For the first time, scientists have found evidence of liquid recently flowing on Pluto's surface — and it appears to be liquid nitrogen rising from beneath the dwarf planet's famous heart-shaped glacier.
The study, led by the Southwest Research Institute's Dr. Alan Stern — principal investigator of NASA's New Horizons mission — used spacecraft imagery to identify dark features on the northern edge of Sputnik Planitia, a vast frozen nitrogen glacier larger than Texas and Oklahoma combined. The dark, linear features appear to be occasionally wetted by liquid, most likely nitrogen, the team reports in The Planetary Science Journal.
Pluto's atmospheric and thermal conditions make liquid nitrogen rain physically impossible. Instead, computer models led by Dr. Orkan Umurhan of the SETI Institute show that nitrogen ice at the base of the kilometers-deep glacier can melt and be transported upward through small conduits — similar to lava or geyser tubes — driven by buoyancy or pressure from below. Once at the surface, the melted nitrogen stays liquid long enough to flow down slopes, wetting the icy ground and producing the observed darkening.
The researchers compared the New Horizons images with NASA Landsat 9 imagery of Greenland, where similar dark features appear where liquid water occurs on ice. "Pluto never stops surprising us," Stern said. The findings could also help explain the geysers Voyager 2 observed on Neptune's moon Triton — and make a case for mapping the half of Pluto still unseen at high resolution.
