Someone want to have fun with asteroid simulation?

[DaveC426913]

I'm playing matchmaker again. A guy on another board (ADP) is doing research for a story about a near-miss asteroid and he wants to get his physics right. I am strongly suggesting he do a proper simulation so he's got his numbers straight.

Would anyone with the right software be willing to do a simulation for him and provide some numbers?

 

[tony873004]

I could attempt it. What are his starting conditions?

 

[DaveC426913]

I have answered most of his questions qualitatively though not with authority (I'm not an expert).

As I've pointed out to him, he needs to nail down the mechanics of the orbit to make a plausible story. That's why I think the best thing is to do a sim.

I'll going to post his thread in its entirety along with my responses. Can you tell if it's possible, and what you think of the orbital mechanics details?

- msg begins -

I am currently working on a short story myself and i would be very greatfull if anyone could answer any of my questions.

1) In the story an asteroid will be discovered which is approx. 1.5 km wide, so firstly is this the correct way to describe an asteroids size?

Sure. You might have a two measurements: l x w since they are so irregular. A more descriptive way might be to measure its tonnage, however, that's not a number that the layperson will find of much use. Consider framing it in terms of the size of bodies that have already hit Earth and the damage they do (Arizona crater, Chicxulub).


I. Could an asteroid as large as this really be spotted only 18 months befor it will pass the earth?

Can't say for sure, someone else may be able to. If the body had a particularly low albedo (i.e. blackened with soot) then it might have been missed.


II. As the asteroid is so close, would this allow astronomers to be completely confident that there obeservations and projections would be correct, or even with an asteroid that is already as close to us as one that has been discovered, could there still be a dangerously large margin of error?

The confidence increases with observation time. In the first few hours, they would have a rough idea, but as more hours passed, their estimate would get much better, as they watched its orbit.


III. The asteroid will pass us within 18 months of it's discovery so how far from the Earth would this put the asteroid at the time of discovery (e.g 750,000 miles, 1,000,000 miles ect.. away)?

I think what you'll need to do is actually make a hypothetical asteroid in a simulator and get all your measurements nailed down. I'm sure if you look hard enough, someone could do this. I'll ask around.


3) How much does the rotation/spin of a an asteroid effect projected trajectories (are some asteroids very unpredictable because of their irregular rotations)?

Not at all. Rotation has no effect on trajectories. Now, if this were a comet OTOH... see, comets are icy balls of frozen water and gasses. As they near the sun, they heat up, the gasses sublimate and act like little jets. But that's a different story.


5) do asteroids orbit around the sun like the planets?

Yes.


6) IF so what is the size of the average orbit in distance and time (e.g could an asteroid swing as far out as pluto then return passing the giant planets then the midgets then swing around the sun, or doesn't it work this way?)

Most asteroids are in a roughly circular orbit between Mars and Jupiter. There are some NEOs (Near Earth Orbit) asteroids. In fact, last week's APOD lists them: http://antwrp.gsfc.nasa.gov/apod/ap060328.html

It is possible for asteroids to follow highly elliptical orbits, yes. They can get knocked out of the asteroid belt with the right kick (though these ones will have a perihelion in the belt, not out at Pluto). You'd need to have an asteroid out near Pluto that got a kick, and began falling inward.


7) Do all asteroids come from the asteroid belt or do some travel through the galaxy/universe for millions of years befor they come close enough for us to discover them?

All but a small percentage of asteroids come from the Mars-Jupiter belt, though there are lots of things floating around in our SS. It would be incredible to find something entering from outside the SS. If there were, it would be traveling too fast for us to do much about it.


8) What materials are asteroids made from?

C-type - carbonaceous, 75% of known asteroids
S-type - silicaceous, 17% of known asteroids
M-type - metallic, most of the remaining asteroids


9)Now supposing the asteroid in my story has now traveled 3/4 of the distance toward the Earth and it is now about 4 months away from passing us, is there anything that could suddenly alter the course of the asteroid ( such as collisions will other bodies in space ect) meaning it could now pass as close as 12,000 miles to the Earth instead of the previously predicted 80,000 mile miss. Or could there be something happening to the asteroid which could slowly alter it's course ( is there any possibility or president for such a thing happening: an asteroids corse slowley changing be say 8-10 degrees)?

No - a near miss by ANOTHER astronomical body would be far-fetched. Regardless, they could calculate it, so it wouldn't be a surprise.

The only likely effect on the asteroid would be the Earth's gravity, which would be taken into account. Again, a comet could be somewhat less predictable due to offgassing, though comets are much smaller than asteoids so different kind of threat.


10) how close can an asteroid pass the Earth without being dragged into us by the Earth's gravity?

As close as it wants. The asteroid would be under Earth's influence once it got within many millions of miles. This would alter its orbit, but would not cause them to crash. The influence of gravity is a continuum, not a discrete event. Hard to explain more succinctly.

You should get a simulation done.


11) Would an Asteroid that was 1.5 km in size that came as close as this one be visable from Earth (if it passed closest to the side of the Earth that was in daytime)with the naked eye in the daytime if skies were clear and (e.g would it reflect the suns light enough to be visable?)or is there no way it would be visable without burning up in the Earth's atmoshere, which it won't)?

Not sure. Think it might be visible as a tiny, very faint dot.


12) would astronomers be able to predict the city that the asteroid would pass closest to (e.g paris, london ect)?

It will be visible from an entire hemisphere, not one particular city. Locations that it is visible at nighttime would be preferred viewing spots.


13) what would be your own reaction and fellow astromers be to such an event taking place (would the astromical world descend upon this place that the asteroid passes in order to witness this event)?

Not so much the place it's going to pass over; more likely one of the large telescope sites, any ones that are in nighttime during the event. Astronomers would not bother with viewing by day.


14) if the asteroid was visable with the naked eye, how long would it be visable for (e.g would it be like a shooting star and flash by in seconds or would it be visable for hours, days ect...)

I think days to weeks. (Think of comets, heck, think of the moon).
It could theoretically, come VERY close, in which case the actual flyby would only take hours.


15) Could such an event be watched on tv, so there would be a satellite or space telescope pointed at the place on Earth where the asteroid is predicted to pass and at the moment it passes we would see a dark to appear to pass infront of the earth?

Where it cast a shadow would not be the place where it passed closest to the Earth. In fact, this is impossible, since that would mean the asteroid would pass closest to the Earth when that spot was at local noon. It would have pass closest to Earth at a spot that was near dawn or dusk.

That does not mean it wouldn't cast a shadow at some point, but it might be fairly far away by then. Nonetheless, you would only get a penumbral eclipse, not a full eclipse like the Moon does. (A 1.5km asteroid would have to pass less than 250km from the Earth to cast a full eclipse).


16)Would this asteroid pass the Earth again at some point in the future (e.g it could be a threat again in the year 2155, whatever)?

Passing that close to Earth, its future orbit would be wildly different. It could be flung into a smaller or a larger orbit, depending on how it interacted with Earth. But it would be predictable as time passed. The chances of it coming back this way are pretty slim.


17) in what way would the astronmical society or NASA take advantage of this close miss, would they try to land something on the asteroid befor it passed to study it or would this be too risky
and they would wait until after it had passed?

Probably not have much time to do more than throw something in its path and wait for impact. The big problem is matching speed - that takes time and favourable circumstances.


18) at what spped to asteroids travel?

Same as anybody in a similar orbit - which is not really that fast (Remember, the Earth takes a year to orbit). The observed speed is due to differential velocities between the two bodies.

Suggestions:
1] Make a real asteroid in a simulator. You can get free softare that will do this, or you can befriend someone.

2] Learn as much s you can about asteroids. Your story will fall apart very fast if you try to fudge facts. Wiki is your friend. So is Google. So is the local library.

There are some well-thought-through scenarios for likely collisions with known bodies in Earth's future. Doing some research might turn something up that could suit your purpose AND make a plausible story event.

Some links:
http://en.wikipedia.org/wiki/List_of_impact_craters_on_Earth
http://antwrp.gsfc.nasa.gov/apod/ap060328.html

Some terms:
stony asteroids
carbonaceous asteroids
NEOs

 

[tribdog]

as a published author I would like to make a suggestion. If he doesn't know the difference between "there" and "their" he has no business writing short stories.

 

[DaveC426913]

I know, Trib. But mine is not to judge.

Besides, many people write very differently online than they do elsewhere.

(Or at least, that's what I tell myself.)

 

[DaveC426913]

So, no takers then?