Are metals depleted for life in the ocean of Enceladus? Laboratory investigations for trace metals in ocean environments beyond Earth

1. Key Points

• Enceladus^※1, a Saturnian moon, has a subsurface ocean. There are various ingredients for life and seafloor hydrothermal environments^※2, attracting attention in terms of life. This study performed laboratory experiments and calculations to investigate behaviors of trace metals essential for life in the ocean.

• Concentrations of the metals would be controlled by chemical reactions between the seawater and rocks on the seafloor. Some metals, such as cobalt and copper, could be insoluble in the ocean.

• Even if other ingredients for life are abundant in Enceladus’ ocean, depletion of trace metals would limit life activity. This study investigated the availability of trace metals essential for life in ocean environments beyond Earth for the first time.

Figure 1　Schematic illustration of the interior of Enceladus. There is the ocean and rocky seafloor beneath the surface ice. The seawater is erupting from the surface through fractures. The presence of hydrothermal environments is suggested on the seafloor. Various materials, such as hydrogen and phosphate, would be dissolved from seafloor rocks. Metals essential for life would be insoluble from rocks and depleted for microbes.

2. Overview

Dr. Shuya Tan and Dr. Takazo Shibuya of the Japan Agency for Marine–Earth Science and Technology (JAMSTEC; President, Hiroyuki Yamato), in collaboration with Prof. Yasuhito Sekine of Earth-Life Science Institute (ELSI), Institute of Science Tokyo, have revealed the possibility that trace metals are depleted for life in Enceladus, the Saturn’s moon.

Enceladus would have the ocean beneath its ice-covered surface, attracting attention in terms of the potential presence of life, such as microbes. The researchers conducted laboratory experiments and calculations simulating chemical reactions in the ocean in order to investigate behaviors of trace metals essential for life. Microbes require some trace metals, such as cobalt, nickel, copper, zinc, and molybdenum. Results of experiments and calculations suggest that concentrations of such metals, particularly cobalt and copper, are not enough for microbes in the ocean. The metal depletion could limit life activity. The present study reports the laboratory-experimental investigations for trace metals in ocean environments beyond Earth for the first time.

These findings will be published in Journal of Geophysical Research: Planets on March 19 (Japan Standard Time). This work was supported by the Grant-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (JSPS: 22K21344, 23H00144, and 23K13158).