Researchers at Tokyo Metropolitan University have used simulations to show that a newly developed small X-ray telescope could help create a chemical map of the entire lunar surface. Maps like this would be a big step toward understanding how the moon formed, changed, and evolved over time.
Their detailed modeling, which includes both telescope detectors and a realistic lunar orbiter mission, suggests that a single telescope could map five important elements in about two years. Increasing the detector array to 5 × 5 may produce a sharper map and get the job done more quickly.
Mapping the moon’s chemical structure
The moon’s geological history is still not fully understood. One of the main reasons is that scientists do not yet have a complete geochemical map of the lunar surface. Researchers cannot simply collect samples from every location on the moon, so they must rely on remote sensing techniques.
One of these methods is X-ray fluorescence imaging. This approach points a detector at the moon to capture the X-rays emitted by certain elements after they are hit by solar radiation. These signals help reveal which elements are present in different areas of the surface.
Why is it difficult to create a complete map of the moon?
Previous observations by the Apollo and Chandrayaan missions have produced useful partial maps, but a complete map of Earth is still missing. Creating one is technically difficult for several reasons. Missions only have a limited amount of time to collect enough X-ray signals from sunlight, and long stays in space can degrade detectors.
This problem is especially difficult near the moon’s poles. The weak solar X-rays in these regions make it difficult to collect the signals needed to identify surface elements.
Small X-ray telescope for lunar orbit
To address these obstacles, a team led by Airi Toida and Professor Yuichiro Ezoe of Tokyo Metropolitan University proposed mounting a small X-ray telescope on a satellite orbiting the moon. The telescope will enable observation of large areas of the moon’s surface during strong solar flares, when the sun provides more intense X-ray radiation.
Traditional X-ray telescopes are often too large and heavy for these types of missions. In contrast, the team’s small telescope, originally designed to study Earth’s magnetosphere, weighs less than 10 kilograms. Its small size could make it practical for long-term lunar satellite observations.
The detector has also been tested in much harsher radiation conditions than expected in lunar orbit. This durability has the potential to support robust, wide-range, high-resolution imaging over long-duration missions.
Simulation shows the way to full moon map
The researchers then added the telescope’s specifications to a numerical simulation to test whether the satellite mission could successfully map the moon. Simulations assuming 300 solar flares per year and one telescope on a lunar orbiter showed that five elements (oxygen, iron, magnesium, aluminum, and silicon) could be mapped across the entire lunar surface within two years using a grid size of 70 x 70 kilometers.
Because this telescope is so compact, the researchers also investigated a satellite carrying a five-by-five telescope. According to simulations, this 25-telescope system could reduce the mission duration to one year. Two years of operation have improved the grid size to 30 x 30 kilometers while also enabling sodium mapping.
A new window into the geology of the moon
If either mission concept becomes a reality, it would create the first complete map of elemental abundance across the moon. This result will provide scientists with powerful new tools to study the Moon’s geology and reconstruct the Moon’s long and complex history.
This research was supported by JSPS KAKENHI Grant Number 21H04972.
