Last year, NASA announced that Jupiter’s largest moon, Ganymede, may have water underneath the surface. Last week, Hubble scientists essentially confirmed that Ganymede has an ocean 60 miles (about 100km) deep located underneath nearly 100 miles of ice. For comparative purposes, the surface ocean of Earth is only about 11km deep (though we have a larger subsurface ocean that has still gone largely unexplored).
This development obviously increases the likelihood that Ganymede hosts extraterrestrial life. Add in new data suggesting that Enceladus’ underground ocean may actually be warm due to geothermal activity, and the soon-to-be-visited underground ocean on Europa, and the number of moons in our solar system plausibly capable of hosting life stands at three and counting.
Ganymede is likely to be the last of the three to be probed, and with that much water it’s going to take decades to do the job. With the James Webb Space Telescope going live in 2018 and the SETI project ongoing, the search for extraterrestrial life is likely to continue—both within this solar system, and outside of it—for the rest of our lives.