Redefining the world count in a system

[tjoneslo]

In reviewing the T5SS data for several worlds, and based upon comments from others in that thread, the Worlds calculation (Worlds Chart F, sub chart W page 436) has several issues. This is a proposal to fix that process. This post is in two parts. The first part is background for the process, for people who want to understand why the changes are proposed. The second part is specific rule changes.

In the basis of planetary formation, you have a cloud of dust and gas around a star. The dust particles accrete into large bodies over a period of time. These then collide, get bigger, some get ejected out of the system by gravitational forces. Eventually these settle into the stable orbits (usually).

There are two limits of where you would most likely have planets. The inner limit is based upon the size of the star. I used this table. The size of the star (in solar radii) converted to orbit numbers gives the minimum orbit number. The values are also shown in the Orbital Distances table (Table 5, 5, page 43).

Based upon the star's mass, there is an outer limit of where there is enough material to accumulate into a real planetary mass. Beyond this outer limit you will only get small bodies like comets and the occasional dwarf planet. This is based upon both density of the proto-planetary disk itself and the orbital speed to allow collisions. For this I used a rule from GURPS Traveller: First In, page 56 sidebar (last formula at the bottom of the column).

Under ideal circumstances all the orbits between these two limits would be filled with objects (companion stars, gas giants, planets, or belts). As we know, the real world doesn't work that way, so add a randomization factor.

Specific Rule Changes:

Remove step B 4 - Gas Giants and Belts.
Remove step F W - Worlds in the system.

Perform Steps F 1 and F 2 to generate the primary star in the system

Then generate the number of object in the system:

	Ia	Ib	II	III	IV	V	VI
A0	11	11	12	11	11	10	9
A5	9	11	11	11	10	9	9
F0	8	11	11	11	10	9	9
F5	8	10	11	11	10	9	9
G0	7	8	10	9	9	9	8
G5	6	7	9	10	9	8	8
K0	6	7	8	10	9	8	8
K5	6	6	8	9	9	8	8
M0	6	7	9	10	10	8	7
M5	3	4	5	7	9	7	7
M9	-1	0	1	3	4	7	7

Number of object in the system based on primary type in the chart + Flux die, to a minimum of 1 world (the main world).

Generate companion stars based upon steps F 1 and F 2, and place them in orbits according to step F 3.

Roll 2D/2 - 2 for number of gas giants (not to exceed the number of worlds in the system).
Roll 1D - 3 for number of belts, if there are worlds remaining.

Place the worlds in orbits according to the rules in step G.

Because the world gen section E (Economic Extension) relies upon the number of gas giants and belts, this step must be done after the world generation section.

 

[DonM]

I had proposed something similar, but your method is cleaner than mine.

I like it, for what that's worth...

 

[aramis]

One problem - the Titus-Bode Relationship (which is behind the orbit numbers' related distances) apparently hasn't stood up to the data in the real world.
At least two extrasolar systems violate it from what I've read.

 

[tjoneslo]

One problem - the Titus-Bode Relationship (which is behind the orbit numbers' related distances) apparently hasn't stood up to the data in the real world.
At least two extrasolar systems violate it from what I've read.

True, if Titus-Bode were a real thing, the orbits of the moon's of Jupiter (for example) would also follow the same relationship. And other examples even in our own solar system.

There are two parts to that. First is using the orbit numbers as range markers in a system without any relationship to anything real is useful. The second is the fractional orbit and orbital eccentricity descriptions, which if used more aggressively during the planetary placement may get rid of the "every system looks the same" with the orbit numbers. But that adds steps and complexity to the system.

 

[Drakon]

Assuming your rule change is approved, will this change the world numbers on a future pass of the Travellermap data? Should I hold off on fleshing out the Lemish system until after that pass is completed?

 

[aramis]

True, if Titus-Bode were a real thing, the orbits of the moon's of Jupiter (for example) would also follow the same relationship. And other examples even in our own solar system.

There are two parts to that. First is using the orbit numbers as range markers in a system without any relationship to anything real is useful. The second is the fractional orbit and orbital eccentricity descriptions, which if used more aggressively during the planetary placement may get rid of the "every system looks the same" with the orbit numbers. But that adds steps and complexity to the system.

Taking a real system for a moment HD 10180 - and noting that these are all >1 M⊕...

Companion (in order from star)	Semimajor axis (AU)	Traveller Orbit	Mass (M⊕)
b	0.02222 ± 0.00011	-1	>1.3 ± 0.8 M⊕
c	0.0641 ± 0.0010	-2	>13.0 ± 2.0 M⊕
i (unconfirmed)	0.0904 ± 0.047	-1	>1.9 ± 1.8 M⊕
d	0.1284 ± 0.0061	0	>11.9 ± 2.15 M⊕
e	0.270 ± 0.0013	0	>25.0 ± 3.9 M⊕
j (unconfirmed)	0.330 ± 0.016	1	>5.1 ± 3.2 M⊕
f	0.4929 ± 0.0078	1	>23.9 ± 1.4 M⊕
g	1.415 ± 0.091	4	>21.4 ± 3.4 M⊕
h	3.49 ± 0.60	5	>65.8 ± 12.9 M⊕

Real systems can have multiples in the same orbit number. (And those are surprisingly close in.) Gliese 667C is even more crowded - 4 in orbit 0.

 

[tjoneslo]

Real systems can have multiples in the same orbit number. (And those are surprisingly close in.) Gliese 667C is even more crowded - 4 in orbit 0.

I'll refer you you to this article about planetary formation. The important facts from this article are first that it takes 10,000 years to go from gas cloud to having planet sized object circling the primary. The simulation estimate are as many as 1000 planet sized objects. It then takes on the order of 100 million years to have the final collisions and planetary ejections to render the system "stable".

Those systems may not be stable over geological time scales. I highly doubt any of the worlds are habitable. But for the time scales of the Imperium, they would be interesting systems. Making a simple Traveller simulation of that would be... an interesting challenge.