Sitting in the middle of a vast landscape, bordered by a ridge and filled with loose rocks, Lauren Edgar held a hand lens to her eye as she peered at the minerals inside one of the rocks. 

For two weeks at the end of spring, researchers from USGS, Northern Arizona University, and NASA met in southern Iceland to study eskers, or the features left behind by a retreating glacier. Jutting out as ridges, eskers curve over the landscape like otherworldly river channels.  

In fact, the sinuous eskers may have counterparts over 100 million miles away on the fourth planet from the Sun. “Our work will help us understand eskers on Earth so we can identify potential eskers on Mars,” said Edgar, a USGS research geologist. If Mars has eskers, it’s more likely to have once had a similar climate to the one we know on Earth.  

“When early Earth was inhospitable to life, Mars had this whole record of ancient lakes and rivers and deltas,” Edgar said, “so why is Mars seemingly no longer able to support life? What can we learn about our own existence and the evolution of Earth by studying other planets?” 

In addition to exploring Iceland as an analog to Mars, Edgar also uses analogs to study the Moon. She leads the Terrestrial Analogs for Research and Geologic Exploration Training, or TARGET, program out of the USGS Astrogeology Science Center in Flagstaff, Arizona. The program provides research and training opportunities for planetary scientists and astronaut candidates to learn about celestial bodies without blasting off to space. 

Step 1: Find a terrestrial analog 

Edgar found herself sitting on some gravel in Iceland this past spring, because the country’s grey volcanic terrain and chilly temperatures recall what you would see and feel on the Red Planet.  

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The team visited Breiðamerkurjökull, a large glacier that drains the south side of the Vatnajökull ice cap in southeast Iceland. At just over 8 miles across, it sticks out into the Jökulsárlón glacial lagoon, forming lumps of blue-white icebergs.  

The glacier has been retreating for most of the 20th century, shrinking by approximately 3 miles from its maximum extent in 1890. “Some glaciers have retreated so much that our satellite imagery doesn’t go back far enough in time to capture when they started melting,” said Kristen Bennett, a USGS research space scientist who was part of the Iceland trip. 

Breiðamerkurjökull is a wet-based glacier, which means it sits on top of meltwater. Cold-based glaciers, on the other hand, usually cover colder polar regions and are frozen all the way through. So far, all the known glaciers on Mars are cold based – but that could soon change.  

Wet-based glaciers leave behind eskers, which are liquid conduits under the ice that transport a lot of gravel. When the glacier recedes, the eskers are revealed.  

"Eskers are really weird looking features and we think we might see them on Mars,” Bennett said. If eskers really do exist on Mars, then it’s likely that the planet’s climate was once warm enough to allow the glaciers to melt at their base. 

Step 2: Study the analog  

To figure out what makes an esker an esker, the team visited different sites off Breiðamerkurjökull. They looked at a couple eskers that formed 60 or so years ago and several that were revealed in the past couple years.  

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The older eskers are further from the glacier and can be more complex, with multiple ridges that all connect, while the younger eskers are simple ridges very close to the edge of the glacier.  

Bennett and Edgar, along with the rest of the team, used the same techniques in the field as they have available on Mars. They studied satellite images of the landscape and replicated what the Mars Rovers do, which is take photos and analyze sediments. The Mars Perseverance Rover is equipped with multiple instruments that can detect minerals, temperature, wind speed, and geologic structure, among many variables. 

On Earth, the team is looking for specific clues about eskers so that it can distinguish them from inverted river channels, which are also long, sinuous ridges. The inverted channels form when water carves its path into the ground, dries up, and leaves a trench that gets filled with sediments. When everything around this filled in trench erodes, an inverted channel remains. “We’re not sure if we’re seeing an esker on Mars or an inverted channel,” Bennett said. 

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The team is analyzing minerals within eskers to pinpoint specific esker attributes. Minerals store a lot of information that tells you not only how they formed, but how they’ve changed over time. For instance, researchers could deduce if the mineral interacted with a cold or wet based glacier based on its geochemical signature. The team is also looking at mineral grain sizes. If the mineral grains are very fine, like flour, then it’s likely that mineral spent some time being worn down by a glacier.  

Having both a newly forming esker and an established esker is also useful to pinpoint specific attributes to each. “We could see what had changed over time, and note how certain processes, like rain and wind, affected the older esker,” Bennett said.  

Step 3: Extrapolate the analog to something far from Earth  

The team has another trip to Iceland planned for next year also in late spring. They’ll continue their efforts to take photos using drones, collect samples, and study the eskers’ sedimentology and stratigraphy. 

Once all the field work is complete, Bennett will re-examine the possible eskers on Mars. “I’ll take the knowledge that we learned and figure out if the sinuous ridges on Mars meet our criteria to be eskers,” Bennett said.  

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Step 4: Repeat step 1 

The TARGET program currently runs multiple projects, from monitoring volcanic fields in San Francisco to training astronauts in New Mexico. 

“The approach to doing field geology on an analog for the Moon or Mars is very similar in terms of thinking about the overarching science questions and goals,” Edgar said.  

However, there are some considerations. The Moon lacks an atmosphere and never had an Earth-like climate. However, it does have specific features, like impact craters, that are also on Earth. 

“The Moon has been a longtime witness to what’s happened on Earth,” Edgar said. The Earth’s only natural satellite lacks Earth’s plate tectonics, which have a habit of shifting and destroying our rock record over millions of years, so the Moon still has 4-billion-year-old rocks that can tell us about the origin of the solar system.  

“We study the Moon and other planets in part to better understand our own,” Edgar said.  

Building partnerships during each step 

As part of the TARGET program, Edgar and others train engineers, flight directors, and more on how to do field geology so they understand what to do when we have people and instruments on the Moon. “We’re really trying to bring together the community by hosting things like workshops and providing products and services to help others conduct field analog studies” Edgar said. 

Workshops and field-based efforts are crucial for collaborating with people all over the world. For instance, the Iceland mission opened an opportunity to work with the U.S. Embassy based in Iceland. “It was really great to see how the USGS can help the embassy by doing some outreach and keeping it updated on how Iceland is informing Mars studies,” Bennett said.  

The TARGET program aims to enable terrestrial analog work through four key components, including: training, research, data archiving, and sample collections. Team members are currently participating in a variety of research projects in northern Arizona, elsewhere in the southwest, and at common analog sites like Iceland.  

“Bringing together astronauts, engineers, and scientists during field simulations helps us build important connections,” Edgar said. “Some of the astronauts that we trained are currently on the Space Station sending back pictures of some of the areas we brought them to on Earth." 

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To learn more about the TARGET program and ways to get involved, visit: https://www.usgs.gov/centers/astrogeology-science-center/science/terrestrial-analogs-research-and-geologic-exploration#overview  

Or email astroanalogs@usgs.gov