Moons of our Solar System
Moons of our Solar System

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Moons of our Solar System

Week 6: Water on the Moon


Scientists had long debated the presence of water, but the Apollo missions appeared to settle the matter – the Moon rocks were dry. In the few cases where water was detected, it appeared to be terrestrial contamination.

Jess introduces Week 6 and the debate around water on the Moon.

And here’s a note from Jess on her research:

My research fits into the hot debate ‘dry versus wet Moon’ as I’m working on determining the water content of a specific lunar mineral: apatite. This calcium phosphate mineral is important because it can lock up water in its crystal structure. Incidentally, apatite is the most commonly occurring hydrous lunar mineral and occurs in almost every rock type we have from the Moon. Knowing how much water is contained in a range of lunar rocks permits us to assess the water budget of the lunar interior including in some cases rocks that date back to just after the Moon was formed (c. 4.5 billion years ago).

In addition to quantifying the amount of water in lunar apatite my colleagues and I are measuring the hydrogen isotopic composition of the water. This is a very powerful tool since different Solar System objects have characteristic hydrogen isotopic signatures, allowing us to infer the origin of lunar-interior water. Our current understanding suggests that there is a strong link to some examples of a class of meteorites called carbonaceous chondrites and hints to a common origin for water within the Earth and the Moon.

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One of the big questions that we thought had been answered by the Apollo missions was the question of water on the Moon. Rocks on the Earth's surface contain lots of water locked into minerals. But after careful analysis of Moon rocks in the 1970s, it appeared that the Moon was bone dry.
Since then, scientists, such as myself, have been re-analysing the Apollo samples and lunar meteorites using new techniques. Some of this work suggests that there is both water on and inside the Moon.
As you work through this week, you'll find that there are, in fact, at least two kinds of Moon water. There's very tiny traces inside some minerals, which indicates the presence of water that's, well, actually been there all along inside the Moon.
There's also ice in permanently shadowed parts of some craters near the poles, which we think comes from comets hitting the surface of the Moon, a process that continues today.
The long-running debate about lunar water is a really good example of the way that science advances by continually testing hypotheses. It is a process that's taken over 30 years to achieve a near consensus.
Enjoy this one. See you next week.
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By the end of this week, you will be able to:

  • understand the debate around lunar water and the two kinds of Moon water
  • explore examples of how science advances by continuously testing hypotheses.

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