Does Saturn’s Moon Enceladus Contain the Ingredients needed for Life?

Artist concept of Cassini and Enceladus. Credits: NASA/JPL-CalTech

The 13-year long NASA Cassini mission to Saturn ended in a grand finale in 2017, but Saturn’s moon Enceladus continues to be explored on Earth through laboratory experiments. Cassini made the groundbreaking discovery that beneath the icy shell of Enceladus there is a vast liquid water ocean. The rocky floor of Enceladus’ ocean has activity similar to hot water vents of Earth’s Pacific Ocean. The hot water vents on Earth have the right chemistry to support life (Fig. 1). So are the similar conditions on Enceladus also able to host life?

Figure 1. Lava rocks near the Hawaiian underwater volcano, Loihi coated in reddish- orange rust made from the abundance of iron-oxidizing bacteria. Image obtained from the Schmidt Ocean Institute.

According to a recent Astrobiology review article by Barge and White of NASA JPL, we are close to learning the answer. These researchers discussed the various lab experiments that can be used to learn more about the chemical exchanges within underwater vent systems that support life. The chemical exchanges in these environments occur between the cold circulating seawater, hot vent fluids, and rocks. These interactions are quite complex because ocean conditions such as temperature, pressure, and pH heavily affect if microbial life can survive. These systems are also very difficult to study, even on Earth, because they are miles beneath the surface of the ocean. Therefore, researchers have to deconstruct and experiment on the important aspects of this system in order to gain more insight.

Figure 2. Laboratory experiment outline of vent chimney growth via injection of different chemical solutions. Obtained from Barge and White, 2017.

Some of these experiments include growing miniature underwater vent chimneys (Fig. 2). Natural chimneys are vertical tubes formed by the buildup of rock precipitates around a vent. An example of an underwater vent chimney on Earth is a black smoker vent shown in Figure 3. Bacteria love to hang around these vent chimneys because the structures physically separate the inner vent fluids from outer ocean water and it is this interface that creates the bacteria’s food. These structures can be duplicated in the lab by injecting carefully prepared solutions into one another under different conditions. A lining can also be used to increase rigidity and integrity of the structures as well as allow researchers to monitor and sample the progress of the experiment.

Figure 3. Black smoker chimney structure at 17 °S on the East Pacific Rise. Obtained from the Woods Hole Oceanographic Institution.

Other related experiments include building special equipment to recreate the pressure and flow conditions on Enceladus to learn more about how the elements are moving when ocean water circulates around rocks. When water flows over rocks they trade elements—this chemical exchange is the basis for why stone statues wear down from acid rain over time as illustrated in Figure 4. The experiments are used to gain a fundamental understanding of how materials on Enceladus react to each other and hypothesize if biologically relevant chemistry can be created.

Figure 4. Acid rain damage to a sandstone statue in Westphalia, Germany. The image on left was taken in 1908 and the image on the left was taken in 1968. This figure shows the effect water-rock element exchange. Photo taken by Herr Schmidt-Thomsen.

The Cassini mission made many incredible and unexpected discoveries— now its legacy continues through completing these types of experiments. Is Enceladus, the seemly inhospitable ice ball, actually hiding forms of alien life? We will have to return to Enceladus and dig deep into its mysterious interior to know definitively! But before we return to the icy moon, we have to be more prepared and informed on what we might encounter. That is why we are learning as much as we can about Enceladus from experiments on Earth such as that laid out by Barge and White.

Barge, L. M., & White, L. M. (2017). Experimentally testing hydrothermal vent origin of life on Enceladus and other icy/ocean worlds. Astrobiology, 17(9), 820-833