Here's a link to another article that mentions the argument for the planet Tyche:
Planet TycheSome of the advocates arguing for the existence of the planet have been doing so since 1999. From what I understand, it's all theoretical. They haven't "discovered" a new planet. Scientists and astronomers just think that there must be a gigantic planet way out in the outer reaches of our solar system and have theorized its size and what its made of because of data they have compiled. Based on the way comet trajectories that originate from that area of space and other factors, makes them think that there must be a gigantic planet out there whose gravitational pull is affecting them.
But, again, this is all just an argument based on evidence. It's sort of like detectives looking at a crime scene and using the clues to say "the killer must be like this, and act like this because of the evidence left at the crime scene." They haven't proven anything and science is about proof. It makes sense that a huge gas planet would be out there, but they haven't been able to locate one or prove it yet, so they've been trying to argue that it exists because they want to get the funding in order to find out for sure. But since it costs so much money to research a thing like that, the people providing the money (government) wants to make sure it's "worth it" and not some huge waste of money.
What I was saying in my previous post, is that the case for planet Tyche's existence must be gaining momentum and credibility because it seems (based on the new article) that more scientists are beginning to consider the possibility that this planet exists. The more evidence that is collected that seems to point to it being out there, the more likely they will spend the time and money to make sure.