# How could the presence of 3He be detected on the lunar surface?

I have been investigating this isotope of helium for a while, which is extremely abundant on the moon (and in general in the entire solar system except on planets with atmosphere). It is believed that it could be used as a fusion fuel (2H $${->}$$ $$\sf^3$$He) and since it is not radioactive and nothing would be the perfect energy source, but there is very little on earth because the atmosphere "does not let it pass".

It is known that the moon is full of it, but my question is, how do we detect it?

There are many articles that this element could be a source of infinite energy etc. but I have not found published explanations on how presence and concentration could or has be detected.

While China is already planning to do some tests with this element on the moon, there are (as yet) no published concentration maps.

• thespacereview.com/article/2834/1 The moon is not really "full of it". " The problem is that helium-3 is probably spread very thinly over millions of square kilometers of lunar regolith. Collecting it would require a vast strip-mining effort with lots of machinery, not to mention equipment for locating the material in the first place. Nobody has even begun to look at the engineering and scientific developments necessary to achieve this. " – Organic Marble Feb 18 '20 at 0:41

NASA [1] indicates that helium-3 can be assessed indirectly by measuring the presence of titanium dioxide and soil characteristics ("maturity"), the correlation having been derived from the study of Apollo lunar rock samples. The helium-3 is "detected" through remote analysis for these favorable mineral and soil characteristics. Using data on the titanium level and soil characteristics from the Clementine spacecraft combined with with it's own microwave measurements of the thickness of the regolith, Chang-e 1 produced a map of likely helium-3 concentrations in the regolith [2, 3]. Although the near and far sides contain roughly equal amounts of helium-3 overall, higher concentrations (or at least, more favorable titanium levels and soil characteristics) are found in regions of the near side corresponding roughly to the major lunar seas. Chang-e 1's map, taken from [3], is given below.

References

1. Lunar Helium-3 and Fusion Power, NASA Publication 10018 (1988), p. 26.

2. W.-Z. Fa and Y.-Q. Jin, "Global inventory of Helium-3 in lunar regoliths estimated by a multi-channel microwave radiometer on the Chang-E 1 lunar satellite", Chinese Svience Bulletin 55, pages4005–4009(2010). (Link)

3. "Chang-e 1 Maps Moon's Helium-3 Inventory", http://lunarnetworks.blogspot.com/2010/12/change-1-maps-moons-helium-3-inventory.html?m=1

• Not sure about those units. Ppb or ppm usually is not based on area or volume. – Oscar Lanzi Mar 30 '20 at 11:16
• @OscarLanzi ya agreed, it's a blogpost so probably hasn't seen any peer review. Areal density (for example picograms/m^2) would make sense for a deposited material that will only be found near the surface, but ppb can't have a /m^2 after it. – uhoh Mar 30 '20 at 11:25
• @Cornelisinspace thanks for that, but I have a hunch it's a typo or something else. – uhoh Mar 30 '20 at 11:26
• – Cornelis Mar 30 '20 at 11:34
• @Cornelisinspace yep, that looks nicer :-) – uhoh Mar 30 '20 at 11:36