Wanted to talk about our solar system's asteroid belt in this thread, due to some things I've read posted in various threads here and there on ATS
over the past half year or so.
I've seen a lot of statements like the following:
"The asteroid belt was a planet that was destroyed."
"Comet (insert name here) is going through the asteroid belt."
"The (insert celestial body here) going through the asteroid belt could cause impacts or fling asteroids towards Earth with it's
I'll touch on on these, but first let us look at a picture:
Most of us should remember being taught in school about the solar system, that the asteroid belt lays between the orbits of Mars and Jupiter. Normally
we are presented with a image such as the one above, showing the belt's position.
Unfortunately, this type of visual image does a bit of damage in that it gives people, especially those that only have a passing knowledge of
astronomy, a mental image that our asteroid belt actually looks like a very thick, densly populated area of floating rocks.
Hollywood doesn't help in this are either. Say the words "Asteroid Belt" and it can conjur up images like what we saw in Star Wars: The Empire
These are extreme exaggertations of what the belt looks like. Even the Wikipedia doesn't help. Visual representation of the asteroid belt is much
more accurate, but again, people with only a passing knowledge of astronomy do not undrestand the scale of the picture being shown. Here it is:
It looks like swarms of bees. However, one must realize the distance at which the image is being shown and the scale of the objects.
Most of what you are seeing, you would not be able to see. That is, the majority of asteroids are so small, that the dots that are representing the
asteroids, are much to big. However, the creation of this image requires using dots large enough for you to see.
The area of space in between Jupiter and Mars is around 1,849,500,000,000,000,000 square kilometers. The largest of the asteroids is Ceres at only 900
So far around 100,000 asteroids in the asteroid belt have been found. And they are spread out in that vast number of square kilometers up there.
Here is a good example of showing how isolated many of them are, and not groupted together like we see in images representing them, or like in the
Star Wars movie. This is a animated image of the asteroid known as Ida as the space probe Galileo approached it.
As you can see........or rather, as you can NOT see a bunch of other asteroids around it. Instead, we see it as a isolated pice of rock:
To give you a good analogy, imagine having 100 coins. Now dump them on a table in front of you. They look closely packed together. Imagine that each
coin is a asteroid.
Now, to give you a better sense of the actual asteroid belt, take those same coins, and spread them out so that they cover the city of New York.
Mmmmmm. They aren't as bunched together now, are they? That's the distances we are dealing with.
Now the reason that is important is to cover those statements I see about other objects 'plowing' through our asteroid belt and colliding with the
The chances are there of course, and are much higher than else where in the solar system......but considering the distances between asteroids in the
belt.......you have a better chance of winning a power ball lottery.
Realize too that space is 3 dimensional, and that not all objects fall within the plane of the solar system. Most of the asteroids in the asteroid
belt do fall within the solar plane. However, some objects, like many comets, may have a highly inclined orbit, meaning they do not travel within the
plane of the solar system. This decreases their chances of hitting an asteroid even more so.
Let's talk about where the asteroid belt came from.
Please realize that when we talk about things like "Where the planets come from." or the asteroid belt in this case, we are not dealing with fact,
but instead are dealing with theories and models.
This is because: unless you have a time machine and can go back and actually SEE how it was done, we can't really say that it's a fact.
Since 1802, the idea that the asteroid belt was from a planet that had exploded or broke apart from a collision has been suggested. Of course it
wasn't until 1850 that the term "Asteroid Belt" was first used, but as far back as 1802 after looking at Ceres and Pallas (2 of the largest
asteroids), that the idea came into being.
However, over time, this theory has fallen deeply out of favor, and with good reasons:
1) The total mass of all the asteroids in the asteroid belt if put together would equal only 4% of the mass of our moon. That's small...very, very
small. Way too small to be a planet.
2) Chemical make up of the asteroids in the asteroid belt varies quite a bit. Because they vary so much, it's hard to explain if they all came from a
common source (such as they all made up a planet). If the asteroid belt had been formed from the explosion or collision of a planet, the chemical make
up of those asteroids would be very close in nature. Instead, they vary all over the place, suggesting that they did not come from a common point.
The generally accepted theory is that the asteroids in the asteroid belt formed right where you see them, but were unable to form into a planet
because of Jupiter's influence on them.
Asteroid Belt Formation
So how often do these asteroids "bump" into each other, possibly sending smaller fragments on a collision course with the Earth?
Here's an answer to that very question:
The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on
astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million
Please note some words in the above quote that I've bolded. Frequent on a astronomical time scale is 10 million years. So not as often as one might
think. And that's with larger bodies reaching up to 10km in size.
Okay, well let us assume the worst. Let us say objects did collide (asteroid to asteroid, or a comet actually does smack into one), and it just
happened to do it right so that it means a possible collision for Earth. How long before it get's here?
Answer: tens of millions of years.
as it typically takes many tens of millions of years for an asteroid to reach a resonance with Earth and then collide
Does this mean the fireballs that many have been talking about of late didn't come from a impact of objects from our asteroid belt?
Why no, it is quite possible that they have come from there. But if they did, it was something that happens a very long time ago.
That means that even if say comet ISON were to hit an asteroid (very low chance of it doing that), it would take tens of millions of years for any
possible fragments to intersect with Earth's orbit.
Hope this thread is informative and helps anyone interested.