Claims of superplanet found on edge of solar system met with skepticism

Ars Technica : Small apparent anomalies in the orbits of our solar system’s exterior planets have occasionally been attributed to an undiscovered “planet X,” but observations have continued to discount the possibility. However, in papers posted to the arXiv eprint server, two teams that used the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile claim to have spotted a point source emitting blackbody radiation far beyond the orbit of Pluto. One of the possible explanations they present is a large rocky planet about six times as far from the Sun as Pluto at its most distant. The teams also propose that the object could be a brown dwarf star about 20 000 AU from the Sun. But astronomers have been skeptical for two reasons: ALMA’s field of view is so small that it is unlikely it could have found such an object, and NASA’s Wide-field Infrared Survey Explorer has ruled out the possibility of a planet larger than Saturn out to a distance of 10 000 AU and of a planet larger than Jupiter out to 26 000 AU. As the papers go through the peer-review process, it is likely that other explanations for the point source may be found.