Jae Tellona Star-System in MgT:Traveller Compendium I

[whulorigan]

I am trying to understand the following text-description of the Jae Tellona system as described in MgT: Traveller Compendium I, p.12:

MgT: Traveller Compendium I, p.12 (right-hand column):
. . . There is a single large gas giant locked in a solitary orbit and a pair of twin gas giants, which are fairly small. The pair of small gas giants are in possession of an unusually high periodicity, as well as being closely linked in their stellar orbits, making them all but inaccessible throughout most of the Jae Taellonan year. The remaining gas giant, which accommodates a reasonably impressive satellite system of its own, is the only other major body in the system that will remotely interest most visitors . . .

Concerning the LGG:

1) What is being implied for the LGG by the phrase: "...locked in a solitary orbit..."? As opposed to a non-solitary orbit? Is the orbit being compared to the orbit(s) of the two SGGs?

2) What does it mean for the LGG to be "locked" in its orbit?
​

Concerning the two SGGs:

1) Is the implication here that these two SGGs are orbiting about each other around a barycenter?

2) What is being implied by the term "having an extremely high periodicity"

3) If so, what is meant by the phrase "... being closely linked in their stellar orbits"?

4) How do the above considerations make the SGGs inaccessible throughout most of the Jae Taellonan year?

​

Am I just being unusually thick-headed at the moment? I don't know if I am grasping what this system configuration is supposed to look like. Anyone have any interpretive insight?

 

[robject]

1) Is the implication here that these two SGGs are orbiting about each other around a barycenter?

2) What is being implied by the term "having an extremely high periodicity"

Yeah, I think it means they spin rapidly around each other in the same orbit. Maybe.

 

[Adam Dray]

Just guessing here, too. My opinion: Yes, what you and robject said.

Periodicity in astronomy is used most often with long-range x-ray or other EM scans. Detection of planets is made via blips on readings as they transit their stars. For these gas giants to have a high periodicity in that sense, they'd need a very short solar year (i.e., a short orbital period). Because this is determined entirely by mass and gravity for stable orbits, and gas giants (even small ones) are by nature large, high mass objects, I don't think the author means this.

Small gas giants would be about the size of earth. Put two of them together, and they end up in an orbit smaller than Jupiter's but larger than Earth's, assuming it's not too eccentric.

So that leads me to the conclusion that your barycenter hypothesis is the correct interpretation. Two small gas giants are rotating around each other at a very high rate of speed, meaning they're very close.

I think "solitary orbit" just means a typical planet. Of course, in the real universe, planets are rarely alone, as they lead and trail all kinds of objects in their orbit. But we all understand what they mean.

"Closely linked in their stellar orbits" just means, treat them as one object going around the star. They're so close together, the pair can be found in basically the same position relative to the star.

Why are they inaccessible? Because REASONS, man.

I suspect the author is suggesting that they orbit each other so closely, and with such rotational speed, that ships can't safely approach them. But this is basically silly. A ship merely tells its computer to match the very predictable rotational speed of one of the planets, and then that planet looks like it's not moving relative to the ship, but the rest of the universe is spinning like a top. So what? A little care is all that is needed, then you can safely scoop up fuel or whatever.

 

[robject]

Regardless of true physics, I suppose the author was injecting a little Space Opera-style drama into things. For various possible reasons due to their barycentric twinnitude (flares? unpredictable tidal forces? crazy micrometeroid missiles? "something else" that no-one has bothered to explore yet?), they are dangerous to get near. I can handle that, and that makes for an interesting twist to a scenario setting.

 

[whulorigan]

@Adam & Rob: Thanks for your responses.

@Adam: Basically you are leaning in the direction I was leaning, but you gave me some additional angles to ponder. Thanks.

@Rob: I agree. I can make up some interesting fluff text to add to the sci-fi flavor. I just wanted to make sure I wasn't overlooking something simple and/or obvious.


But if you guys or anyone else has some other interesting ideas . . .

 

[inexorabletash]

The only thing that comes to mind that hasn't been mentioned is that the SGGs could be co-orbital like Saturn's Janus and Epimethius - a 1:1 resonance where they effectively swap orbits on a regular basis.

I'd like to hope that something terrible happened to that paragraph between the author and the editor. Otherwise, someone made it pretty far in life never having seen a a science documentary about the solar system.

 

[robject]

The text does sound sort of mangled. Even without the need of an astronomy class, published materials should be clear.

 

[Highorbit_drifter]

Just guessing here, too. My opinion: Yes, what you and robject said.

Periodicity in astronomy is used most often with long-range x-ray or other EM scans. Detection of planets is made via blips on readings as they transit their stars. For these gas giants to have a high periodicity in that sense, they'd need a very short solar year (i.e., a short orbital period). Because this is determined entirely by mass and gravity for stable orbits, and gas giants (even small ones) are by nature large, high mass objects, I don't think the author means this.

Small gas giants would be about the size of earth. Put two of them together, and they end up in an orbit smaller than Jupiter's but larger than Earth's, assuming it's not too eccentric.

So that leads me to the conclusion that your barycenter hypothesis is the correct interpretation. Two small gas giants are rotating around each other at a very high rate of speed, meaning they're very close.

In the system write-up I did for Dimmurak in a JTAS article, I had two Neptune sized gas giants locked in a death spiral orbit around each other. I picture this as the what they were trying to describe for Jae Tallona.

Note that I hadn't read treatment this before now. I got the idea after playing with an orbit simulator online, where you can drop masses into a star system. Not easy to do, and it didn't last all that long, but I was able to shoot a large planet out of the inner system to nearly hit one in the outer system and go into a frantic spin around each other.

Here I thought I was being so clever...

It looks like the Jae Tallona write up probably went through a couple of editing passes, and either an earlier version was used instead of the final, or it just got pruned to the point it no longer was as clear as it could have been. I've been there

 

[SanDragon]

What about a great, big electro-magnetic dynamo spitting dangerous radiation and/or lightning between the two giants?

 

[GypsyComet]

The "inaccessible for much of the year" thing could also point to them being waaay out there, and thus only practical to visit when Jae Telona is on the same side of the star.

Or they could have mangled things and meant eccentricity. Not one but TWO small gas giants in highly eccentric orbits, also possibly off the system's orbital plane by quite a lot, would make them tricky to visit.

 

[whulorigan]

Thanks for all of the comments, everyone. That gives me a couple of extra options to think about.

 

[Highorbit_drifter]

I uploaded to the Gallery a not very good image of what I thought two gas giants spiraling around each other might look like.

 

[77topaz]

I uploaded to the Gallery a not very good image of what I thought two gas giants spiraling around each other might look like.

That picture looks like they are colliding with each other, not orbiting around a common barycentre. The gas giants should probably be farther apart, and I'm not sure what all those swirly colours around them are meant to represent?

 

[whulorigan]

I uploaded to the Gallery a not very good image of what I thought two gas giants spiraling around each other might look like.

My first impression is that I would not want to refuel there . . .

 

[Highorbit_drifter]

That picture looks like they are colliding with each other, not orbiting around a common barycentre. The gas giants should probably be farther apart, and I'm not sure what all those swirly colours around them are meant to represent?

Thats true. But I'm neither an astrophysicist nor an artist.

They should be 55,000 km apart, each planet is around 45,000, give or take a thousand km. So a little more than their own diameter separating them. The pretty colors are spirals of gas and ice crystals stripped out of the upper atmospheres of the planets. I'm not sure what color they would actually be, so I just went with something that to me implied power, radiation and electrical storms.

 

[G. Kashkanun Anderson]

The "inaccessible for much of the year" thing could also point to them being waaay out there, and thus only practical to visit when Jae Telona is on the same side of the star.

I agree with this. 'High Periodicity' in this case probably refers to the length of their orbit in days around the primary, which for an F9V star should be -- as you put it -- waaay out there. So it's either a pair of gas giants orbiting a common barycenter in an Outer Orbit, or it's one gas giant in a Trojan position with the other.

Of course, it shouldn't really matter what side of the star the two are on if they are that far out. If Jae Tellona is orbiting at about 1.5AU and the two baby giants are dancing around out at about 15AU (for example), you're looking at a difference of 13.5AU on one end and 16.5AU on the other. Either way, it's still a heckuva schlep on a Free Trader's M-Drive.

Also, if they're in the Outer System, they can still be gravitationally bound to each other without having to be contact binaries. Going back to that 15AU example, they could easily have up to an AU between them and still be co-orbitals, providing that other gas giant isn't in a position to harass them too much.

 

[whulorigan]

I agree with this. 'High Periodicity' in this case probably refers to the length of their orbit in days around the primary, which for an F9V star should be -- as you put it -- waaay out there. So it's either a pair of gas giants orbiting a common barycenter in an Outer Orbit, or it's one gas giant in a Trojan position with the other.

Another thought: what is the likelihood/viability of them being quasi-satellites of one another in similar outer-system orbits?
(EDIT: Either something like what inexorabletash suggested earlier for Janus-Epimetheus (a horseshoe orbit) or something closer to the Earth-Cruithne quasi-satellite transition-orbit).

 

[Spartan159]

Another thought I had was, what if you effectively had one gas giant with two cores sharing the atmospheres? Granted my science here might be influenced by Larry Niven's The Smoke Ring, would it maybe look like a space going doughnut? Just a passing thought here.

 

[Highorbit_drifter]

I agree with this. 'High Periodicity' in this case probably refers to the length of their orbit in days around the primary, which for an F9V star should be -- as you put it -- waaay out there. So it's either a pair of gas giants orbiting a common barycenter in an Outer Orbit, or it's one gas giant in a Trojan position with the other.

Of course, it shouldn't really matter what side of the star the two are on if they are that far out. If Jae Tellona is orbiting at about 1.5AU and the two baby giants are dancing around out at about 15AU (for example), you're looking at a difference of 13.5AU on one end and 16.5AU on the other. Either way, it's still a heckuva schlep on a Free Trader's M-Drive.

But you can do a micro-jump in the system to get to the planets. While it might not be economical for a Free Trader, its certainly not inaccessible.

Another thought I had was, what if you effectively had one gas giant with two cores sharing the atmospheres? Granted my science here might be influenced by Larry Niven's The Smoke Ring, would it maybe look like a space going doughnut? Just a passing thought here.

This might explain it. Jump limit is only defines by diameter. "Take it as a matter of faith" I think is the way MM described it. So that great gas torus might be the defining feature, its diameter shadowing a huge swath of the system. If they are in a cometary orbit, that shadow is going to wobble all about during their 'year' so chunks of the system are inaccessible to j-drives for most of the year, but not all of the year.

 

[77topaz]

Of course, it shouldn't really matter what side of the star the two are on if they are that far out. If Jae Tellona is orbiting at about 1.5AU and the two baby giants are dancing around out at about 15AU (for example), you're looking at a difference of 13.5AU on one end and 16.5AU on the other. Either way, it's still a heckuva schlep on a Free Trader's M-Drive.

That's assuming both Jae Tellona's and the gas giants' orbits are circular, though. If, for example, the gas giants had a highly elliptical (eccentric) orbit, then they'd be a lot closer to Jae Tellona for part of their cycle then for the rest.