Are volcanic depressions on the Moon a fountain of youth?
05-17-2024
Purdue researchers found that volcanic mare patches on the Moon appear youthful but may hide their age especially well
Some volcanic areas on the Moon have a youthful appearance. These areas are known as Irregular Mare Patches, (pronounced MAHR-ay), or IMPs, and are considered youthful looking in that, by appearance alone, seem as though they were formed over a billion years after the Moon is thought to have stopped having volcanic eruptions. It’s a puzzle that lunar scientists have tried to resolve since their discovery and has major implications for the Moon’s evolution. Researchers at Purdue University recently published their findings on the composition of these IMPs and how they have managed to hide the proverbial fine lines and wrinkles.
Hunter Vannier, PhD Candidate at Purdue University, is the lead author of the study published in AGU’s JGR Planets. IMPs are found in many places on the lunar mare, the dark lava flows that cover much of the near-side of the Moon, and appear as large shallow pits with a rough floor covered by many smooth mounds. These IMPs spark lively debate among planetary scientists, so much so that NASA is even funding a mission, DIMPLE, to send a robot to one of the IMP sites to have a good look around. DIMPLE, short for Dating an Irregular Mare Patch with a Lunar Explorer, will help resolve whether IMPs are in fact young or old.
The age of the Moon’s surface is typically determined in two ways: the number of craters present and amount of space weathering. For cratering, the more craters that are present in an area of the Moon, the older it is interpreted to be. For space weathering, tiny meteorites and high energy photons emitted from the Sun and celestial bodies outside the solar system bombard the surface of the Moon, causing the surface to darken. Very fresh surfaces on the Moon tend to be bright.
“IMPs are some of the youngest looking volcanic features on the Moon, appearing both bright and seriously lacking in craters,” says Vannier. “This is particularly puzzling because volcanism on the Moon was expected to end over a billion years ago, but IMPs look like they’re less than 100 million years old, very young for the Moon! Multiple hypotheses have been put forth but fall into two main categories: IMPs are ancient material with a unique physical property that only makes them look young, or IMPs are in fact from extremely recent volcanic eruptions. Thus, there is an ongoing debate as to how they formed and why they appear so young. If they are recent eruptions, this would require a fundamental rewrite of the Moon's evolution because the interior of the Moon today is thought to be too cold to produce magma, and would need to be much warmer for eruptions to occur recently. The goal of our project was to look at what the IMPs are made of to provide constraints on these formation hypotheses.”
The team found that IMPs did not contain telltale signs of recent explosive eruptions like volcanic glass. So the IMPs were likely not formed by recent volcanic eruption of new material. But also, the team cannot rule out that they were formed by some kind of recent magma-poor gas explosion – a "burp" from the lunar interior.
“Our results most strongly support that IMPs have some kind of strange physical characteristic, like high porosity, that only makes them appear young, and that they were likely formed over 3 billion years ago,” he explains. “Our results provide an important constraint on how IMPs form, which do not require a major rethinking of the Moon's internal evolution.”
Vannier is advised by Briony Horgan, Professor with the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at Purdue University’s College of Science. She along with Julie Stopar, of the Lunar and Planetary Institute, and Purdue PhD alum Marie Henderson, of NASA Goddard Space Flight Center and the University of Maryland, used data collected by spacecraft orbiting the Moon, which are critical for interpreting the geology and physical processes of the Moon on a global and regional scale. For this project, the team mainly used data from the Moon Mineralogy Mapper (M3), an instrument that measures the sunlight reflected off the surface of the Moon across visible and infrared wavelengths, called “spectra.” When sunlight hits the Moon's surface, some of the light is absorbed by minerals on the surface before being reflected to the spacecraft. These absorptions occur at very specific wavelengths of light and are like fingerprints in the spectra that help the team identify specific types of minerals, which in turn allows us to connect them to specific types of volcanic deposits.
“Dr. Horgan taught me how to use programs she developed for processing data in this project, which I then used to analyze the lunar data needed to interpret the irregular mare patches,” Vannier explains. “Along the way, Dr. Horgan provided invaluable feedback on data interpretation and guided the scope of the project… she's a great advisor! Dr. Julie Stopar is an expert on irregular mare patches and lunar volcanism, and brought an excellent perspective for contextualizing and interpreting our results. Dr. Marie Henderson, who is a Purdue EAPS and Horgan Lab alumna, enabled field work in Hawaii, where we collected volcanic samples to compare to the IMPs.”
With a renewed vigor for the space programs of the world to return to the Moon, lunar research is especially important. Gathering as much data as possible will aid in the success of these missions. But for Vannier, this research goes well beyond simple data collection and evaluation.
“Visualizing the Moon's past, when the surface spewed fiery molten material, captures my imagination and inspires me to contribute to our understanding of how volcanoes formed on the Moon,” he says. “When you look up at the Moon and see the dark patches on the surfaces, they are the result of huge volcanic eruptions. It is a process that influenced a huge amount of the lunar surface and is fundamental in how the Moon released heat and evolved through time. The better we understand volcanism on the Moon, the better we understand its history. The Moon’s volcanic regions also often have higher concentrations of hydrogen, oxygen, and metals, which could be extracted and converted into useful resources on the Moon like rocket fuel or solar panel components. Understanding volcanic deposits better enables a long-term human presence on the Moon.”
Now that research for this project has concluded, Vannier and fellow PhD student Thanos Klidaras have been working on ways to visualize the data and its relationship to the topography of irregular mare patches.
“Excitingly, the IMP Ina (a focus of the paper) has been selected as a landing site for a small rover/landed spacecraft mission called DIMPLE, which will arrive in 2028. We are not team members, but we hope that these kinds of visualizations will be helpful for future mission planning like where to safely drive the rover, and what parts of the IMP are most interesting to visit,” says Vannier.
Research of this type is made possible at Purdue University due to the emphasis on planetary sciences as well as high tech labs that allow for thorough data analysis. Vannier says that without having access to computers with large amounts of storage, it would be especially difficult to download and interpret spacecraft data. He explains that Horgan’s lab also has high tech instruments which they use to measure samples on Earth, which are then used as a basis to interpret data from the Moon.
Funding for this research was provided in part by the Lunar Data and Analysis Program, and the fieldwork was supported by the NASA Goddard Instrument Field Team (GIFT).
About the Department of Earth, Atmospheric, and Planetary Sciences at Purdue University
The Department of Earth, Atmospheric, and Planetary Sciences (EAPS) combines four of Purdue’s most interdisciplinary programs: Geology & Geophysics, Environmental Sciences, Atmospheric Sciences, and Planetary Sciences. EAPS conducts world-class research, educates undergraduate and graduate students, and provides our college, university, state and country with the information necessary to understand the world and universe around us. Our research is globally recognized, our students are highly valued by graduate schools, employers, and our alumni continue to make significant contributions in academia, industry, and federal and state government.
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Contributors:
Hunter Vannier, PhD candidate with the Department of Earth, Atmospheric, and Planetary Sciences
Written by Cheryl Pierce, Communications Specialist