Geysers on Earth and in Space: How astrobiology studies in Yellowstone might teach us about life on other planets!

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Conor Nixon, research space scientist with the NASA Goddard Space Flight Center.

In 1989, NASA’s Voyager 2 spacecraft made an incredible discovery—geyser activity on Triton, a moon of Neptune.  It was the first time a geyser had been observed away from Earth (not counting the volcanic eruptions discovered on Jupiter’s moon Io by Voyager 1 in 1979).  In the decades that followed, geysers were discovered on even more moons in the outer solar system.

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Yellowstone’s geysers are driven by heating from deep inside the Earth. In the cold outer solar system, however, the heat source powering geysers on some of the moons of Jupiter, Saturn, Uranus, and Neptune is provided by tidal forces—the internal mashing that occurs as the moons orbit close to their massive parent planet. Consider the force of ocean tides on Earth caused by the Sun and the Moon. Now imagine similar amounts of energy directed inwards in these small, water rich moons of the outer solar system. Deep beneath their frozen outer crusts lie warm watery oceans, blanketed from freezing solid by the thick ice above, but heated within by the constant sloshing of tides driven back and forth as they orbit their parent planet. Where fractures occur in the ice crust, the pressurized, warm water from beneath is ejected far out into space.

This combination of frozen ice crust and warm water preserved beneath is in some respects similar to a frozen pond on the Earth, but can we take the analogy a step further? Do these deep, warm seas hidden from sight also harbor life, like the creatures happily feeding below the surface of frozen ponds on the Earth? How might we find out? In future, NASA’s goal is to send increasingly sophisticated probes to the outer planets to land on these worlds to search for evidence of life. But…the warm oceans lie miles below the frozen surface. So how can we access these watery reservoirs? Geysers provide the answer.

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In late February 2019 a group of planetary scientists journeyed to Yellowstone National Park in winter to find out how deep the parallels go between the geysers of Earth and space. Geysers in Yellowstone are known to harbor extremophile bacteria and archaea—microbes who call the hot, acidic or alkaline waters their home. Microorganisms such as these might also find the oceans of the outer solar system hospitable, so the team resolved to find out as much as possible about the both the environment and the microbes themselves. The ‘toolbox’ of scientific instruments the team deployed contained apparatus to measure water properties such as temperature, pH and dissolved oxygen; spectrometers, to measure the organic molecular composition of the ices and crystalline nature of the rocks; and gas sensors to sniff the air. In addition, the team collected small samples of rock, ice and geyser plume water itself: frozen droplets collected on carefully laid out sheets of foil that became coated in geyser spray before being carefully stowed away.

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The key target on the trip was Great Fountain Geyser in Yellowstone’s Midway Geyser Basin, which hosts a spectacular plume erupting two to three times per day. However, since the trip was to be in the depths of winter, when conditions were as similar as possible to the frozen worlds of the outer solar system, the logistics would not be easy. Some of the scientists were delayed by 12 hours due to snowy airports, arriving only after midnight on the same day they were due to enter the park! The full-size SUV then became stuck in a deep snow drift in a blizzard in West Yellowstone Village and had to be towed free by a snowplow.

The next day, after conveyance into the park by tracked snow coach, the team had to break trail for almost a mile through waist-deep snow along the normally minivan-laden Firehole Lake Drive, keeping a close watch out for skittish elk and bison (not to mention bears and mountain lions). As the team of six dragged their gear along on sleds, they were able to appreciate the awesome challenges that must have faced early explorers of the region. On the way to Great Fountain Geyser, the team stopped to rest and take measurements and samples at several other non-eruptive pools along the road with evocative names: Lemon Pool, Surprise Pool, and Firehole Spring.

Finally, after three days of dragging gear, making measurements and collecting samples, the team was ready to head home, taking a precious cargo of data and specimens back to the lab for detailed analysis. Although analyses are still ongoing, delayed in 2020 by the COVID-engendered disruptions to our world, the team already intends to return to Yellowstone in the future to conduct a follow-up study based on the findings of the first foray. While Yellowstone might seem remote, it is not nearly as far off as worlds such as Enceladus and Triton.  Indeed, Yellowstone is an exceptional natural laboratory that has much to teach us about life on Earth and beyond.