Ars Technica reports The Solar System may have two undiscovered planets
"The presence of the closer of the two planets had already been suggested in a previous work. The new study provides more evidence for its existence and adds a second planet. Both studies are based on observations of objects far beyond Neptune’s orbit, called extreme trans-Neptunian objects (ETNOs). These ETNOs display shared patterns in their orbits, which suggests they’re all being influenced gravitationally by heavier objects, much further away from the Sun. While this conclusion is based on a small sample (13 bodies), the authors confirm that their results are statistically significant and that at least two planets, orbiting far beyond Pluto’s orbit, are the most likely explanation for the observations."