Seeing What's Beneath from High Above
Former Abbey Road Studios doorman Gerry O’Driscoll provided the final words on Pink Floyd’s legendary The Dark Side of the Moon album, quipping, “There is no dark side of the moon, really; as a matter of fact, it’s all dark.” Nearly a half-century after that album was recorded at London’s Abbey Road Studios, a Baylor planetary geophysics assistant professor is shedding new light on the far side of the moon.
Dr. Peter James, founder of Baylor’s Planetary Research Group in the College of Arts and Sciences, was lead author of Deep Structure of the Lunar South Pole-Aitken Basin, published in the journal Geophysical Research Letters (April 2019). His research discovered a large mass beneath the Moon’s South Pole-Aitken Basin that may contain metal from an asteroid that crashed into the Moon and formed the crater, widely recognized as our solar system’s largest impact crater.
“Imagine taking a pile of metal five times larger than the Big Island of Hawai‘i and burying it underground,” James said. “That’s roughly how much unexpected mass we detected.”
James’ study is based on data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL), a 2011-12 lunar science mission that used high-quality gravitational field mapping to determine the Moon’s interior structure.
“The Gospel and the idea of grace are all the more extraordinary when we realize just how small and insignificant we are in the grand scheme of creation.”
“When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin,” James said. “One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon’s mantle.”
The oval-shaped South Pole-Aitken Basin is as wide as 2,000 kilometers (1,243 miles) — roughly the distance between Waco and Washington, D.C. — and as much as 13 kilometers (8.1 miles) deep. According to James, the dense mass weighs the basin floor downward by more than a half mile. Computer simulations of large asteroid impacts suggest that, under the right conditions, an iron-nickel core of an asteroid may be dispersed into the upper mantle (the layer between the Moon’s crust and core) during impact.
“We did the math and showed that a sufficiently dispersed core of the asteroid that made the impact could remain suspended in the Moon’s mantle until the present day, rather than sinking into the Moon’s core,” James said.
Another possibility is that the large mass might be a concentration of dense oxides associated with the last stage of lunar magma ocean solidification.
Assisting James in the research was Dr. David E. Smith, principle investigator of the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter at NASA’s Goddard Space Flight Center. Other co-researchers were Dr. Paul K. Byrne (North Carolina State University), Dr. Jordan D. Kendall (Goddard Space Flight Center), Dr. H. Jay Melosh (Purdue University) and Dr. Maria T. Zuber (GRAIL principal investigator).
The South Pole-Aitken Basin is our solar system’s largest preserved crater. Larger impacts may have occurred throughout the solar system, including on Earth, but most traces of those have been lost.
“It is one of the best natural laboratories for studying catastrophic impact events, an ancient process that shaped all of the rocky planets and moons we see today,” James said.
An Urey Research Fellow at Houston’s Lunar and Planetary Institute since August 2016, James joined Baylor’s faculty in August 2017. He was a post-doctorate research scientist at Columbia University and Massachusetts Institute of Technology (MIT). He holds bachelor’s degrees in geology and physics from Brown University and a doctorate in planetary science from MIT.
The Moon findings garnered widespread recognition for James and Baylor. However, this is far from where his research vision ends. James is collaborating with NASA’s Goddard Space Flight Center to study Mercury’s crust.
“The ultimate aim of using geophysical techniques to explore the structure and inner workings of rocky planets in our solar system is to understand how Earth-like planets form and evolve,” he said.
The robotic spacecraft MESSENGER, a backronym for “MErcury Surface, Space ENvironment, GEochemistry, and Ranging,” orbited Mercury between 2011 and 2015. It was the first spacecraft to enter Mercury’s orbit.
“Four planets in our solar system have a surface made of rock (Mercury, Venus, Earth and Mars), but each of those planets is unique in a weird way,” James said. “Mercury is particularly exciting to study because we get to see parts of that planet for the first time.”
Along with engineers at Goddard Space Flight Center, James is analyzing MESSENGER’s tracking data to calculate the density of the planet’s bedrock.
“Mercury has a lot of odd features that don’t exist anywhere else,” James said. “It has thousands of pits that we call ‘hollows.’ They’re clearly different from craters, but we haven’t yet figure out how they form. Mercury also has some broad bulges called ‘rises’ that are about a thousand miles wide and about a mile tall. We haven’t figured out what those are either.”
James said the most exciting discovery about Mercury is that it contains ice, despite the planet’s close proximity to the Sun. He was on a team that used MESSENGER’s laser to measure the thickness of these ice deposits.
“The bottoms of some craters near the north pole never see sunlight, so those areas stay cold enough to have ice,” James said. “There is still a lot we want to learn about how the ice got there and whether it could be mined by future astronauts.”
James was drawn to planetary geophysics through his love of contour maps from Boy Scout hikes as a child. His website displays author and theologian C.S. Lewis’ quote: Aim for heaven, and you will get Earth thrown in.
“We talk about having a ‘kingdom mindset,’ meaning that we keep heaven in mind while making choices in our daily lives,” James said. “That also encapsulates the best ideals of space exploration. Each of the Apollo astronauts would tell you that going above the Earth and looking down fundamentally changed his worldview — no pun intended.
“A lot of social and political maneuvering tends to be rooted in selfishness. But out in space, you realize exactly how much larger and more complex the universe is than our personal ambitions. That’s good for society, and it gives us a richer understanding of Christian theology, as well. The Gospel and the idea of grace are all the more extraordinary when we realize just how small and insignificant we are in the grand scheme of creation.”