Odd surface patterns on Pluto hinted to astronomers that, sometime in the past—quite possibly not that long ago—liquid existed on its surface. A new analysis of New Horizon images of the Sputnik Planitia, a section of Pluto’s massive, heart-shaped glacier, suggests that liquid nitrogen once existed on the dwarf planet’s surface. However, Pluto’s thin atmosphere, as we observe it today, makes liquid nitrogen rain physically impossible, the researchers explained in the statement. The latest paper, on the other hand, evaluates the hypothesis that there is currently or recently liquid nitrogen below the glacier. The researchers found that it was possible for liquid nitrogen to travel up small conduits, like lava or geyser tubes, and remain liquid long enough to create dark patterns on the nitrogen glacier.