<p>Different sources give significantly different values for the conditions under which hydrogen shifts from molecular to metallic. See the discussion in the comments associated with <a href="https://astronomy.stackexchange.com/questions/25444/what-would-the-pressure-and-temperature-of-gas-be-right-above-jupiters-gas-liq/25451?noredirect=1#comment43745_25451">this question</a>. Pressures from about 20 to 300 GPa and temperatures very broadly around 10 000 K seem to be the most common.  </p>

<p>Experiments can only just reach these pressures, at lower temperatures, for tiny volumes of material, and the question of whether anyone has made metallic hydrogen at all remains controversial. Certainly no one can make it repeatably. (<a href="https://en.wikipedia.org/wiki/Metallic_hydrogen" rel="noreferrer">wikipedia</a> has a reasonable summary of the history) or make enough of it and keep it for long enough to check to what extent, if any, helium is soluble in it.</p>

<p>That said, analysing from theory whether it will be soluble shouldn't be that hard, since both hydrogen and helium are relatively simple atoms. <a href="http://iopscience.iop.org/article/10.1088/0305-4608/9/5/007/meta" rel="noreferrer">An early paper</a> concludes that the hydrogen would be at or close to the limit of how much helium could be dissolved. I'm sure there is more accurate recent work, but I couldn't find it quickly.</p>

CC BY-SA 3.0
2018-03-14T10:39:31.990Z
Thanks for the answer and the links! More about the sketchy room-temperature observation [here](https://physics.stackexchange.com/q/308155/83380) and [here](https://physics.stackexchange.com/q/308290/83380).
uhoh
CC BY-SA 3.0
2018-03-14T10:28:36.900Z
2018-03-14T10:28:36.900Z
Steve Linton
<p>In response to today being <a href="https://en.wikipedia.org/wiki/Pi_Day" rel="nofollow noreferrer">pi day</a> (also see <a href="http://www.piday.org/" rel="nofollow noreferrer">http://www.piday.org/</a>), NASA has published it's fifth annual <a href="https://www.jpl.nasa.gov/edu/teach/activity/pi-in-the-sky-5/" rel="nofollow noreferrer">pi in the sky day 5</a> activity set (see also <a href="https://www.jpl.nasa.gov/edu/news/2018/3/9/pi-goes-the-distance-at-nasa/" rel="nofollow noreferrer">NASA goes the distance</a> and <a href="https://www.jpl.nasa.gov/edu/events/2018/3/9/celebrate-pi-day-with-nasa/" rel="nofollow noreferrer">Celebrate Pi Day with NASA</a>).</p>

<p>This year's NASA activity includes the problem set <a href="https://www.jpl.nasa.gov/edu/teach/activity/helium-heist-a-pi-in-the-sky-math-challenge/" rel="nofollow noreferrer">Helium Heist: A 'Pi in the Sky' Math Challenge</a>. Below is a cropped screen shot of the illustration from this <a href="https://www.jpl.nasa.gov/edu/pdfs/piday2018_jupiter_handout.pdf" rel="nofollow noreferrer">PDF</a> version.</p>

<p>The part of the text that I found most striking is:</p>

<blockquote>
  <p>It has been hypothesized that the helium was depleted out of the upper atmosphere and transported deeper inside the planet. The extreme pressure inside Jupiter condenses helium into droplets that form inside a liquid metallic hydrogen layer below. Because the helium is denser than the surrounding hydrogen, the helium droplets fall like rain through the liquid metallic hydrogen.</p>
</blockquote>

<p><strong>Question:</strong> Roughly what are the pressure and temperature thought to be at this depth in Jupiter? Is this regime at all accessible experimentally on Earth to confirm that these two fluids are immiscible, or is this behavior purely theoretical?</p>

<hr>

<p><strong>below:</strong> cropped screen shot from <a href="https://www.jpl.nasa.gov/edu/pdfs/piday2018_jupiter_handout.pdf" rel="nofollow noreferrer">here</a> (NASA). Click for full size.</p>

<p><a href="https://i.sstatic.net/dzoik.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dzoikm.jpg" alt="enter image description here"></a></p>

<jupiter><hydrogen><helium>
Helium rain inside metallic hydrogen within Jupiter, conditions and experiments?
uhoh
# Helium rain inside metallic hydrogen within Jupiter, conditions and experiments?

(Asked by: username_0 on 2018-03-14)

In response to today being [pi day](https://en.wikipedia.org/wiki/Pi_Day) (also see <http://www.piday.org/>), NASA has published it's fifth annual [pi in the sky day 5](https://www.jpl.nasa.gov/edu/teach/activity/pi-in-the-sky-5/) activity set (see also [NASA goes the distance](https://www.jpl.nasa.gov/edu/news/2018/3/9/pi-goes-the-distance-at-nasa/) and [Celebrate Pi Day with NASA](https://www.jpl.nasa.gov/edu/events/2018/3/9/celebrate-pi-day-with-nasa/)).

This year's NASA activity includes the problem set [Helium Heist: A 'Pi in the Sky' Math Challenge](https://www.jpl.nasa.gov/edu/teach/activity/helium-heist-a-pi-in-the-sky-math-challenge/). Below is a cropped screen shot of the illustration from this [PDF](https://www.jpl.nasa.gov/edu/pdfs/piday2018_jupiter_handout.pdf) version.

The part of the text that I found most striking is:

> It has been hypothesized that the helium was depleted out of the upper atmosphere and transported deeper inside the planet. The extreme pressure inside Jupiter condenses helium into droplets that form inside a liquid metallic hydrogen layer below. Because the helium is denser than the surrounding hydrogen, the helium droplets fall like rain through the liquid metallic hydrogen.

**Question:** Roughly what are the pressure and temperature thought to be at this depth in Jupiter? Is this regime at all accessible experimentally on Earth to confirm that these two fluids are immiscible, or is this behavior purely theoretical?

---

**below:** cropped screen shot from [here](https://www.jpl.nasa.gov/edu/pdfs/piday2018_jupiter_handout.pdf) (NASA). Click for full size.

[![enter image description here](https://i.sstatic.net/dzoikm.jpg)](https://i.sstatic.net/dzoik.jpg)

**Tags:** jupiter, hydrogen, helium

---

## 1 answers

### Answer by username_1 on 2018-03-14. Score: 5 | Accepted answer

Different sources give significantly different values for the conditions under which hydrogen shifts from molecular to metallic. See the discussion in the comments associated with [this question](https://astronomy.stackexchange.com/questions/25444/what-would-the-pressure-and-temperature-of-gas-be-right-above-jupiters-gas-liq/25451?noredirect=1#comment43745_25451). Pressures from about 20 to 300 GPa and temperatures very broadly around 10 000 K seem to be the most common.

Experiments can only just reach these pressures, at lower temperatures, for tiny volumes of material, and the question of whether anyone has made metallic hydrogen at all remains controversial. Certainly no one can make it repeatably. ([wikipedia](https://en.wikipedia.org/wiki/Metallic_hydrogen) has a reasonable summary of the history) or make enough of it and keep it for long enough to check to what extent, if any, helium is soluble in it.

That said, analysing from theory whether it will be soluble shouldn't be that hard, since both hydrogen and helium are relatively simple atoms. [An early paper](http://iopscience.iop.org/article/10.1088/0305-4608/9/5/007/meta) concludes that the hydrogen would be at or close to the limit of how much helium could be dissolved. I'm sure there is more accurate recent work, but I couldn't find it quickly.

> **Comments:**
> **username_0**: Thanks for the answer and the links! More about the sketchy room-temperature observation [here](https://physics.stackexchange.com/q/308155/83380) and [here](https://physics.stackexchange.com/q/308290/83380).  

---

