NASA’s New Horizons spacecraft may have caught Pluto doing something nobody expected: letting liquid ooze across its surface. A new study led by the Southwest Research Institute finds dark markings on Pluto’s giant heart-shaped glacier that look a lot like patches left behind when liquid spreads over ice.
The features sit near the northern edge of Sputnik Planitia, the enormous nitrogen-ice glacier that forms the left half of Pluto’s famous “heart.” The team believes the most likely explanation is liquid nitrogen rising through cracks from below, then wetting the surface as it moves.
Dark lines on a young glacier
New Horizons photographed Sputnik Planitia during its 2015 flyby, revealing city-sized convection cells separated by thin dark lines. Researchers compared those images with NASA Landsat 9 pictures of Earth’s ice sheets, including Greenland. On Earth, similar dark streaks appear where liquid water sits on top of ice.
Since Pluto is far too cold for rain, the team suspects the liquid comes from underneath. Computer models by the SETI Institute’s Orkan Umurhan and colleagues show that nitrogen ice at the glacier’s base, several kilometers down, can melt under pressure. That liquid could then climb through narrow channels, pushed by pressure and buoyancy, and spill across the surface before refreezing.
“Pluto never stops surprising us,” said Alan Stern, the New Horizons principal investigator who led the study.
Why it matters
The surface of Sputnik Planitia is young, probably less than a million years old, which means the dark markings formed recently. Until now, scientists thought liquid only flowed on Pluto billions of years ago. The study, published in the Planetary Science Journal, suggests it may have happened in the geologically recent past, and possibly today.
The discovery also hints that other icy worlds could be hiding similar activity. Voyager 2 spotted geysers on Neptune’s big moon Triton, and the same melting-and-rising mechanism might explain them. More than half of Pluto has never been mapped in high resolution, so similar features could be waiting elsewhere.
Pluto is not the only world keeping secrets. Mercury is shrinking with hidden scars that suggest more change than scientists expected, and Mars may have a deep south that is partially molten.
Sources
NASA New Horizons, Johns Hopkins Applied Physics Laboratory
Featured image: NASA/JHUAPL/SwRI, Global LORRI mosaic of Pluto in true colour, Public domain, via Wikimedia Commons.