Someday on Europa, there’ll be a robotic explorer diving beneath its icy surface to find volcanoes. Yes, even though it’s an ice world, Europa shows signs of internal activity. Planetary scientists think volcanic features, similar to hydrothermal vents here on Earth, exist on Europa’s ocean floor. But, how to understand them?
It turns out, there’s a very good analog for Europan volcanism deep beneath Earth’s Arctic Ocean. It’s called Aurora and it has a lot to show about the role of such vents here at home. Scientists discovered Aurora in 2014 and cataloged it as another hydrothermal system. Not that it wasn’t an amazing find. Locating any vent in the Arctic Ocean is a rarity. “We figured what we had found was one of the least interesting kinds of vent sites that there are,” said Chris German, senior scientist with the Woods Hole Oceanographic Institution’s (WHOI) Department of Geology and Geophysics. “We came home from the expedition thinking, ‘Okay, we found a site in the Arctic. That’s great, but if you take away the ice cover, it is just another vent site’.”
The Aurora hydrothermal system lies right on top of a spreading ridge, also known as a mid-ocean ridge. It’s basically a mountain on the sea floor. As tectonic plates pull apart, material from underneath moves up between the plates to build up mountains and islands. This is exactly what’s happening in Iceland, for example.
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What’s Special about Aurora’s Hydrothermal Vents?
The Aurora site is one form of underwater volcanism. We are familiar with the famous towering “black smoker” and “white smoker” volcanic vents discovered in the late 1970s. It turns out that volcanic eruptions on the sea bed take many forms. Most of them happen along the tectonic plate boundaries and isolated hot spots. At Aurora, the site lies on something called the Gakkel Ridge rift-valley floor. It’s about 100 meters across, which is fairly large. The vent sends out a plume of water heated to high temperatures by the molten lava coming up from below. The chemical composition of the plumes tells a lot about the material oozing up from beneath the plates. In some cases, there’s information about valuable minerals (like magnesium, for example, that could be mined in the future.
Deep-sea mining is a tricky subject. Discoveries of mineral deposits are subject to decision-making bodies such as the International Seabed Authority and the Aurora site falls under its purview. German points out that there are high levels of copper and gold present in the Aurora deposits. They might be a lot more abundant along one-half of all the world’s ridge crests, he pointed out. “This is a class of vent sites that previously had been dismissed as unable to sustain the growth of large hydrothermal mineral deposits. Until now, scientists assumed that such small volcanic systems could not sustain hydrothermal circulation for long enough to grow such large mineral deposits,” he said.
Europa on Earth
The chemical composition of the region around Aurora also reveals a lot about life. The mineral nutrients sustain life around such vents. And, that fascinates WHOI and other scientists as they focus attention on Aurora as an analog for other worlds.
For planetary scientists looking for habitable spots elsewhere in the solar system, studies of Aurora are particularly helpful. The discovery of life forms nestled happily in the ultra-hot waters surrounding vents was the first clue that it exists in what we’d consider intolerable conditions—for us. Yet, volcanic vents—including “black smokers”—provide habitats for an astonishing diversity of life. Those range from clams and worms to other planets and animals all the way up the marine food chain. The smallest forms subsist quite well on the chemicals ejected in the plumes. Everything “down there” thrives in the darkness, flourishing in high-pressure environments that are rich with the nutrients they need.
Life Around Hydrothermal Vents
Finding a vent beneath an icy surface raises the question: could such volcanic activity in Europa’s oceans also nurture life? It’s one that the WHOI team asked as they studied the Aurora system. “The single biggest part of what we may have discovered is a vent site beneath an ice-covered ocean that is also a great place to study organic synthesis relevant to the origin of life and the search for life beyond Earth,” said German. “The combination of studying the geology of the seafloor and the chemistry of the overlying water column is what gives us particular insights into this vent site and reveals that it has these special qualities.”
The same special qualities could very well exist on Europa. And, for that matter, on Saturn’s moon Enceladus. And, perhaps other places in the solar system. Knowing that those moons could be similar to the Arctic site makes Aurora a natural lab for further studies.