Planetary Invasion Bug

Sorry I don't have an answer for your question, but ... attackers and inhabitiants are measured in billions?

What ship can carry 3.5 billion people. Soldiers. In gear. 

The more I read about this game, the more i'm put off.

Heh... it gets worse. Until those soldiers were loaded onto the transport, they were just normal citizens.

I posted this as a question in the last stream thread, I came to the same conclusion.  Don't know if anyone's filed a bug report.  It's a bug that positively effects the player (who's usually the invader) so certain people won't be inclined to

It has to do with planetary invasion mechanics.  Check out the WIKI, http://galciv3.gamepedia.com/Ground_invasions . It was very enlightening.  It explains resistance and the most important factor, planetary defenses.  If Planetary defenses are at 75% (from an Elurium Shield for example), then you lose 75% of your troops before they even land.  You can get planetary defenses well above 100% as well, without the Elurium Shield, using high end techs, or smartly placing the military buildings for max Adjacency Bonuses (and if you have a Military Bonus tile, its even easier).  

Planetary bombardment can help nuetralize planetary defenses, but a) its expensive huge pop death on enemy side, who you want to keep, or atleast have them replace YOUR losses c) huge approval hit.  I havent tried BIO or Informational warefare.  Info Warefare would probably have no approval hit, but probably not as affective.  And those propganda fliers and the fuel to drop them can get expensive as well

In your specific case however, they must have had good defenses (resistance and planetary defenses).  The proof of that, is that the surviving pop was less then your losses, so yo took a net pop loss, which is never good.

This is the opposite though.  All the numbers from the actual invasion seem ok to me.  It makes sense that I could have invaded successfully and lost roughly half of my population.  What doesn't make sense is that the population on the planet is so high.  I invade with 3.5 and the end result is an additional 1.8, for a total of 4.9.

I start with 3.5 and lose 1.8 

They start with 6.1 and lose 4.7

The planet should be populated with 1.7 of my remaining population, plus 1.4 of their remaining population. A total of 3.1

Somehow though the planet has a population of 4.9 after the invasion.

Either they aren't doing the math correctly or they aren't displaying the numbers correctly.

Perhaps your soldiers discover some clone bay... or maybe they discover some cryogenic capsule... who know... only devs can answer for this question... ohhhh i know, your soldier freed prisoners and they all decide to attache to your nation.

Sorry for my grammar

Or perhaps they went to the local brothel and caused a population spirt? (all 1.7B soldiers in a one tile brothel as well) haha.  ok, I do see your point.  I never bothered checking after the invasion to see if I'm getting 'cheated'.  Good to know, will keep a lookout.