A solution to a long-unsolved question may have been found with scientists showing that the Moon already had water when it formed and that the water didn’t arrive with comets or asteroids.
The study published in Nature Geoscience by researchers at Vrije University in Amsterdam adds weight to the claims that water was present on the moon and Earth from the outset and weakens the theories that have pegged water-bearing comets and/or asteroids as being the source of water on Moon. The studies based on data from Rosetta spacecraft when it visited comet 67P showed that the water on the comet had a combination of isotopes that did not match Earth’s and that blew a dent in the theories that asteroids or comets had a role to play in presence of water on our planet and its natural satellite.
Wim van Westrenen and team carried out a study in their lab by making up a mixture containing oxygen and silica along with other ingredients including magnesium, calcium, iron, titanium and aluminium. With 10 milligrams of this mixture – something that resembled the mixture with which the moon is thought to have originated – they carried out experiments in lab to mimic the components that gave rise to the lunar magma ocean, the initial liquefied mass that gradually cooled and solidified to form the moon.
Scientists came up with the recipe based on the seismic data collected from the moon’s surface by instruments left there by Apollo astronauts. The team then went about simulating the conditions on moon as it would have been while it was evolving by subjecting the mixture to various temperature and pressure conditions. What they specifically did was to subject the mixture both with and without water to see whether this affected the type and amount of rocks formed.
What the team found was surprising. When water was included in the mix, at levels of just 0.5 to 1 per cent by weight, the end result was formation of compounds that reflect the rock composition that has been detected or measured on the moon. Most importantly, the water-based mixture generated a layer of plagioclase—the dominant component of the crust – that when extrapolated to the moon would be around 34 to 43 kilometres thick. This tallies with the average thickness reported in 2013 based on data from satellites orbiting the moon.
In absence of water, the plagioclase layer ended up twice as deep, at 68 kilometres suggesting that the existing make-up of the moon’s geology could only have evolved if water was there at the outset.