The minerals were probably formed as a result of intense vaporisation and deposition triggered by the constant, powerful bombardment of micrometeorites from space, the team says in Nature Astronomy. Photo: Chinese National Space Agency Lunar Exploration and Space Engineering Center
Scientists could be a step closer to solving the mystery of how the surface of the moon got its weathered and cratered appearance, after the discovery of unique minerals in lunar soil samples collected by the Chang’e 5 mission.
Titanium compounds, including Ti2O, which have never been seen in natural samples on Earth, were found on the surface of a tiny glass bead brought back by China’s Chang’e 5 spacecraft in 2020, according to researchers from the Institute of Geochemistry in Guiyang and their colleagues in Guangzhou and Macau.
The minerals had probably formed as a result of intense vaporisation and deposition – the transition of gas into solid without passing through the liquid phase – triggered by the constant, powerful bombardment of micrometeorites from space, the team wrote in the journal Nature Astronomy last week.
“Micrometeorite impacts have been known to play a key role in altering the lunar landscape, but how those transformations actually happened remained elusive,” the researchers wrote in a release on the institute’s website.
“Our study provided new clues to the weathering processes on the moon as well as on other airless planetary bodies in the solar system, such as Mercury and asteroids,” they wrote.
The titanium compounds were found on a 9-micrometer-diameter meteorite impact crater on the surface of a Chang’e 5 glass bead. Photo: Handout
The team said that Ti2O, which came in two structures on the bead, became the seventh and eighth minerals ever discovered by humankind on the moon. The first five were found in US Apollo missions and Russian Luna missions, while a sixth one, named Changesite-(Y), was detected by China in Chang’e 5 samples in 2022.
Titanium is an element commonly found on Earth and the moon. However, it only exists as an oxide in nature. In its dominant form, titanium dioxide (TiO2), each titanium atom is bonded to two oxygen atoms to create a stable, energetically favourable structure.
In this study, the researchers first collected a total of 25 glass beads – which measured 0.05mm-0.4mm across – from Chang’e 5 samples acquired from the China National Space Administration.
They then used cutting-edge transmission electron microscopy techniques to examine the glass beads, and found a tiny impact crater on the surface of one of the beads, according to the paper.
The formation scenario proposed by the Chinese team explains how a micrometeorite impact results in the vaporisation-deposition of Ti-oxide compounds on the lunar surface. Photo: Handout
On the rim of the crater, they detected three titanium-containing minerals – rutile (TiO2), trigonal Ti2O, and triclinic Ti2O. The latter two share the same chemical composition but have different crystal structures.
While Ti2O does not exist in nature on Earth, it has been prepared in a laboratory to make photocatalytic thin film materials, the researchers said.
The team went on to propose that micrometeorites, travelling at the speed of over 20km per second, crashed into the moon’s surface and hit a common and significant mineral known as ilmenite, which contains iron, titanium and oxygen. These collisions created sufficient energy to cause the ilmenite grains to melt, vaporise and then redeposit onto the rim of the impact crater, they said.
Such a scenario was predicted by US planetary scientist Bruce Hapke five decades ago, the researchers said.
Their work was supported by the National Key Research & Development Programme, the Strategic Priority Programme of the Chinese Academy of Sciences and the National Natural Science Foundation of China.
