Naturally occurring graphene has been found in lunar samples, a discovery that potentially reshapes the debate on the formation of Earth’s Moon, according to Chinese researchers at the Jilin University School of Materials Science & Engineering.
“This is the first study to verify the presence of natural few-layer graphene in lunar soil samples by examining its microstructure and composition,” explained study lead author Wei Zhang in a paper published in the journal National Science Review. “Our finding provides new insights into the origin of the Moon, supporting the hypothesis of a carbon-containing Moon.”
Graphene, a form of carbon known as a fullerene that is also produced on Earth through man-made technological processes, could be a missing key to unlocking lunar mysteries, as well as practical material science and engineering prospects on Earth.
How the Moon Was Formed
Based on studies of lunar samples from the US Apollo space missions that were analyzed decades ago, a consensus has formed involving what scientists call the “giant-impact hypothesis.” The concept was first proposed by geologist Reginald Daly in 1946, and speculates that in the distant past, Earth collided with another celestial body about the size of Mars, resulting in an ejection of rock into space, which later coalesced into the moon.
Yet certain problems with that idea have accumulated over time. Two examples of this exist in earlier work involving lunar basalts, the same type of material that Zhang’s team looked at. These previous analyses included the identification of H2O, water on the Moon when hydrogen should have been lost in such an impact, and carbon, which should have met a similar fate.
New Lunar Samples
The Jilin University scientists worked with samples obtained during the Chang’e 5 mission, christened in honor of the Chinese moon goddess, Chang’e. China’s fifth excursion to the Moon on December 1, 2020, it was the first to return with samples when it landed back on Earth on December 16 of that year. Notably, the sample this team looked at came from the northern Oceanus Procellarum, a portion of the surface free of previous human interaction.
It was not only the first Chinese mission to return a lunar sample to Earth, but also the first mission from any nation to do so since a 1976 Soviet mission. This accomplishment made China the third and most recent country to conduct such a mission after the United States and the Soviet Union.
Graphene, a Modern Discovery
Graphene is a two-dimensional material comprised of a honeycomb-patterned single layer of carbon atoms. After decades of speculation by scientists, it was only isolated for the first time in 2004.
The demand for the 2D metamaterial has blossomed into a $570 million global market in the last two decades. While its flexibility and conductivity have long made it of interest in electronics and battery applications, its antibacterial and antiviral efficacy only increase its utility in the post-COVID-19 world.
“Graphene has revolutionized the research of condensed matter physics and materials science with its novel physical phenomena and extraordinary properties,” Zhang and the research team involved with the recent discovery explained in a newly published study.
With about 1.9% of interstellar carbon taking the form of graphene, its role in planetary science is growing. Twenty years of work on developing artificial graphene have left its formation, composition, and structure well understood. Armed with this information, the team was well positioned to examine natural graphene and extrapolate from it information on the Moon’s geological evolution.
Lunar Graphene is Analyzed
With the youngest basalt samples so far obtained from lunar regolith the researchers decided to take a closer look. Targeting high carbon spots with correlative scanning electron microscopy and the Raman technique, where scattered light measures vibrational energy to create hyperspectral images, they found that “graphene is embedded as individual flakes or formed as part of a carbon shell enclosing mineral particles.”
Other elements were also noticed to coexist in high carbon in significant measurements. Most notable was iron, followed by a combination of silicon and calcium compounds. Finding the graphene in a carbon shell was a significant clue to the researchers, as it suggests a bottom-up synthesis, usually the result of a high-temperature catalytic reaction.
The paper proposes two potential formation hypotheses on lunar graphene formation that conform to this high-temperature parameter. The first is a volcanic eruption, known to have occurred on the Moon, although the heaviest period ended about three million years ago, combined with solar wind stirring up lunar dust.
The second, a theoretical meteorite impact, only further points to a local process of generation due to the scarcity of graphene in known meteorite samples. Iron potentially comes into play as a catalyzing agent for the natural graphene production process. Either scenario points to a process whereby the Moon gradually accumulates indigenous carbon through a natural capture process.
Toward a Better Understanding of The Moon and Material Science
This discovery illuminates the previously unknown natural graphene formation processes that may be occurring on the Moon, pointing in the direction of further research to grapple with what exactly is transpiring. With the current focus on the economic side of space exploration, such as private endeavors like SpaceX, tying lunar discoveries to technology-driving commodities like graphene only increases the utility of such research.
Concluding their paper, the researchers envision a shared future of expanding knowledge of our closest celestial partner’s birth and meeting our material needs here on Earth.
“Further in-depth property investigation of natural graphene would provide more information on the geologic evolution of the Moon,” they write. “In turn, the mineral-catalyzed formation of natural graphene sheds light on the development of low-cost scalable synthesis techniques for high-quality graphene.”
“Therefore, a new lunar exploration program may be promoted, and some forthcoming breakthroughs can be expected.”
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org.