<p>That asteroid diagram is a bit misleading. It's showing the distribution of the asteroids, but it greatly exaggerates the sizes of all the bodies relative to the sizes of the orbits. Even the dot representing the Sun is too big. If the body sizes were to scale in that diagram, all of the planets &amp; asteroids would be smaller than a pixel, so they'd be invisible.</p>
<p>The asteroid belt isn't dense. A typical estimate of the mean distance between asteroids is around 1,000,000 km (2.6× the distance between the Earth and the Moon), but that's for asteroids of diameter 1 km and larger. There are probably estimates for smaller bodies, but they aren't easy to find, although there's probably useful info in the articles linked at <a href="https://physics.stackexchange.com/q/26712/123208">What is the average distance between objects in our asteroid belt?</a></p>
<p>There are around 10,000 asteroids with a diameter of 10 km or greater, but they aren't close to each other, so your &quot;chain reaction&quot; scenario with a comet launching a fleet of Mount Everest sized asteroids heading towards the Earth isn't really possible. Even with much smaller asteroids it's still <em>extremely</em> unlikely.</p>
<p>From <a href="https://en.wikipedia.org/wiki/Asteroid#Size_distribution" rel="noreferrer">Wikipedia</a>, here's a diagram show the numbers of asteroids of different sizes.</p>
<p><a href="https://upload.wikimedia.org/wikipedia/commons/6/63/Asteroids_by_size_and_number.svg" rel="noreferrer"><img src="https://upload.wikimedia.org/wikipedia/commons/6/63/Asteroids_by_size_and_number.svg" alt="Asteroid size distribution" /></a></p>
<p>Also from that article,</p>
<blockquote>
<p>The orbital distribution of the asteroids reaches a maximum at an eccentricity of around 0.07 and an inclination below 4°. Thus although a typical asteroid has a relatively circular orbit and lies near the plane of the ecliptic, some asteroid orbits can be highly eccentric or travel well outside the ecliptic plane.</p>
</blockquote>
<p>Most of the asteroids of any significant size are in well-behaved orbits of low eccentricity. Major collisions aren't impossible, but they have low probability. And that includes collisions with bodies passing through the asteroid belt, like comets or spacecraft.</p>
<p>According to veteran asteroid hunter Tom Gehrels of the University of Arizona, in this <a href="https://www.scientificamerican.com/article/in-science-fiction-movies/" rel="noreferrer">Scientific American article from 1997</a>,</p>
<blockquote>
<p>In some ways, the asteroid belt is actually emptier than we might like. In the early 1990s, the National Aeronautics and Space Administration wanted the Galileo spacecraft to encounter an asteroid while it was passing through the asteroid belt on its way to Jupiter. But it took some effort to find an object that was located even roughly along Galileo's path. Special targeting was required to reach this object, but the result was the first close-up view of an asteroid, the one called Gaspra.</p>
<p>The number of objects in the asteroid belt increases steeply with decreasing size, but even at micrometer sizes the Pioneer spacecraft were hit only a few times during their passage.</p>
</blockquote>
<p>It takes a lot of energy to perturb the orbit of a large asteroid. Yes, a large comet <em>could</em> supply that energy, and send dangerous material towards us. We <em>do</em> need to keep watch on the asteroids, but we don't expect a fleet of them to head our way anytime soon. Most of the exciting planetary bombardments happened billions of years ago, when the young Solar System still had plenty of bodies with &quot;wild&quot; eccentric orbits. The last big episode, known as the <a href="https://en.wikipedia.org/wiki/Late_Heavy_Bombardment" rel="noreferrer">Late Heavy Bombardment</a>, happened around 4 billion years ago... or perhaps it didn't actually happen. ;)</p>
<blockquote>
<p>The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth and Mars.
Since 2018, the existence of the Late Heavy Bombardment has been questioned.</p>
</blockquote>

CC BY-SA 4.0
2021-10-01T17:25:06.113Z
I "recycled" several sections of this answer from https://space.stackexchange.com/a/49027/38535
PM 2Ring
CC BY-SA 4.0
2021-10-02T04:28:39.913Z
Now this is a considerable answer, and I also got a point a point that as universe is expanding the space is also becoming more, so the probabilty also decreases, right?
Gamin8ing
CC BY-SA 4.0
2021-10-02T04:35:23.650Z
@Gamin8ing The universe is expanding, solar system is not really expanding for that, the galaxies are going far from each other for that.
Was'
CC BY-SA 4.0
2021-10-02T05:36:27.677Z
@WalidSiddik oh yes so silly me
Gamin8ing
CC BY-SA 4.0
2021-10-01T17:24:11.973Z
2021-10-01T17:24:11.973Z
PM 2Ring
<p>We know that there is a big and dense ring of asteroids between the orbits of Jupiter and Mars and also <em>&quot;<a href="https://en.wikipedia.org/wiki/List_of_Jupiter_trojans_(Trojan_camp)" rel="nofollow noreferrer">Trojans</a>&quot;</em> and <em>&quot;<a href="https://en.wikipedia.org/wiki/List_of_Jupiter_trojans_(Greek_camp)" rel="nofollow noreferrer">Greeks</a>&quot;</em> in Jupiter's orbit too. We also <a href="https://en.wikipedia.org/wiki/Comet#:%7E:text=As%20of%20April%202021%20there,estimated%20to%20be%20one%20trillion." rel="nofollow noreferrer">know that</a></p>
<blockquote>
<p>there are around 4595 <em>known</em> comets in solar system, as of April, 2021</p>
</blockquote>
<p><a href="https://i.sstatic.net/0Cnqsm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/0Cnqsm.png" alt="By Mdf at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1951518" /></a></p>
<p>Also, Earth got hit by around 6100 meteors large enough to reach the ground, that's around <a href="https://cosmosmagazine.com/space/astronomy/earth-hit-by-17-meteors-a-day/" rel="nofollow noreferrer">17 meteors a day</a>, which is a lot!</p>
<p>If any of them hit any asteroid so wouldn't it be a disaster! As no atmosphere is there to stop them and meteorites have high speed, high enough to break Jupiter's gravity, so there should be a chain reaction as one asteroid hitting other two and the two becomes four, growing exponentially. So a sudden impulse can cause this, then we should get a fleet of big rocks as high as Mt. Everest coming at high speed towards us? Is it so, or anything am I missing?</p>

CC BY-SA 4.0
2021-09-30T08:04:19.053Z
Asteroid belts are far from being a billiard pool.
Alchimista
CC BY-SA 4.0
2021-09-30T08:10:45.353Z
agree that, but possiblities are real, isn't it?
Gamin8ing
CC BY-SA 4.0
2021-09-30T09:35:38.587Z
Also, suppose two asteroid merge. If they do, most likely they overall momentum gets lower while their mass increases. So they will be again under the attraction of Jupiter. But I am going far. This is just to say that the situation is far from the scenario implicit in your question. The system is certainly more complicated and especially somewhat stable.
Alchimista
CC BY-SA 4.0
2021-09-30T11:10:58.977Z
Recently asked: https://astronomy.stackexchange.com/questions/46907/is-there-any-chance-comet-bernardinelli-bernstein-could-collide-with-earth
Nilay Ghosh
CC BY-SA 4.0
2021-10-01T12:38:54.937Z
We have had "asteroid attacks" in the past. Quite distant past, admittedly, but the least stable asteroids certainly did a bit of "attacking" of planets back in the day...
Rory Alsop
<asteroids><comets><asteroid-belt>
Why haven't we had an "asteroid attack" until now?
Gamin8ing
# Why haven't we had an "asteroid attack" until now?

(Asked by: username_0 on 2021-09-30)

We know that there is a big and dense ring of asteroids between the orbits of Jupiter and Mars and also *"[Trojans](https://en.wikipedia.org/wiki/List_of_Jupiter_trojans_(Trojan_camp))"* and *"[Greeks](https://en.wikipedia.org/wiki/List_of_Jupiter_trojans_(Greek_camp))"* in Jupiter's orbit too. We also [know that](https://en.wikipedia.org/wiki/Comet#:%7E:text=As%20of%20April%202021%20there,estimated%20to%20be%20one%20trillion.)

> there are around 4595 *known* comets in solar system, as of April, 2021

[![By Mdf at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1951518](https://i.sstatic.net/0Cnqsm.png)](https://i.sstatic.net/0Cnqsm.png)

Also, Earth got hit by around 6100 meteors large enough to reach the ground, that's around [17 meteors a day](https://cosmosmagazine.com/space/astronomy/earth-hit-by-17-meteors-a-day/), which is a lot!

If any of them hit any asteroid so wouldn't it be a disaster! As no atmosphere is there to stop them and meteorites have high speed, high enough to break Jupiter's gravity, so there should be a chain reaction as one asteroid hitting other two and the two becomes four, growing exponentially. So a sudden impulse can cause this, then we should get a fleet of big rocks as high as Mt. Everest coming at high speed towards us? Is it so, or anything am I missing?

**Tags:** asteroids, comets, asteroid-belt

> **Comments:**
> **username_1**: Asteroid belts are far from being a billiard pool.  
> **username_0**: agree that, but possiblities are real, isn't it?  
> **username_1**: Also, suppose two asteroid merge. If they do, most likely they overall momentum gets lower while their mass increases. So they will be again under the attraction of Jupiter. But I am going far. This is just to say that the situation is far from the scenario implicit in your question. The system is certainly more complicated and especially somewhat stable.  
> **username_2**: Recently asked: https://astronomy.stackexchange.com/questions/46907/is-there-any-chance-comet-bernardinelli-bernstein-could-collide-with-earth  
> **username_3**: We have had "asteroid attacks" in the past. Quite distant past, admittedly, but the least stable asteroids certainly did a bit of "attacking" of planets back in the day...  

---

## 1 answers

### Answer by username_4 on 2021-10-01. Score: 5 | Accepted answer

That asteroid diagram is a bit misleading. It's showing the distribution of the asteroids, but it greatly exaggerates the sizes of all the bodies relative to the sizes of the orbits. Even the dot representing the Sun is too big. If the body sizes were to scale in that diagram, all of the planets & asteroids would be smaller than a pixel, so they'd be invisible.

The asteroid belt isn't dense. A typical estimate of the mean distance between asteroids is around 1,000,000 km (2.6× the distance between the Earth and the Moon), but that's for asteroids of diameter 1 km and larger. There are probably estimates for smaller bodies, but they aren't easy to find, although there's probably useful info in the articles linked at [What is the average distance between objects in our asteroid belt?](https://physics.stackexchange.com/q/26712/123208)

There are around 10,000 asteroids with a diameter of 10 km or greater, but they aren't close to each other, so your "chain reaction" scenario with a comet launching a fleet of Mount Everest sized asteroids heading towards the Earth isn't really possible. Even with much smaller asteroids it's still *extremely* unlikely.

From [Wikipedia](https://en.wikipedia.org/wiki/Asteroid#Size_distribution), here's a diagram show the numbers of asteroids of different sizes.

[![Asteroid size distribution](https://upload.wikimedia.org/wikipedia/commons/6/63/Asteroids_by_size_and_number.svg)](https://upload.wikimedia.org/wikipedia/commons/6/63/Asteroids_by_size_and_number.svg)

Also from that article,

> The orbital distribution of the asteroids reaches a maximum at an eccentricity of around 0.07 and an inclination below 4°. Thus although a typical asteroid has a relatively circular orbit and lies near the plane of the ecliptic, some asteroid orbits can be highly eccentric or travel well outside the ecliptic plane.

Most of the asteroids of any significant size are in well-behaved orbits of low eccentricity. Major collisions aren't impossible, but they have low probability. And that includes collisions with bodies passing through the asteroid belt, like comets or spacecraft.

According to veteran asteroid hunter Tom Gehrels of the University of Arizona, in this [Scientific American article from 1997](https://www.scientificamerican.com/article/in-science-fiction-movies/),

> In some ways, the asteroid belt is actually emptier than we might like. In the early 1990s, the National Aeronautics and Space Administration wanted the Galileo spacecraft to encounter an asteroid while it was passing through the asteroid belt on its way to Jupiter. But it took some effort to find an object that was located even roughly along Galileo's path. Special targeting was required to reach this object, but the result was the first close-up view of an asteroid, the one called Gaspra.
>
> The number of objects in the asteroid belt increases steeply with decreasing size, but even at micrometer sizes the Pioneer spacecraft were hit only a few times during their passage.

It takes a lot of energy to perturb the orbit of a large asteroid. Yes, a large comet *could* supply that energy, and send dangerous material towards us. We *do* need to keep watch on the asteroids, but we don't expect a fleet of them to head our way anytime soon. Most of the exciting planetary bombardments happened billions of years ago, when the young Solar System still had plenty of bodies with "wild" eccentric orbits. The last big episode, known as the [Late Heavy Bombardment](https://en.wikipedia.org/wiki/Late_Heavy_Bombardment), happened around 4 billion years ago... or perhaps it didn't actually happen. ;)

> The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth and Mars.
> Since 2018, the existence of the Late Heavy Bombardment has been questioned.

> **Comments:**
> **username_4**: I "recycled" several sections of this answer from https://space.stackexchange.com/a/49027/38535  
> **username_0**: Now this is a considerable answer, and I also got a point a point that as universe is expanding the space is also becoming more, so the probabilty also decreases, right?  
> **username_5**: @username_0 The universe is expanding, solar system is not really expanding for that, the galaxies are going far from each other for that.  
> **username_0**: @WalidSiddik oh yes so silly me  

---

