How big is Planet X?
They don’t know, because they have not found it. What the original paper said is that based on a statistical analysis, the probability is high that if one devotes sufficient resources to the search, one would have a high probability of finding a planet that is at least one third the size of Earth, within ten years. However, the probability is not 100% (meaning, maybe such a planet does not exist or maybe it exists and it will take more than 10 years to find it). The context in which the paper is prepared is that the group is trying to convince their government that IF someone gave them sufficient money, they could find this planet. It does not mean that they know that the planet actually exists. It is a bit like saying: in my town, people who walk sometimes find money on the sidewalk. Therefore, if I’m allowed to skip school and walk around all the time, then I’ll become very rich.
