Evidence for subsurface liquids has been found on the moons of which planets?

• A. Jupiter and Saturn only
• B. Earth and Mars
• C. Neptune only
• D. Jupiter, Saturn, and Neptune

Answer: (D)

The idea being tested is how scientists uncover oceans hidden beneath icy moons. These oceans reveal themselves not by direct sampling, but through clues like plumes, magnetic signals, and gravity measurements that point to a conducting, salty layer beneath the surface.

For Jupiter’s moons, strong evidence comes from Europa, where measurements of how the moon responds to Jupiter’s magnetic field imply a global salty ocean beneath its ice shell. Enceladus, a Saturnian moon, provides even more direct proof: plumes of water vapor and ice spray out from its south pole, indicating liquid water beneath the crust. Saturn’s system as a whole also hosts several candidates for subsurface oceans, supported by gravity and thermal models.

Neptune’s moon Triton has long been hypothesized to harbor an internal ocean as well, based on models of its interior and signs of cryovolcanism, though the evidence is not as direct as the clear plume observation from Enceladus or the magnetic-induction hints from Europa.

Because solid evidence exists for subsurface liquids on moons around Jupiter and Saturn, and credible evidence from Neptune’s moon as well, the best overall grouping includes Jupiter, Saturn, and Neptune. Earth and Mars don’t contribute moons with confirmed subsurface oceans in the same way, so they don’t extend the list.