While asteroid belts are not planets per say, they can be worthwhile to to colonize.

Thier biggest drawback is they are always tiny in size, cost 50% maintenance surcharge and you cannot grow food there.
Thier biggest advantage is that they are usually Ultra-Rich and always low G with -100% pollution loss. That means you can get massive ammounts of production out of them, but at a high maintenance cost.

Proerties:
- Extra pollution has no effect
- Low farming only has little effect
- usually Ultra Rich, with rare cases of Rich or Abundant. Also low G (no -25% gravity penalty as many other Ultra rich worlds)
- Cybnetc races have a natural advantage, as they effectively get Androids for free. Photosynthehic races can also get a lot out of them (lower food import/production need). So do subterranean.
- You need bigger habitats. If you get enough of them buildings with "per worker" effect start bringing more then flat bonus buildings. Asteriod Habitats, Acrology, Biosphers - the works.
- You also need a way to feed that population. Easiest way is being cybernetic, photosynthethic or getting Androids asap. Till then then food imports, molo farm, flat bonuses (like Aeroponics Farm) or agricentric races might be worth a look. Food imports make your freighters more vulnerable, but a properly set-up asterod can out-produce any raiding. Still, if one farmer racial or building can feed your entire population that is a big boon.
- They seem not prone to have negative environmental effects, but the same appears to be true for positive ones.

These appear to be a subtype of Asteroid belts, with all the drawbacks and bonuses.
During my test-colonisation I found no apparent bonuses, penalties or specail spawned buildings but they might still exist.

These planets can be very interesting for ship production, but they rarely have good production and very high maintenance.
Most of the stuff for asteroids applies to them too, except they are not guaranteed to have many resources, be tiny or low G.

If you don't got a lot of production, consider only making ship hulls+crews here to get the bonus and retrofit them at another planet (like an asteroid belt or arid world) to thier "full power" versions.

Properties:
- If you produce a lot (actually a little is enough in 1.0d), they spawn a "Hellfire Forge". This ups Ship hulls build here by +15% HP, but you also loose 15% more to pollution (as of 1.0d, they actually loose 15% less rather then more to pollution. That might be a feature of toxic atmosphers or a bug).
- they can get the following specials: "Fire Elemental" (-75% growth), "Beautifull" (+15% approval), Diamong Rain (+6 BC). Then can contains strategic resources
- Again Cybnetic races and Androids have an advantage. But so can have Photosynthethic and subterranean races. Still they do suffer the maintenance penalty.

Another planet that cannot produce food (except with right lategame tech or molo farms). But at least it does not carry a maintenance surcharge. That measn they might be a good place to colonise, depending on the situation.

Properties:
- Cybernetic, Photosynthethc and Android populations have an advantage.
- no maintenance surcharge
- you can put the Subterranan Farms here for cheap, efficient Farming. Molo Farm can be used until availible

Take a barren planet and add +25% maintenance surcharge. You got a radiated planet.

They are slightly less bad then toxic worlds, if you want them for strategic reasons. That is about all that is good about them

Finally a minimally fertile planet, but with a +25% maintenance surcharge.

Properties:
- While they only allow one food per worker, that is rather constant across them
- seems to be normally prone for positive effects and resources, but little for negative effects
- hgher maintenance cost
- a Desert planet calld Dhorn contain the Dhorn Race (good HP, average workers, no High-G trait, can give quests if not conquered, 3R action, Hire Ground Forces)

Tundra is better then Desert, as it allows 1 Food per worker without the maintenance surcharge. Most of the times.

Properties:
- they are rare
- they are exctionally likely to have special properties or resources
- they also appear to be outright cursed with positive or negative effects that remove the Food production (at least for me)
- they can spawn the "Winter Resort" building (+2 BC, +10% approval)

A subtype of Desert without maintenance penalty and good population cap. Very resistant to pollution, hence good candidate for ship building world

Properties:
- x3 Population cap multiplier, with all the ups and downs (see Terran)
- 1 food per Farmer, but might contain an ocean (another +1 per Farmer)
- no maintenance surcharge
- appears rather rare
- Counts as Desert for "Rhigar, Noble Capitalist"
- Can spawn the "Massive Junkyard" (-10% Approval, +10% Ship production) even when not actively producing ships; this might be pollution based
- the Arid Planet Prissia might contain a minor race (Lazy Workers, Buy nice Rug [+5 Diplomatic Relations])
- unlike terran worlds seems virtually immune to pollution

Very easy to populate and support population. Thus exceptional tax income.
By default starting planets are medium terran planets with normal G, but racial traits will modify that.

Properties:
- they have significantly higher population quotas. They have 4 times what a planet of thier size normally would have.
- they are incredibly rare. Chances are good that the only ones in the entire game are starting planets of other races. Wich means racial traits may affect them heavily (including making them high G, low G or different subtypes)
- expansionist cultures tend to be very focussed on getting these and are very likely to go to war over them if they see one - even your homeworld
- appears to be always subject to loss of farming from pollution
- cybernetic and android populations can use the planet primarly for large amounts of workers
- considerable income can be generate via tax or Food Surplus sales. Later tends to atract Agricultre exchange, wich halfes how much food you need to cap out that income
- due to thier abilities to produce a lot of any resource for a time, they attract producion buffing buildings like flies

The starting planets for Aquatic races

- fertiltiy of Terran world, but without population multiplier
- Triggers full power version of aquatic trait
- May have beatifully, deep sees, sharknado or treacherous sea trait
- The Ocean planet Hurmglub might contain the Hurmglub race (3R action, 200 BC for extra approval in entire empire). Hurmglb.

Swamps appear to work like terran worlds, except they only have twice the population capacity of thier size.
The swamp planet Klatak is inahibted by a minor race.

The Gaia type is a Terran type, except better in all regards

Properties:
- Incredibly rare. Might not get even one naturally occuring in a 100 system galaxy
- Terran planets terraform into this via terraforming, wich removes the terraformer;
- may spawn the "tropical resort" (+10% approval)
- 3 base food per farmer
- Population limit 5 times what is normal for thier size (note that terran is already 4 times, so only a minor increase)
- Same resistance to pollution as terran worlds. Previous debuffs are taken over

If you cause a lot of pollution on certain planets, you aqurie a debuff to food production per farmer on said planet.
It is not 100% certain wich planets can be affected by pollution in this way:
Gaian and Terran are always subject. Terran subtypes are propably always affected too.
Tundra appears to be subject if the population exceeds an unknown treshold (around 10; should only apply to subterran races).

What appears certain is that continued subjection to 20 or more pollution causes the debuf to appear (if the planet is succeptible). Long subjection to less pollution is nessesary to remove it.
There appears to be only one level of this debuff, but really high population planets might get aditional ones.