Pluto’s haze layer displays a blue color in this image obtained by the New Horizons spacecraft's Ralph/Multispectral Visible Imaging Camera (MVIC).(Image credit: NASA/JHUAPL/SwRI)
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.
"This says it all — from the little planet with a heart to the amazing degree of geologic diversity and complexity that Pluto revealed," Stern wrote. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Pluto's "far" side
"Pluto's far side was only seen in low-resolution images because Pluto rotates only once every six days and we were still three days away and millions of miles away when we best saw the far side. Still, it's incredibly different than the flyby hemisphere and beckons us to return to see this side in more detail!" (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Glacial flow, convection, wind streaks, and dunes on a young glacier larger than Texas
"Wow! Pluto's vast nitrogen glacier Sputnik [Planitia] is among the most amazing terrains in the solar system. Look closely: You will see no craters, meaning it is very young, but look some more, and see the evidence for ice convection, glacial flows, avalanches, wind streaks, water icebergs in this nitrogen ice sea, and even dune fields! Wow!" (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Blue skies
"I love this one not only for Pluto's blue, seemingly Earth-like sky but also the fact that this image was taken after we passed Pluto, having accomplished a goal many thought we never would, and taking 26 years in the making!" (Image credit: NASA/JHUAPL/SwRI)
A rugged oblique
"This gorgeous image reveals both how rugged Pluto's terrains can be and also the dozens of layers of atmospheric haze it sports, stretching to orbital altitudes, no less!" (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Bladed terrains
"Pluto's bladed mountain terrains are unlike any other we know in the solar system; they are sci-fi-like methane ice mountains stretching across much of the far side and this western-Colorado-sized piece on the eastern edge of the flyby hemisphere as well." (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Cryovolcanoes
"Pluto apparently sports at least three styles of cryovolcanic terrains, including this, Wright Mons, named for the Wright Brothers, who showed us all how to fly. This feature is the scale of Mauna Loa in Hawaii, no less!" (Image credit: NASA/JHUAPL/SwRI)
Old terrains
"Although some parts of Pluto show no craters at all, meaning they are geologically young, other parts of the planet are old and battered, and have been dated to the time of Pluto's formation over 4 billion years ago." (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
A paleo-lake
"Who ordered this? Apparently an ancient nitrogen lake sits in a rugged mountain valley, haunting forensic evidence for past epochs of far higher atmospheric pressure." (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Snowcaps in the Kuiper Belt
"These mountains tower as far above Pluto as the Rockies tower above our planet, but these mountains are not rock with water snow at all. They are alien: water ice mountains frosted by methane snowcaps. Imagine, snowcaps in the faraway Kuiper Belt!" (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
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.
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Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.
