Chinese scientists have identified the chemical makeup and likely origin of a mysterious gel-like substance found on the moon in 2019.
The dark green material was first observed by China’s Yutu-2 rover while exploring terrain near the Von Kármán crater, a famous impact site on the far side of the moon that measures around 110 miles in diameter.
New analysis by a group of researchers at the Chinese Academy of Sciences confirms that the substance wasn’t actually a gel but a hard and glassy mineral compound that had been melted and reformed at high heat by an ancient asteroid impact.
The team identified it specifically as a form of breccia, a kind of rock formed by mineral fragments that are ‘cemented’ together by some external force.
According to the team, the substance was ‘formed by impact-generated welding, cementing and agglutinating of lunar regolity and breccia.’
The substance initially caught the eye of scientists controlling the Yutu-2 rover because of how dissimilar it was to the surrounding soil at the Von Kármán crater, according to a report in Newsweek.
At the time it was widely described as dark green and ‘gel-like’ because of how it appeared through the rover camera, with glossy sheen that stood in sharp contrast to the dry lunar soil around it.
It’s likely the first wave of reports about the substance were due to a mistranslation from the original documents shared by the Chinese authorities.
Some had suggested the substance might have come from volcanic activity, but the Chinese researchers later ruled that out as the moon hasn’t seen any active volcanos in over three billion years.
Instead, the team determined the substance was a mix of pagioclase, a whitish gray crystal, iron-magnesium silicate, olivine and pyroxene, all of which were melted and mixed together by the heat of an asteroid impact.
Scientists are still puzzled by how the substance ended up in the Von Kármán crater given how different it is from the surrounding soil.
The researchers suggest the likeliest explanation is that it was thrown across a significant distance by an especially intense impact, though where and when the impact occurred are still unknown.