How does Greenland help explain Pluto?

The SwRI-led team compared New Horizons images with NASA Landsat 9 images of icy regions on Earth, including Greenland's ice sheet. On Greenland, narrow dark markings appear where liquid water sits on top of ice and snow. Similar patterns on Sputnik Planitia led the researchers to propose that subsurface liquid — specifically nitrogen — may be rising and wetting Pluto's frozen surface.

"The surface of Sputnik Planitia is quite young, probably less than one million years based on modeling of the surface overturn, and thus these features that we are looking at must have formed since then," said co-author Dr. Kelsi Singer, a principal scientist at SwRI. "Pluto has many unique terrains seen nowhere else in the solar system, and this area of Sputnik Planitia is one of them."

Earlier studies, including work led by Stern, had proposed that liquid flowed on Pluto in the distant past. The new findings go further: liquid nitrogen may exist beneath Sputnik Planitia today, or may have been present very recently.

How could liquid nitrogen reach the surface?

Computer simulations led by Dr. Orkan Umurhan of the SETI Institute offer a possible mechanism. In plain terms, the models work like this:

• Nitrogen ice at the bottom of the glacier, which sits several kilometers deep, can melt under stress and strain.
• The resulting liquid rises through narrow channels, much like material moving through lava or geyser tubes.
• Buoyancy or pressure from below helps push the liquid upward.
• At the surface, it stays liquid long enough to flow downhill, wetting the surrounding nitrogen ice and leaving the dark markings New Horizons photographed.

Umurhan said the findings should motivate new laboratory work on solid nitrogen at very low temperatures. "It's important to examine the physics taking place in solid nitrogen materials under stress and strain, which can cause them to melt," he said. "These processes have never been studied in real detail in the laboratory."

What are the caveats and wider implications?

The evidence is indirect and preliminary: researchers have not identified clear signs of this type of basal liquid flow anywhere else on Pluto. More than half of the dwarf planet has never been mapped at high resolution, so similar processes could be occurring unseen in other regions.

The proposed mechanism may also apply elsewhere in the solar system. One candidate is Triton, Neptune's largest moon, where NASA's Voyager 2 spacecraft observed geysers erupting from the surface.

Scientists say additional high-resolution observations of Pluto and other Kuiper Belt worlds will be needed to confirm whether such processes operate across the distant solar system. For now, the finding suggests Pluto is far more geologically active — and far wetter — than its frozen appearance suggests.