Our understanding of life on exoplanets and exomoons must be based on what we know about life on Earth. Water is a common ecological requirement for all life on Earth. Temperature on an exoplanet is the first parameter to consider, both because of its influence on liquid water and because it can be directly estimated from orbital and climate models of exoplanetary systems.
Water is required for life, but deserts demonstrate that even a small amount can suffice. Only a small amount of light from the central star is required to support photosynthesis. Some nitrogen is required for life, and the presence of oxygen would be a good indicator of photosynthesis and possibly complex life. When scientists discovered a hydrothermal vent site in the Arctic Ocean’s Aurora hydrothermal system in 2014, they did not immediately realize just how exciting their discovery was.
“Although finding any vent in the Arctic Ocean was a first for us, we figured what we had found was one of the least interesting types of vent sites,” said Chris German, senior scientist with the Woods Hole Oceanographic Institution’s Department of Geology and Geophysics. “‘OK, we found a site in the Arctic,’ we thought when we returned from the expedition. That’s wonderful, but without the ice cover, it’s just another vent site.'”
However, following additional analysis and a 2019 expedition to the remote site, German and other researchers believe this is a significant discovery. They believe that this vent—and others still to be located within the Arctic Ocean’s Gakkel Ridge rift-valley floor—could change our understanding of ultra-slow spreading mid-ocean ridges, substantially expand the estimates of valuable marine mineral deposits rich in copper and gold and serve as natural laboratories to help inform the search for extraterrestrial life.
Our findings have implications for ultra-slow ridge cooling, global marine mineral distributions, and the diversity of geologic settings that can host abiotic organic synthesis–pertinent to the search for life beyond Earth. Volcanically hosted venting with indications of ultramafic influence at Aurora hydrothermal field on Gakkel Ridge.
Chris German
“Our findings have implications for ultra-slow ridge cooling, global marine mineral distributions, and the diversity of geologic settings that can host abiotic organic synthesis–pertinent to the search for life beyond Earth,” according to the paper, “Volcanically hosted venting with indications of ultramafic influence at Aurora hydrothermal field on Gakkel Ridge,” published in Nature Communications.
“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, who is lead author of the paper. “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 vent site could serve as a natural laboratory for future explorations of Saturn’s moon Enceladus, Jupiter’s moon Europa, and other Solar System bodies with subsurface oceans that could support life, he said.
According to German, there has also been significant progress in our understanding of subsurface minerals.
The findings about the vent site “suggest that hydrothermal mineral deposits that could be economically viable in the future—for example, because of the high levels of copper and gold present in the deposits—might be a lot more abundant along one-half of all the world’s ridge crests than we have previously appreciated,” he said.
“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.”
“As scientists, we feel that we should get this information out to decision makers, such as the International Seabed Authority, so that they can make informed decisions with a better understanding of the natural world,” German said of marine mining.
The Aurora hydrothermal system is home to active submarine venting and a large field of relict mineral deposits, as well as a neovolcanic mound on the Gakkel Ridge rift-valley floor. Researchers’ deep-tow camera and sidescan surveys, however, show that the site is larger than 100 meters across. According to the paper, this is unusually large for a volcanically hosted vent on a slow spreading ridge and is more comparable to tectonically hosted systems that require large heat fluxes over a long period of time to form.
The hydrothermal plume from Aurora exhibits much higher dissolved methane values, relative to manganese, than do typical basalt-hosted “black smoker” vents. Instead, the plume closely resembles plumes from high-temperature ultramafic-influenced vents at slow spreading ridges.
Ultramafic rocks are primitive rocks from the Earth’s interior that are similar to the bulk composition of meteorites. Ultraslow spreading ridges such as the Gakkel Ridge rift-valley spread at 1centimeter (cm; about a half inch) per year; by comparison, North America and Europe are spreading apart more than twice as fast at 2.5 cm (one inch) per year while the Pacific Ocean seafloor is spreading even faster at 10–20 cm (4–8 inches) per year.
The significance of the Aurora discovery, according to journal article co-author Eoghan Reeves, is that it may soon add a crucial new data point to what is currently a very sparse chemical plot of these types of hot springs.
“The few systems we currently know of emit fluids that chemically differ greatly from one another, and they have transformed our understanding of what microbiological and geochemical processes occur in these types of systems. Aurora’s plume has some chemical similarities with another known hot spring, but there is still much to learn about the newly discovered site. It will be very interesting to see if Aurora fits into the known chemical plot or expands on it in the future.”
Article co-author Vera Schlindwein said she is “intrigued by the high-temperature venting at Aurora.” The basalt mound “is at a weird location right where the seafloor drops to large depths of the magma-starved Lena Trough,” said Schlindwein, professor at the Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research. Lena Trough is the southern continuation of the Gakkel Ridge.
“Shallow ultramafic rocks appear natural at this location, but a heat and melt source large enough to build the Aurora basalt mound and sustain high-temperature venting is a surprise. With their highly discontinuous melt supply, ultraslow spreading ridges may hold even more surprises in store for the geological setting of vent fields.”
German stated after considering the findings, “We are continually astounded by how diverse and beautiful the seafloor is. Every time we go out and explore, we are surprised because we do not find more of the same. Rather, we continue to discover completely new things that are unlike anything we have ever seen before.”
