This happened after you completed the challenge to unlock the Outbreak Prime quest. It is a known issue but they are not going to fix it, it will just reset after the weekly reset. There won't be a heroic mission on earth for you to complete as the weekly flashpoint for everyone else is on Titan. I have it that way on two of my characters and one kept Titan (one went to EDZ and the other to Io). Not much can be done, just do public events / lost sectors and it will complete for you.