Every so often, a fleet of tyranid forces will land on Earth, listen to radio 99 for when that happen and for quest info. Usually the UFO researcher will inform you on the broadcast radio channel. Defeat them, earn tokens, and turn them in for quest prizes.
Note: This is different from the global rifts eventmobs system where shards drop.
Sample broadcast: A UFO researcher broadcasts, 'Help! Help help! A large fleet of tyranids just landed near Neo-Chicago at Electric Avenue; Ruined Section! Somebody, anybody, help!' A UFO researcher broadcasts, 'If you are above level 10 and brave of heart, come help defend Earth for every living thing's sake!' A UFO researcher broadcasts, 'Find me and join my quests...before they do!'
The broadcast gives you the clue of where the invasion is taking place. In this caes, it's near Neo-Chicago at Electric Avenue; Ruined Section. That's the zone and the room name. Once you know the general area, you should race to him as soon as you can. The UFO researcher suicides after about 2 minutes, so be quick if you want to take the quest. If he suicides before you get there, you are out of luck until he broadcasts again.
The quest consists of one of 5.
Kill One Eye (non-repeatable)
Kill 100 rippers (level 10-15)
Kill 50 genestealers (level 15-20)
Kill 50 hormas (level 20-30)
Kill 10 spore pods (level 30+)
The rewards consist of quest points, small exp and money, and the most important, a defender token. Go to Linux in the Rift Tower to take the defender token quest (but not until you have enough tokens to hand in). Hand in 5 tokens, or 10 tokens, or 20 tokens and he will give you randomly one of many prizes based on the quest level. For example, if you take the 10 token quest, he will randomly give you one of the 10-token quest prizes. It's possible you may get the same 10-token quest item over and over, and it's possible you may get a new one each time you hand in 10 tokens, likewise for the 5 or 20 token quests.
After level 24 you stop gaining ripper exp.
At level 30 you stop gaining genestealer exp.
Max ripper exp is at level 20.
Max genestealer exp is at level 25.