Pluto’s surface, including its distinctive heart, is covered by several different types of ice.
They are 5 billion kilometres from the Sun in the dim, far-flung outskirts of the Solar System, but Pluto and its large moon Charon turn out to be astonishingly vital worlds.
Images from NASA’s New Horizons spacecraft, which flew within 12,500 kilometres of Pluto on 14 July, reveal frosty plains, soaring mountains and much more geological activity than anyone anticipated. “What’s unexpected to me is how dynamic a world both Pluto and Charon are,” says Mark Sykes, director of the Planetary Science Institute in Tucson, Arizona. “Who would have expected to see such young surfaces? They are absolutely spectacular and fascinating.”
Giant icy mountains in Pluto’s southern hemisphere tower more than 3,500 metres high in the first high-resolution images that New Horizons sent back. The peaks’ sheer height signals that they are made of water ice, the only material that could buttress such huge ridges at Pluto’s frigid temperatures of less than −223 °C, just 50 °C above absolute zero. Bright rims near the tops of the peaks — named after Nepalese explorer Tenzing Norgay — could represent a fresh coat of frozen nitrogen or other types of ice.