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This pretty much means that there were only 3 large collisions in the asteroid belt in the past 40M years... Which is astonishing considering how busy the belt

This pretty much means that there were only 3 large collisions in the asteroid belt in the past 40M years... Which is astonishing considering how busy the belt is...

ryandrake 2y ago
It's not that "busy" though, is it? My understanding is that asteroids are pretty damn small and very far away from each other. It's always funny to see an "Asteroid Belt" in Sci Fi movies and TV, where it looks like they're flying their spaceships through a raging river of rocks dodging one every second. In reality: if you were standing on any asteroid in the belt, would you even be able to see any other one with the naked eye?
- dylan604 2y ago
  So you have a gripe about sci-fi for not being realistic about asteroid fields, but the ability to fly a space craft with the agility of a fighter jet on Earth is okay? I love the arbitrary nature every single sci-fi person has in their application of suspension of disbelief. There's a lot of times I end up thinking, "oh I didn't think about that" after someone mentions a hang up they have, and there's other times where I'm laughing at the ridiculous nature while someone else thought it was much more acceptable.
  - ARandumGuy 2y ago
    I think it's less "this asteroid belt is unrealistic," and more "I assumed asteroid belts were dense because that's what it's like in movies." For a lot of people, they know that super nimble spaceships aren't real, but they may have never thought about asteroid belt density. People often see something in media that seems plausible, and assume that's what it's like in reality, even if the media portrayal was way off. I can guarantee it's happened to you at some point.
    - dylan604 2y ago
      The asteroid belt around Sol might be sparse, but what about other solar systems, other galaxies far far away?
      - dotancohen 2y ago
        Then gravity would condense it all down into a planet in very short order, geologically speaking. For an example in our own system, see Saturn's rings.
        shiroiushi 2y ago
        Geologically speaking, sure. But humans don't live in geological timescales: it seems possible that, if humans could somehow explore other star systems on a regular basis, they might come across some systems where there was a relatively recent collision leaving lots of close-together asteroids that haven't yet had enough time to condense into a new body.
        adastra22 2y ago
        Yes, like Saturn's rings.
        dotancohen 2y ago
        If such collisions are common, then yes.
      - gus_massa 2y ago
        If the density of the asteroid belt is too high, I guess it (slowly) collapses and you get a planet.
      - kadoban 2y ago
        A belt like shown in many movies would become a damn black hole with how dense and large they are. They're not just unlike Sol's, they're completely ridiculous.
  - buran77 2y ago
    > the arbitrary nature "Sci-fi" already tells you what's the fictional part of the story: the science/tech, and maybe some fundamental rules around those. Fantasy is where you get to rewrite the basic rules of the universe. In the span of a few decades we went from no planes to flying at almost Mach 10 in air (X-43) and 600.000km/h in space (Parker probe), and from AM radio to a super-computer in everyone's pocket. So you can bet any person can reasonably imagine that in a few centuries we could be advanced enough to build today's sci-fi. That's because they have a few real anchor points in the history of human civilization or even their own lifetime and an easy assessment of the progress of science between them. Most people also actually think asteroid belts are that dense. But that's because even basic concepts about gravity aren't immediately apparent from day to day experience. Basic grasp of gravity will never allow you to believe it naturally "wears off" in an asteroid field so the chunks stay close enough to even collide but magically never clump together, or that 1000 years "in the future" will change what was constant for billions of years. It only seems arbitrary if you don't bother to think about it.
    - everforward 2y ago
      I feel like most people grasp the decay of gravity because of space, and because the moon doesn’t crash into us, etc. I would wager it’s because the space involved is incomprehensible. It’s not obvious why rocks being 600k miles apart forms any kind of feature. That’s 24 trips around the circumference of the earth. I had honestly presumed they were closer. Not sci-fi movie close, but maybe a few miles in between? Space is incomprehensibly large to me.
      - haccount 2y ago
        If they grasp how gravity is "decaying" because things are in orbit then they've failed to understand both orbital mechanics and how gravity drops off at distance.
    - adastra22 2y ago
      I think what you're saying is right but the explanation is backwards. I think of "science fiction" as being fiction in which the science is held constant--the universe works more or less the same way, but with humanity and their technology exploring a different landscape of the possibility space. So the science is real, not fictional. The plot is fiction. Of course this assumes we're talking about hard sci-fi, which doesn't include stuff like Star Wars.
  - andrewflnr 2y ago
    > but the ability to fly a space craft with the agility of a fighter jet on Earth is okay? What makes you think that GP thinks that? The mere fact that they didn't mention that, among all extant silliness in scifi media, in the context of a discussion about asteroids?
    - dylan604 2y ago
      because they said "where it looks like they're flying their spaceships through a raging river of rocks dodging one every second.
- dpedu 2y ago
  Wikipedia puts the average distance between 'roids at about 600,000 miles, so I'm going with no. Also mentioned is the estimate that the mass of the entire belt is thought to be 3% of weight of the moon. That's crazy tiny, considering how much space it is spread out over. It would been like seeing an object 1/3000 the size of our moon at twice the distance away.
  - shiroiushi 2y ago
    >Also mentioned is the estimate that the mass of the entire belt is thought to be 3% of weight of the moon. That's crazy tiny It's worse than that: 60% of that mass is contained in only 4 asteroids, the largest of which is the dwarf planet Ceres. So if you ignore those 4 bodies for a moment, the rest of the asteroids are only around 1.2% of the Moon's mass.
  - mandevil 2y ago
    I remember doing the math once years ago and if you presume that all of the asteroids are pure Fe, you have on the order of 100 atoms/m^3 of density in the "asteroid belt."
bongodongobob 2y ago
The asteroid belt isn't like in Star Wars/Trek. The distances are huge. Average distance, from a quick Google says about 1 million kilometers apart.
- dark-star 2y ago
  true but 40M years is a very long time
  - bongodongobob 2y ago
    Not with those kind of distances. They really shouldn't hit each other ever. Think of two grains of rice in a pot of water. Stir and and see how long it takes for them to touch.
ianburrell 2y ago
We can't tell how many other collisions there were in belt from looking at the debris that intersect Earth. There were likely lots more that didn't kick debris our direction.
- haccount 2y ago
  Any sufficiently energetic collision would produce a population of fragments that intersect the orbit of our planet. The op headline is also using meteorite, which by definition is a rock which reaches the surface of the earth.

This pretty much means that there were only 3 large collisions in the asteroid belt in the past 40M years... Which is astonishing considering how busy the belt is...

ryandrake 2y ago

It's not that "busy" though, is it? My understanding is that asteroids are pretty damn small and very far away from each other. It's always funny to see an "Asteroid Belt" in Sci Fi movies and TV, where it looks like they're flying their spaceships through a raging river of rocks dodging one every second. In reality: if you were standing on any asteroid in the belt, would you even be able to see any other one with the naked eye?

dylan604 2y ago
So you have a gripe about sci-fi for not being realistic about asteroid fields, but the ability to fly a space craft with the agility of a fighter jet on Earth is okay? I love the arbitrary nature every single sci-fi person has in their application of suspension of disbelief. There's a lot of times I end up thinking, "oh I didn't think about that" after someone mentions a hang up they have, and there's other times where I'm laughing at the ridiculous nature while someone else thought it was much more acceptable.
- ARandumGuy 2y ago
  I think it's less "this asteroid belt is unrealistic," and more "I assumed asteroid belts were dense because that's what it's like in movies." For a lot of people, they know that super nimble spaceships aren't real, but they may have never thought about asteroid belt density. People often see something in media that seems plausible, and assume that's what it's like in reality, even if the media portrayal was way off. I can guarantee it's happened to you at some point.
  - dylan604 2y ago
    The asteroid belt around Sol might be sparse, but what about other solar systems, other galaxies far far away?
    - dotancohen 2y ago
      Then gravity would condense it all down into a planet in very short order, geologically speaking. For an example in our own system, see Saturn's rings.
      - shiroiushi 2y ago
        Geologically speaking, sure. But humans don't live in geological timescales: it seems possible that, if humans could somehow explore other star systems on a regular basis, they might come across some systems where there was a relatively recent collision leaving lots of close-together asteroids that haven't yet had enough time to condense into a new body.
        adastra22 2y ago
        Yes, like Saturn's rings.
        dotancohen 2y ago
        If such collisions are common, then yes.
    - gus_massa 2y ago
      If the density of the asteroid belt is too high, I guess it (slowly) collapses and you get a planet.
    - kadoban 2y ago
      A belt like shown in many movies would become a damn black hole with how dense and large they are. They're not just unlike Sol's, they're completely ridiculous.
- buran77 2y ago
  > the arbitrary nature "Sci-fi" already tells you what's the fictional part of the story: the science/tech, and maybe some fundamental rules around those. Fantasy is where you get to rewrite the basic rules of the universe. In the span of a few decades we went from no planes to flying at almost Mach 10 in air (X-43) and 600.000km/h in space (Parker probe), and from AM radio to a super-computer in everyone's pocket. So you can bet any person can reasonably imagine that in a few centuries we could be advanced enough to build today's sci-fi. That's because they have a few real anchor points in the history of human civilization or even their own lifetime and an easy assessment of the progress of science between them. Most people also actually think asteroid belts are that dense. But that's because even basic concepts about gravity aren't immediately apparent from day to day experience. Basic grasp of gravity will never allow you to believe it naturally "wears off" in an asteroid field so the chunks stay close enough to even collide but magically never clump together, or that 1000 years "in the future" will change what was constant for billions of years. It only seems arbitrary if you don't bother to think about it.
  - everforward 2y ago
    I feel like most people grasp the decay of gravity because of space, and because the moon doesn’t crash into us, etc. I would wager it’s because the space involved is incomprehensible. It’s not obvious why rocks being 600k miles apart forms any kind of feature. That’s 24 trips around the circumference of the earth. I had honestly presumed they were closer. Not sci-fi movie close, but maybe a few miles in between? Space is incomprehensibly large to me.
    - haccount 2y ago
      If they grasp how gravity is "decaying" because things are in orbit then they've failed to understand both orbital mechanics and how gravity drops off at distance.
  - adastra22 2y ago
    I think what you're saying is right but the explanation is backwards. I think of "science fiction" as being fiction in which the science is held constant--the universe works more or less the same way, but with humanity and their technology exploring a different landscape of the possibility space. So the science is real, not fictional. The plot is fiction. Of course this assumes we're talking about hard sci-fi, which doesn't include stuff like Star Wars.
- andrewflnr 2y ago
  > but the ability to fly a space craft with the agility of a fighter jet on Earth is okay? What makes you think that GP thinks that? The mere fact that they didn't mention that, among all extant silliness in scifi media, in the context of a discussion about asteroids?
  - dylan604 2y ago
    because they said "where it looks like they're flying their spaceships through a raging river of rocks dodging one every second.
dpedu 2y ago
Wikipedia puts the average distance between 'roids at about 600,000 miles, so I'm going with no. Also mentioned is the estimate that the mass of the entire belt is thought to be 3% of weight of the moon. That's crazy tiny, considering how much space it is spread out over. It would been like seeing an object 1/3000 the size of our moon at twice the distance away.
- shiroiushi 2y ago
  >Also mentioned is the estimate that the mass of the entire belt is thought to be 3% of weight of the moon. That's crazy tiny It's worse than that: 60% of that mass is contained in only 4 asteroids, the largest of which is the dwarf planet Ceres. So if you ignore those 4 bodies for a moment, the rest of the asteroids are only around 1.2% of the Moon's mass.
- mandevil 2y ago
  I remember doing the math once years ago and if you presume that all of the asteroids are pure Fe, you have on the order of 100 atoms/m^3 of density in the "asteroid belt."

bongodongobob 2y ago

The asteroid belt isn't like in Star Wars/Trek. The distances are huge. Average distance, from a quick Google says about 1 million kilometers apart.

dark-star 2y ago
true but 40M years is a very long time
- bongodongobob 2y ago
  Not with those kind of distances. They really shouldn't hit each other ever. Think of two grains of rice in a pot of water. Stir and and see how long it takes for them to touch.

ianburrell 2y ago

We can't tell how many other collisions there were in belt from looking at the debris that intersect Earth. There were likely lots more that didn't kick debris our direction.

haccount 2y ago
Any sufficiently energetic collision would produce a population of fragments that intersect the orbit of our planet. The op headline is also using meteorite, which by definition is a rock which reaches the surface of the earth.