For decades astronomers have searched for a possible “Planet X” in the far outer reaches of our solar system, speculating that something big and dark may be lurking out there, its gravitational influence occasionally stirring up trouble in the orbits of the objects that we do see. There are major incentives to look: When astronomers sought a Planet X beyond Uranus in 1846, they discovered Neptune; when they looked for one beyond Neptune in 1930, they found Pluto. Since then, the search for a Planet X beyond Pluto has almost been too successful—astronomers have found so many new and Plutolike “trans-Neptunian objects” (TNOs) that it became more sensible to demote Pluto from planethood rather than swell the solar system’s planetary population into the hundreds. After all, even the largest of the newfound TNOs were just about Pluto’s size—astronomers knew of nothing out there worthy of the “Planet X” name.
That is, perhaps, until now. On December 8 researchers from Sweden and Mexico quietly submitted two papers to the prestigious journal Astronomy & Astrophysics, announcing their discovery of not one but two possible Planet X candidates. The quiet did not last for long. Even though neither paper has yet been accepted for peer-review and publication, the researchers uploaded both to the arXiv, a public online repository for preprint papers, where they appeared last night. Today, as claims of newfound planets in our solar system reverberate around the world in news stories and blog posts, other astronomers are reviewing the papers and reacting mostly with skepticism. The ensuing discussions between experts in public forums like Twitter and Facebook offer a rare, real-time glimpse of the sometimes messy scientific process as it unfolds.
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