"Iron snow" brings hope for finding life on Jupiter's moon Europa

Ever since the discovery of icy ocean worlds like Europa and Enceladus within our solar system, the scientific community has been captivated by the potential for life beneath their frozen surfaces.

These subsurface oceans have intrigued astrobiologists for decades, as they ponder whether the conditions necessary for life exist in these hidden waters.

Jupiter’s moon Europa

Europa, one of Jupiter’s largest moons, captivates scientists with its potential for harboring life. Discovered by Galileo Galilei in 1610, Europa is slightly smaller than Earth’s moon.

Its surface is a shell of ice, believed to cover a vast subsurface ocean. This ocean, possibly containing twice the water volume of Earth’s oceans, lies beneath a layer of ice estimated to be 10 to 15 miles thick.

Europa’s surface is relatively smooth, with few craters, suggesting a young and active icy crust. The surface features extensive cracks and streaks, caused by the tidal forces from Jupiter’s gravity.

These tidal forces also likely generate heat, maintaining the subsurface ocean in a liquid state. This heating could create conditions suitable for life.

Past, present and future space missions

The Galileo spacecraft, which orbited Jupiter from 1995 to 2003, provided most of our current knowledge about Europa. It revealed a magnetic field indicative of a salty, conductive ocean beneath the ice.

Scheduled for launch in late 2024, the Europa Clipper mission will conduct detailed reconnaissance of Europa’s ice shell and subsurface ocean, searching for signs of habitability and providing critical data for future missions that may seek to land on Europa and probe its hidden ocean.

Finally ESA’s Jupiter Icy Moons Explorer (Juice) launched in April 2023 to study Jupiter and its three largest icy moons: Ganymede, Callisto, and Europa.

This mission aims to unravel the mysteries surrounding these celestial bodies and shed light on their potential habitability.

Juice’s journey is expected to last approximately 7.6 years, with the spacecraft using gravity assist maneuvers around Earth and Venus to reach Jupiter.

Upon arrival, Juice will conduct multiple flybys of the moons before entering orbit around Ganymede in 2034. This extended mission phase will allow for detailed studies of the largest moon in the solar system.

Iron and metabolic processes on Europa

A recent study offers compelling insights into this enigma, delving deep into the bioenergetics of Europa’s ocean.

Dr. Sahai, professor and Ohio Research Scholar in the School of Engineering and Polymer Science at the University of Akron, collaborated with Dr. John Senko, professor of geomicrobiology at UA, and Dr. Doug LaRowe, associate professor of Earth science at the University of Southern California.

The team explored the potential for various forms of bacterial metabolisms to thrive in Europa’s ocean, including iron reduction, sulfate reduction, and methanogenesis. They investigated whether these metabolic processes could sustain life.

Iron snow model for life on Europa

Using sophisticated model simulations, the researchers examined the feasibility of these bacterial processes occurring under the specific environmental conditions present on Europa.

They considered factors such as temperature, pressure, and the chemical composition of the ocean.

Their simulations aimed to determine how iron reduction, sulfate reduction, and methanogenesis could take place within Europa’s unique and extreme environment, assessing the energy yields and viability of these metabolisms in supporting microbial life.

What sets this research apart is the innovative “iron snow” model proposed by Dr. Sahai and her team.

Drawing parallels with acid mine drainage systems on Earth, this model suggests a plausible mechanism for enhanced bacterial productivity in Europa’s ocean.

The iron snow model eliminates the need for highly reactive oxygen species (ROS) to be transported from the surface to the ocean floor.

This not only increases the likelihood of detecting life but also mitigates the harmful effects of ROS on biological molecules.

Iron, Europa, and life beyond Earth

The implications of this research are profound. The study not only sheds light on the potential habitability of Europa’s ocean but also expands our understanding of the conditions necessary for life to thrive in extreme environments.

The greater diversity of microbial metabolisms identified by Dr. Sahai and her team suggests a wealth of potential biosignature molecules that could be targeted for detection.

“The iron snow model overcomes critical conceptual roadblocks to life in the oceans of Europa and other icy worlds,” Dr. Sahai concluded.

Significantly, our model increases the diversity of habitable ecological niches in icy ocean worlds, their habitable space, and total productivity driven primarily by iron reduction, which is usually neglected in models of metabolism in icy ocean world oceans.

The research brings us one step closer to unraveling the mystery of life beyond Earth. By enhancing our understanding of the bioenergetics of Europa’s ocean and proposing the innovative iron snow model, scientists are paving the way for future explorations and discoveries in the quest for extraterrestrial life.

The study is published in the journal Proceedings of the National Academy of Sciences.

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