants answering: how to completely annihilate the Earth using whatever the cosmos provides! 

Listen on Apple Podcast or on your favourite podcast player through Anchor.

Chris  

Welcome to The Astroholic Explains

Alfredo   

A podcast where we try to explain the Universe’s greatest mysteries with fictional stories, Q&A’s, and interviews.

Chris  

Join Dr. Alfredo Carpineti, the self-styled Astroholic 

Alfredo   

and Chris, my partner in life and in science,

Chris  

featuring experts and brilliant voice actors, join us in a light-hearted journey of discovery.

Chris  

Welcome back to a brand new series! It’s really good to be back! 

Alfredo   

Welcome back!

Chris  

So shall we dive straight into a brand new question for a brand new series?

Alfredo   

Absolutely. I’ve been waiting for this for a very long time. Well… six months, 

Chris  

It’s gone really fast.

Alfredo   

Yeah! 

Chris  

Really fast, but we won’t keep you waiting any longer. So today’s first question comes from the lovely neuroscientist, Dr. Steven Di Costa. Who asks: “Are there things that could suddenly destroy the Earth without warning and more or less instantly? If so, could you please itemize such things? And bonus points for including rough likelihood of occurrence. Thank you!”

Alfredo   

Well, okay, we need to consider a few things. But having in mind that we’re focusing on the Earth allows us to make certain assumptions that will make our discussion easier. If it was a generic planet, things will be a little bit different, but I think I can give good estimates about the Earth. In general, it’s very difficult to completely annihilate a planet. Destroying its surface? Very easy in cosmic terms. You can have big asteroids, you can have volcanism, you can have an intelligent civilization that decide to run the environment and the climate into the ground. 

Chris  

Ouch. 

Alfredo   

Yes. But to completely destroy, completely annihilate a planet you need to have a… 

Chris  

Death Star! 

Alfredo   

A Death Star. 

Chris  

Yes [laughs] 

Alfredo   

This is why it’s fascinating to think of that in the Star Wars universe, realize just how powerful of a weapon that is. And they’re just like… Ooh, takes a lot of energy for a little bit over-the-top effect. 

Chris  

Well, I mean, I don’t think you can destroy a planet and it not be over the top. 

Alfredo   

Yes, but if you want to threaten 10,000 planets, you don’t need a weapon that completely pulverizes a planet. You need a weapon that just destroys the surface, kills any living being on it, something like that.

Chris  

 But let’s not get too happy,

Alfredo   

Let’s not get on a tangent, like we always do. So the complete annihilation of our planet is an extremely remote possibility for two connected reasons. As I said, planets are much sturdier than we might realize. And things that could destroy the planet are very, very rare. 

Chris  

Thankfully! 

Alfredo   

Yes, thankfully. Otherwise, most likely we wouldn’t be here. So the gravitational binding energy of the Earth is 2×10^32 Joule. To give you a comparison, because that is just a big number with no meaning otherwise, it’s about the total energy the Sun produces over nine days, which is what would be necessary to just rip the Earth apart. 

Chris  

Wow. 

Alfredo   

So planets are sturdy. Steve has asked for instantaneous. So we need something that can deliver that amount of energy..

Chris  

in a quick blast!

Alfredo   

in a quick blast!

Chris  

I know where you’re going! 

Alfredo   

where am I going, Chris? 

Chris  

Supernova!

Alfredo   

Supernova! A supernova is certainly the first one up! A supernova certainly has the energy to rip a planet to smithereens. But how close must it be? At the point of ejection the material released by a supernova moves at 30,000 kilometre per second, that’s 10% of the speed of light. That is definitely enough to pulverize anything in the solar system. But the Sun is not going to be a supernova. 

Chris  

It’s gonna be a red giant. 

Alfredo   

Yes, but spoilers for a future episode. The sun is never going to turn supernova. So we need to look at nearby stars. The Crab Nebula is probably the most famous supernova remnant. It’s gorgeous. And the supernova that caused this was recorded in China in 1054 CE, and the material after almost 1000 years is expanding at 1500 kilometer per second. Still enough to erode the planet pretty quickly. You know: dust to dust, ashes to ashes, but the edge of that nebula is only five light-years from where the supernova exploded, from the center. We could see the apocalypse coming, quite a way off. But also there are no stars that could go supernova within 600 light-years. 

Chris  

What about Proxima Centauri? 

Alfredo   

Proxima Centauri is a red dwarf. So it’s even smaller than the Sun. So it’s definitely not going to go supernova. What is the closest super red giant to Earth, Christopher? Or all our lovely listeners? Please scream the answer if you know it! 

Chris  

Shall I say it three times? 

Alfredo   

You can say three times! 

Chris  

Beetlejuice. 

Alfredo   

Yes, it’s Beetlejuice. 

Chris  

Beet… no, I’m not gonna say it just in case. 

Alfredo   

All right.

Chris  

Is that classed as a niche joke now? I hope not.. 

Alfredo   

Probably not!

Alfredo   

The likelihood that we, in the very near future… because obviously the sun is moving around the Milky Way with a lot of other stars, so we might encounter at some point, in the far distant future, a supernova that is close enough to see, exploding.

Chris:

But it’s far away enough to not damage us.

Alfredo 

The Likelihood of the scenario, ballpark figure is probably around 1 in a trillion. 

Chris  

Okay, that’s fine then. So I’ll take those odds.

Alfredo   

Okay. What next? What can destroy our planet?

Chris  

Okay, so this is a good time for me to jump in with something that I thought at the start when you were talking about meteors, or asteroids. Yeah. How big do asteroids actually get? Because I’m thinking, even the Chicxulub. Is that how you say Chicxulub? The dinosaur killer!

Alfredo   

Yes

Chris  

I mean, that was, what, like 10 kilometers wide?

Alfredo   

I think I think it was… 

Chris  

I mean, it was pretty massive, because even that destroyed a lot of life on Earth and kind of blacked out the Sun with the amount of debris it threw up into the atmosphere, but it only dented, a tiny little nimp, in the surface of the Earth. So how big can they get? I don’t want to derail the entire episode, so be as fast as you want with this. How big can meteors technically get? And could they destroy Earth? Can you have like planet-sized ones? No, because that would probably be a planet. Can you have ones that are massive enough to actually smash a planet into pieces like that?

Alfredo   

Actually, there’s no upper-limit in the size. The biggest asteroid in the solar system is Ceres, which is now classified as a dwarf planet and is 930 kilometres in diameter. Don’t remember the exact number [939 km] but it’s…

Chris  

So if Ceres, for some reason spontaneously decided to smash into Earth, would that be enough to obliterate the Earth? 

Alfredo   

No!

Chris  

What?????

Alfredo   

Do you remember how the moon form? Sorry, that made it feel like you were there when the moon formed!

Chris  

Do you remember those times? I was there, Gandalf! I don’t remember how the moon was formed. I’m gonna guess it was some big… Hang on, wasn’t it a rock from Mars smashed into Earth?

Alfredo   

A rock??

Chris  

A chunk of Mars?

Alfredo   

No, but the Mars-thing is good. 

Chris  

Broke a bit off the Earth.

Alfredo   

No. 

Chris  

Maybe it was like debris from Earth sort of thing. I don’t know. You tell me.

Alfredo   

No, but… You see it is fascinating to see how Chris memorized things and what leaves an impression!

Chris  

[Laughs]

Alfredo   

No, it’s wonderful because your connection with Mars is that Earth was hit by a planetoid the size of Mars. 

Chris  

Oh, that’s where I got the Mars connection. 

Alfredo   

Yeah. And this cataclysmic impact didn’t destroy the Earth, but threw enough material into space! Half of it fell back down on Earth and half turned into the moon. 

Chris  

Okay!

Alfredo   

Even that! Even hitting our planet with something the size of Mars didn’t destroy it. 

Chris  

What if it just wasn’t going fast enough? 

Alfredo   

Okay, but you need the right conditions for something to get to that speed and you will not find them in the solar system with those kind of odds. 

Alfredo   

Okay, 

Alfredo   

But spoilers, because we’re gonna touch on those potential odds. 

Chris  

Okay. 

Alfredo   

So if it’s not a supernova what is the first thing that pops into your mind that can destroy our planet Completely? 

Alfredo   

Nukes? 

Alfredo   

[STUNNED SILENCE]

Chris  

No? Okay! 

Alfredo   

No, sweetie, we’re still thinking in cosmic terms. 

Chris  

But I’ve already thought… like meteor and supernova were my only two things!

Alfredo   

Is there nothing in the universe that ….? 

Chris  

Aliens?

Alfredo   

No! Something that we know they exist. And it’s usually seen… 

Chris  

Black holes! 

Alfredo   

Black Holes! We got there in the end! Assuming that all the stars in the Milky Way disc are evenly spaced, which are not because we have the spiral arms, but let’s go with it. And we are an average galaxy in terms of stars, there should be about a million black holes just going around, not bothering anyone. 

Chris  

Doing their own thing.. 

Alfredo   

Doing nothing, at least not eating because if they were eating, we would see their signature. 

Chris  

Okay

Alfredo   

Because the way we spot black holes, they just exist. They’re not bothering anyone 

Chris  

Not a phone in sight, 

Alfredo   

Not a phone in sight! Just black holes living in the moment. 

Alfredo   

If that is the case, There should be roughly one of this million black holes every 125 light years, how likely is that we can encounter these black holes. Remember the black holes despite being quite massive (and here we’re talking about solar-size, so between 8 and 100 times the mass of the Sun) they’re still really, really small. They would be between island size to country size, probably like there would be really small. So the chance to find that, the chance that not only they pass near the solar system but they managed to hit Earth. It’s tiny. I would say the upper limit is around two in a billion billion, just based on my calculations.

Chris  

So that’s very good odds to that not happening, huh? If it were to happen how fast would the Earth be annihilated? Would it be instantaneous? Or would it sort of gently go towards this black hole and it will just [poof noise]

Alfredo   

No, the moment that black hole is near enough, the Earth will be completely ripped apart. I think we discussed last season about spaghettification and what it’s like to jump into a black hole. So would be that on a planetary scale. 

Chris  

Wow. 

Alfredo   

Yeah. 

Chris  

Wow.

Alfredo   

Now, before we get to Earth getting destroyed by a planet, how about if another star hit us? That could lead to two things. You could have the star hitting the Sun and that could turn supernova or the star hitting the Earth. And that could happen even if it was a smaller star. So I’m going with that case just because it’s slightly more likely, simply because smaller stars, like red dwarfs are more common than bigger stars that could turn the sun into a supernova.

Chris  

Is this something that there is a shred of a chance occurring during the Andromeda merger?

Alfredo   

Ah, no. Again, all these chances and all my upper limits are literally like saying “Imagine that all of these objects in the Milky Way, act like billiard balls, and they’re just going around and eventually cross path at the wrong possible moment.” You need to consider there is gravitational interaction, there is a lot more so I’m pretty much saying: “Okay, if we have an idealized case, and I can do some quick maths, this is the chance.” Probably it’s way less likely. And also, if it’s more likely, and it happens, so we’ll be dead so nobody can blame me for getting the numbers wrong. The Milky Way has an idealized star density of about 0.02 star per cubic light here. 

Chris  

I can’t even picture that. 

Alfredo   

Yeah. This is why maths  is easier in this case than trying to picture vast volumes in space and what it does mean. So what is the chance of a collision? Higher than collision with a black hole, still quite small in my idealized case: it is about 7.5 in 100 trillion. 

Chris

Wow!

Alfredo   

Slightly more than 10,000 times more likely than a black hole. But still very… 

Chris  

Little bit unlikely still..

Alfredo   

And finally is a planet. And again, this is a bit of a cheat because…

Chris  

You mean a planet crashing into Earth? 

Alfredo   

Yeah! There’s nothing in the solar system that can do that. But what about a rogue planet? Rogue planets are those planets that we believe exist between stars unbounded.

Chris  

Ones that aren’t in a solar system? 

Alfredo   

No, that’s why the rogue! 

Chris  

Oh! I like this!

Alfredo   

If the estimates for these objects are true, there should be twice as many of these rogue planets than stars in the Milky Way.

Chris  

WoooHWooh…That was a weird noise. Okay, trying to picture that I would have thought that stars would be the more abundant but I suppose now I think about it. There are obviously going to be more planets than stars.

Alfredo   

And we think every star has planets or at least every star forms planets when it forms. So stars can lose their planets!

Chris  

Oh, so rogue planets wouldn’t have just formed out of nothing… obviously, they’re not gonna fall out of nothing. 

Alfredo   

No, they don’t just form on their own. They form around stars.

Chris  

These stars can lose planets?

Alfredo   

Stars can lose planets. 

Chris  

Interesting. 

Alfredo   

I would put the likelihood of a rogue planet hitting Earth though, sorry Steve that’s a bit of a cheat that is not completely annihilation, to about twice the likelihood of a star hitting Earth

Chris  

Twice the likelihood of a star hitting Earth. But I suppose if a planet did hit Earth then it could destroy instantly.

Alfredo   

Yes, but Steve specifically said utter annihilation, complete annihilation. So at that point, if you need to wait for a rogue planet… I’m now picturing Steve just having a little master plan of villainy on how to destroy Earth. 

Chris  

It was a very specific question. 

Alfredo   

Yes.

Chris  

Fed up of physical distancing!

Alfredo   

Enough with the lockdown. Let’s destroy everything! I hope that answered the question. 

Chris  

Wasn’t there something actually quite recently about a planet that had been destroyed?

Alfredo   

Yes, there was. Are you talking about the ‘Oumuamua formation theory? 

Chris  

Yes, the not-alien-spacecraft.

Alfredo   

Definitely, definitely, definitely not alien spacecraft. ‘Oumuamua, if you’re not familiar, is the first Interstellar object discovered in the solar system.

Chris  

It’s a visitor.

Alfredo   

It’s a visitor from another star system. 

Chris  

That’s so cool. 

Alfredo   

So ‘Oumuamua is a fascinating object. First of all, we were expecting comets to be the first interstellar visitors that we could observe because they are more luminous and usually comets form at the edges of a star system so they can be lost more easily because they are less tightly bound. And we found an interstellar comet, comet Borisov that just recently started breaking apart after it passed through the solar system. ‘Oumuamua instead was quite the peculiar thing. First of all, it’s very weirdly shaped, a little bit like a cigar. It’s very long and thin.

Chris  

A space sausage!

Alfredo   

Yeah, but also it rotates in a weird way. And he had something that is called a non-gravitational acceleration. Now, that’s where people, even famous researchers, which are my nemesis,

Chris

your nemesis-es

Alfredo   

My nemeses. Even they have discussed ‘what is this non-gravitational acceleration?’ Pretty much your workout. How much it should accelerate, but getting closer to the Sun, and then moving away. And what it appeared to be happening was it was going faster. But since it didn’t form an atmosphere, didn’t have a coma, like it’s technically called for comet, or tail, we couldn’t work out how that acceleration was happening. So for comets, it would be the evaporation, the release of material that would produce that non-gravitational acceleration.

Chris  

Could it have been knocked? 

Alfredo   

No, no, no. It needs to be intrinsic. The issue was to understand all these peculiar properties and researchers have recently worked out a scenario, a formation scenario for ‘Oumuamua that explains everything. We don’t know for certain, but it’s a fascinating theory and has a really good prediction. So the idea is that the parent body of ‘Oumuamua was either a planet or planetoid or a large asteroid that got too close to its star or its white dwarf. It also would work around the white dwarf. What happened is that the planet, the planetoid, asteroid, was completely destroyed. And it was so close that the material was stretched. So the fragments, these shards of a shattered planet were stretched into what will become ‘Oumuamua. But was not only stretched but also baked. So the surface of this asteroid was baked, but they worked out that material inside this shard could still be rich in water and other volatiles. So, when it got near enough to our Sun, it wasn’t enough to form a coma, but it was enough to release some material from the deeper layer and give this non-gravitational acceleration. And so you explain the weird shape, the reason why it’s rotating in a funny way because… 

Chris  

I was gonna ask how it escaped its own star. I guess that’s how.. 

Alfredo   

Yeah. The shattering of the planet threw all this material in space and they estimate that a single planet could create something like 10,000 ‘Oumuamua.

Chris  

Wow!

Alfredo   

Probably there are as many interstellar comets, as there are interstellar asteroids like ‘Oumumua. And their prediction, and this is why I like it, because we could soon find out if this idea is correct or not. If we see other interstellar asteroids, they should be looking like ‘Oumumua, so weird shape.They need to be planetary shards rather than something more like Ceres, which is quite round, or asteroids like Vesta or ida that are potato shaped. They need to be something quite peculiar because asteroids tend to form closer to their stars and then need to be kicked out. Because if they form very close to their star, they need to get a really good kick to be thrown out into space. 

Chris  

Wow, that’s absolutely amazing.

Alfredo   

And I’m sorry, Steve, the Earth is in a very, very stable orbit, so it’s not going to happen to our planets. So you cannot destroy Earth just by getting close to the sun. And you cannot even push Earth close to the Sun.

Chris  

Maybe don’t challenge Steve. I feel like he’s on a bit of a mission with this question… Never know what he could do!

Alfredo   

But if he becomes a super villain with this plan, we have the sort of responsibility to stop him and imagine what that would do for the listener of The Astroholic Explains! It’s all good publicity!

Chris  

Okay, well, Nice try, Steve, and thank you Alf for answering this apocalyptic question. 

Alfredo   

Thank you Steve you for asking this fascinating “and I don’t find it problematic but some people might find it problematic” question. And thank you very much for listening to The Astroholic Explains.

Alfredo   

And this is it for another episode of The Astroholic Explains. 

Chris  

Follow us on social media at the Astroholic and feel free to send in more questions.