This method is best suited for detecting massive planets located near their parent star, and it can only estimate the minimum mass of such planets. (science.howstuffworks.com)
It's also not clear how massive a planet can be and still have a solid surface for life to take hold. (sciencenews.org)
A less massive planet, such as one made entirely of gas, would not be able to hold together in such a tight orbit. (sciencedaily.com)