The Icy Heart of Pluto
It appears that Earth isn’t the only planet in our solar system with observable oceans. Recent photographs from NASA’s New Horizons deep space telescope have revealed that Pluto, the 9th planet in our solar system (at least that’s what I was taught in 4th grade), may in fact have a watery mass beneath a crust of ice on the surface. This discovery comes a transport related pressure drop that has pushed the ocean towards Pluto’s surface, revealing the subterranean mass of liquid water.
The discovery is based on an argument about the nature of Pluto’s relationship with its largest moon, Charon. The two masses are tidally locked, meaning that they both orbit their center of gravity and that, if one were to stand on the surface of Pluto and look up, Charon would always be at the exact same point in the sky relative to the horizon. The anomaly that helped to reveal Pluto’s liquid subsurface is the location of a massive basin that runs directly through this tidal axis on the opposite side of the planet. This basin, Sputnik Planitia, which is approximately 1300km across, is believed to have been formed ages ago by an impact by an asteroid. Conventional wisdom suggests that the absence of mass in the basin would decrease the density of that part of the planet (or dwarf planet). However, it is possible that this fracture created a pressure drop in the planet’s crust, enabling the fluid to flow towards the surface. It’s counter-intuitive, but since the ice-water slush is much more dense than the majority of Pluto’s crust matter, this movement of the fluid towards the surface increased actually increased the mass on that part of the planet. When oriented along the tidal axis, this conformation of the planet and moon is extremely stable and causes the two masses to be tidally locked.
Since there is likely an abundance of radioactive elements in Pluto’s core, the heat produced from their decay creates a temperature gradient between the core and the shell where liquid water most likely exists. I thought this whole explanation was really interesting and extremely cool that there is potentially liquid water on planets in our solar system! Water is critical for life (at least, life as we know it) so it inspires further questions of what all might be out there to observe phenomena like this as “close” to us as Pluto is.