Lately I've read some articles about the possibility of a Jupiter-sized planet hidden in the Oort cloud. This assertion is based on analysis of cometary deflections and observations of Sedna. What is the likelihood of this? We all know that there must be lots of planet-sized stuff out there besides Sedna, but Jupiter-sized? If Neptune and Uranus have been known for so long, then how could a Jupiter-sized planet remain undetected for all this time?