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Exploring new terrain

Wheaton professor leads mapping of Jovian moon

Geology Professor Geoffrey Collins led a team of researchers, including Wheaton students, in producing the first global geologic map of Ganymede, Jupiter’s largest moon and the largest satellite in our solar system.

The map, published by the U.S. Geological Survey, is the first complete global map of an outer-planet moon. It will provide critical data to scientists planning future studies and exploration of our solar system, including follow-up missions to Ganymede and other satellites of Jupiter.

The work is particularly significant because the moon offers a good model for understanding icy worlds that appear to be common in our solar system and beyond.

“On icy worlds such as Ganymede, liquid water probably exists below the surface and may be in contact with nutrients from rocky materials,” said Collins, who led the mapping team. “That’s one of the reasons we’re so interested in understanding how icy worlds work, so we can understand the possibility of life beneath the surface and how we should go about looking for it.”

The publication of the map marks a major development in our understanding of Jupiter’s moons, which were discovered more than 400 years ago by Galileo and have been the subject of ongoing study by Earth-based telescopes and, more recently, by spacecraft flying by or orbiting the fifth planet from the sun.

“The surface of Ganymede is over half as large as all the land area on Earth, so there is a wide diversity of locations to choose from,” Collins said. “Ganymede also shows features that are ancient alongside much more recently formed features, adding historical diversity in addition to geographic diversity.”

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Ganymede, the map (at left), paired with an image of the satellite, courtesy of the United States Geological Survey.

Despite its size, Ganymede and its fellow Jovian moons were simply points of light for Galileo and astronomers working up until the 1970s. NASA’s Voyager 1 and 2 missions as well as the Galileo orbiter, which orbited Jupiter from 1995 until 2003, provided the data to map the surface of Ganymede. The images captured depict a complex icy world whose surface is characterized by the striking contrast between its two major terrain types; the dark, very old, highly cratered regions, and the lighter, somewhat younger (but still ancient) regions marked with an extensive array of grooves and ridges.

“We didn’t start on the mapping in earnest until after the Galileo mission ended in 2003,” said Collins, “but I drew the first digital lines on what would eventually become the global map of Ganymede in 1999.”

At the time, he was a graduate student, working with James Head, a professor of geological sciences at Brown University and the lead scientist in charge of directing Galileo’s onboard camera at Ganymede.

“There has been a long string of Wheaton students who have worked on some aspect of this project,” Collins said. One student, Jonathan Kay ‘08, contributed a large enough portion of the work to be included as a co-author of the map, along with Collins, Head and others.

“My part of the project involved finding all craters larger than 30 kilometers and mapping them, as well as classifying them based on crater morphologies,” said Kay, who noted that the experience led to his first research post as a graduate student at the University of Idaho. He is currently completing his Ph.D. in earth and environmental science at the University of Illinois in Chicago.

Emily Martin ‘06 also credits her experience working on the project with Professor Collins in its earliest days for setting her on the path toward a Ph.D. in geological science at the University of Idaho.

“I remember that there was a big learning curve when I had started this project back in 2005,” said Martin, who is currently conducting NASA-funded research on the tectonic history of Saturn’s moon Enceladus. “I used GIS software to complete most of the work, and it's not simple. I continue to struggle with it today as my projects have gained more complexity, but I am very thankful that I got a head start learning this valuable tool.”

A major challenge of the project stemmed from data and images of varying levels of detail, Collins said. “We had to come up with a logically consistent set of criteria for how we were going to classify the terrain based on data of highly varying quality.”

In addition, smaller regional maps produced by earlier teams of scientists used a variety of classification systems. Collins and his collaborators dug into the earlier work to set global standards for the complete map, as well as filling in areas that had been previously unstudied.

The European Space Agency is currently planning a new mission to orbit Ganymede, and NASA is currently studying a mission to visit Jupiter and its satellites. The Ganymede map will serve as an indispensable guide to those plans, which will take more than a decade to unfold.

“That’s one of the weird things about the field of icy world geology: it operates on this very long timescale,” he said. “You’re working really hard to design scientific experiments, but you know that they won’t bear fruit for another two decades.”

“I will be approaching retirement by the time that we get the data to supplant this map,” he said. “But as good as this map is, I’m looking forward to getting new information that will make it obsolete.”