Ra Patera is an extraterrestrial volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 located on Io

Io (moon)

Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

. An active volcano, it was first studied in 1979 via Voyager stereo imagery to determine its geology, topography, and the source of its eruptions. When first discovered, the mountain reached about 1 kilometre (0.621372736649807 mi) in height and featured numerous lava flows of either low viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 or "high eruption rates". It is possibly a liquid sulfur-erupting volcano.