Free Republic

...for astronomer Scott Sheppard of the Carnegie Institution for Science in Washington DC, it was a much quieter affair. "It wasn't like there was a eureka moment," he says. "The evidence just built up slowly." He's a master of understatement. Ever since he and his collaborator Chad Trujillo of Northern Arizona University, first published their suspicions about the unseen planet in 2014, the evidence has only continued to grow. Yet when asked how convinced he is that the new world, which he calls Planet X (though many other astronomers call it Planet 9), is really out there, Sheppard will only...

Over the past few years, researchers have noticed an odd clustering in the orbits of multiple trans-Neptunian objects (TNOs), which dwell in the dark depths of the far outer solar system. Some scientists have hypothesized that the TNOs' paths have been sculpted by the gravitational pull of a big object way out there, something five to 10 times more massive than Earth (though others think the TNOs may just be tugging on each other). This big "perturber," if it exists, may be a planet — the so-called "Planet Nine," or "Planet X" or "Planet Next" for those who will always...