Here's a fun little bit of speculation that I sometimes engage in: what is the Solar System like in the 41st Millenium? What Imperial Organisations are based on which planets? Who has embassies on Holy Terra?

There's a fair bit of fluff on this, but it revolves mainly around Terra, Mars, Titan etc. I like to speculate about links between major Imperial Organisations and certain planetary "real estate" in the Solar System.

One would imagine that Terra is one of the most crowded and overpopulated worlds in the entire Imperium, the ultimate shrine world and the ultimate hive world rolled into one. Every Imperial organisation of any size is probably based there...

Mars is of course the original and archetypal Forge World, the home of the Adeptus Mechanicus.

Titan is the home of the Grey Knights.

That's pretty much all we know for sure...everything else is speculation. And I love speculation. Here's a few of my thoughts:

On most other Imperial systems there will only be one habitable world, a handful of space stations and a selection of uninhabited rocky plantes and gas giants.

In the Sol system, the situation would be much more complicated. The solar system is going to be massively overpopulated. Its vast population and importance would probably mean that even the tiniest moon and planetoid is inhabited in some way by some organisation or embassy that struggles for the attention and time of the High Lords. It would be a bit like in a big city where rich professionals pay vast sums for tiny and squalid apartments just so they can be close to the action...but on a vast scale. One would imagine bidding wars for properties or spaces inside minor planetoids like Ceres changing hands for the price of whole subsectors out in the wider Imperium.

Every asteroid or planetoid is likely to be riddled with tunnels, hab-chambers etc. System ships of all sizes and shapes, from one man shuttles to Monitors the size of battleships flit from planetoid to planetoid like fish or plankton in a coral reef. Space would resemble the sky over a busy airport, with thousands of tiny lights flowing back and forth.

Earth's Moon would (I imagine) be the base of the Battlefleet Solar, but I imagine it's also dotted with cool abandoned fortresses previously owned by the Lunar Wolves (cf Sones of Horus, cf Black Legion). There may also have been attempts to terraform it in the past: perhaps these were successful, perhaps not.

Venus almost certainly remains uninhabitable, but may have heavily shielded subterranean mining bases. Plus it MAY have some link with the Morning Stars Titan Legion, given that Venus is the Morning Star. (I know a morningstar is also a weapon, but the Imperium is capable of giving things a double meaning...)

Mercury is probably very similar, but maybe has lots of Admech facilities for observing the sun.

Jupiter almost certainly remains uninhabited, but its moons are a totally different story. Worlds like Europa may even have habitable atmospheres and rich histories of independence from Terra following thousands of years of terraforming and isolation during the Dark Age of Technology. Certain moons may be Inquisitorial fortresses, or the homes to peculiar traditions, mysteries or industries. Maybe particularly powerful Navigator families live on some planetoids...maybe they form Ghetto worlds where rich Navigators from across the galaxy congregate and intrigue against each other?

So...any thoughts? Which Imperial organisations might be based in some of the more obscure Solar Syatem planets, asteroids or planetoids?

I always imagined its really not a place your can go wandering around and the inhabitants at hillbilly levels of shoot-first, who cares. The kind of security, sensors and armament levels beyond a joke, because lets face it, there's been about a dozen or so Black Crusades that went gallivanting around the galaxy, nids, eldar and god emperor knows what else wandering around blowing things up and "lookin 'ard"... but no one seems to actually want to go to Terra.

Its not like its hard to find, great big becon and all, even Cletus the halfwit, inbred navis can find it at least some of the time

But for some reason none of the Chaos, Orks, Nids, Eldar, Tau (lol) or anyone else with aspirations of granduer just said "Bugger it, we're going to earth and finish those bastards off once and for all so we might have our rightful place in the galaxy"

Well they might have, but instead found arsehole tearing levels of firepower they didn't actually bother recording it. I think if you are going there it might be worth letting them know your coming

Yeah, I think you could be onto something there, MKX...I guess it's a bit like the White House: everyone knows the big guy's there, but it's so well guarded that no one expect the truly insane would ever try and get to him there. Humanity's greatest enemies probably prefer to nibble away at the edges of the Imperium rather than attack it in its heartland.

For what its worth and sci-fi writers are often ignorant of, is Jupiter as a natural defence of the outer parts of the Earth solar system.

That big ugly bastard puts out so much radiation (and Saturn to some extent) that its really just not funny and it does radiate more than it receives from the sun, its not of enough mass to become a small red dwarf or anything like that, but rest assured without something extraordinarily hardened... and then harden it many, many magnitudes beyond what would be considered sensible and you might just be able to fly past it without cooking your crew in minutes.

It literally is that bad, a normal guy in a normal spacesuit would be dead in 5 minutes just running around the surface of one of its moons and its radiation belts cover a very large part of this solar system. To survive on those moons you would need to be very deep underground, which sort of limits them as a manned defence platform- automated however is another story.

Saturn is just as terrible as Jupiter for radiation but not as far reaching, its still up there with 'very bad places to be if you're made of meat' for a place to live. It has satellites and they're all fairly awful places to be.

Uranus and Neptune are possibilities for somewhere on the outer planets as they don't radiate as much, but still cop it when Jupiter goes floating past. Both also have satellites you could hang around on provided you can keep them warm and heavily shielded enough. What is of interest out that way though is the Kuiper Belt which is beyond Neptune (mostly) and has a lot of very large (100,000+) floaty bits of rock and ice that would lend themselves to something of an outer defence/sensor grid for anything on the way in. Pluto and Charon are the biggest bits of rock out there.

Inner planets.

Venus is a complete sh*t hole full of nasty corrosive acids and running at 400degC all the time and more trouble than its worth, then bombard it with lethal levels and then some of radiation from the sun. It's about as rubbish as it gets in its current form, it has no magnetic field to hold its atmosphere with so there's something down there spewing out a lot of crap into whatever passes for atmosphere. No satellites.

Mercury would be worth mining. Its got a massive density for its size suggesting an extremely high amount of iron, it would also be quite terrible in fairly much every possible being right next to the biggest nuke reactor in the whole system. It also produces some fairly weird magnetic/radiation effects that you dont really want anything to do with.

Mars, Earth, its been covered to death. The asteroid belt past Mars though is up there for infinate expansion of people, space defences and exploitation of mineral wealth that would keep humanity busy for many millenia. What is also out there is the Hilda, Greek and Trojan asteroid belts that are sort of around the same orbit as Jupiter or a little closer to Mars depending on how you view them... just in case you got bored mining and jumping around all the others. The only limits there are logistically ways of supplying adequate air, food, water and gravity to anyone out there, however in the great tradition of humanity, there's probably a half-arsed way of doing it badly...

Considering the Dark Age of Technology, what all those planets look like right now is pretty much anyone's guess, especially since they alone in the Imperium never suffered from being cut-off from the main AdMech world.

It has been mentioned in canon a couple of times that Jupiter has particularly extensive shipyards. The League of Blackships seem to get thier vessels from Jovian docks, and vessels for the Adeptus Astartes are produced there, if memory serves

MKX said:

For sufficient protection, how thick an armour plate are we talking ?

How thick is the armour on Imperium vessels ?

When you say radiation do you mean ionising radiation (from radioactive stuff) or it a more general sense (the rest of the light spectrum) ?

I haven't heard anything about significant ionising radiation from Jupiter and can't see how it would be produced, but I can see how Jupiter could be hotter than the Sun alone would make it which would cause the rest.

Having manned stations on the moons is quite dangerous from the information I have just read but considering the technology that is being hypothosised in 40k literature with gun barrels the size of my uncles propert and shields that take nuclear bombs to the chest and no harm done, ships that fly within touching distance of a sun... that it is realtively easy to create shileding for a vessel (esp if it is already needing to be Warp capable) to travel near.

Also the radiation belts appear to be mainly along one axis of the planet and so having space stations and gun batteries etc along a different axis will also alleviate the problem.

Jupiter Produces a lot of electromagnetic radiation across the whole spectrum.but imo, the Imperium would have to have that problem 'solved' to be a successful galaxy spanning civilisation.

Personally I'd say every square inch of physical material would have 40,000 years of accreted human occupation.

Notably I would argue.

• Mercury no longer exists, mined to dust.
• Venus is habitable, though it geologically unstable due to extensive mining.
• Mega engineering structures at Lagrange points. ruins of implausably massive structures constructed in the DAoT, now converted into void Hive cities, weapons batteries, dockyards, etc.
• I'm pretty sure its canon that Luna is one massive battlestation.
• Ganymede is destroyed/Quarantined (pretty sure this is still canon, but it might not be anymore)
• Asteroid belts are heavily populated, the likes of Ceres are honeycombed pseudo-hives
• there is debris everywhere, the whole solar system is covered in floating mess, from broken and ruined starships to clouds of dust and ash.

For sufficient protection, how thick an armour plate are we talking ?
How thick is the armour on Imperium vessels ?

When you say radiation do you mean ionising radiation (from radioactive stuff) or it a more general sense (the rest of the light spectrum) ?

I haven't heard anything about significant ionising radiation from Jupiter and can't see how it would be produced, but I can see how Jupiter could be hotter than the Sun alone would make it which would cause the rest.

It produces the whole spectrum of goods when it comes to radiation, ionizing and non-ionizing

Io for example cops about 3500 rem a day just from Jupiter alone in addition you've got cosmic radiation from the sun and anything else floating past, Europa gets 540 a day (500 a day = you're dead). Ganymede has a magnetosphere which reduces the down to about 8 (a heavy CT scan) and Callisto might be far enough away not to get barely anything (almost earth-like). They're the moons of note which people think might be worth doing something with as they're quite large.

Basically, Jupiter is effectively a very weak pulsar, not the "fun space-anomaly" thing people check out in sci-fi movies and literature out of curiosity, its the run the opposite direction kind of "crap its gunna kill us!" event. I'm specialised in RF (non-ionizing) radiation as part of my job, but there's an effect which most of these big planetary bodies produce radiation by compression of the planet by its gravity, that causes it to heat up and begin emitting. For the life of me I can't remember the name, Kelvin/Kevin-Helmsomeone effect or something... crap

It's really not somewhere you want to build a shipyard unless you're doing it with automated units. That said, space is an extremely hostile to human life environment with radiation and at some point, humans will have to find a way around avoiding it. Just had to go digging through my notes back from when I was doing stuff for other games and worked out that you need about 50kg of Lead per tonne or about 25kg of Gold per tonne of ships mass to keep out the worst effects of radiation (Alpha and Beta), but there are some (Gamma) which will fly right through the material protection... So, that got abandonded as being unworkable in the game system and I lumped into simplicity of being either figured into the ships chassis with some kind of counter-shielding of advanced technology to create a magnetosphere (or something!) around the vessel and protect it from Gamma radiation, while not cooking the inhabitants.

Thanks for the Details MKX, I love that stuff .

As I recall lead in fact enhance some radiation (fast neutron?), as its so dense, it knocks a lot of neutrons out, making the lead itself a hazard. Given what a hazard radiation is for space travel and how much space weapons would make (ie: terrifying amounts) Imperial ships would have complex, multilayered Radiation defense. Void shields would logically keep out at least some electromagnetic radiation (what's a laser after all) and their hulls are very thick, often mentioned being meters thick, theres enough in there for a variety of materials to absorb different types of radiation.

I think any Jovian shipyards would be massive enough to have battleships in drydock, so you wouldn't have any guys foating around in space suits soaking up all that rem.

Given there's no mention of a dedicated shield anywhere, I'd imagine that they've come up with a special alloy of some sort, set up kind of like a Faraday cage to keep out electromagnetic radiation across the spectrum like a whole heap of polarising filters. It might well be for the sake of simplicity that the actual hull keeps it out.

I do remember from the old BFG tabletop effects there was a number of things like fighting sunward, radiation bursts and solar flares that would mess up your fleet, so maybe the problem is still there to some extent that the technology cannot completely compensate for. Anyway, got to run... work and all that.

Agmar_Strick said:

The process is called Bremsstralung, and essentially it's the production of radiation by slowing down other radiation - in this instance (if memory serves), slowing down neutrons and producing x-rays. You need a less-dense secondary shielding material, such as perspex, to prevent it

To my knowledge, everything that has been covered (Besides Titan being The GK homeworld, Mars being the AdMech home, Luna being a massive defense station of doom, and Terra) that I know of. I didn't know Ganymede was under Quarantine.

Only other stuff I can think of in the Sol System is the HUGEMASSIVEOHGODEMPRAH Sol Battle Fleet, which takes a good chunk of room on it's own, and is the biggest in the imperium.

All this radiation stuff is very interesting: I was aware that radiation in space was a problem (more from the old Near Space supplement for Cyberpunk than from any actual formal scientific research) but I didn't realise it was that intense around Jupiter!

I suppose the typical 40k answer would be "Oh, don't worry about radiation, it's neutralised by..er...void shields, yes, let's say void shields." Rogue Trader talks about how void shields are an essential ship component because they are used to protect the ship from stellar phenomena, which I guess would include radiation...But it would be nice to have a more rounded scientific rationale for inhabiting the worlds of the solar system.

Would the inner Jovian satellite moons be habitable within their cores? If the Imperium decided to create deep subterranean tunnels/mines/bunkers way below the surface, would the radiation penetrate that far?

Alternatively, if any of these moons were terraformed - given nitrogen/oxygen rich atmospheres - would these protect from radiation to some extent?

I'm pretty sure its canon that Luna is one massive battlestation.

But it's still a moon? That's going to put Obi-Wan into some trouble...

Agmar_Strick said:

I'd agree with every square inch being used. And yes, 40,000 years of human junk would certainly have accumulated , too. Whole sections of Terra or other Sol worlds probably look like the junk bound Earth in the Pixar movie Wall-E. You might even have a junk planet, a place where all the junk is dumped, to later be picked apart by Mechanicus.

I was all set to argue with your idea about Mercury being mined to nothing, but then I checked on Wikipedia and saw that it has one of the highest iron contents in the Solar System. So maybe...

Venus...I have to say I can't see it's surface being habitable, but perhaps, given the availability of void shields/tunnels under the surface, it could be massively populated under the surface? Perhaps it's an Administratum commuter world? A world where the drudges/clerks of the Adeptus Terra live, and commute daily to Terra for their day job. There are precedents for people living in virtually uninhabitable hellholes and travelling via dangeorus journeys to tedious jobs...look at Croydon.

I'd agree with the mega engineering structures, perhaps things like Babylon 5 or the O'Neill cylinders are really common, relics - just as you say - from the Dark Age of Technology now put into new uses by the Imperium. That's a very cool concept.

Yeah, I'd got the same impression, that Luna is the ultimate military fortress, but I can;t recall where I'd got that idea from. Is it the base of the battlefleet solar, or am I imagining that?

I didn't know that about Ganymede...what's going on there, then?

Yes, I imagine the asteroid belt is heavily populated, especially the larger asteroids. If you're a mega rich trillionaire or industrial combine looking for a base in the solar system, a large asteroid could be converted into a floating palace: cheaper than a true planetoid or dwarf planet, but larger than a space station.

And yes to millions of tonnes of space junk. The Battlefleet Solar probably spends as much time sweeping up the junk as patrolling!

Probably dozens of little tribes of void born scavengers running around the system trailing the navy ships and collecting what falls off, mining their respective dirtball for water, gasses and metals. I could both see them being loved and hated by the IN, on one hand it would make for fun shooting practice in an otherwise boring place and on the other, they pick up all the bits and pieces which could potentially (and embarrassingly) hole your cruiser.

Lightbringer said:

Heh, typical 40k answer would be wrong because then they'd have to retcon Monitors and other non-warp capable, non-void shielded ships... the Orky answer of course "We iz tuff", the Eldar answer would be something poncy-rubbish about wraithbone and no one really cares what the Tau think because theyre space going peons of the galaxy

I've not done the maths on just how deep the penetration of radiation would go from Jupiter, it involves lots of calculations about radioactive push, density, presence of a magnetosphere... and I'm just a broke arse scrub who makes wireless networks work, not an astrophysicist. However, not to be completely useless, I do remember seeing a documentary some years ago which suggested that habitable regions on those moons would be under several hundred metres of ice or rock. Things like Gamma radiation will always penetrate that to some degree, but it will be reduced to a safe level under enough of it, things like Alpha and Beta ionising radiation don't really penetrate that far.

The main key there to terraforming which sci-fi authors ignore is something that is quite hard to make- the Magnetosphere which is basically a whole arseload of molten metal running around under the crust of the planet, its the one thing that stops Earth from being another radioactive, blasted rock from the solar winds (more on them later) If you have a weak magnetic field like Mars, the result is quite obvious, it turns into a dustbowl with a thin atmosphere and bombarded by radiation to the point its mostly uninhabitable. Its theoretically quite possible to make a lot of atmosphere around a planet with enough energy, time and raw materials (like in Total Recall)... actually keeping it there requires a magnetosphere or it'll just go floating off. Atmospheres also function, as we all know when we burnt off large chunks of our Ozone layer with CFC's, to block various wavelengths of radiation, retain heat and they extend out quite a long distance from Earth.

So its a bit more than just pumping gas into the surrounding area around a planet, I have no idea of how to make magnetosphere easily, the forces involved would literally be titanic to cause the magma below to behave in a predictable manner.