Evidence mounts for a liquid ocean on Pluto - CNET

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Data from the New Horizons mission revealed many previously unknown things about Pluto, and hinted at others. One tantalising tidbit was the prospect of an ammonia-rich ocean of water under the surface, a liquid sea beneath the frozen plains.

"Thanks to the incredible data retued by New Horizons, we were able to observe tectonic features on Pluto's surface, update our thermal evolution model with new data and infer that Pluto most likely has a subsurface ocean today," said lead author Noah Hammond, a graduate student in Brown University's Department of Earth, Environmental and Planetary Sciences. The paper has been published in the joual Geophysical Research Letters.

The team updated a thermal model of Pluto based on detailed data from the New Horizons probe, with tectonic features such as fault lines hundreds of kilometres long and up to 4 km (2.5 miles) deep, and mountains of water ice that indicated Pluto is slowly expanding over time. If Pluto had had oceans that completely froze long ago, then the dwarf planet would have been shrinking over time.

"What New Horizons showed was that there are extensional tectonic features, which indicate that Pluto underwent a period of global expansion," Hammond said. "A subsurface ocean that was slowly freezing over would cause this kind of expansion."

How could the water remain liquid so far from the sun? The slow natural decay of radioactive elements in Pluto's core may have been sufficient to keep the water unfrozen beneath the icy surface. Over time, however, that water could have started to refreeze. Since water expands as it tus into ice, this would have produced the features seen on Pluto's surface.