China will ‘hop’ a probe into a Moon crater for frozen water

Next week, China will launch Chang’e-7, a robotic mission designed to directly sample frozen water deposits in a crater near the lunar south pole, marking the first time a spacecraft will attempt this direct sampling. The mission aims to determine the quantity, distribution, and origin of ice in these permanently shadowed regions, where temperatures remain among the coldest in the solar system. Yuqi Qian, a planetary geologist at the University of Hong Kong, says that Chinese scientists have steadily grown their capabilities in lunar science with the Chang’e missions.

Lunar base planners are considering the strategic use of these potential resources, and Carolyn van der Bogert, a planetary geologist at the University of Münster, adds that understanding the source of the water is vital. These ice deposits are crucial for potential lunar outposts, offering resources like drinking water and rocket fuel.

Chang’e-7’s “Hopping” Probe Explores Shackleton Crater Terrain

The Chang’e-7 mission will employ a unique “hopping” probe to investigate terrain inaccessible to conventional rovers within Shackleton crater, a permanently shadowed region near the Moon’s south pole. Unlike static landers or rolling rovers, this probe utilizes small thrusters to navigate steep slopes and explore areas where sunlight never reaches, allowing for targeted sampling of potentially ice-rich deposits.

This capability is crucial because the mission aims to determine not only the presence of water ice, but also its geological context and depth distribution. Shackleton crater was selected as the primary landing site due to its proximity to both sunlight and permanent shadow; nearly continuous sunlight will power the mission’s components while shadowed terrain lies within a short distance.

The probe is equipped to drill as deep as 1 meter into the lunar soil, heat the extracted samples, and analyze the released gases, providing a direct assessment of the ice’s composition and quantity. Beyond simply confirming the existence of water, the mission will analyze the ratio of hydrogen to deuterium, its heavier isotope, within the ice.

This isotopic fingerprint will help scientists determine the origin of the lunar water, potentially differentiating between sources like ancient comet and asteroid impacts versus water formed on the Moon itself through solar wind interactions. Some theories suggest a substantial fraction of the ice originated from hydrogen ions reacting with lunar minerals, a process that would leave a distinct deuterium signature.

Van der Bogert also notes that previous missions didn’t provide many details about the geological setting of the water ice. The Chang’e-7 orbiter will complement the surface measurements by mapping hydrogen concentrations from above, detecting neutrons emitted when cosmic rays interact with the lunar surface. While other missions, like NASA’s VIPER rover, also target lunar ice, Qian believes that the science from these missions will be complementary and collectively advance our understanding of the Moon’s polar regions.

Isotopic Ratios Reveal Water’s Origin and Lunar History

The upcoming Chang’e-7 mission isn’t solely focused on confirming the presence of water ice in lunar craters; it will also analyze the composition of that ice to unravel its origins. Instruments aboard the “hopping” probe will measure the ratio of hydrogen to deuterium, a critical step in determining whether the water arrived via comets and asteroids or formed in place through reactions involving the solar wind.

Water delivered by impacts would carry a higher concentration of deuterium compared to water created by solar wind interactions, allowing scientists to differentiate between these scenarios. Water released from ancient volcanic activity would exhibit an intermediate isotopic signature, potentially revealing a third source.

Regions with fewer emitted neutrons are expected to contain more hydrogen, and thus more water. While the Apollo missions established that sunlit regions of the Moon are largely dry, the true extent and distribution of water ice within the permanently shadowed craters remained unknown. NASA’s earlier missions, Clementine and Lunar Prospector, provided initial evidence of ice, but relied on indirect measurements.

A 2009 mission, which crashed a rocket stage into a shadowed crater, confirmed the presence of water vapor. The mission’s ability to analyze samples at this depth will be crucial in determining whether the ice is pure or mixed with lunar regolith, and ultimately, how sustainable a resource it might be for future lunar outposts.