New study finds Moon emits high levels of carbon

S. Yokota

The Earth’s moon has been found to emit carbon ions, according to a new study published in Science Advances. This new study is the latest to challenge the most commonly accepted origin theory of the Moon—the giant-impact hypothesis. 

Based on early samples obtained from NASA's Apollo missions, the Moon was said to have been formed on the impact of a Mars-sized protoplanet named Theia and the planet Earth. The consequent high temperatures drove matter into orbit around Earth, eventually coalescing into what we know as the Moon, some 4.5 billion years ago. 

This genesis event, which is sometimes called the Big Splash, depended on the idea that the Moon was a dry satellite, lacking volatile elements such as carbon and water. With temperatures hitting peaks between 3,500-5,800 ºC due to the clash, volatile substances were thought to have been depleted. Recent studies, however, have found evidence to the contrary. 

Researchers in Japan analysed the Moon’s global carbon emissions data gathered by the lunar orbiter KAGUYA—named for a moon princess from old Japanese folklore—of the Japanese Aerospace Exploration Agency. KAGUYA orbited the Moon for a year and a half over a decade ago. 

An ion mass spectrometer on KAGUYA took note of carbon ion fluxes, with traces of both carbon and water found in volcanic lunar crystals.So, the Moon appeared to emit carbon ions across its surface. “Our estimates show that carbon exists throughout the moon, supporting the hypothesis of a carbon-containing moon, where carbon was embedded in its formation and/or transported billions of years ago,” the researchers claim. 

KAGUYA’s ion mass spectrometer found regional differences in the carbon fluxes—51,000 carbon ions per square centimetre every second across the lunar seas and around 45,000 ions in the highlands. Despite these variations, the carbon levels were too high to simply be attributed to solar wind or small meteorites—two mechanisms by which the Moon receives carbon. 

Carbon has the potential to markedly alter planetary evolution. Thus, this evidence of carbon emissions on the Moon necessitates a revision, but not a complete discarding, of its theory of origin. 

Reference: Shoichiro Yokota et al. KAGUYA observation of global emissions of indigenous carbon ions from the Moon, Science Advances (2020). DOI: 10.1126 / sciadv.aba1050

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