Astronomy people! I need help!

[RMSistight]

What properties of a satellite would suggest that it my be a captured asteroid?

Under what conditions is tidal heating likely to be important for a satellite?

 

[BatmanNate]

Do your own homework.

 

[RMSistight]

I'm doing it right now. Can't fvcking find the answer in my book.

 

[bernse]

Off the top of my head..

If the orbit and/or rotation were retrograde that would suggest it be a captured asteroid.

 

[bernse]

So was I right?

 

[tritium4ever]

Why would retrograde motion be indicative of a captured asteroid? It could easily be captured going in the "correct" direction.

 

[Chaotic42]

Differing composition, irregular shape/size, eccentric orbit, and differing orbital plane.

 

[hjo3]

Originally posted by: tritium4ever
Why would retrograde motion be indicative of a captured asteroid? It could easily be captured going in the "correct" direction.

Your logic's bad. Retrograde = captured. Normal orbit direction = captured OR natural. Of course, nothing's absolute; a satellite orbitting something the "wrong" way could actually be natural.

 

[RMSistight]

Originally posted by: bernse
So was I right?

Part of it was right about the retrograde motion.

 

[RossGr]

First of a it is a difficult thing to "capture" something. If a stray asteroid starts at a large distance from a planet, it must have some velocity, and therefore some Kinetic energy with respect to the planet. Its distance from the planet is potential energy with respect to the planet. In the normal run of things the astroid will gain kinetic energy and lose potential energy as it approaches the planet, conservation of energy tells us that the total energy, that is the sum of the potential and kinetic energies must remain the same. One could essentially charaterize an orbit by its energy, that is the total of the kinetic and potential energy of the satilite in that orbit. At any point the energy will be shared between kinetic and potential but the total wil remain constant. If you think about this it means that a body is either in orbit or NOT in orbit. There is some threshold energy, below which a body is in orbit and above which it is not. So if some body, with to much energy approaches a planet it cannot be captured unless it LOSSES some energy. This can be done by collison or if the approach is just right, a reverse sling shot effect could happen.

You have all heard about the sling shot effect in refernece to the deep space satilites we have launched. They do a close approach to Jupiter or Saturn and gain huge amounts of velocity which is the same as energy in passing. In regards to my previous paragraph how is this possible?

Well as the satilite falls into the gravitational well of the large planet it is drug along with the planets ORBITAL velocity. This is all gained energy. The velocity gained due to the close approach is all lost as the satilite leaves the vacinity of the large planet, what is not lost is the velocity imbued to the satilite by the ORBITAL motion of the planet, thus the slingshot.

So now if an asteroid approachs on an exact reverse of the slingshot approach it, instead of gaining velocity, will lose velocity, and thus could be captured. You must realize that the chances of this happening are very slim.

Thus any captured satilite MUST have motion retrograde to the orbital motion of the planet. If its original motion is in the same direction as the orbital motion it will get the slingshot ride and be sent away at an even higher velocity then with which it approached.

The only other possible way to capture something is for it to collide with either the planet or an orbiting body, this case would be indicated by lots of rubble in the orbit.

 

[Chaotic42]

Originally posted by: RossGr
First of a it is a difficult thing to "capture" something. If a stray asteroid starts at a large distance from a planet, it must have some velocity, and therefore some Kinetic energy with respect to the planet. Its distance from the planet is potential energy with respect to the planet. In the normal run of things the astroid will gain kinetic energy and lose potential energy as it approaches the planet, conservation of energy tells us that the total energy, that is the sum of the potential and kinetic energies must remain the same. One could essentially charaterize an orbit by its energy, that is the total of the kinetic and potential energy of the satilite in that orbit. At any point the energy will be shared between kinetic and potential but the total wil remain constant. If you think about this it means that a body is either in orbit or NOT in orbit. There is some threshold energy, below which a body is in orbit and above which it is not. So if some body, with to much energy approaches a planet it cannot be captured unless it LOSSES some energy. This can be done by collison or if the approach is just right, a reverse sling shot effect could happen.

You have all heard about the sling shot effect in refernece to the deep space satilites we have launched. They do a close approach to Jupiter or Saturn and gain huge amounts of velocity which is the same as energy in passing. In regards to my previous paragraph how is this possible?

Well as the satilite falls into the gravitational well of the large planet it is drug along with the planets ORBITAL velocity. This is all gained energy. The velocity gained due to the close approach is all lost as the satilite leaves the vacinity of the large planet, what is not lost is the velocity imbued to the satilite by the ORBITAL motion of the planet, thus the slingshot.

So now if an asteroid approachs on an exact reverse of the slingshot approach it, instead of gaining velocity, will lose velocity, and thus could be captured. You must realize that the chances of this happening are very slim.

Thus any captured satilite MUST have motion retrograde to the orbital motion of the planet. If its original motion is in the same direction as the orbital motion it will get the slingshot ride and be sent away at an even higher velocity then with which it approached.

The only other possible way to capture something is for it to collide with either the planet or an orbiting body, this case would be indicated by lots of rubble in the orbit.

I suppose this would also be true for the sun. Could that mean that Pluto is not a captured satellite?

 

[RossGr]

I have seen it mentioned that Pluto may be captured, but I have not heard of the possible mechanism of its caputure. We really know very little of Pluto, other then that it is there. Perhaps with time we will lean enough to know more of its history. I do not believe that it is in a retrograde orbit, it does have an orbital plane at a high angle with respect to the rest of the solar system, which is strange. I do not know it is or is not captured, but it is not possible for it to simply come wandering past and fall into that orbit naturally.

 

[bernse]

Could that mean that Pluto is not a captured satellite?

For the sun to "capture a satellite" it would have to come from outside the solar system. I think the discussion RE: Pluto is that it is a large Kuiper belt object, which it almost certainly is. But, even if its orbit was changed from an outside influnence (say, Neptune) it was still a "satellite" of the Sun before.