PLUTO AND THE HUMAN IMAGINATION

The human relationship with Pluto has been one of overcoming challenges and going to extremes. 23-year old Clyde Tombaugh spent nearly a year of long, lonely nights at Lowell Observatory in search of “Planet X” before announcing Pluto’s discovery in March, 1930. Over subsequent decades telescopic observers painstakingly gleaned just enough information about the Pluto system to show that it was unique, complex and highly worthy of in depth investigation. The 1970s “grand tour” mission concept, which begat NASA’s Voyager program, was originally planned to culminate with a Pluto flyby, but this option was lost when the decision was made for Voyager 1 to instead visit Titan, which deflected it out of the plane of the ecliptic. Voyager 2’s final encounter, with the complex, enigmatic methane- and nitrogen-rich moon Triton in 1989 heightened the desire of many in the planetary science community to explore Pluto. Shortly thereafter, a group of young planetary scientists, the “Pluto Underground” began to advocate for a dedicated mission to what was then the farthest known planet. Over the ensuing quarter century a series of seemingly intractable hurdles: technical, budgetary, and political, were overcome, ultimately resulting in the New Horizons mission and it’s successful flyby of Pluto on July 14, 2015. Every time humanity reaches a new realm of the Solar System we discover that our expectations were too limited, too blinded by our geocentric assumptions. The New Horizons mission has revealed Pluto, and the third zone over which it presides, to be full of surprising geological activity and diverse landscapes evolving over a wide range of timescales. Ongoing arguments about the very meaning of the word “planet” highlight the fact that, as an outlier, Pluto has always served to push us to expand our concepts, our boundaries, and our ability to explore distant realms. The history of exploration also reminds us that flyby missions are only a first step. There is an entire hemisphere of Pluto that we have, as yet, only seen at low resolution. Its enigmatic forms, indistinct and tantalizing, will draw us back.