There's a going theory out there that an undiscovered planet resides in our solar system somewhere beyond the orbit of Pluto. But NASA just finished an exhaustive survey — and it completely failed to turn up any evidence that "Planet X" exists.
Researchers working with NASA's Wide-Field Infrared Survey Explorer (WISE) put it fairly bluntly.
"The outer solar system probably does not contain a large gas giant planet, or a small, companion star," noted astronomer Kevin Luhman in a statement.
The scientists recently poured over WISE data covering the entire sky in infrared light. They say no object the size of Saturn or larger exists out to a distance of 10,000 AU, and no object larger than Jupiter exists out to 26,000 AU. Pluto is about 40 AU from the sun (AU = average distance of Earth to the sun, about 93 million miles).
One of the reasons for the so-called Nemesis Theory is the apparent observation of periodic mass extinction events on Earth. It's conceivable, say scientists, that a rogue planet sweeps in after a prolonged sojourn in the solar system's outer region, perturbing the asteroid field as it comes back in and sending these objects flying towards Earth. This theory has largely been discredited (even before this latest survey), but other theories based on irregular comet orbits also predicted a Planet X-type object.