1:45 PM - 2:05 PM
[SIT17-01] Some research topics on subsurface oceans in the Solar System
★Invited Papers
Keywords:Subsurface oceans, Icy bodies, Solar System
Planetary explorations for decades have enabled us to conduct various types of detailed flyby and in-situ observations. Based on these results, the existence of oceans is strongly suggested for Solar System bodies other than the Earth. Such oceans are called "subsurface oceans" because they are in a deep part of the body. Now, a wide variety of studies related to subsurface oceans is performed based on limited information we have. Among them, I consider three research subjects in this talk.
First is the depth to the ocean (the thickness of the crust made of ice that covers the ocean). This is an important factor controlling the tectonics of the surface of icy bodies and material exchange between the surface and the ocean. For Europa and Enceladus, surface topography and rotational motion, respectively, are the major constraints. For Ganymede, the observations of tidal deformation during the JUICE mission would provide a constraint on the depth to the ocean.
Second is the composition of the oceans, which is critical to assess the habitability of the ocean. For Europa and Enceladus, surface material and plume material, respectively, are the major constraints. For Enceladus, high-temperature water-rock interaction is also suggested.
Third is the maintenance mechanism of the oceans, which is important to understand to what extent such oceans are universal. From the point of heat transfer, the "lid" made of water ice cannot maintain oceans until today. Consequently, the presence of an ocean requires substantial heat production and/or inefficient heat transportation inside the body. Tidal heating is important for icy satellites, though the classical tidal theory often predicts insufficient amount of heat. Thus, theoretical studies on tides for a satellite system are now being conducted. On the other hand, tidal heating is not important for Trans-Neptunian objects such as Pluto, requiring inefficient heat transportation. The formation of clathrate hydrates largely contributes to decrease the efficiency of heat transportation.
First is the depth to the ocean (the thickness of the crust made of ice that covers the ocean). This is an important factor controlling the tectonics of the surface of icy bodies and material exchange between the surface and the ocean. For Europa and Enceladus, surface topography and rotational motion, respectively, are the major constraints. For Ganymede, the observations of tidal deformation during the JUICE mission would provide a constraint on the depth to the ocean.
Second is the composition of the oceans, which is critical to assess the habitability of the ocean. For Europa and Enceladus, surface material and plume material, respectively, are the major constraints. For Enceladus, high-temperature water-rock interaction is also suggested.
Third is the maintenance mechanism of the oceans, which is important to understand to what extent such oceans are universal. From the point of heat transfer, the "lid" made of water ice cannot maintain oceans until today. Consequently, the presence of an ocean requires substantial heat production and/or inefficient heat transportation inside the body. Tidal heating is important for icy satellites, though the classical tidal theory often predicts insufficient amount of heat. Thus, theoretical studies on tides for a satellite system are now being conducted. On the other hand, tidal heating is not important for Trans-Neptunian objects such as Pluto, requiring inefficient heat transportation. The formation of clathrate hydrates largely contributes to decrease the efficiency of heat transportation.