Tiny X-ray telescope could unlock the Moon’s hidden chemistry

Their detailed modeling, which included both the telescope detector and a realistic Moon orbiting satellite mission, suggests that one telescope could map five important elements in about two years. A larger five by five array of detectors could produce sharper maps and complete the work more quickly.

Mapping the Moon’s Chemistry

The Moon’s geological history is still not fully understood. One major reason is that scientists do not yet have a complete geochemical map of the lunar surface. Because researchers cannot simply collect samples from every part of the Moon, they must rely on remote sensing methods.

One of these methods is X-ray fluorescence imaging. In this approach, detectors are pointed at the Moon to capture X-rays emitted by specific elements after they are struck by solar radiation. Those signals can help reveal which elements are present across different regions of the surface.

Why Complete Lunar Maps Are Difficult

Earlier observations from the Apollo and Chandrayaan missions produced useful partial maps, but a full global map is still missing. Creating one is technically difficult for several reasons. Missions have limited time to gather enough sunlight driven X-ray signals, and detectors can degrade during long periods in space.

The problem is especially difficult near the Moon’s poles. In these regions, solar X-rays are weaker, which makes it harder to collect the signals needed to identify surface elements.

A Compact X-Ray Telescope for Lunar Orbit

To address these obstacles, a team led by Airi Toida and Prof. Yuichiro Ezoe of Tokyo Metropolitan University has proposed using a compact X-ray telescope on a satellite orbiting the Moon. The telescope would allow wide area observations of the lunar surface during strong solar flares, when the Sun provides more intense X-ray illumination.

Traditional X-ray telescopes are often too large and heavy for this type of mission. By contrast, the team’s compact telescope was originally designed for studying Earth’s magnetosphere and weighs less than ten kilograms. Its small size could make it practical for long term lunar satellite observations.

The detector has also been tested in radiation conditions far harsher than those expected in lunar orbit. That durability could support robust, wide area, high resolution imaging over an extended mission.

Simulations Show a Path to a Full Moon Map

The researchers then added the telescope’s specifications into a numerical simulation to test whether a satellite mission could successfully map the Moon. Assuming 300 solar flares per year and a single telescope aboard a Moon orbiting satellite, the simulation showed that the whole lunar surface could be mapped for five elements (oxygen, iron, magnesium, aluminum, silicon) in two years, using a grid size of 70 x 70 kilometers.

Because the telescope is so compact, the team also examined a satellite carrying a five by five array of telescopes. According to the simulations, this 25 telescope system could reduce the mission time to one year. With two years of operation, it could also map sodium, while improving the grid size to 30 x 30 kilometers.

A New Window Into Lunar Geology

If either mission concept becomes reality, it would produce the first complete map of elemental abundance across the entire Moon. That achievement would give scientists a powerful new tool for studying lunar geology and reconstructing the Moon’s long and complex history.

This work was supported by JSPS KAKENHI Grant Number 21H04972.