When attacking an enemy planet the second attack won't kill any population. The planet takes damage and I use 5 energy but the population stays the same. This happen to anyone else?

common bug. been around for awhile. somebody had some big technical explanation about the pop actually refiling past the max and the first attack being needed to fix that.

I've seen this happen quite a lot.

Yeah. It's actually the first attack that doesn't work. The population overfills. It reaches, say, 1000/100 population (though displays as 100/100) and the first attack does 20 damage, taking it to 980/100. Then, the game notices that it's overfilled and sets the pop to 100. Of course, he should make it check the pop before the damage is dealt and fix this bug completely, but it beats the alternative.

can't you just hit the planet with an arti before your first attack ?

that works on npc's that are teetering on the brink of death and you want your last (first) hit to count if it dies.

Works differently. With that, the artifact puts you on the damagers list. Essentially, you get rewarded for the artifact and not the attack.