new pictures of saturn's moon!

[freespace2dotcom]

http://www.newscientist.com/news/news.jsp?id=ns99995106

It's awesome, and the last pictures of phoebe before were just blurs? very cool.

Just look at this!  Hopefully new textures for orbiter will come out soon...

[AphelionHellion]

Oo I wanna build a base in that giant dent

[AphelionHellion]

One thing I've always wondered (hopefully some of you physics geeks out there can help me out on this) is how so
many bodies are randomly captured by larger bodies and manage to work their way into roughly circular orbits?
For instance, it's been suggested that Mars' two moons are both captured asteroids, as well as a number of other
moonlets circling other planets. Now, if my experience with Orbiter is any indication, space is a very very very very very
largish sort of place - and when you're out very very far from a gravity source, it doesn't take much deltaV at all to
send you on your way back out into alone-ness again. You need to get pretty close to a planet for it to exert a lot of
influence.
Also, even when performing a gentle Hohmann transfer, you still typically need to perform a burn of some sort, even if
it's a small one, to insert yourself into orbit so you don't just get slingshotted past your target.
Even if you do manage to slide right into orbit around your target body, your orbit, before performing at least a burn at
periapsis, usually tends to look more like the outline of a rubber egg in a trash compactor than a circle. And yes, I
know that all orbits are elipses, but many (for instance those of Earth and the moon) are circular enough that they
appear as circles to the naked eye on a map...
So in a nutshell what I'm trying to figure out is how exactly does a "dumb" unpiloted object (that was not
created/coalesced in that position, like the planets ostensibly were) wandering through the solar system get near a
planet and actually enter orbit instead of just exiting again, but traveling a somewhat different direction? And
assuming an accidental aerobrake or something, how are some of those orbits so darn circular?

I'd appreciate any conjecture or schooling

[DanSteph]

AphelionHellion wrote:
 it's been suggested that Mars' two moons are both captured asteroids, as well as a number of other
moonlets circling other planets.

Notice that Ive read somewhere that given their orbital parameter, mass etc etc
they will obviously fall on mars or brake in small part before doing so in some
millions years. nothing eternal uh ?

About trajectory the most amazing things I've read latelly in a space magazine
was a reconstruction of the solar system's trajectory trought the milky ways
since the sun lightened.
absolutely amazing, this trajectory was nothing near a quiet Orbit, we approached
many objects, nebulae, group of star etc etc.... and it seem our trajectory was
modified several time by others object.

I don't recall exactly the article but it seem that we made only a few orbit around
the center of the galaxy. (15-20-100 ?)

About saturn I was waiting the phoebe's close picture but mostly I wait the saturn's ring
closeview , THAT will be amazing.
official site: http://saturn.jpl.nasa.gov/index.cfm

Dan



Post Edited ( 06-15-04 13:06 )

[Simonpro]

AphelionHellion wrote:
So in a nutshell what I'm trying to figure out is how exactly does a "dumb" unpiloted object (that was not
created/coalesced in that position, like the planets ostensibly were) wandering through the solar system get near a
planet and actually enter orbit instead of just exiting again, but traveling a somewhat different direction? And
assuming an accidental aerobrake or something, how are some of those orbits so darn circular?

Atmospheric drag will always tend to circulrise your orbit.
Try it in orbiter, put yourself in an Earth orbit where the perigee is in the top edge of the atmosphere. Now let it run
for a while, every time you pass through the atmosphere your apogee will decrease while your perigee will remain
roughly constant. Eventually your orbit will be approximately a circle, which wil slowly reduce in size due to the equal
atmospheric drag.

The same type of thing happens to moons, and they will eventually find themselves in a circular orbit. Eventually
phobos and deimos will fall into the martian surface due to atmospheric drag, but the timescales are immense.

[DocHoliday]

The same type of thing happens to moons, and they will eventually find themselves in a circular orbit.
Eventually
phobos and deimos will fall into the martian surface due to atmospheric drag, but the timescales are immense.

Rather bad news for would-be colonists, like myself ESPECIALLY if we intend to do some kind of atmosphere
enhancement down the line. That will probably increase the drag on the two potato moon, bringing the colision
closer.

If you guys want to see aerobraking in action; one of the MER addons on avsim (there are at least three) also
features a fictional (I was reminded of that once before) scenario where a probe uses Mars's feeble atmosphere to
actually slow itself down into a relatively nice elliptical orbit. If you wait for another orbit or two, the orbit gets almost
curcular, then you only nudge a little at the apoapsis and you're curcular and out of reentry danger. I'll see if I can
find it and post it on the Scenario Trading Post. If we get it right one day, we might simulate Leonov's trajectory as it
goes passed Europa, swings around Jupiter and finds itself in orbit of Io.. hehe looks dynamite on paper, but noone
ever tried it for (sim)real

Cheers,
Janez

[AphelionHellion]

Interesting... Phobos and Deimos are (I'd think) far enough away from Mars that atmospheric drag is about nil, but
then everything is relative in space...  Much as we'd like to assign a "hard" upper edge to our atmosphere (or any
atmosphere of any planet, that's just our nature as anal retentive catagorizing apes ) I guess there really is no such
thing when you start getting down into the realm of stray wandering molecules.

One thing I was picturing, also, is a reverse slingshot scenario - where the moon/asteroid approaches the planet from
the back but passing in "front" (prograde) of the planet and being slowed slightly that way so it can be captured. Ok
I'm not sure exactly what vectors are involved in something like that, but NASA's been doing this stuff for years

As for Phobos and Deimos falling on Mars - even assuming humankind is still around by then, by that time no doubt
we'd have the technology to boost them to a higher orbit.
They are pretty small, as moons go. I bet we could do it now, if our lives depended on it

[freespace2dotcom]

No, if our lives depended on doing something to avoid them right now, we'd just turn them into space dust. (nukes)
but about atmospheric drag... as doc said about that addon, you still need a bit of a extra push to avoid a continual
dipping into the atmosphere and having the thing fall down quickly. or perhaps that's only in the case considering
massive atmosphereic friction... going a tad higher in mar's moon's case wouldn't matter much...

But then I'm also wondering about the planet's orbits. certainly the sun doesn't have an atmosphere...  

[AphelionHellion]

Freespace: Well, IIRC, the planets coalesced out of the disc-shaped cloud of dust and gas that surrounded our sun
when it was born, so their orbits have always been more or less round (so the current astrophysics theory goes).
Also our moon is thought to have formed when a very large planetoid rear-ended the earth billions of years ago and
the cloud of hot rock and gas and miscellania condensed to form the moon.
Again it's thought to have formed in that position.
It's the "capture" part I was having trouble with

[freespace2dotcom]

Yes, yes, I'm aware of all that, but overall,  I would think that some exception would apply. look at ganymede,
certainly, no collision with jupiter would produce something like that. and I have problems seeing how anything solid
could have been formed when a giant ball of gas is right next to it. (^_^)

I would have thought that a gas moon would form next to a gas planet, but who knows? maybe massive gravity
causes so much pressure and heat that elements are melted and then evaporate?

I recall reading somewhere that earth (and all the other planets) pick up tons of stellar dust every year. One could
argue that that could make the plantet's orbits circular in a similar fashion. that would throw the scientific
community for a loop because it would certainly change the current perspective on how the solar system was formed.
we'd get closer to the sun because of that dust and we'd never have to worry about it exploding or expanding or
anything because we'd fall in first. Of course mars orbit isn't very circular, but then I'm sure jupiter is saying
something in that matter.

I'm pushing my mental boundaries. I'm not very knowledgable about this sort of thing...

[DocHoliday]

Hehe, I don't think space dust has much influence. For one its mass is probably insignificant compared to the planets,
also I'd say it's falling from different directions, perhaps cancelling out the effect altogether.

Now the interesting thing is Venus. It is the only one with a reversed spin One ideas was, that Venus itself was
captured. But it's position from the sun sort of justifies, it was always there (was it Kepler that mathematically
predicted the positions of the planets - thus discovering one is "missing" between Mars and Jupiter). So another
explanation might be that an object (possibly the one that whacked Earth - Moon's father), passed by Venus so close
that it actually reversed its spin by gravitational pull alone.

Another interesting matter is Jupiter. Its class of planet is sometimes called a "failed star", because if you added
slightly more mass to it, it would ignite, just like Clarke portrayed it in "2010".

I mean, everything is so full of coincidence, that you sometimes wonder if it really wasn't some sort of divine
influence

As to the capture phenomenon. I think if you have two major bodies in play. For example and object passes by Mars,
tilting it's orbital path, so that it then slingshots around say Jupiter, making another warped trip around Mars, getting
further pulled of course and then it's orbit "adjusted" by Jupiter's remote influence, it could be possible it would put it
exactly into a nice orbit around Mars.

Try this:
http://www.orbitsimulator.com/gravity/articles/what.html

and try our this scenario:
http://www.orbitsimulator.com/gravity/articles/capture.html

Seems in space, anything REALLY is possible

Cheers,

[freespace2dotcom]

Including 0 Degrees Celsius on the sun?

On a serious note though. I don't think that the space dust is falling on earth evenly becasue earth's MOVING. a speeding car tends to hit things in front of it, and slow it down. surely the effect (considering the mass difference between earth and the dust) is small, but small effects add up over time.....



Post Edited ( 06-16-04 10:11 )

[Simonpro]

AphelionHellion wrote:
Interesting... Phobos and Deimos are (I'd think) far enough away from Mars that atmospheric drag is about nil, but
then everything is relative in space...  Much as we'd like to assign a "hard" upper edge to our atmosphere
(or any atmosphere of any planet, that's just our nature as anal retentive catagorizing apes ) I guess there really
is no such thing when you start getting down into the realm of stray wandering molecules.

Indeed, we are talking about very long timescales here, phobos and deimos will probably stil lbe up there when the
human race becomes extinct.

One thing I was picturing, also, is a reverse slingshot scenario - where the moon/asteroid approaches the planet
from the back but passing in "front" (prograde) of the planet and being slowed slightly that way so it can
be captured. Ok I'm not sure exactly what vectors are involved in something like that, but NASA's been doing this
stuff for years

Just as likely.

As for Phobos and Deimos falling on Mars - even assuming humankind is still around by then, by that time no doubt
we'd have the technology to boost them to a higher orbit.
They are pretty small, as moons go. I bet we could do it now, if our lives depended on it

We could probably do it now, all we need is a load of ion engines :p

[DocHoliday]

freespace2dotcom wrote:
Including 0 Degrees Celsius on the sun?

Well, you take a brown dwarf, you're not far from it

On a serious note though. I don't think that the space dust is falling on earth evenly becasue earth's MOVING. a
speeding car tends to hit things in front of it, and slow it down. surely the effect (considering the mass difference
between earth and the dust) is small, but small effects add up over time.....

Assuming that the space debris moves slowly compared to earth. Otherwise the effect might be more similar to a
sailing ship, where the wind either pushes or slows down the ship..

[AphelionHellion]

Freespace: I was under the impression that the magnetic fields of gas giants and charged particles from the sun
trapped in them pretty much rule out the possibility of "gas moons" - they get swept away
Not sure how Titan fits into that equation with that atmosphere, though. Perhaps because it's far enough out not to
be affected, and has gravity strong enough to maintain that atmosphere?
You're right though, of course. Who knows how many of the moons in our solar system are actually captured Kuiper
Belt objects and various other floating leftovers? I'm sure you've read all the hubbub over Pluto's status in this regard

[AphelionHellion]

D'oh!
That link you posted looks fascinating, Doc, but the site seems to be down  
I'll check it again tomorrow.

[freespace2dotcom]

Freespace: I was under the impression that the magnetic fields of gas giants and charged particles from the
sun trapped in them pretty much rule out the possibility of "gas moons" - they get swept away

of course, I really don't think that a gas moon would have really been able to form. if anything, something that would
have would have formed, would probably just gotten eaten up by jupiter or saturn, or whatever other gas planet. but
if titan has some form of atmosphere, then is it not at least probable that a gas moon, if it was about the same size,
at the same distance, would be able to hold on to it's mass as well? I would think that such a thing would be more
likely to form around the vicinity than a solid moon, but who knows? I don't.

[DocHoliday]

AphelionHellion wrote:
D'oh!
That link you posted looks fascinating, Doc, but the site seems to be down  
I'll check it again tomorrow.

Strange, works fine from my end. Keep trying.

[AphelionHellion]

"Document contains no data"

Who stole the data? Who??
Lock the doors, we hafta search everyone!!

[DocHoliday]

hehe

[freespace2dotcom]

Stop the presses. Now take a gander at this little tidbit.

http://www.wired.com/news/technology/0,1282,64034,00.html?tw=wn_tophead_3

[schumanna]

Well that probibly means we most change that configuration in Orbiter to mach it, right?  

[freespace2dotcom]

Definately. I'd do it now, but I'm lazy and I fear that I'd inherantly screw up some pattern with the saturn
cloud/surface textures. I'd rather wait it out. It's not a huge difference, but notable.