Right now I'm really worried about my planets, because I alerted an 18x MR Irradiated with 23k attack, 800 defence. I failed at 6% chance, then a rank 400 took it. To me, that planet was amazingly well defended, so I'm really worried about defences.

So what kind of defences should the very best planets have?

18k cloak.

depends... what % chance to invade would you like your enemies to have?

and it's 18.5k+ cloak now

some legions can "safely" take a planet with over 300k invasion def if every player in the legion give it a shot...
and invasion def cap at ~200-250k w/o limited artifact and/or event boost(moon/the 30% def event thingy)

by "safely" i mean over 80% chance

so yeah..... cloak is the closest thing u can get to "safe"

exactly this...

no matter what kind of invasion defense your planet has, if enough people can take a shot at the invasion odds are good that someone will roll that lucky % and get the planet

although i can guarantee that nobody has anywhere near an 80% chance at a planet with 300k invasion defense though, someone with 50k invasion attack(which would mean they have an attack of 150k) would only have a 16% chance against a planet with 300k invasion defense. i believe that the person with the current highest fully buffed attack, has around the 45-50k mark, so only 15k invasion attack.

you're gonna confuse people by dividing by 3 and calling it invasion attack...

keep the 3x separate from the two values...

( total ship invasion attack ) / ( 3 x total planetary invasion defense ) = invasion chance

I said as a LEGION if EVERYONE take a shot.
Take a legion of say 30k atk each, 50 ppl
each person have 30k/300k/3=1/30 chance of succeeding
50 such players will have a chance of 1-(1-1/30)^50=81.6% chance that ONE of those person will get the planet.