To the few places in the solar system like Earth or Titan, the moon of Saturn, where we know liquids exist on the surface, we can now add Pluto. We found evidence of liquid nitrogen flowing on its surface.
Pluto is very frigid at -232 degrees Celsius. This is below the temperature at which nitrogen can stay liquid, especially since Pluto’s atmosphere is tenuous with very low pressure. However, the interior is probably warmer, and pressure at the base of solid-state nitrogen glaciers provides some heat.
The iconic heart-shaped feature on Pluto is called Sputnik Planitia and is composed of such glaciers. The New Horizons mission was launched in 2006, and it took 9 years to perform the first-ever human flyby of Pluto. In 2015, it sent us invaluable images and data.
Upon recent reexamination, researchers found evidence of liquid nitrogen flowing at the base of glaciers on Sputnik Planitia in the recent past. Pluto now joins the few places in the solar system with evidence of liquid on the surface.
Earth has water oceans; Titan, the moon of Saturn, has seas and lakes of hydrocarbons; there are similar water streaks on Mars as on Pluto; there are geysers on Enceladus, the moon of Saturn, and Triton, the moon of Neptune; and there are lava flows on Io, the moon of Jupiter. Additionally, many moons of gas and ice giant planets and planetoids like Ceres in the solar system have subsurface oceans or pockets of brine