General Rogue Gas Giants

[Stei'awtliyrl]

I have a question for all us Traveller Astronomers (and real world Astronomers) in the forums. Can a gas giant be a rogue planet? I can't think of a reason why not, since there's no issue with heat being necessary to form the gas layers, it's just gravity.

Anyway this question has been stuck in my head, and now I'm sticking it in yours. You're welcome.

 

[Stei'awtliyrl]

.... and I answered my own question. nasa.gov directed me to this article https://manyworlds.space/2023/08/11/getting-to-know-rogue-planets/ which states that there are rogue-planets a-plenty drifting through the cosmos, and most of them are gas giants.

So, the more y'know. Y'know?

 

[whartung]

that there are rogue-planets a-plenty drifting through the cosmos, and most of them are gas giants.

Perfect for those secret deep space wilderness fueling stations.

 

[Badenov]

I was going to say 'except that they're in motion independently, so it's useful for maybe a few hundred years, and by then, it's in the next hex'. Then I rechecked the quote: "They then travel through interstellar space at speeds estimated to be in the millions of miles per hour." If 'In the millions' is five million mph, that's roughly 434 years to cross a one-parsec hex. That's probably longer than most campaigns, though you might make a one-off event for one rogue planet exiting its hex and cutting off some remote station in the Reft or Corridor, now players need to help evacuate the station, or make better maps to the rogue planet so it can still be found (and refueled from, if a gas giant). Maybe the station orbits the rogue planet, so has all the fuel it needs, and huge hydroponics for food, but it's so close to the edge of the hex, the maps that the rest of the galaxy has need to be updated?

 

[whartung]

"They then travel through interstellar space at speeds estimated to be in the millions of miles per hour."

Well, that's an interesting point.

Going 5Mmph makes for a hard target to catch. AT 1G, it's 62 hrs just to accelerate to match the velocity, much less actually catch up to where the planet actually is. It makes the 32 hr jump arrival window important, and it also makes it quite important how well your arrival vector matches that of the planet. Show up on the wrong side of the jump window, and your refueling stop may take longer than you might like.

 

[Stei'awtliyrl]

Well, that's an interesting point.

Going 5Mmph makes for a hard target to catch. AT 1G, it's 62 hrs just to accelerate to match the velocity, much less actually catch up to where the planet actually is. It makes the 32 hr jump arrival window important, and it also makes it quite important how well your arrival vector matches that of the planet. Show up on the wrong side of the jump window, and your refueling stop may take longer than you might like.

I believe the assumption is, since everything in the cosmos is traveling at speeds of millions of km/h, that a ship's nav computer accounts for the vector of the destination body. It *does* make for an issue if a ship is jumping into a parsec where there is a Rogue Planet drifting through, but it's presence is not yet logged into the ships computer. It's why star-charts are important and why they're likely updated when a ship passes within comms range of a starport.

 

[Badenov]

I believe the assumption is, since everything in the cosmos is traveling at speeds of millions of km/h, that a ship's nav computer accounts for the vector of the destination body. It *does* make for an issue if a ship is jumping into a parsec where there is a Rogue Planet drifting through, but it's presence is not yet logged into the ships computer. It's why star-charts are important and why they're likely updated when a ship passes within comms range of a starport.

The thing is, our sun is 'only' rotating through the galaxy at ~517,500 mph, so the rogue planet is moving much faster than our sun, and while our sun is orbiting neatly along with the rest of the galaxy, as it condensed from the gas originally rotating around, only some rogue planets formed that way. Rogue planets that were expelled from the solar systems where they formed can be going anywhere.

Perfect for those secret deep space wilderness fueling stations.

If you can find them, yes. But finding things with a chart should be fairly easy, and it's not like charts are not updated in 500 years. Which brings up another adventure idea: if a 500-year old map was found pointing to a rogue planet, where might that planet be now? You'd almost have to fit a ship especially to search, with extra fuel tanks and life support supplies. And survey gear, so you could plot the planet's position NOW and go home and come back later. The fact that you can refuel there makes it a legit destination, regardless.

Off-topic, I looked up rogue planets on wikipedia, and it says "In an Earth-sized object the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life." (https://en.wikipedia.org/wiki/Rogue_planet, links unlinked). That implies that some terrestrial rogue planets may even be inhabitable, which I find fascinating.

 

[Carlobrand]

...
Off-topic, I looked up rogue planets on wikipedia, and it says "In an Earth-sized object the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life." (https://en.wikipedia.org/wiki/Rogue_planet, links unlinked). That implies that some terrestrial rogue planets may even be inhabitable, which I find fascinating.

Being habitable by hydrothermal vent life doesn't mean an extraplanetary visitor is going to be able to contact such life. There could be a mile or more of ice between an explorer and the sea floor hydrothermal vent.

I don't recall much in canon about jump and conservation of momentum. I was under the impression you exited jump retaining whatever vector with which you entered but that would be a major, and to my knowledge unspoken, complication if your target world is at a significantly different point in its orbit than your departure world. Any canon answers to that particular conundrum?

 

[Dragoner]

In my universe I have rogue gas giant, planetoids, even ice reefs, oceans worth of H2O, free floating. Sometimes people put stations near them to help cross a rift, or have them secretly known, for smuggling. They can also be home to alive or extinct Hider cultures, such as from Orion's Arm: https://www.orionsarm.com/eg-topic/45bd1a9eb4a5c Space is vast, and not empty, we are just very small, so we can cross distances without hitting things, mostly. Here is a cool map someone made, Centauri Highway by Thobewill:

 

[Badenov]

Being habitable by hydrothermal vent life doesn't mean an extraplanetary visitor is going to be able to contact such life. There could be a mile or more of ice between an explorer and the sea floor hydrothermal vent.

I don't recall much in canon about jump and conservation of momentum. I was under the impression you exited jump retaining whatever vector with which you entered but that would be a major, and to my knowledge unspoken, complication if your target world is at a significantly different point in its orbit than your departure world. Any canon answers to that particular conundrum?

So, it specifically says in the quote, that such a planet "could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist." I will buy that there might be no light-dependent surface life, and obviously nothing native with photosynthesis would evolve, but if there is sufficient warmth to keep the surface water warm, colonists may be able to set up hydroponics and such to feed themselves.

The undersea biota might be like earth's deep sea biota, which also never sees sunlight. Bacteria using chemosynthesis can oxidise hydrogen sulfide, hydrogen, and methane could form mats as they do on earth around hydrothermal vents, which are food for the next stage of the food chain. (ref https://www.scisnack.com/2020/04/15...oes-life-thrive-there-without-photosynthesis/, which explains how life on earth exists independent of sunlight). I totally agree that surface inhabitants might have nothing to do with these native lifeforms, but that doesn't preclude moving in.

As far as conservation of momentum goes, I've always considered that the roll for arriving in the hex closer or farther from the planet covers both variances due to jumpspace irregularities and plotting errors, and vagaries of where in the hex a planet is just at the moment you arrive.

 

[Marcatlas]

As far as conservation of momentum goes, I've always considered that the roll for arriving in the hex closer or farther from the planet covers both variances due to jumpspace irregularities and plotting errors, and vagaries of where in the hex a planet is just at the moment you arrive.

IMU a ship loses its real space inertia when it enters J-space and when it translates back to real space it comes in with a vector equal to 90% of the mass within 1 ly. So almost standing still in relation to the system's star. So positioning can be important. If you reenter "in front" of the local world, it is coming at you. Behind and is moving away, etc.

 

[casquilho]

This could be a cool basis for an adventure. A rouge planet is "found" in the empty hex next door so to speak. Some scientists want to go visit it, but the local university can't afford a ship. So they hire the characters to take them to see the rogue planet. Fun and hijinks ensure.

 

[Carlobrand]

So, it specifically says in the quote, that such a planet "could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist." I will buy that there might be no light-dependent surface life, and obviously nothing native with photosynthesis would evolve, but if there is sufficient warmth to keep the surface water warm, colonists may be able to set up hydroponics and such to feed themselves.

The undersea biota might be like earth's deep sea biota, which also never sees sunlight. Bacteria using chemosynthesis can oxidise hydrogen sulfide, hydrogen, and methane could form mats as they do on earth around hydrothermal vents, which are food for the next stage of the food chain. (ref https://www.scisnack.com/2020/04/15...oes-life-thrive-there-without-photosynthesis/, which explains how life on earth exists independent of sunlight). I totally agree that surface inhabitants might have nothing to do with these native lifeforms, but that doesn't preclude moving in.

As far as conservation of momentum goes, I've always considered that the roll for arriving in the hex closer or farther from the planet covers both variances due to jumpspace irregularities and plotting errors, and vagaries of where in the hex a planet is just at the moment you arrive.

I read it. I don't buy it. He proposes temperatures low enough that hydrogen wouldn't escape and yet high enough for liquid surface water. I can buy a hydrogen atmosphere in deep space, but it's asking a lot to expect that a planet alone in space will happen on exactly the right balance of geological processes to maintain liquid surface water with geothermal processes only without heating away the hydrogen atmosphere.

It's a unicorn planet. There might be one just because there are so many candidates that even a wildly improbable combination might occur, but there will be far more near-misses - hydrogen atmosphere iceballs with thermal vents or worlds that briefly held hydrogen atmospheres and liquid water until the hydrogen finally thinned out and the water froze.

 

[Badenov]

I read it. I don't buy it. He proposes temperatures low enough that hydrogen wouldn't escape and yet high enough for liquid surface water. I can buy a hydrogen atmosphere in deep space, but it's asking a lot to expect that a planet alone in space will happen on exactly the right balance of geological processes to maintain liquid surface water with geothermal processes only without heating away the hydrogen atmosphere.

It's a unicorn planet. There might be one just because there are so many candidates that even a wildly improbable combination might occur, but there will be far more near-misses - hydrogen atmosphere iceballs with thermal vents or worlds that briefly held hydrogen atmospheres and liquid water until the hydrogen finally thinned out and the water froze.

Turns out the science supports this. If you check the original article and follow the footnote on that statement to https://www.nature.com/articles/21811 you find their reasoning. In summary, the hydrogen atmosphere of the rogue planet never gets stripped down by solar wind, and forms an insulating layer that prevents the internal heat from escaping.

From the footnoted article:

The melting point of water is typically exceeded for basal pressures of the order of one kilobar. The atmosphere will have several cloud layers (methane, ammonia and perhaps water, like Uranus), but this has little influence on the temperature estimate.

It seems, then, that bodies with water oceans are possible in interstellar space. The ideal conditions are plausibly at an Earth mass or slightly less, similar to the expected masses of embryos ejected during the formation of giant planets. Bodies with Earthlike water reservoirs may have an ocean underlain with a rock core. Either way, these bodies are expected to have volcanism in the rocky component and a dynamo-generated magnetic field leading to a well developed (very large) magnetosphere. Despite thermal radiation at microwave frequencies that corresponds to the temperatures deep within their atmospheres (analogous to Uranus9), and despite the possibility of non-thermal radio emission, they will be very difficult to detect.

So, your colonists won't be able to play outside (without spacesuits), but it sounds like it's far from unlikely.

 

[Grav_Moped]

It's a unicorn planet.

Well, canon has the Ancients messing with planets. So, it's not literally impossible. Means there might be interesting stuff left behind though...

 

[Marcatlas]

Well, canon has the Ancients messing with planets. So, it's not literally impossible. Means there might be interesting stuff left behind though...

Something like that should be as possible as the GMs story line makes it. It's something that could be a lot of fun for the players

 

[Carlobrand]

Well, canon has the Ancients messing with planets. So, it's not literally impossible. Means there might be interesting stuff left behind though...

Well, to be fair, we appear to be a unicorn planet.

 

[Marcatlas]

Well, to be fair, we appear to be a unicorn planet.

Well, we already KNOW that the Ancients messed with Earth.

 

[Dragoner]

Well, to be fair, we appear to be a unicorn planet.

I read a paper by an astronomer the other day, and they were rather exasperated by people trying to state anything certain, in that "everything is different" - there are processes though highly complex. Part of it is also how much arguing is going on in the community, without the current data being resolved, we do not really know what we are looking at.

 

[slayman]

Well, canon has the Ancients messing with planets. So, it's not literally impossible. Means there might be interesting stuff left behind though...

Unicorn out of 8,000 + known worlds. We could probably extrapolate from the percentage of the known universe that has been scanned for exoplanets. We can't assume that only one exists, and we can't assume that 1 in every 8,000 is an Earth-type planet. Guess we won't be able to make even a WAG until we find Earth II.

But yes, so far it appears we are living on a Unicorn's back. Which makes me a little disappointed being a fan of galactic empires! I favor the ancient progenitors' hypothesis. Then the answer could be "as many as they wanted". LOL!