Dave Tholen: A Closer Look at Pluto

Billions of miles from Earth, traffic on the Kuiper Belt freeway never stops. It’s where Pluto and around 100,000 smaller icy bodies preserve Solar System history in a kind of cosmic deep freeze.

Earlier in his career, Dave Tholen observed Pluto and its largest moon Charon as they engaged in a dance of mutual eclipses. His observations led to fundamental knowledge of Pluto and Charon, including their sizes, densities, rotation rates, and surface contrasts. In 2007, he used the Keck telescope and its adaptive optics system to take an image of the Pluto system that exceeded the sharpness possible with the Hubble Space Telescope. Such observations were needed to optimize NASA’s New Horizons spacecraft’s spectacular flyby in July 2015.

Just 15 minutes after its closest approach to Pluto on July 14, 2015, NASA’s New Horizons Spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon. The smooth expanse of terrain is flanked to the west by rugged mountains up to 11,000 feet high, including the informally named Norgay Montes in the foreground and Hillary Montes on the skyline. The image was taken 11,000 miles from Pluto; the scene is 230 miles across., Credit: NASA

New Horizons’ images of the dwarf planet sent back to Earth revealed an unexpectedly beautiful and complex icy terrain of dramatic mountain ranges, canyons and possible geological activity.

Tholen credits Mauna Kea’s clear skies, excellent image quality, and stable atmospheric transparency for the collection of the highest-quality data unmatched by any other observatory in the world.

“Pluto has been such an enigmatic world. Despite being almost spherical it shows a brightness variation of 35 percent as it rotates…it has one large satellite and four smaller ones, yet Pluto is smaller than our own Moon. How did it form? Are there other Pluto-like objects even farther from the Sun?”  —  Dave Tholen