So I'm a little late on this (started on Wednesday), but WAR HAS BROKEN OUT
Alad V, the corpus foreign relations dude (and soon to be stage boss) finds a bunch of tenno in stasis even the lotus isn't aware of. He immediately takes them and attempts to turn them into super weapons, without informing the grineer. Sargas Ruk, grineer orokin tech hound, finds out about this, and demands he hand them over. He doesn't. So now the grineer are rolling over mars and enslaving corpus colonies.
Basically here's how it works, every planet has battle pay. This can be anything from Potatoes to morphics for grineer, and primarily credits for corpus, although they've put forth some potatoes and blueprints (vauban helmet blueprint up now actually), when you fight five successful battles for a planet on one side, you get their battle pay. The missions are exterminate missions with a special map, and a ton of just stuff going on. You periodically hear missles impact the ship, explosions, alarms, the stage is always on fire, the screen shakes periodically etc. If you fight for the other side, it adds one point to the battle pay for that side, and reduces the battle pay for the other side should you have any. So stick to one side per planet at the very least. When a planet is conquered by the grineer, it changes the race on that planet to grineer, when it's defended it stays corpus. I would be surpised if this doesn't leak into phobos as well, with corpus being on the offensive. This thing has a week to play itself out, then a winner is declared, judged by how many factions own planets. The most win. It's looking a little leaning towarrds grineer now, but if nothing else it's a good source of credits rare mats, and the occasional potato/hard to find BP.
Naturally there are end event rewards, detailed
here. So yeah. Take out the corpus to get the tenno they took back, or help the corpus and prevent the grineer from holding an even larger amount of space? Also preventing the whole enslavement of entire star systems thing. It's kinda fun honestly! Missions are fairly hard for exterminate, corpus got a new unit with a flux rifle that just melts through you, and the grineer have more flame launcher troops then you can shake a stick at. Soloing is difficult at best with all the fire pits around, and even team matches tend to get chaotic.
So yeah. That's happening. Go to mars to participate!