The Moon is practically on our doorstep, and yet, after decades of orbital missions and Apollo sample returns, we still don’t have a complete chemical map of its surface. A new study published in Earth, Planets and Space proposes an elegant fix: a compact, lightweight X-ray telescope that could finally read the Moon’s elemental chemistry from orbit, pixel by pixel.

Why Don’t We Already Know What the Moon Is Made Of?

We know a lot, but not everything. Sample return missions like Apollo gave us rich chemical data, but only for a handful of landing sites. Remote sensing from orbit has helped paint a broader picture, yet each technique has blind spots.

Gamma-ray spectroscopy, for example, can measure elements like potassium, iron, and titanium, but struggles badly with lighter elements such as magnesium, aluminum, and silicon. Optical and infrared spectroscopy is powerful for mapping minerals, but converting those measurements into reliable elemental abundances requires complex modeling that introduces large uncertainties, especially for light elements.

X-ray fluorescence (XRF) is the ideal complement. When solar X-rays strike the lunar surface, they excite atoms in the soil, which then re-emit X-rays at energies unique to each element, a kind of atomic fingerprint. XRF directly measures elemental abundances and is particularly good at detecting lighter elements like oxygen, sodium, magnesium, aluminum, and silicon.

The problem? Previous XRF instruments on missions like SMART-1, Chandrayaan-1, Chandrayaan-2, and SELENE (Kaguya) all ran into the same obstacles: solar flares were too infrequent or too weak during observation windows, detectors suffered radiation damage in the harsh space environment, and the polar regions, now of enormous scientific and exploratory interest, proved especially difficult because solar X-rays arrive at very low angles there, producing weak fluorescent signals.

The result: no complete global elemental map of the Moon. Not even close.

Enter the Lobster-Eye Telescope

Researchers at Tokyo Metropolitan University and affiliated institutions have now run detailed simulations for a new kind of XRF instrument, one light enough and compact enough to actually solve these problems.

The instrument is based on the GEO-X satellite design, originally built for imaging Earth’s magnetosphere in soft X-rays. Its key innovation is a lobster-eye X-ray optic, a technology inspired by, yes, the compound eyes of crustaceans. These eyes focus light by reflecting it twice off the walls of a grid of tiny square pores. The result is a wide field of view (10° × 10°) in a package weighing less than 10 kilograms and fitting inside a volume of about 3U (roughly the size of three stacked coffee cans).

Earlier XRF instruments couldn’t use telescopes at all, they relied on heavy mechanical collimators that made miniaturization impossible. The lobster-eye design, fabricated using MEMS (Micro-Electro-Mechanical Systems) silicon processing, sidesteps that constraint entirely.

The detector is a CMOS sensor sensitive to X-rays in the 0.3–2 keV energy range, with an energy resolution of about 120 eV, fine enough to distinguish the fluorescent signals of neighboring light elements like magnesium, aluminum, and silicon, something earlier instruments consistently failed to do.

What the Simulations Show

The team ran numerical simulations assuming the spacecraft orbits at 4,000 km altitude in a polar circular orbit, similar to what NASA’s Artemis Gateway platform will use, and that roughly 300 M-class solar flare events occur annually (a reasonable estimate accounting for M-class, C-class, and X-class flares together).

The results are promising. With a single telescope and a field of view divided into segments of about 70 km × 70 km resolution, global maps of oxygen, iron, magnesium, aluminum, and silicon could be completed in approximately two years. Sodium would take longer.

Scale the instrument up, mount 25 telescopes in a 5×5 array, and the picture changes dramatically. The combined field of view expands to 50° × 50°, the orbital altitude can be lowered to 1,700 km for sharper 30 km × 30 km resolution, and the mission timeline shrinks to about 27 days for oxygen and iron, around two months for magnesium, aluminum, and silicon, and two years for sodium.

Critically, the simulations show that even the lunar south pole, where solar X-rays arrive at extremely shallow angles, falls within reach, as long as solar X-ray incidence stays below 88°. That covers nearly the entire globe, including the polar regions that are the focus of upcoming human exploration and resource-prospecting missions.

Why the Lunar South Pole Matters

The lunar south pole has become one of the most contested and scientifically coveted destinations in planetary exploration. It harbors permanently shadowed regions (PSRs), craters that haven’t seen sunlight in billions of years, where water ice is thought to be trapped. Understanding the chemical composition of the polar surface is crucial for evaluating landing sites, interpreting results from rovers, and planning future sample return missions.

Until now, XRF coverage of the poles has been essentially nonexistent. The new instrument’s wide-field design, paired with smart flare-timing strategies, could change that.

The Bigger Picture

A complete global elemental map of the Moon would be far more than a scientific trophy. It would ground-truth the deep-learning models already being used to extrapolate chemical compositions from sample data. It would constrain models of lunar formation and the early magma ocean that shaped the Moon’s internal structure. And it would give mission planners the chemical context they need to make informed decisions about where to land and what to expect.

There is something quietly thrilling about the idea that the instrument capable of doing all of this might weigh less than a carry-on bag, and take design inspiration from a crustacean.

Source: Toida et al. (2026). “Numerical simulation of light-element geochemistry of the lunar surface using a compact and lightweight XRF imaging spectrometer.” Earth, Planets and Space, 78, 58. https://doi.org/10.1186/s40623-025-02326-2