Scientists May Have Overestimated the Amount of Water Present on Moon

Scientists studying the lunar mineral apatite may have overestimated the amount of water present on moon, according to a new finding.

The study, led by Jeremy Boyce at the UCLA Department of Earth, Planetary and Space Sciences, claims that the mineral led the scientists to overestimate the amount of water in the moon. This new finding knocks down the long held theory that hydrogen in the apatite is a strong indicator of the overall water content in the moon.

Apatite is the group of calcium and phosphate mineral occurring in several colors. Derived from the Greek work meaning 'deceit', apatite has a similar appearance to other minerals.

The finding is based on the computer model created by the researchers to precisely predict how apatite would have solidified from the cooling agents of the lunar magma in lunar history. Based on the model they learnt that the hydrogen-rich apatite crystals observed in several samples of lunar rocks might not have formed in a water-rich environment as previously thought.

"The mineral apatite is the most widely used method for estimating the amount of water in lunar rocks, but it cannot be trusted," Boyce said in a news statement. "Our new results show that there is not as much water in lunar magma as apatite would have us believe."

It was assumed earlier that liquid water cannot exist on the lunar surface as it has no atmosphere that can retain moisture. But the presence of hydrogen-rich apatite in the lunar rocks seen in 2010, offered clues that the lunar surface did hold water in the past. They initially considered that the data retrieved from a small sample of apatite could help predict the actual water content o of the entire moon, but this study refutes such theories claiming apatite is a deceptive indicator.

According to Boyce, the large water content within the lunar apatite is due to crystallization and not due to a water rich lunar environment.The apatite forms by combining the hydrogen atoms into its crystal structure. This hydrogen is present in the new crystallizing mineral only when fluorine and chlorine from the apatite are completely exhausted. In this case, the cooling body of magma forms the hydrogen rich apatite and does not accurately reveal the original water content in the magma.

"Early-forming apatite is so fluorine-rich that it vacuums all the fluorine out of the magma, followed by chlorine," Boyce said. "Apatite that forms later doesn't see any fluorine or chlorine and becomes hydrogen-rich because it has no choice."

It is believed that moon was formed when a mysterious Mars-sized planet slammed into Earth over 4 billion years ago. If this theory holds true, moon should be completely molten and have lighter elements such as hydrogen. And above all it should be dry.  The samples collected show the presence of lighter elements and also reflect a dry lunar surface. 

"We had 40 years of believing in a dry moon, and now we have some evidence that the old dry model of the moon wasn't perfect," Boyce said. "However, we need to be cautious and look carefully at each piece of evidence before we decide that rocks on the moon are as wet as those on Earth."

The study clearly hints at the vast unexplored composition and environment of the early moon.

"We're knocking out one of the most important pillars of evidence regarding the conditions of the formation and evolution of the moon," Boyce said. "Next, we plan to determine how badly apatite has distorted our view of the moon and how we can best see past it to get at the moon's origin."

The study was documented in the journal Science.