THS Rogue Planet

[tantric]

Remember Rogue Planet - a terrestrial planet passes through the solar system, dislodges Earth and takes its orbit....yeah, no. But the premise got me thinking - what are the real possibilities, astronomically? Say, a superearth iceball with a hot core. Just seems like it'd have campaign possibilities.

[johndallman]

There are quite a lot of campaign possibilities, but they're mostly for pretty science-ey campaigns. Read Arthur C Clarke's novel Rendezvous with Rama if you haven't already: it's rather relevant.

The first thing to decide about this planet is its trajectory. If it seems to be something that's fallen in from the Oort cloud, it has huge potential for illuminating the history of the solar system, as well as trying to figure out what perturbed its orbit.

If it's on a trajectory that implies it didn't originate in our solar system, it's really interesting, but it will be moving fast enough that it won't be around for long.

If it's in orbit around the sun, its period is a very important question, and I'd advise you to make it at least 5,000 years so there's no question of it showing up in historical records. That implies a very eccentric orbit, like that of a long-period comet, which is the only way it could have escaped notice until 2100.

If it's going to come close enough to another planet to perturb it significantly, or even collide, the solar system has a big problem: the technology to divert or demolish a large body isn't available.

Landing on it depends on its mass. Even with THS technology, a lander that can go down a Mars-sized gravity well and get its upper stage back out to orbit is not a trivial job. It may well be easier to send a one-way robot lander with SAIs who get transmitted back off the planet. One thing that will be of extreme interest is its isotope ratios: those can say a lot about its formation and its relationship to our system.

If it has life on it - that's a big deal, especially if it's not part of our solar system.

[Flyndaran]

THS is very good at astronomy. It's hard to imagine how they would have missed something so large anywhere near the solar system. If it still has a hot core, it should shine pretty brightly in infrared against the backdrop of 2 K.

I suppose its disruption of the oort cloud might be how they found it. Unlikely, I think, but possible. Still a major project to get any moderate sized expedition out there.

[malloyd]

Originally Posted by johndallman

If it's going to come close enough to another planet to perturb it significantly, or even collide, the solar system has a big problem: the technology to divert or demolish a large body isn't available.

A uniquely huge object that *just happens* to be a collision course with something is slightly more likely than one that is going to knock the Earth out of orbit and take it's place, but not by enough to make it too plausible. Sure, statistics of unique events and all, but it's in the meddling alien gods are more likely than chance range. Going to pass close enough to something to perturb it a bit is more reasonable.

If it is big enough to be spherical and originated inside the solar system, it's a hobby telescope target somewhere outside the orbit of Saturn, which means it's picked up at least a decade before it comes anywhere near the inner system. If it's periodic and big enough to perturb orbits, it's got a millions of years orbit or the perturbations from the last time would show up.

If it's extra-solar it can be moving faster than that of course and there hasn't been a previous orbit to worry about.

Landing on it depends on its mass. Even with THS technology, a lander that can go down a Mars-sized gravity well and get its upper stage back out to orbit is not a trivial job. It may well be easier to send a one-way robot lander with SAIs who get transmitted back off the planet. One thing that will be of extreme interest is its isotope ratios: those can say a lot about its formation and its relationship to our system.

If it has life on it - that's a big deal, especially if it's not part of our solar system.

I think TS technology can do a landing and return mission without much trouble, provided it's passing somewhere close to Earth or Mars, where there are vehicles capable of doing surface to orbit. There's a lot of space delta-v capability and in-orbit refueling is not hard, especially if you are willing to throw away your tankers rather than get them home again. If it's crossing the inner system at all, you should be able do a manned sample return mission to anything that isn't moving too many hundreds of miles per second if there is a good reason to.

[Johnny1A.2]

Originally Posted by tantric

Remember Rogue Planet - a terrestrial planet passes through the solar system, dislodges Earth and takes its orbit....yeah, no. But the premise got me thinking - what are the real possibilities, astronomically? Say, a superearth iceball with a hot core. Just seems like it'd have campaign possibilities.

If you want to stir up some scientific interest in the THS2100 world, let a comet come sliding into the Solar System on a hyperbolic path, at a high rate so it won't be in-System all that long. The point is that it's an object from outside the Solar System, at the very least it could be a McGuffin as the science community will want to observe it and take some samples (esp. if they can track its path back to a particular star, it's a change to get extra-solar sample data for that star system).

If you want to stir things up more, let the expedition discover alien tech or ruins or Whatever on the comet. It's a perfect temporary window of opportunity because the thing is going to swing around the Sun and fly back out into interstellar space again in short order.

If you want to stir things up a lot, let the comet be made of antimatter. That'll really stir up the science community, make the thing easily detectable a long way out to give time to do something about it, and have enormous military and political implications (a chance to lay hands on tons of antimatter at one cheap stroke).

If you want to gild the lily, let the anticomet still have ruins or aliens or whatever made out of antimatter.

[Flyndaran]

The scientific mission to the extrasolar comet could just be the backdrop for the story; why the crew is so out of contact with everyone and under so much stress and secrecy, regardless of the actual features of said object..

[malloyd]

Originally Posted by Johnny1A.2

If you want to stir things up a lot, let the comet be made of antimatter. That'll really stir up the science community, make the thing easily detectable a long way out to give time to do something about it, and have enormous military and political implications (a chance to lay hands on tons of antimatter at one cheap stroke).

I'm fairly sure an anti-comet would be detectable *too* far out to be very interesting.

Annihilation gamma ray peaks are very distinctive. Unless I've seriously blown the calculation, a chunk of antimatter a meter across moving at a typical stellar proper motion should be hitting enough interstellar hydrogen for the annihilations to be detectable with our recent gamma ray telescopes at half a light year. We might not have more than a few thousand years warning....

[Johnny1A.2]

Originally Posted by malloyd

I'm fairly sure an anti-comet would be detectable *too* far out to be very interesting.

Annihilation gamma ray peaks are very distinctive. Unless I've seriously blown the calculation, a chunk of antimatter a meter across moving at a typical stellar proper motion should be hitting enough interstellar hydrogen for the annihilations to be detectable with our recent gamma ray telescopes at half a light year. We might not have more than a few thousand years warning....

Good point. Of course that could just be incorporated into the McGuffin of it: "Why did we not pick this signal up sooner? Why did we only start picking up the annihilation signature when it's a year out?"

[jeff_wilson]

Originally Posted by Owen Smith

What happens if it's a Dark Matter comet? Do we only detect it then by it's gravitational effect on the rest of the solar system?

(Yes I am aware we have no clue what Dark Matter is, or Dark Energy, and hence we have no idea if a Dark Matter comet is even possible. But it's cool.)

Yes; "dark matter" was invented to explain why galaxies appeared to rotate faster than their luminous parts made necessary. More mass was needed to provide the gravity to bind their visible parts into the faster orbits, and "dark matter" fills the gap. Little or no other observations require additional properties than this, so it is hypothesized that "dark matter" has no other interaction with normal matter than gravitational.

So, a "dark matter comet" would be an invisible body of mass similar to that estimated for comets, but comets are aren't that big and are all about luminous streams of gas and dust and ions, so unless it happens to closely encounter an existing, small luminous body there will be no hint of its presence. But since it doesn't actually impact anything it encounters, it probably would do nothing but stir the aurora slightly even if it "hit" the earth.

[jeff_wilson]

Originally Posted by Owen Smith

OK so we need a Dark Matter rogue planet of significant mass to actually be detected and get people worried in THS.

Oh, I forgot for a moment how densely "occupied" the solar system is with infomorphs and probe shells; if the dark comet passed through the Saturn system, it could easily cause measurable disruption of ring particles and allow its path to be determined. There then might be a rush to examine it, and plots like "PLAN-SF will to interact by bombarding the dark comet with antimatter" could arise. Probably the antimatter wouldn't hurt or visibly affect the dark comet, but perhaps dark matter's "dark" quality works by some kind of electromagnetic cancellation process that might zap the anti-matter somehow, due to its reversed magnetism.