Monday, 7 October 2024
The search for a place like home takes us to the jovian moon europa
Europa Clipper: The Moon Mission Making Waves
NASA is “following the water.” It is gearing up for a mission to one of Jupiter’s Galilean moons. The Europa Clipper spacecraft is set to launch on Thursday, October 10, and arrive at Jupiter in April 2030. During its 3.5-year mission, Clipper will perform up to 44 close flybys of Europa, getting as close as 16 miles from its icy surface. The spacecraft will study the moon’s chemistry, geology, and the characteristics of its hidden ocean. Astrobiologists hope this mission will help answer a couple of big questions in astrobiology: Could Europa’s ocean be habitable, and could it harbor life? Certainly, the recipe for life is more than “just add water,” but how much more?
Frozen Dreams: Europa’s Once-Hot Prospects for Life
For years, Europa has been seen as one of the most promising places to look for life beyond Earth. Its global ocean, containing twice as much water as all of Earth’s oceans combined, seems to some like it could be a perfect home for some form of extraterrestrial life.
Henry Dawson, from Washington University in St. Louis, isn’t so sure. He has been studying whether Europa’s seafloor could support the kind of geological activity that might make life possible. His team’s findings, presented at a recent meeting of the 55th Lunar and Planetary Science Conference, suggest that Europa’s ocean floor might be disappointingly inactive.1
On Earth, areas where tectonic plates meet on the seafloor can create hydrothermal vents. These vents spew out mineral-rich hot water that supports small communities of organisms. Astrobiologists have wondered if similar processes might occur on Europa, providing energy and nutrients for potential life forms
Rock Bottom: The Stagnant Reality of Europa’s Seafloor
Dawson’s team found that the forces acting on Europa’s seafloor are probably too weak to cause significant geological activity. The tidal forces from Jupiter that squeeze and stretch Europa aren’t strong enough to crack the seafloor rocks or cause fault lines to slip. This means there might not be any hydrothermal vents or other processes that could provide the chemical ingredients and energy needed for life.
The researchers also calculated that Europa’s “brittle layer” of rock could be anywhere from 30 to 180 kilometers thick — potentially much thicker than similar layers on Earth or even the Moon. This thick, strong layer of rock would make it even harder for any volcanic or tectonic activity to occur on the ocean floor.
Another problem is the lack of essential elements. While Europa’s ocean contains water, carbon, and possibly some phosphorus, it’s likely missing many other elements that life on Earth needs, like iron, calcium, and various metals. The ocean might be more like a stagnant pool than the dynamic, nutrient-rich environment scientists had hoped for.
This adds to the list of reasons to be skeptical about the prospects for life in Europa’s ocean that Jay Richards and I give in Chapter 5 of The Privileged Planet. Other challenges to Europan life we list include the ocean’s salt content, its variable volume over its history, and the pressure at its base.
Icy Moons: A Solar System-Wide Deep Freeze?
But Europa isn’t the only icy moon that’s caught the attention of astrobiologists. Saturn’s moon Enceladus has also been an object of interest (see, “Enceladus as a Habitability Test,” by David Coppedge). Like Europa, Enceladus has a subsurface ocean, but it also has something Europa doesn’t: active geysers shooting water into space. NASA’s Cassini spacecraft flew through these geysers and detected organic molecules, which got some people excited about the possibility of life there.
However, Dawson’s team also looked at Enceladus and other icy moons , including Titan (also covered by David Coppedge). They found that the tidal forces on these moons are probably not strong enough to cause significant geological activity either. This suggests that the challenges for life might be similar across many of the icy moons in our Solar System.
So why do we keep searching for life in these seemingly inhospitable places? It’s because many astrobiologists believe life only requires liquid water and a few other common compounds. Just let these chemical ingredients percolate long enough and out pops life.
Still, every time we study these distant worlds, we learn something new about planetary processes. This knowledge not only helps us understand other planets and moons but also gives us new insights into our own planet Earth. This research reminds us of how special and rare the conditions for life on Earth really are. It highlights the delicate balance of factors that allow life on our planet, from plate tectonics to our protective magnetic field.
In addition to NASA’s Europa Clipper, the European Space Agency is also planning a mission to Jupiter’s moons. The Jupiter Icy Moons Explorer (JUICE) was launched in April 2023 and is expected to reach Jupiter in 2031. It will study not only Europa but also Ganymede and Callisto, two other large moons of Jupiter that might have subsurface oceans.
These missions will use a variety of instruments to peer beneath the icy surfaces of these moons. They’ll measure the strength of the moons’ magnetic fields (which can tell us about the oceans beneath the ice), analyze the composition of their surfaces, and even sample particles ejected from Europa’s suspected plumes of water vapor.
References
Byrne, P. K., H. G. Dawson, C. Klimczak, P. V. Regensburger, S. D. Vance, M. Melwani Daswani, D. J. Hemingway et al. “Likely little to no geological activity on the Europan seafloor.” LPI Contributions 3040 (2024): 2780.
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