A long quest has ended: there is no tenth planet. But there may be a hundred or a thousand mini-planets in the dark beyond Pluto.
For more than a century, a few dedicated astronomers have braved the skepticism of their colleagues to champion an alluring idea: the idea that the known planets are not enough. In the dark and frigid boondocks of the outer solar system, these researchers have argued, there lurks a large, undiscovered planet, Planet X, whose gravitational pull is needed to explain why Uranus and Neptune have sometimes seemed to deviate slightly from the orbits astronomers (and Newton’s laws) have prescribed for them. When Pluto was discovered in 1930, some astronomers thought Planet X had been found, but Pluto turned out to be far too puny to pull Uranus or Neptune out of line. The search continued, long and fruitless.
Now at last it may be coming ...
