There is a vast water reservoir beneath Enceladus’s icy crust — now dubbed as “global ocean”. Among other things, the flyby will probe the ocean’s potential habitability for simple forms of life, the US space agency said. The spacecraft will make its closest approach on Wednesday at an altitude of 49 kilometres above the moon’s south polar region.
The encounter will be Cassini’s deepest-ever dive through the Enceladus plume, and is expected to provide valuable data about activity in the global ocean stirring beneath the moon’s frozen surface, NASA said. Cassini scientists are hopeful the flyby will provide insights into how much hydrothermal activity is occurring within Enceladus, and how this hot-water chemistry might impact the ocean’s potential habitability for simple forms of life. If the spacecraft’s ion and neutral mass spectrometer instrument (INMS) detects molecular hydrogen as it travels through the plume, scientists may get the measurements they need to answer these questions. “Confirmation of molecular hydrogen in the plume would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean, on the seafloor,” said Hunter Waite, INMS team lead at Southwest Research Institute in San Antonio.
“The amount of hydrogen would reveal how much hydrothermal activity is going on,” Waite noted. Using Cassini’s cosmic dust analyzer (CDA) instrument, scientists expect the flyby will lead to a better understanding of the chemistry of the plume. Scientists also hope the flyby will help solve the mystery of whether the plume is comprised of column-like, individual jets, or sinuous, icy curtain eruptions — or a combination of both. Given the important astrobiology implications of these observations, the scientists cautioned that it will be several months before they are ready to present their detailed findings.