What will it take to confirm the existence of “Planet Nine”?
AH: An image of the purported body will do the trick. The trouble is, it's a big sky up there and no one knows exactly where to look. The rough alignment of the orbits of several non-planetary bodies in the outer solar system give only a general sense of where the object may lie -- if it exists at all.
Why has it been a focus for so many astronomers to discover a "Planet X"?
AH: To find another planet on our "cosmic doorstep" would be an incredible achievement, comparable to the previous discoveries of Uranus, Neptune, and Pluto (even though Pluto was subsequently demoted).
How could this potential new planet shed light on the early years of the solar system?
AH: Planetary scientists would have to account for the formation of such a large body so far from the existing band of large Jovian planets: Jupiter, Saturn, Uranus, Neptune. It would provide valuable input data for today's computer models of planetary formation.
About Alan Hirshfeld
Professor Alan Hirshfeld conducts research in the history of physics and astronomy. He is the author of "Parallax: The Race to Measure the Cosmos," published by Henry Holt & Co. in 2002, "The Electric Life of Michael Faraday," published by Walker & Co. in 2006, the "Astronomy Activity and Laboratory Manual," published by Jones & Bartlett Publishers in 2008, "Eureka Man: The Life and Legacy of Archimedes, published by Walker & Co. in 2009, and "Starlight Detectives: How Astronomers, Inventors, and Eccentrics Discovered the Modern Universe," published by the Bellevue Literary Press in 2014. Hirshfeld is the director of the UMass Dartmouth Observatory and has been named an Associate of the Harvard College Observatory.