On July 14, 2015, NASA's New Horizons spacecraft zoomed within 7,800 miles (12,550 kilometers) of Pluto, capturing the first-ever up-close images of that distant and mysterious world.
The photos stunned even the most imaginative researchers and space fans, revealing a mind-boggling diversity and complexity of terrain on the frigid dwarf planet.
Take Pluto's famous "heart," whose left lobe is a nitrogen-ice glacier 600 miles wide (1,000 kilometers). New Horizons also saw huge mountains of water ice, weird "bladed terrain" sculpted out of methane ice, and enormous ice volcanoes unlike anything planetary scientists had ever seen.
"I was floored," New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, told Space.com. "It is one amazing world — more than we could have asked for."
Stern has been the driving force behind New Horizons — which flew by another object, the distant Arrokoth, in 2019 and is still going strong — from its inception as a concept in the early 1990s. So, to help celebrate the fifth anniversary of the Pluto flyby, Space.com asked Stern to highlight some of his favorite photos from the epic encounter. Here are 10 that stood out to him, with captions he provided. They're presented in no particular order.
Glacial flow, convection, wind streaks, and dunes on a young glacier larger than Texas
A rugged oblique
Snowcaps in the Kuiper Belt
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.