How long would it take an asteroid...

[CthulhuRises]

Hello,

New to the site. I'm a writer and general astronomy enthusiast working on a current project set in space. I have a question needed for the work, as I want to keep things as scientifically accurate as possible. How long would it take an asteroid (a large one) originating in the asteroid belt to reach Mars (hypothetically an asteroid has been deflected from the belt is on course to hit Mars, how many years would it take to reach the Red Planet?)

Thanks in advance!

 

[SteveCNC]

Welcome aboard !
While I can't tell you a time frame even with all the data as that's not in my realm of understanding . However I do know enough to know that for the accuracy your after you would need to supply more information . Like why did this asteroid get ejected from the asteroid belt ? Collision , human influence , jupiters influence or something else ? And how big is it ? What's it's composition ?

 

[MeteorWayne]

Really, the size and composition don't affect it. The relevant questions are what was it's orbit before the change, and what changed the orbit. Mass and composition might make a difference as far as how much the orbit was changed from the original event. Depending on what that event was, as Steve said.

Once established, heliocentric (sun centered) orbits don't care about the mass of the object.

 

[kelvinzero]

In a way size does matter because we are talking statistics and luck. If we were talking grain sized, they are probably hitting all the time, so the time to divert one to hit would be zero.

I found this list of mars crossing asteroids. Perhaps we should restrict ourselves to one of these?
http://en.wikipedia.org/wiki/List_of_Ma ... or_planets

(hmm.. I looked at a few and noticed that they dont seem to have sizes, only brightness)

 

[MeteorWayne]

That's because brightness is all that can be measured for asteroids out there. The size can be estimated using assumptions about the albedo and are usually given as a range.

Here's a tutorial and the conversion chart:

http://www.cfa.harvard.edu/iau/lists/Sizes.html

 

[nimbus]

Hi CR! Welcome to SDC.

You might want to look at Project Rho's pages, if you haven't already.

While this site originally focused on rocketry equations, as you can see it has grown to encompass other topics of interest to SF authors and game designers.

http://www.projectrho.com/rocket/index.html

 

[DarkSands]

To answer this question you'll need to know a little about planetary and asteroid orbits. As others have stated a little more information is needed, but I can give you an example:

The asteroid 4179 Toutatis originates in the asteroid belt and, during its orbit, crosses Mars orbit and also passes close to the Earth, this asteroid at some point could collide with either Earth or Mars. This asteroid passed extremely close to the Earth in 2004, only 2.3 times farther than the distance to the Moon (basically like getting grazed by a bullet).

Toutatis is being "tugged" on by both Jupiter and Earth causing variations in its orbit making it difficult to predict, over a long period of time, whether or not it will collide with a planet. Within in the next few hundred years Toutatis could collide with Mars, though the possibility of this happening is very small.

Back to your question, if an orbit of an asteroid is changed by some event, such as a planet tugging on it (Toutatis), we would need to know the new orbit to tell when it would hit a planet. The time frame could be anywhere from a couple years (highly unlikely), to thousands of years.

 

[robnissen]

As Mars sits just inside of the asteroid belt, an asteroid near the inner edge of the belt that somehow got booted perpindicular to its orbit could hit Mars in a matter of days, IF it was coincidentally just outside of Mars' orbit when it was booted. Of course it it was near the other side of the sun from Mars and got booted perpindicuular to its orbit, it would take a few years to reach Mars. Of course, the VAST majority of bootings, would not be perpindicular and as others have stated, it would depend on the individual orbits.

 

[MeteorWayne]

It would be nearly impossible for an orbit to be shifted perpendicularly. In fact it would no longer be in orbit, but heading directly toward the sun. That would require an unimaginable amount of energy, which surely would vaporize the object.

 

[neilsox]

Hi meterorWayne: Doesn't perpendicular mean at a 90 degree angle to the direction of travel at the moment that the change occurred? In solid geometry there are an infinite number of directions only one of which will cause straight into the sun. Most of the possibilities will give an orbit with high inclination, or am I missing something?
If the new orbit hits Mars on the first pass, then about ten months is minimum time, on the 1000th pass of the Mars orbit, probably about 3000 years? Neil

 

[MeteorWayne]

Yes, that's what perpendicular means, which is why it's close to impossible. It means the asteroid would have to make a 90 degree left turn (when viewed from the "north" side of the solar system). Denpeding on the moment of impact, the inclination of the asteroid's orbit, and where Mars is in it's orbit there would also probably need to be some inclination change added as well.

As far as fixing a time scale, there are so many variables. Mars' orbit is very eccentric, so at times it's much close to the sun and other times close to the asteroid belt. The asteroid's orbit is also eccentric.

It would be more plausible to create a minor deflection of a Mars crossing asteroid; there are hundreds:

http://en.wikipedia.org/wiki/List_of_Ma ... _asteroids

Very close approaches to Mercury, Venus, Earth, and Mars through 2200:

http://members.shaw.ca/andrewlowe/ALL-PHAS.HTM#Mars