If life is to be found elsewhere in our Solar System, astrobiologists believe it is likely to be simple (microbial) in nature. While most of our astrobiology efforts are currently focused on Mars, multiple missions will be sent to the outer Solar System in the coming years to search for possible signs of life inside Jupiter's icy moon Europa. For decades, scientists have theorized that life could exist beneath the moon's surface around hydrothermal vents located at the core-mantle boundary. Searching for possible evidence of this life is the purpose of the ESA's JUpiter ICy moons Explorer (JUICE) and NASA's Europa Clipper mission, which are currently en route to the Jupiter system.
Based on fossilized bacteria found around deep-sea vents, hydrothermal activity is believed to have played a key role in the emergence of life roughly 4 billion years ago. NASA recently awarded $621,000 to James Holden, a microbiology researcher in the School of Earth and Sustainability at the University of Massachusetts Amherst. Per the award, Holden will conduct a three-year study on microbes that live around volcanic fissures on the ocean floor. This study aims to help scientists predict what microbial life inside Europa could look like in anticipation of what missions like JUICE and the Europa Clipper could find.
Scientists got their first hints of a possible liquid ocean beneath Europa's icy exterior when the Voyager 1 and 2 probes passed through the system in 1979. Since then, observations by multiple robotic missions and the Hubble Space Telescope confirmed the presence of plume activity on the moon's surface. Similar to Saturn's moon Enceladus and other "Ocean Worlds" in the Solar System, these plumes are the result of "cryovolcanism," a geological process where volatiles (like water, methane, and ammonia) erupts from the surface of a body rather than molten rock.
Holden has been studying deep-sea volcanoes since 1988. With NASA's support, he established a lab simulating the lightless and oxygen-less conditions typically found around deep-sea vents. It is here that extremophiles can obtain the energy and nutrients they need from the hot gases and minerals flowing from these vents. As Holden explained in a UMass Amherst press release:
To get our microbes from them, we use submarines—sometimes human-occupied, sometimes robotic—to dive a mile below the surface and bring the samples ashore and back into my lab at UMass Amherst. Because Europa's conditions might be similar to the conditions these microbes come from, we think that Europan life, if it exists, should look something like our own hydrothermal microbes.
However, Europa's interior ocean will likely be different from Earth's in many ways, owing to the moon's different chemistry, size, and gravity (roughly 13.5% of Earth's). This essentially means that while life inside Europa will have some things in common with extremophiles here on Earth, they will not be exactly the same. On Earth, the type of extremophiles that Holden and other microbiologists study break down hydrogen to get their energy using special enzymes called hydrogenases. These enzymes come in many types that work in different ways, and may have different functions in different kinds of cells. As a result, organisms that merely on different sets of hydrogenases may not resemble each other or function in the same way.
In addition, the iron, sulfur, and carbon released by Earth's hydrothermal vents are known to bond with hydrogen to generate energy. But scientists are unsure how those processes work biologically since the amounts of hydrogen involved vary.
We have long had a basic interest in knowing if there is life beyond our planet and how that life would function. It's exciting to think that the answer to the secret might be here on our own planet. So, we need to figure out the different chemical processes that Europan microbial life might be using in order to create energy. Different chemistries could create very different kinds of microbes. Our research will be to determine how the different chemical processes contribute to an organism's physiology.
Further Reading: University of Massachusetts Amherst
