July 19, 2023 — NASA has selected Southwest Research Institute to lead a $50 million lunar lander/rover instrument suite, Dating an Irregular Mare Patch with a Lunar Explorer, or DIMPLE, designed to understand if the Moon has been volcanically active in the geologically recent past. DIMPLE, which was developed by SwRI, will use cameras and radioisotope-based dating to determine the age and composition of an anomalously young-looking patch of basalt named Ina.
“I am thrilled for the opportunity to send DIMPLE to the Moon to better understand the age and composition of Ina,” said SwRI Staff Scientist Dr. F. Scott Anderson, who is principal investigator of DIMPLE. “We are going to date the rocks at Ina directly using the first-ever purpose-built radioisotope rock dating instrument for use in space, called CODEX (Chemistry Organic and Dating Experiment).”
Ina is an enigmatic formation of unusually smooth mounds surrounded by rough troughs, all inside the central crater of a large volcano. Ina looks much younger than other places on the Moon because it has very few impact craters. Impact craters build up on the lunar surface over time, so older surfaces generally have more impact craters compared to younger surfaces.
“This challenges our understanding of lunar geochemical evolution, since a geologically recent eruption requires unexpectedly long-lived heat sources in the lunar interior,” Anderson said. “If Ina really is as young as it appears, that means that the Moon has been volcanically active much more recently than scientists have thought. Or, if we find that Ina is as old as typical lunar rocks, that indicates that the material properties of certain rocks can fool us, if we are not careful, as we try to understand the ages of planetary surfaces throughout the solar system.”
If rock formations like Ina do not give rise to impact craters, or do not preserve them over the eons, then some current ideas about solar system history could be wrong.
“That’s why radioisotope dating is so important,” says Dr. Jonathan Levine, a physicist at Colgate University who serves as DIMPLE’s deputy principal investigator. “Radioactive decay is a clock that ticks at a known rate. These techniques accurately determine the ages of rocks and minerals, allowing scientists to date events such as crystallization, metamorphism and impacts.”
The CODEX instrument exploits the natural radioactive decay of rubidium into strontium as a measure of how much time has elapsed since a rock sample formed. The SwRI-led team has been developing CODEX for two decades.
“Dating is a challenging process. Traditional techniques are not easily adapted to spaceflight, requiring a sizable laboratory and several months to determine a date,” Anderson said. “By contrast, the entire DIMPLE payload is going to weigh less than 50 kilograms and needs to run autonomously on the Moon. In our lab, we have shown that CODEX can accurately date rock samples like those we expect to find at Ina with a precision of better than ±375 million years, which is more than sufficient to situate the origin of Ina in the billions-of-years-long history of the Moon.”
DIMPLE is part of NASA’s Payloads and Research Investigations on the Surface of the Moon (PRISM), which will be delivered to Ina through the Commercial Lunar Payload Services (CLPS) initiative. A camera, sample collection arm and the CODEX instrument will remain on the lander, while a rover equipped with a camera and rake will scoop and transport samples back to the lander instruments for detailed study. The DIMPLE team includes The Aerospace Corporation, the University of Bern, Colgate University and Lockheed Martin.
CLPS is a key part of NASA’s Artemis lunar exploration plans. The science and technology payloads sent to the Moon’s surface will help lay the foundation for human missions on and around the Moon.