By Lucinda Manlick, GSA 2022 Science Communication Intern, master’s student at the University of Massachusetts–Dartmouth

Does life, or the potential for it, exist on other worlds in our solar system? As we strive to learn more about habitability of worlds beyond Earth, and what it would take to establish a human colony on the moon, Mars, and beyond, the eyes of the public and scientific communities have once again turned to the sky.

Recent NASA missions like Dragonfly, the Mars 2020 Perseverance rover, and the Europa Clipper (anticipated to launch 2024) seek to investigate habitability of other worlds in our solar system. To better understand different environments, and interpret whether or not they could sustain life, scientists use remote sensing and “Earth-by-proxy” or “Earth Analog” research.

Remote sensing is a term for the use of distant imaging and software to interpret an environment. On Earth, satellites are used for different kinds of long-range analysis, such as 3D-scanning (LiDAR) or infrared imaging. Scientists use software to analyze the data, overlay image types (topography, infrared, etc.) and answer questions about the surface of Earth. For other worlds, spacecraft such as orbiters and flybys can be used for remote sensing. For example, the Lucy mission is expected to image a handful of the Trojan asteroids during flybys. These images are used to understand the surface of other worlds, their chemical compositions, and their geologic histories. Telescopes such as the Hubble and James Webb telescopes provide images of worlds in the solar system and beyond.
“Earth-by-proxy” research is when scientists find an environment on Earth that reflects the expected conditions of another world. Instead of spending billions of dollars to send a spacecraft for in situ (in place) research, the scientists study the environment on Earth instead, and often state that they expect to see similar conditions on the other world of interest.

What do scientists hope to learn from other bodies in our solar system? How can we use remote sensing and Earth-by-proxy research to understand the surface and habitability of worlds like Jupiter’s icy moon Europa? What advice do seasoned scientists have for students and early career professionals? At the Geological Society of America’s (GSA) annual conference this past October in Denver, Colorado, USA, I spoke with two scientists, Dr. Josh Sebree, and master’s student Robin Van Auken, to answer these questions.

Robin Van Auken and poster at GSA Connects 2022 in Denver, Colorado, USA. Photo credit: Robin Van Auken.

A Study in Structure: Using GPlates to Understand the Surface of Europa

Robin Van Auken, a second-year master’s student at the University of Alaska-Anchorage, presented a poster titled “Ice Shell Fragmentation and Cataclastic Features Suggest Regional Distributed Shearing on Europa.” For her work, she uses a program called GPlates to interpret remote sensing data and reconstruct the movement and behavior of the icy surface of Europa.

Europa is one of the icy moons orbiting Jupiter, and is “about 90% of the size of our [Earth’s] moon.” Europa possesses an icy shell and, underneath that, a subsurface ocean, making it one of the most promising worlds in our solar system to search for potential life. Imaging of Europa’s surface taken by the Voyager and Galileo missions has revealed a number of “crazy cracks” (regional surface features) resulting from deformation of the surface ice shell.

Europa as imaged by the Hubble Space Telescope. Image released October 2021 at Europa (hubblesite.org).

Van Auken explained that these features are usually attributed to “global scale stresses” on Europa’s ice shell (i.e., they affect the moon as a whole). One source of these stresses is diurnal tides. Van Auken explains that these occur because “as Europa goes around Jupiter, it has an eccentric (non-circular) orbit, so it gets pulled a little different at different places in its orbit. It gets tidally heated over time, and contracts and extends in different places at different times over the whole body.” Other global-scale stresses include “non-synchronous rotation,” [which] is basically when the ice moves a little faster than the ocean underneath,” and “true polar wander,” which describes how the pole of the ice shell may have moved relative to the pole of the interior. Obliquity, essentially the tilt of Europa’s axis, and the thickening of Europa’s ice shell over time are other global stresses that play a role in fracturing the ice shell.

These stresses, however, do not fully explain all of the features on Europa’s surface, as evidenced by investigation of a region known as Argadnel Regio by one of Dr. Kattenhorn’s previous students, Charlie Detelich. Van Auken, with advisor Dr. Simon Kattenhorn, posed the question: might these fractures be the result of tectonics in the ice shell, similar to how Earth experiences plate tectonics?

To investigate this question, Van Auken looked for two features seen on Earth that could indicate the presence of tectonic forces on Europa: cataclasis and sigmoidal features.

Van Auken explains how sigmoidal or “s-shaped” fractures form, “On Earth, when you have a shear zone, you can develop tension gashes, which form at 45 degrees to the principal stress angle. Over time, as it continues to shear, it rotates. At the same time, the edges can continue to grow, resulting in an s-shaped feature.”

“Another thing we see on Earth is cataclasis, where rocks roll into each other, shattering and breaking. In that situation, if it is left-lateral [the shear zone], we would see counterclockwise rotation,” explains Van Auken. She explains how “we thought that, if we see counterclockwise rotation, then we might be able to see that cataclasis has occurred.”

Europa’s surface features (i.e., bands and ridges) can be used to “hindcast” or trace backwards in time how the surface ice of Europa has moved. Using a program called GPlates, Van Auken broke the surface of a region called Argadnel Regio into 21 small “microplates.” Then she manually moved the plates around, identifying the relative ages of different pieces of ice, and hindcasting their movements.

Van Auken’s GPlates reconstruction from her poster, “Ice Shell Fragmentation and Cataclastic Features Suggest Regional Disturbed Shearing on Europa.” Photo credit: Robin Van Auken.

Van Auken concluded that the diagnostic features on Europa’s surface, the sigmoidal bands and the mapped microplate rotations, suggest that this region of Europa’s surface experiences left-lateral shearing and counterclockwise rotation indicating large-scale cataclasis of Europa’s surface. According to Van Auken, next steps include reconstructing the upper portion of her study region (she has only reconstructed the bottom portion so far) and investigating what appears to be the loss of a portion of the icy surface, which may have been lost due to contraction or destruction.

“It’s super exciting, and I want to do it forever,” says Van Auken.

Van Auken’s work may influence the objectives of missions sent to the surface for future research into Europa’s geology, chemistry, and habitability.

Karst Chemistry as a Proxy for Researching Titan

Dr. Josh Sebree is an associate professor of astrochemistry and astrobiology at the University of Northern Iowa who studies karst systems on Earth to provide insight into the nutrients and chemistry that may be able to support life on other worlds.

Dr. Josh Sebree conducting research in situ. Photo credit: Josh Sebree.

In his invited presentation at the GSA Connects conference, “Astrobiological Analog Studies in Karst Systems,” Sebree explained his work studying nutrient-limited environments on Earth as a proxy to understand what conditions may exist on worlds in our solar system with liquid environments, such as Europa’s subsurface oceans. Sebree studies two caves for this purpose: Wind Cave, South Dakota, and Coldwater Cave, Iowa. Wind Cave has ancient water tens of thousands of years old, with nutrient-limited water and low biomass, providing an analog environment to study conditions that may exist on Enceladus or Europa. Sebree studies the microbes present in this environment to understand what nutrients and energy sources are utilized to sustain life in such a remote environment. Coldwater cave is fluvial (a “river cave”) with frequent water exchange with the environment, and possesses waters rich in runoff nutrients from the surface. Sebree studies this cave to use as an Earth analog study for Titan, which possesses liquid methane in place of water. Both cave systems are difficult to access, are mostly untouched by human influence, possess extreme biologic systems, and provide a unique environment for Earth analog studies.

“Karst” is a term used to describe landscape features produced when the bedrock has dissolved away, such as caves.
Two of Dr. Sebree’s students conducting research in Coldwater Cave. Photo credit: Josh Sebree.
Students of Dr. Sebree conducting field work in Wind Cave. Photo credit: Josh Sebree.

Spectroscpy Application Challenge Winner 2022 – UNI at Wind Cave 2021 Spectroscopy Team – YouTube

Sebree’s lab maintains a YouTube channel, Astrobiology Underground – YouTube, sharing videos exploring their research sites and methods. Maintaining this channel is one way that Sebree makes his research more accessible, and helps viewers to get a taste for what it is like to conduct Earth analog research.

By studying and comparing the chemistry and biology in these two caves, Sebree works to develop scientific understanding of the flow of organic molecules in each system, what organics are present in each environment, the microbial diversity of the cave systems, and even anthropogenic (human) impacts on these remote environments. Sebree hopes his work will inform research on the icy moons, and promote karst systems on Earth as an analog for further extraterrestrial research. According to Sebree, “life is more adaptable than you can ever imagine.”

Advice For Students and Early-Career Professionals

Being a student myself, I asked Sebree and Van Auken what advice they would have for aspiring scientists.

Sebree’s advice is to not be “afraid to get your feet wet,” to “keep in touch with those who helped you get there [where you are],” and to “never answer a question with ‘I’m not qualified,’ regardless of how you feel. Ask for more information instead, and keep the conversation going.” Sebree found himself researching karst systems somewhat by accident, but loves to “make things work in new ways,” and has embraced this area of research wholeheartedly. Regarding impostor syndrome, Sebree says “You’ll never quite get over it,” but “when faculty have invested in you, [they are showing you] you are worth it. I’ll always invest in someone I believe in, whether they think [they are worth it] or not.”

Van Auken had a non-linear education path, with experiences in physics, acting, tutoring, and more. After realizing that the young women she tutored often seemed to “self-select away from science and math,” Van Auken theorized that one cause may be a lack of female role models. Upon reflection, she realized that she never had a female professor during her undergraduate education. With this epiphany, Van Auken decided this was another compelling reason to return to academia for her master’s degree.

Van Auken’s advice for aspiring scientists, especially young women looking for a career in STEM, is as follows: first, “Try to get as much research experience as possible. Often that can mean talking to your professors or other researchers in your department in order to find opportunities. Even if it takes multiple inquires, it’s worth it, because research experience is so important when applying for master’s or PhD programs.” Second, “Trust your gut about where you should be for you.” She advises not to pursue academic programs or professors solely for their prestige, but rather to consider where you’ll be most likely to excel. And third, “If you just keep going, you’ll make it!” Getting a low grade in a class doesn’t mean you can’t succeed in the sciences. According to Van Auken, “The people who have continued in the face of obstacles are the most successful scientists I know. In my experience, perseverance above all else will push you to success.”

Further reading:

The abstract for Van Auken’s poster is online at at https://doi.org/10.1130/abs/2022AM-382292.

The abstract for Sebree’s presentation can be found at https://doi.org/10.1130/abs/2022AM-379263.

Contact information:

Dr. Joshua Sebree can be contacted at Joshua.sebree@uni.edu.

Robin Van Auken can be contacted at rbvanauken@alaska.edu.