Hmm, tricky! The thing about space, of course, is that there tends to be lots of, well, space in which to manoeuvre!
So, it seems to me that part of the idea is to have something... untoward in that space.
One idea might be a massive space-cloud—not a real "nebula", as I think that those are rather more diffuse up-close than shown in sci-fi, but something with significant density at a human scale.
I'm imagining an actual, multicoloured cloud, filled with lightning—and within which there's a "tunnel" that winds around the sun: entering from the outside a little "above" the plane of the planets, spiralling inwards and "down" to meet the innermost planet, and then spiralling along the plane of the planets outwards past the second planet, and on to the third—around which it stops.
Another thought might be to do similarly with an "Asteroid Thicket", maybe composed of ultra-dense asteroids too tough to be simply blasted apart and too massy to be feasibly shunted aside.
One final idea for this post might be that the region surrounding the inner planets is filled with particles that emit a deadly field or radiation of some sort—impossibly charged particles that blast objects with lightning; incredibly radioactive particles; virtual particles of exotic properties that warp and damage ship-hulls; etc. etc.
The planets, meanwhile, would be immune to this hazard, perhaps holding it off via their magnetic fields, or absorbing it in their upper atmospheres, or deflecting it by some other means.
But there is one means of passage: from time to time, an asteroid from a nearby belt will break away—for no discernable reason—and fly into this region. It will always be aimed such that it flies first to the innermost planet (possibly via the sun), is thence slingshotted to the second planet, and is finally sent on to the third planet. After the third planet it circles two or three times in orbit—then breaks away unnaturally to fly straight into the sun.
And here's the thing: these asteroids emit a field that holds back the hazard. This then allows a ship to trail in their wake, in that small bubble of safety that they provide—as long as they don't stray from it.
My Games & Writing
The Cosmopolitan Fictioneer
I'm imagining an actual, multicoloured cloud, filled with lightning—and within which there's a "tunnel" that winds around the sun: entering from the outside a little "above" the plane of the planets, spiralling inwards and "down" to meet the innermost planet, and then spiralling along the plane of the planets outwards past the second planet, and on to the third—around which it stops.
This sounds somewhat like what I was having in mind when I mentioned anomalous stellar winds (which are composed of high-energy electrons and protons, making them heavily electro-charged); there would be a "tunnel" of sorts through the bubble that is formed by said winds and goes in a similar way to what you describe, and trying to go out of it causes the ship to be ravaged by extremely intense electrical and magnetic fields that can and will fry within minutes any electronic systems on the ship, no matter how hardened they are. The outcome of not heeding this hazard is that the ship would quickly end up dead in the void, with its crew and passengers doomed to slowly die off as life-support systems gradually wink out one by one.
This would do nicely as the first layer of obstruction.
The planets, meanwhile, would be immune to this hazard, perhaps holding it off via their magnetic fields, or absorbing it in their upper atmospheres, or deflecting it by some other means.
But there is one means of passage: from time to time, an asteroid from a nearby belt will break away—for no discernable reason—and fly into this region. It will always be aimed such that it flies first to the innermost planet (possibly via the sun), is thence slingshotted to the second planet, and is finally sent on to the third planet. After the third planet it circles two or three times in orbit—then breaks away unnaturally to fly straight into the sun.
And here's the thing: these asteroids emit a field that holds back the hazard. This then allows a ship to trail in their wake, in that small bubble of safety that they provide—as long as they don't stray from it.
Interesting. I could even have the particles be produced by the system's sun itself, and observing scientists would be flabbergasted at how it doesn't go further than about half way between the third and fourth planets, even though all physical data from their sophisticated tech of both the magnetosphere's power and the particles' properties indicate that they should be spread evenly throughout the sun's stellar-wind bubble, so what they're actually observing should be flat-out impossible.
That said, I would make the asteroid be slingshot-flung back into the asteroid belt, both to ensure the belt doesn't run out (unless you have a mechanism for replenishing its "stock"?) and to further enhance the science-defying nature of the whole phenomenon.
Edited by MarqFJA on Jun 8th 2023 at 3:02:37 PM
Fiat iustitia, et pereat mundus.
Having the asteroid be slung back out should work indeed, I daresay.
(I originally avoided that because I was concerned about ships being able to follow its trail backwards. But I realise now that I was still thinking in terms of "tunnels" rather than "wakes", and of course in this case the asteroid's effect would be long gone by the time one backtracked along its path for any real distance.)
If the asteroid is to be slung out again, I might suggest having there be just one such asteroid. One really weird rock that's not like all of the others, that emits a strange field that offers protection from the inner-planet hazard, and that alone occasionally deviates from its usual orbit to go on a jaunt around the inner planets...
Regarding the particles being produced by stellar wind, note that they don't have to be: as far as I understand it, "virtual particles" can just... appear in mid-space, albeit very briefly.
It would still be really really weird for them to be appearing thick and fast in just this one region, I daresay!
Still, there's nothing wrong with switching the "virtual particles" out for a strange form of stellar wind!
My Games & Writing
The Cosmopolitan Fictioneer
Oh hey, maybe instead of an asteroid, it's a comet that periodically follows this weird path, with its outgassing being what provides the small shielded space. And for extra weirdness, long-term analysis would show that this comet somehow maintains the exact same mass and coma
size when both should be decreasing, implying that it actively generates its own volatiles at a steady rate that directly matches its loss rate (so it rises as it comes closer to the sun, and decreases to virtually zero as it goes further away).
Or maybe combine the two: asteroids frequently experience this phenomenon several times a year, but they're quite small and thus only allow hitchhiking by spaceships that are so small they're incapable of travelling interstellar distances (thus an interstellar "mothership" would have to wait on the outer region while the small in-system ships make the journey), and even then only one ship per asteroid. Every year, however, a rather big comet makes the journey, and its wake is big enough for smaller classes of interstellar spaceships to hitch a ride, though their visits would have to be either short or they have to wait until next year to get back out.
Also, I could just have the exotic particles of the stellar wind cause the spontaneous generation of virtual particles within that specific volume, which would leave scientists just as baffled because none of the physical data justifies this phenomenon happening only within that range and not throughout the entire astrosphere.
Edited by MarqFJA on Jun 8th 2023 at 4:49:45 PM
Fiat iustitia, et pereat mundus.
Yup, all of that sounds good, I do think! ^_^
My Games & Writing
The Cosmopolitan Fictioneer
Another idea that I'm considering is that a ship can take a path that "skims" the surface of the sphere that is effectively formed by all these hazardous phenomena, and sooner or later it will find itself able to "dive" into the sphere without any problems; the catch is that this dive happens entirely due to an anomalous pulling force being exerted on the ship, and it always follows a path that avoids the third planet entirely and instead takes the ship to one of the innermost two planets first. Active propulsion will simply accelerate the ship along this path, and while the ship has considerable leeway in positioning itself within the "tunnel" they're moving through and can more or less pick whether to head for the first or second planet, trying to divert itself towards the third will quickly result in the same onslaught of hazards.
Leaving this inner sphere is astonishingly far easier, on the other hand, as one can essentially pick any direction out of it and find absolutely no resistance to their passage; in fact, some swear that it's as if there's some force that pushes on their ships from behind so that they leave faster, as fuel expenditure is mysteriously incongruent with the speed and distance that the ships had travelled.
Edited by MarqFJA on Jun 9th 2023 at 5:05:27 PM
Fiat iustitia, et pereat mundus.
I will note—without this being an argument against—that such a tunnel would presumably move over time, in keeping with the orbits of the planets.
My Games & Writing
The Cosmopolitan Fictioneer
Oh, definitely. In fact, as I imagine it, the tunnel only comes into existence when a "foreign" body approaches the "Zone of Forbiddance" in the first place. And if an actual threat to the third planet has manifested, not only would the path vanish, the entire Zone's hazardousness to outsiders would dial up to 11, and the entire system will literally be actively trying to kill you.
... Now that I think about, I need some way of drawing first-time visitors' attention to the path's existence. How about having free-ranging asteroids that hit the Zone's outer border and are physically repelled, except for those that happen to go through that particular path? With a brief "flare" of static electricity as a visual sign?
PS: If anyone is reading this and is wondering why a path would even exist if the third planet is supposed to be taboo, the intention is to tell visitors that they can only visit the planet in relatively small numbers and to leave the planet in question "unspoiled", otherwise there would be hell to pay beyond most mortals' nightmares.
Edited by MarqFJA on Jun 9th 2023 at 8:48:31 PM
Fiat iustitia, et pereat mundus.
Hmmm... The tunnel might show up on sensors, it occurs to me: After all, if the hazard-zone is detectable, then a localised lack of the hazard zone might be observable within that detection.
Otherwise, your idea works, or you could have a bit of a light-show accompany the tunnel.
My Games & Writing
Why make it obvious? Forcing your protags to figure out the path, maybe using some sort of future-tech sensor, might add drama to the scene.
The Cosmopolitan Fictioneer
Because none of the visitors are protagonists; they may be viewpoint characters for considerable stretches of narrative "time", but they're never going to be the protagonists, and in fact many of them will be outright antagonists in one shape or form.
Basically, imagine the likes of Archimedes Q. Porter and Clayton from Disney's Tarzan. That's what the out-system visitors tend to be like.
Edited by MarqFJA on Jun 9th 2023 at 6:51:29 PM
Fiat iustitia, et pereat mundus.
Oh, then you want to make the system defenses look dangerous while the antags cross it with relative ease.
The Cosmopolitan Fictioneer
Oh no, the defenses don't just look dangerous, they are dangerous. And really, if the antagonists could have things go their way, they'd bring a whole fleet chock full of enough mercenaries, corporate extraction crews, tomb raiders, etc. to establish a stronghold and start a full-blown operation to strip the entire planet of everything it's worth in within a few years/decades, leaving it a barren husk. As it is, they're forced to bring a far smaller party at any given time, only enough to escort some scientists as they survey the planet, and maybe snag some trophies for their trouble (which, unfortunate to them, is also a taboo, but one which will be punished in a far more "limited" fashionnote ).
Edited by MarqFJA on Jun 10th 2023 at 3:43:37 PM
Fiat iustitia, et pereat mundus.
Be careful, if your antags are not demonstratively stronger than the protags, then your story can lose some of its dramatic tension.
The Cosmopolitan Fictioneer
I have a planetary system created by cosmic entities note in which the third planet is essentially a guarded treasure, and the entire system is designed to provide ample warning to outsiders that they should mind their own business and leave that planet alone, or else.
For examples of the warnings:
Now, I want to make it so that visitors to this planetary system would be unable to make a beeline for the third planet in it; they can visit the fourth and outer planets in whichever order they want, but to venture further inside, they have to take a roundabout path that has them pass the second and first planets first before they can finally approach the third, regardless of the planets' positions at the time.
Can you guys think of any celestial phenomena or obstacles — even ones that flagrantly flout real-life physics — that would enable this, as well as make the visitors go "... WTF is up with this system?! This shouldn't be scientifically possible!" all the while? The setting is decidedly on the soft side of science fiction, if not outright science fantasy. FWIW, all I could think of right now is that any spacecraft trying to take a "shortcut" to the third planet will be beset by anomalies in the system's combined gravity well and the sun's stellar winds that threaten to destroy it in short order should it not quickly correct its course and return to the path it's intended to be railroaded on.
Fiat iustitia, et pereat mundus.