During NASA’s Cassini spacecraft’s deepest-ever dive through Enceladus’ plume of gas and ice grains, researchers discovered molecular hydrogen in the material spewing from the icy moon. This discovery provides further evidence for hydrothermal activity in the ocean beneath Enceladus’ surface and heightens the possibility that the ocean could have conditions suitable for microbial life.
Molecular hydrogen points to hydrothermal activity in an ocean beneath the icy surface of Enceladus. Image credit: NASA / JPL-Caltech.
Cassini’s Ion Neutral Mass Spectrometer (INMS) detected hydrogen gas during a close flyby of Enceladus on October 28, 2015. Previous flybys provided evidence for a global subsurface ocean residing above Enceladus’ rocky core.
Molecular hydrogen in the plumes could serve as a marker for hydrothermal processes, which could provide the chemical energy necessary to support life.
To search for hydrogen specifically native to Enceladus, the robotic orbiter flew particularly close to the surface and operated INMS in a specific mode to minimize and quantify any spurious sources.
“Hydrogen is a source of chemical energy for microbes that live in the Earth’s oceans near hydrothermal vents. Our results indicate the same chemical energy source is present in the ocean of Enceladus,” said Dr. Hunter Waite, a researcher at the Space Science and Engineering Division at the Southwest Research Institute and lead author of a paper published in the journal Science.
“We have not found evidence of the presence of microbial life in the ocean of Enceladus, but the discovery of hydrogen gas and the evidence for ongoing hydrothermal activity offer a tantalizing suggestion that habitable conditions could exist beneath the moon’s icy crust.”
“We developed new operations methods for INMS for Cassini’s final flight through Enceladus’ plume,” said co-author Dr. Rebecca Perryman, also from the Southwest Research Institute.
“We conducted extensive simulations, data analyses, and laboratory tests to identify background sources of hydrogen, allowing us to quantify just how much molecular hydrogen was truly originating from Enceladus itself.”
This graphic illustrates how Cassini scientists think water interacts with rock at the bottom of Enceladus’ ocean, producing hydrogen gas. Image credit: NASA / JPL-Caltech / Southwest Research Institute.
On the Earth’s ocean floor, hydrothermal vents emit hot, mineral-laden fluid, allowing unique ecosystems teeming with unusual creatures to thrive.
Microorganisms that convert mineral-laden fluid into metabolic energy make these ecosystems possible.
“The amount of molecular hydrogen we detected is high enough to support microbes similar to those that live near hydrothermal vents on Earth,” said co-author Dr. Christopher Glein, also from the Southwest Research Institute.
“If similar organisms are present in Enceladus, they could ‘burn’ the hydrogen to obtain energy for chemosynthesis, which could conceivably serve as a foundation for a larger ecosystem.”
The researchers also considered other sources of hydrogen from Enceladus itself, such as a preexisting reservoir in the ice shell or global ocean.
Analysis determined that it was unlikely that the observed hydrogen was acquired during the formation of Enceladus or from other processes on the moon’s surface or in the interior.
“Everything indicates that the hydrogen originates in the moon’s rocky core,” Dr. Waite said.
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J. Hunter Waite et al. 2017. Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes. Science 356 (6334): 155-159; doi: 10.1126/science.aai8703
This article is based on text provided by the Southwest Research Institute.
