Planet Nine - a newly proposed but not yet confirmed world perhaps 10 times more massive than Earth that's thought to orbit far beyond Pluto — probably could not have triggered such "death from the skies" events, researchers said. Planet Nine likely has an elliptical orbit, coming within 200 to 300 astronomical units (AU) of the sun at its closest approach and getting as far away as 600 to 1,200 AU, Brown said. (One AU is the distance from Earth to the sun - about 93 million miles, or 150 million kilometers). Neptune orbits about 30 AU from the sun,...