NASA Cassini Spacecraft Discovered Ingredients That Could Sustain Life on One of Saturn’s Moons

Fig. 1. Enhanced image taken of Saturn’s moon Enceladus showing the erupting geyser spray of fine particles that the Cassini spacecraft flew through. (NASA/JPL)

Evidence is mounting that Saturn’s ice-covered moon Enceladus may be able to support microscopic life. NASA’s Cassini spacecraft flew through an erupting geyser on Enceladus (Fig. 1) and detected large amounts of molecular hydrogen, or H₂. This chemical signature is the critical ingredient needed to support a chemical reaction that feeds certain microbes on Earth (Fig. 2), called methanogenisis. Methanogenisis produces methane from hydrogen and water and creates usable energy for the microorganisms.

Fig. 2. Electron microscope image of methanogens. Methanogens are microbes that get their chemical energy from a reaction that makes methane from hydrogen and water. Recent discoveries from NASA suggest that Enceladus may be able to support such life (Maryland Astrobiology Consortium, NASA, and STSci)

This discovery also reveals information about what the subsurface environments on Enceladus could look like.  According to a recent Science article by NASA scientists (Waite et al., 2017), the detection of H₂ is most plausibly caused by ongoing water-rock hydrothermal reactions at Enceladus’ seafloor (Fig. 3). In such a scenario, hot fluids would flow over and through cracks in rocks releasing H₂ into the overlying ocean. Hydrothermal vents on Earth host massive communities of simple life forms, further strengthening the idea that Enceladus is ripe for life.

Fig. 3. Graphic illustration of the hydrothermal reactions that NASA scientists think are occurring at the bottom of the ocean of Enceladus, producing H₂ (NASA/JPL)

H₂ will only form under specific environmental conditions. Therefore scientists can also infer that the pH ranges of Enceladus’ subsurface ocean are likely fairly basic, ~9-11 (Fig. 4).

Fig. 4. Graphic illustration of what scientists expect the environmental conditions of Enceladus’ oceans to be. The orange region identifies the H₂ chemical signature detected by the Cassini spacecraft. The dark blue diagonal lines show constant ocean pH values.  The highlighted blue region identifies what pH ranges best coincide with what is expected for Enceladus. (Waite et al., 2017)

In contrast, the most common hydrothermal vents found on Earth are acidic not basic. For example, Figure 5 shows a cloudy acidic plume erupting from a hydrothermal vent in near Guam. However, there are unique hydrothermal systems in Hawaii, specifically the Lōʻihi Seamount that have pH’s similar to the estimates for Enceladus. Therefore, before heading all the way back to Enceladus, NASA scientists are planning to first explore closer to home by sending underwater submarines to the Lōʻihi Seamount. One such research project is the NASA SUBSEA or Systematic Underwater Biogeochemical Science and Exploration Analog project. SUBSEA will explore Lōʻihi this August to September to learn more about how the seamount is capable of supporting life.

Fig. 5. Erupting cloudy plume from a hydrothermal vent near the Island of Guam. (NSF)

The discovery of H₂ doesn’t mean that life currently exists on Enceladus, simply that Enceladus may contain chemical food sources capable of supporting microscopic life. The discovery of H₂ is nonetheless very exciting and makes Enceladus a top choice for future space missions. The discovery of potential microscopic life beyond Earth may soon be within reach.