In a new milestone in lunar exploration, NASA this week said that it’s Lunar Reconnaissance Orbiter (LRO) spacecraft had found evidence that the Moon’s subsurface might have greater quantities of metals such as iron and titanium than thought before. The metallic distribution was observed by the Miniature Radio Frequency (Mini-RF) instrument aboard the LRO.
Published on July 1 in Earth and Planetary Science Letters, the finding could aid in drawing a clearer connection between Earth and the Moon, the press release said.
What NASA has found
In order to understand the origins of the Moon, scientists have for years explored the presence of metal deposits on the satellite comparative to Earth. As more data has become available over time, researchers have been able to further refine their hypotheses.
The new discovery by NASA is expected to challenge some of their past beliefs.
Out on a mission to look for ice in polar lunar craters, the LRO’s Mini-RF instrument was measuring an electrical property within lunar soil in crater floors in the Moon’s northern hemisphere. The property, known as the dielectric constant, is the ratio of the electric permeability of a material to the electric permeability of a vacuum.
To their surprise, the Mini-RF team observed that the level of this property increased as they surveyed larger craters, and kept rising in crater sizes up to 5 km in diameter. Beyond that size, the value of the dielectric constant leveled off. Essam Heggy, the lead author of the published paper and coinvestigator of the Mini-RF experiments, called the observation “a surprising relationship that we had no reason to believe would exist.”
What the discovery means
According to the NASA press release, the findings raise the possibility that the dielectric constant increased in larger craters because the meteors that created them dug up dust containing iron and titanium oxides from beneath the Moon’s surface. Dielectric properties are directly linked to the concentration of these metal minerals.
If true, this logic would imply that beyond a few meters of the Moon’s upper surface– which relatively has lower metal deposits– lie large unknown quantities of iron and titanium oxides.
The Mini-RF findings were backed by metal oxide maps from the LRO Wide-Angle Camera, Japan’s Kaguya mission and NASA’s Lunar Prospector spacecraft, which showed that larger craters with their increased dielectric material were also richer in metals. The maps suggested that more quantities of iron and titanium oxides were dug up from 0.5 to 2 km below the Moon’s surface as compared from the first 0.2 to 0.5 km.
NASA has now undertaken further research to find whether the same relation between metal deposits and crater size holds true on the southern hemisphere of the Moon.
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The Moon formation hypothesis
The most popular theory about the Moon’s creation is that a Mars-sized protoplanet collided with newly formed Earth around 4.5 billion years ago, breaking off a piece of our planet that went on to become its satellite. The hypothesis is also backed by substantial evidence, such as the close resemblance between the Moon’s bulk chemical composition with that of Earth.
However, it is also known that Earth’s crust has lesser amounts of iron oxide than the Moon– a finding that scientists have been trying to explain. Now, the new discovery of even greater quantities of metal on the Moon makes their job even more difficult. “It really raises the question of what this means for our previous formation hypotheses,” Heggy notes.
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According to an article in ScienceAlert, a possible reason could be that the Moon was created from a material much deeper beneath Earth’s surface than was believed before, or that the newly found metal presence could be the result of molten lunar surface cooling down gradually.