If not for the Joshua trees, the tan hills of Cuprite, Nevada, would resemble Mars. Scalded and chemically altered by water from deep underground, the rocks here are earthly analogs for understanding ancient Martian geology. The hills are also rich with minerals. They’ve lured prospectors for more than 100 years and made Cuprite an ideal place to test NASA technology designed to map the minerals, craters, crusts, and ices of our solar system.
Sensors that discovered lunar water, charted Saturn’s moons, even investigated ground zero in New York City were all tested and calibrated at Cuprite, said Robert Green, a senior research scientist at NASA’s Jet Propulsion Laboratory in Southern California. He’s honed instruments in Nevada for decades.
One of Green’s latest projects is to find and map rocky surfaces in the American West that could contain minerals crucial to the nation’s economy and security. Currently, the U.S. is dependent on imports of 50 critical minerals, which include lithium and rare earth elements used in everything from rechargeable batteries to medicine.
The hills of Cuprite, Nevada, appear pink and tan to the eye (top image) but they shine with mica, gypsum, and alunite among other types of minerals when imaged spectroscopically (lower image). NASA sensors used to study Earth and other rocky worlds have been tested there.
Scientists from the U.S. Geological Survey (USGS) are searching nationwide for domestic sources. NASA is contributing to this effort with high-altitude aircraft and sensors capable of detecting the molecular fingerprints of minerals across vast, treeless expanses in wavelengths of light not visible to human eyes.
The collaboration is called GEMx, the Geological Earth Mapping Experiment, and it’s likely the largest airborne spectroscopic survey in U.S. history. Since 2023, scientists working on GEMx have charted more than 190,000 square miles (500,000 square kilometers) of North American soil.
Mapping Partnership Started During Apollo
As NASA instruments fly in aircraft 60,000 feet (18,000 meters) overhead, Todd Hoefen, a geophysicist, and his colleagues from USGS work below. The samples of rock they test and collect in the field are crucial to ensuring that the airborne observations match reality on the ground and are not skewed by the intervening atmosphere.
The GEMx mission marks the latest in a long history of partnerships between NASA and USGS. The two agencies have worked together to map rocky worlds — and keep astronauts and rovers safe — since the early days of the space race.
NASA’s AVIRIS flies aboard a research plane in this animation, identifying minerals on the ground such as hectorite — a lithium-bearing clay — by the unique wavelengths of light that they reflect. The different wavelengths, measured in nanometers, look like colorful squiggles in the box on the right.
For example, geologic maps of the Moon made in the early 1960s at the USGS Astrogeology Science Center in Flagstaff, Arizona, helped Apollo mission planners select safe and scientifically promising sites for the six crewed landings that occurred from 1969 to 1972. Before stepping onto the lunar surface, NASA’s Moon-bound astronauts traveled to Flagstaff to practice fieldwork with USGS geologists. A version of those Apollo boot camps continues today with astronauts and scientists involved in NASA's Artemis mission.
Rainbows and Rocks
To detect minerals and other compounds on the surfaces of rocky bodies across the solar system, including Earth, scientists use a technology pioneered by JPL in the 1980s called imaging spectroscopy. One of the original imaging spectrometers built by Robert Green and his team is central to the GEMx campaign in the Western U.S.
About the size and weight of a minifridge and built to fly on planes, the instrument is called AVIRIS-Classic, short for Airborne Visible/Infrared Imaging Spectrometer. Like all imaging spectrometers, it takes advantage of the fact that every molecule reflects and absorbs light in a unique pattern, like a fingerprint. Spectrometers detect these molecular fingerprints in the light bouncing off or emitted from a sample or a surface.
In the case of GEMx, that’s sunlight shimmering off different kinds of rocks.
Geophysicist Raymond Kokaly, who leads the GEMx campaign for USGS, is pictured here conducting ground-based hyperspectral imaging of rock in Cuprite, Nevada, in April 2019.
Compared to a standard digital camera, which “sees” three color channels (red, green, and blue), imaging spectrometers can see more than 200 channels, including infrared wavelengths of light that are invisible to the human eye.
NASA spectrometers have orbited or flown by every major rocky body in our solar system. They’ve helped scientists investigate methane lakes on Titan, Saturn’s largest moon, and study Pluto’s thin atmosphere. One JPL-built spectrometer is currently en route to Europa, an icy moon of Jupiter, to help search for chemical ingredients necessary to support life.
“One of the cool things about NASA is that we develop technology to look out at the solar system and beyond, but we also turn around and look back down,” said Ben Phillips, a longtime NASA program manager who led GEMx until he retired in 2025.
The Newest Instrument
More than 200 hours of GEMx flights are scheduled through fall 2025. Scientists will process and validate the data, with the first USGS mineral maps to follow. During these flights, an ER-2 research aircraft from NASA’s Armstrong Flight Research Center in Edwards, California, will cruise over the Western U.S. at altitudes twice as high as a passenger jet flies.
At such high altitudes, pilot Dean Neeley must wear a spacesuit similar to those used by astronauts. He flies solo in the cramped cockpit but will be accompanied by state-of-the-art NASA instruments. In the belly of the plane rides AVIRIS-Classic, which will be retiring soon after more than three decades in service. Carefully packed in the plane’s nose is its successor: AVIRIS-5, taking flight for the first time in 2025.
Together, the two instruments provide 10 times the performance of the older spectrometer alone, but even by itself AVIRIS-5 marks a leap forward. It can sample areas ranging from about 30 feet (10 meters) to less than a foot (30 centimeters).
“The newest generation of AVIRIS will more than live up to the original,” Green said.
More About GEMx
The GEMx research project will last four years and is funded by the USGS Earth Mapping Resources Initiative. The initiative will capitalize on both the technology developed by NASA for spectroscopic imaging, as well as the agency’s expertise in analyzing the datasets and extracting critical mineral information from them.
Data collected by GEMx is available here.