<p>The Moon is not "full" of helium-3. <sup>3</sup>He is at most fifty parts per billion of the lunar regolith<sup>1</sup> and that "high" concentration pertains only to permanently shadowed craters. The Moon is bombarded by a steady stream of helium-3 while sunlit. Some of this incoming helium-3 is temporarily embedded in the lunar regolith. Without this steady supply, the helium-3 content would dissipate at a temperature-dependent rate proportional to the amount of helium-3 in the lunar regolith.</p>

<p>The quantity $q(t)$ of in a cubic meter of lunar regolith is thus dictated by a simple differential equation, $\dot q(t) = \alpha(t) - \beta(T)q(t)$. Time averaging the bombardment and escape rates yields $\dot {\bar q}(t) = \bar{\alpha} - \beta(\bar T)q(t)$. This differential equation yields a steady state value of $\bar q = \bar{\alpha}/\beta(\bar T)$.</p>

<p><br>
<sup>1</sup> Cooks, "<sup>3</sup>He in permanently shadowed lunar polar surfaces", <em>Icarus</em>, 206:2 778-779 (2010).</p>

CC BY-SA 3.0
2014-06-27T01:19:45.160Z
2014-06-27T01:19:45.160Z
David Hammen
<p>So the moon is full of helium-3.</p>

<p>Since it's a gas in the moon's vacuum... Why doesn't it escape?</p>

CC BY-SA 3.0
2014-06-26T22:59:57.813Z
Can you provide a reference for your claim?
casey
CC BY-SA 3.0
2014-07-09T13:42:40.580Z
InquilineKea is not in the habit of putting a lot of effort into questions. Rather, of putting a little effort into lot of questions.
naught101
<planetary-science><moon>
Why does helium-3 stay in the moon and not escape from it?
InquilineKea
# Why does helium-3 stay in the moon and not escape from it?

(Asked by: username_0 on 2014-06-26)

So the moon is full of helium-3.

Since it's a gas in the moon's vacuum... Why doesn't it escape?

**Tags:** planetary-science, moon

> **Comments:**
> **username_1**: Can you provide a reference for your claim?  
> **username_2**: username_0 is not in the habit of putting a lot of effort into questions. Rather, of putting a little effort into lot of questions.  

---

## 1 answers

### Answer by username_3 on 2014-06-27. Score: 13 | Accepted answer

The Moon is not "full" of helium-3. 3He is at most fifty parts per billion of the lunar regolith1 and that "high" concentration pertains only to permanently shadowed craters. The Moon is bombarded by a steady stream of helium-3 while sunlit. Some of this incoming helium-3 is temporarily embedded in the lunar regolith. Without this steady supply, the helium-3 content would dissipate at a temperature-dependent rate proportional to the amount of helium-3 in the lunar regolith.

The quantity $q(t)$ of in a cubic meter of lunar regolith is thus dictated by a simple differential equation, $\dot q(t) = \alpha(t) - \beta(T)q(t)$. Time averaging the bombardment and escape rates yields $\dot {\bar q}(t) = \bar{\alpha} - \beta(\bar T)q(t)$. This differential equation yields a steady state value of $\bar q = \bar{\alpha}/\beta(\bar T)$.

1 Cooks, "3He in permanently shadowed lunar polar surfaces", *Icarus*, 206:2 778-779 (2010).


---

