Exploring the Moon from Earth
UI physics researcher uses satellite images to map the moon’s geology
If you want to travel through time, take a look at the moon. Our closest celestial neighbor gives clues to Earth’s earliest days.
“In contrast to the Earth, the moon is largely untouched for the last 3 billion years or so. When we see it today, we are actually peeking into the past,” said Deepak Dhingra, a postdoctoral researcher at the University of Idaho.
Dhingra works with assistant professor of physics Matthew Hedman in the UI College of Science. His postdoctoral research focuses mainly on Saturn’s moon Enceladus, but his interest in the Earth’s moon goes back more than a decade. He studies lunar impact craters — the most common feature on the moon.
Mapping the Moon
Chunks of space debris have pelted the Earth, the moon and other solar system objects throughout time. But since Earth is constantly changing, most of its craters get covered up, and only about 180 are visible today, though many more may be hidden beneath the oceans.
But the moon’s lack of atmosphere and geological change means craters stick around for millions of years.
Dhingra examines these craters to understand how they form, providing clues about Earth’s early days and the way impact craters shape planetary bodies in our solar system.
“There is one all-pervasive process that has happened in our solar system, and that is cratering,” Dhingra said. “Any planet, any surface, you would see craters that range from a small prick on a grain of sand to craters that are several hundred kilometers across. And this process is still active today, although with a much reduced intensity.”
Dhingra began his work with Chandrayaan-1, India’s first mission to the moon, which was launched in 2008 with the goal of mapping the moon’s surface. While earning his doctoral degree from Brown University, Dhingra studied data from the Moon Minerology Mapper, a NASA instrument on board Chandrayaan-1, along with data from several other instruments on other lunar missions.
He came to UI in 2014, and this spring he and colleagues at Brown published a paper in the journal Icarus that examines the geological characteristics of two important craters: Tycho, a 108 million-year-old crater on the side of the moon we see from the Earth, and Jackson, another geologically young crater, less than a billion years old, on the moon’s far side.
Finding Meaning in the Maps
The abundance of detailed satellite imagery of the moon makes it a “natural lab” for studying craters, Dhingra said. Creating lab experiments or computer models to simulate cratering is too limited, because the cratering process involves immense speed and energy.
“In a matter of seconds, an average cratering event can cause large-scale melting, disintegration and displacement of materials over at least a few kilometers,” Dhingra said. “A lot is happening in a very short amount of time.”
Dhingra mapped satellite images of Tycho and Jackson, looking for areas of similarity and patterns — as he likes to say, for “order in chaos.” Specifically, his research focused on understanding the character of the molten material, or impact melt, which is produced during the cratering event. Dhingra mapped the central regions of Tycho and Jackson because the crater floors are the largest repositories of impact melt.
“When you don’t know about a surface, you map it, and that’s the beginning of the story,” Dhingra said. “Once you finish the mapping, then depending on your interest or background, you start defining features and develop over time a logical geological interpretation of the features as well as the area.”
Studying his geological maps, he made several observations, including noting organized elevation differences on the craters’ floors, which he believes, could have multiple causes.
“It was intriguing because here we are talking about a very large area — several 10s of kilometers — neatly divided into units at different elevations,” he said. “This is least expected from impact cratering, which is so energetic, short-duration and involves large-scale material movement.”
Dhingra’s study also reports the evidence for kilometers-wide sheets of once-molten rock occurring in different parts of the craters. He coined the term “impact melt wavefronts” for these features, based on their similarity to waves on a beach. However, he said, the most interesting aspect is these features’ location. Several of them appear to be resting on surfaces that are few hundred meters to a kilometer above the crater floor. Earlier researchers thought that impact melt was too viscous to move much, but newer data like Dhingra’s shows otherwise and is providing new directions for further research.
“These things can actually flow very far. But this is just one of the many flavors of impact melt deposits,” he said.
Dhingra is now digging deeper into the features he mapped, seeking to understand how and why they formed, and what it can teach us about crater formation — which still happens all the time.
“This is a sample of what has been happening since the beginning of the solar system,” he said. “The question is, do you want to understand this fundamental geological process?”
Peek Into a Crater Today
Want to explore the moon? You can study in the UI Department of Physics — but you can also start now. Arizona State University offers unlimited access to high quality images taken by NASA’s Lunar Reconnaissance Orbiter Camera (LROC) and other missions at the LROC Quick Map website. For questions about lunar exploration research, contact Dhingra.