Asteroid Belt Ponderings

[Matthew]

Hello everyone!

I've been reading these boards for a while, and I just had a few questions about the Asteroid Belt I couldn't find answers to with the search engine.

1) How many asteroids are there? And how small are they?
2) Given that, what is the average density of them? Is it possible to send a spacecraft through them without encountering any objects?
3) How big is the total mass of all the asteroids? Is it possible to ever find out an accurate figure for this?
4) What is the accepted for theory for how the belt formed? Remnants of the Solar System formation or destroyed planet?
Links to good websites on this subject would also be helpful, the first search I did showed something about exploding planets, so I figured asking here would get me a more authoritative answer.

[Tom Mazanec]

1 Depends how you define "asteroid". Thousands, millions, bajzillions...
2 Well, we keep sending probes to Jupiter and Saturn without worrying about them.
3 IIRC, Ceres has something like a quarter of the mass of all the asteroids, so it probably would be about like Pluto or a typical Jovian moon.
4 Remnants of planet formation (probably from being "stirred up" by Jupiter's gravity).

[Kaptain K]

Hello everyone!

I've been reading these boards for a while, and I just had a few questions about the Asteroid Belt I couldn't find answers to with the search engine.

1) How many asteroids are there?

Known - Over 100,000.
Unknown - Probably millions.

And how small are they?

Depends on your definition of the dividing line between "asteroids" and "space dust".

2) Given that, what is the average density of them?

Very, very low.

Is it possible to send a spacecraft through them without encountering any objects?

Try not to! Every spacecraft we've sent past Mars (Pioneer I & II, Voyager I & II, Galileo, Cassini, Ulysses, and some I've probably missed) have passed through the asteroid belt unscathed.

3) How big is the total mass of all the asteroids? Is it possible to ever find out an accurate figure for this?

Much less than that of the Moon.

4) What is the accepted for theory for how the belt formed? Remnants of the Solar System formation or destroyed planet?

Remnants. Jupiter prevented a planet from forming there.

Links to good websites on this subject would also be helpful, the first search I did showed something about exploding planets, so I figured asking here would get me a more authoritative answer.

I'm sure that someone will provide some links.

Welcome to the board! 8)

[Matthew]

Depends on your definition of the dividing line between "asteroids" and "space dust".

I knew I should have defined that, lets say something bigger than a meteoroid, or that could survive entry through earth's atmosphere.

[Tom Mazanec]

Then we are talking bajzillions. Even rocks the size of breadboxes have survived to hit the ground if they are iron. Carbonaceous might need a little bigger, I don't know...probably would explode at fairly low altitudes, even if they were the size of a house, and sprinkle the ground. And a comet (which is just an asteroid made of ices and dirt) might have to be even bigger still.
Try wikipedia to find out more.

[Eroica]

Asteroid AstroLinks

[Matthew]

Thanks everyone, that helps very much.

[ChibiVader]

I'd also like to point out that with the Galileo mission actually altered course to pass closer to Ida and then subsequently discovered Dactyl (Ida's satellite).

As far as density is concerned, it generally ranges from a little less than 4 g/cc to just over 1 g/cc. The inner ones are the ones with higher density since they're mostly composed of rocky material. They tend to have less ice since any they did have would evaporate. When you start getting to the outer edges, they become more ice and densities go down (hence the ~1 g/cc).

EDIT: I think this may not have been the kind of density you were talking about. #-o But perhaps you'll find it useful anway.

[eburacum45]

I am always impressed by these maps of the minor planets;
http://cfa-www.harvard.edu/iau/lists/InnerPlot.html
http://cfa-www.harvard.edu/iau/lists/OuterPlot.html

these show the vast number of objects in our solar system; yet they are so far from each other that they would hardly ever be visible from one another, even in the main belt.

[Swift]

I am always impressed by these maps of the minor planets;
http://cfa-www.harvard.edu/iau/lists/InnerPlot.html
http://cfa-www.harvard.edu/iau/lists/OuterPlot.html

these show the vast number of objects in our solar system; yet they are so far from each other that they would hardly ever be visible from one another, even in the main belt.

I've liked those too and their animations are nice. But it is a little deceptive, it makes things look too crowded. That's because a 3-D volume is compressed into a 2-D view and even the tiny dots are scaled too big.

[ChibiVader]

You can also see just how elliptical Mercury's orbit is on that plot.